Dissertations / Theses on the topic 'Disturbance of forest ecosystems'

Freshwater swamp forests are wetland ecosystems of global importance, especially because they provide very valuable ecosystem services such as regulation of flood and maintenance of water quality, and provide suitable habitat for the conservation of wetland ecosystems (flora and fauna). Though they are hosts to important biodiversity as in other tropical ecosystems, their ecology, function and contribution to ecosystem services are poorly understood. With poor baseline data on this threatened ecosystem across the Niger Delta region and the entire West African region, this thesis explores its ecology, biogeography and the capacity to which this ecosystem sequester carbon, in a bid to better prioritize and inform effective conservation and management. Floristic compositions of the ecosystem were varied in density, diversity and rarity across undisturbed, disturbed and transition (mangrove-freshwater) zones. A total of 138 species within 100 genera and 41 families of taxa were identified across the 24 one hectare forest plots; with variations in dominance according to each of the zones. With a stem density which ranged from 94 – 506 stems ha-1, the ecosystem was seen to be comparable with other tropical forest ecosystems, but were poorer in species richness as a result of the environmental constraints associated with the swamp. Though disturbance (local factors) influenced the pattern of species distribution to a great extent, environmental (regional factors) equally contributed to this variation. Above ground carbon estimates (AGC) were also similar to other African forest ecosystems, with the estimates varying at the plot level mainly due to disturbance gradients. Other variables that contributed to AGC variations included the floristic composition (which were found to be more carbon dense towards the transition zones), tree structure and climatic variables. Other ecosystem services derived from the ecosystem (timber and non-timber forest products) were found to be a major source of sustenance and income generation at varying levels. Household usage and dependence on the forests were mainly influenced by the degrees of remoteness of each community, and whether each of the households had other alternative sources of livelihood. With a poor perception of decline in ecosystem services with usage, the forests has steadily shrunk and degraded.

Temperate forests are complex ecosystems that sequester carbon (C) in biomass. C storage is related to ecosystem-scale forest structure, changing over succession, disturbance, and with community composition. We quantified ecosystem biological and physical structure in two forest chronosequences varying in disturbance intensity, and three late successional functional types to examine how multiple structural expressions relate to ecosystem C cycling. We quantified C cycling as wood net primary production (NPP), ecosystem structure as Simpson’s Index, and physical structure as leaf quantity (LAI) and arrangement (rugosity), examining how wood NPP-structure relates to light distribution and use-efficiency. Relationships between structural attributes of biodiversity, LAI, and rugosity differed. Development of rugosity was conserved regardless of disturbance and composition, suggesting optimization of vegetation arrangement over succession. LAI and rugosity showed significant positive productivity trends over succession, particularly within deciduous broadleaf forests, suggesting these measures of structure contain complementary, not redundant, information related to C cycling.

Forest disturbance occurs on a wide gradient of selectiveness and creates new growth opportunities for adapted species. Across the spectrum of disturbance, anthropogenic disturbance influences community assembly in the Midwest more than other mechanisms but is its role in shaping and maintaining ecosystems is inadequately considered in most discussions on the historic range of variability (HRV). Forest resiliency is threatened by unprecedented agents of ecosystem change such as invasive species and reduced regeneration potential of native species. Historic anthropogenic disturbance largely resulted in forest conditions which commonly contained high value attributes like heterogeneity across habitat types and landscape diversity, yet also produced forests of undesirable traits due to high grading for timber and overgrazing by domesticated stock. In order to maintain historical representative forests and improve the degraded forests, active forest management is necessary to continue historic disturbance patterns and combat new threats. Forest transition theory is used here to describe the impacts of human settlement and development activities on forest ecosystems across the Middle Mississippi River Valley. To date, researchers have identified the need for information related to changes of forest attributes such as species composition and stand structure, improved descriptions of short- and medium-term dynamics within the context of the long-term transition, and the integration of biophysical drivers of forest change through time. In Midwestern U.S.A., forest dynamics were influenced by frequent, low intensity disturbance events that mediate forest composition and stand structure by selecting for disturbance regimes that create oak woodland and interspersed prairies and meadows. The onset of Euro-American settlement was accompanied by detailed land-use records with information related to forest attributes, agricultural activities, and parcel ownership patterns. We aggregated multiple sources of historic forest conditions into a geodatabase in order to document changes over the past 200 years in Elsah Township, Illinois, where the pre-settlement (1820) forest, once dominated by oak and hickory species, has largely shifted to a maple dominated system with a declining oak-hickory component, heavily influenced by an invasive shrub species, bush honeysuckle. Using on ordinary kriging interpolation, forest density was estimated at 8.7 stems per acre on average with a mean basal area of 14.6 square feet per acre prior to settlement. Conservation practices of the early 1900s, including fire suppression and erosion control resulted in changes to forest structure with density increases to 127 trees per acre with a basal area of 175.8 square feet per acre. The high degree of topographic variability near the Mississippi River influenced forest cover changes as slopes with low angles were the first to be converted from forest cover to other land uses (circa 1850). Forest re-initiation occurred in areas with steeper slope due to a lack of human activities. Forest cover declined to the lowest point in 1927 and has been rebounding steadily throughout this century. Of the original 15,252 forested acres, 11.6% remained covered throughout the past 200 years and coincided with slopes with an average of 39.1 degrees. These data can provide a spatially explicit and historically accurate tool to guide land management decisions including restoration treatment, disturbance regime management, and land use preservation activities in similarly heterogeneous environments. Forest communities along the bluffs of the Mississippi River differ in species composition and stand structure associated with specific topographic positions of floodplain, transition talus slope, bluff top, and upland. In order to assess current stand characteristics and ecosystem trajectory, we measured all woody stems in 316 fixed radius plots (79 plots per topographic position) with a plot area of 25 m2. Alpha (defined as within system diversity) and Beta (defined as between system diversity) diversity and diameter distributions were determined for seedling, shrub layer, and overstory stems. Stem density increased from 21.4 stems ha-1 in 1820 to 613 stems ha-1 in 1936 followed by reduction to 314 stems ha-1 in 2017. Average stand diameter decreased from 40.9 cm in 1820 to 25.3 cm in 2017 (for upland stems greater than 7.5 cm) while basal area increased from 3.3 m2 ha-1 in 1820 to 40.4 m2 ha-1 in 2017. Alpha diversity was highest in the upland overstory and in the river island shrub layer. Beta diversity in the overstory was highest (0.67) between the bluff and the upland while lowest (0.08) between the bluff and the river island. Importantly, mesophytic species are no longer restricted to watercourses and valleys as reported in historical accounts and confirmed by the spatial analysis of original witness tree records. Currently, bush honeysuckle, an invasive species, dominates the shrub layer on most non-hydric sites of the talus slope, upland, and particularly across the bluff top where it is an indicator. Across all forest sites in the study, we found evidence of a community shift to less diversity and more mesophytic species over the past 80 years. Hill prairie vegetation on the limestone bluffs of the central Mississippi River Valley represents a significant portion of the remaining prairie, savanna, and woodland systems of the Midwest and should be appropriately managed with prescribed fire and woody stem reduction efforts. We examined the structure, composition, and temporal community patterns of the forest-prairie gradient by employing hierarchical cluster analysis and non-metric multi-dimensional scaling in combination with indicator species analysis and dendrochronological methods. Results suggest that four general community types exist across the forest-prairie gradient: Group 1 consists of the woodland community structure with significant indicator values for the density of Juniperus virginiana (indicator value 58.4, p = 0.0002), Carya glabra (45, 0.0022), Quercus stellata (23.7, 0.0424), and Lonicera maackii (74.2, 0.0002) and a high basal area (BA) of J. virgniana (21.4, 0.0276) and L. maackii (47.9, 0.0054). The first year of L. maackii presence was 1964 with the primary wave of invasion beginning around 1990. Group 2 contains bare soil coverage in the subplot (40.4, 0.0002) as the one indicator at a significant level. The species with the highest BA in Group 2 include Acer saccharum (9.08 m2 ha-1), Q. velutina (5.89 m2 ha-1), and Q. muehlenbergii (5.32 m2 ha-1). Group 3 typifies the hill prairie community with the sole indicator of grass coverage in the subplots (39.7, 0.0196). Group 4 represents the stage of forest development following the cessation of disturbance events and the trajectory advancing towards a mesophytic forest and contains 14 significant indicators.

A herbivoria por grandes mamíferos é um fator decisivo no direcionamento de comunidades vegetais, influenciando o crescimento, sobrevivência e reprodução das plantas. Os ungulados, quando exóticos, podem impactar os ecossistemas diferentemente de herbívoros nativos, gerando maiores efeitos nas comunidades de plantas. Os objetivos deste estudo foram avaliar se a presença de búfalos (densidade de 1 animal/ha) impacta as assembléias de plântulas e de arbustos numa floresta estacional semidecídua no sul do Brasil, além de inferir consequências para a manutenção da comunidade vegetal. Para isso realizamos duas abordagens no município de Sentinela do Sul: na primeira, estabelecemos um experimento de exclusão de bubalinos (duração de 14 meses) e na segunda, comparamos três áreas com presença e protegidas desses herbívoros por três e dez anos. Em ambas as abordagens, registramos as seguintes variáveis ecológicas: riqueza, altura média de plantas, cobertura vegetal, diversidade (Shannon), e biomassa. No experimento de exclusão, nenhuma das variáveis apresentou diferenças significativas perante presença e ausência de búfalos (após 14 meses). Na comparação das três áreas as comunidades vegetais mostraram diferenças qualitativas (composição de espécies) no contraste presença versus dez anos de exclusão de búfalos, e as variáveis riqueza e altura média sofreram, respectivamente, significativos incremento e decréscimo. A diferença observada para o incremento de diversidade de zero a dez anos de exclusão foi marginalmente significativa e a compactação do solo apresentou decréscimo em função do tempo de exclusão do gado. Portanto , os resultados do presente trrabalho indicam que as manchas florestais não respondem à remoção de búfalos em baixas densidades no curto prazo e, na ausência de grandes herbívoros, a floresta tende a incrementar sua complexidade via aumento de riqueza e diversidade.
Herbivory by large mammals is a key factor in plant communities, and has effects on growth, survival and reproduction of plants. Ungulates, when exotic, impact ecosystems in a different way compared to the native ones, and may have a more pronounced effect on plant communities. In this study we evaluated buffalo (1 animal/ha density) impact on the seedling and shrub assemblages in a semideciduous seasonal forest in southern Brazil and checked if such impact would affect plant community maintainability. To address these aims we conducted two studies in Sentinela do Sul County: 1. we established a buffalo exclusion experiment (during 14 months) and 2. compared three areas with presence and protected against these herbivores for three and ten years. In both studies, we measured the following ecological variables: plant cover, richness, diversity (Shannon), biomass and average height. In the exclusion experiment, any ecological variable showed significant differences between buffalo presence and absence plots. When the three areas were compared, the communities showed qualitative differences (species composition) in the contrast presence versus ten years of buffalo exclusion, and richness and average height showed, respectively, increase and decrease. The difference observed for an increase of diversity between zero and ten years exclusion was marginally significant, and soil compactation showed retraction in relation to livestock exclusion time. We conclude that forest spots don’t answer in short-term to low densities buffalo removal and, in the absence of large herbivores, the forest tends to develop its complexity by richness and diversity increase, in a long-term basis.

Forests are an important component of the global carbon (C) cycle and contribute to climate change mitigation through atmospheric C uptake and storage in biomass and soils. However, the forest C sink is susceptible to disturbance, which modifies physical and biological structure and limits spatial extent of forests. Unlike severe, stand-replacing disturbances that reset forest successional trajectories and may simplify ecosystem structure, moderate severity disturbances may instead introduce complexity in ways that sustain net primary production (NPP), leading to the phenomenon of “NPP resilience.” In this study, we examined the linkage between disturbance severity and ecosystem biological and physical structural change, and implications for NPP within an experimentally disturbed forest in northern Michigan, USA. We computed spatially resolved and spatially agnostic metrics of forest biological and physical structure before and 10 years after disturbance across a continuum of severity. We found that while biological structure did not change in response to disturbance, three of four physical structural measures increased or were unimodally related to disturbance severity. Physical structural shifts mediated by disturbance were not found to directly influence processes coupled with NPP. However, decadal changes in the spatial aggregation index of Clark and Evans, though not a function of disturbance severity, were found to predict canopy light uptake, leaf physiological variability, and relative NPP within plots. We conclude that ecosystem structural shifts across disturbance severity continua are variable and differ in their relationship to NPP resilience.

The Effects of Tropical Forest Management on Biodiversity and Ecosystem Functioning Eleanor M. Slade 1. Between 35 % and 50 % of all closed-canopy tropical forest has been lost, and the rate of deforestation continues to increase throughout the tropics. Despite a wealth of literature on the effects of tropical forest disturbance on the diversity and composition of a variety of taxa, there is still no clear consensus on the value of disturbed forests for biodiversity. 2. If forest management practises are to be sustainable in the long-term they should maintain both biodiversity and ecosystem functioning (the interactions and processes of the ecosystem), as well as a timber harvest. However, few studies have investigated the extent to which ecosystem functioning is reduced in logged forests. The effects of different logging intensities on a variety of taxa, and the ecosystem processes with which they are associated, were assessed in the Danum Valley Conservation Area in Sabah (Malaysian Borneo). 3. Even under high logging intensities, the forests of Sabah appear to have been managed in a way that maintains timber yields in the short-term. However, other aspects of forest structure had been affected, which could have important consequences ecologically, and for the long-term sustainability of timber harvests. 4. Combining field studies with manipulative experiments allows assessment of the impacts of species changes associated with habitat modification on measures of ecosystem functioning. Dung beetle (Coleoptera: Scarabaeidae: Scarabaeinae) functional group richness and composition were manipulated in a series of field experiments. Certain functional groups and species were found to have a greater impact on ecosystem functioning than others; nevertheless a full complement of species was needed to maintain full ecosystem functioning. 5. Dung beetles appeared to be relatively robust to changes in forest structure associated with selective logging, but species richness was reduced with high-intensity logging. There was a corresponding decrease in ecosystem functioning (dung and seed removal) with a decrease in species richness, and a decrease in the biomass of large nocturnal tunnellers, suggesting that although some species are dominant, rare species are also needed to preserve full ecosystem functioning. 6. A complex interaction between birds and ants resulted in reduced herbivory of seedlings of the important timber tree, Parashorea malaanonan, in some instances. However, this interaction was not affected by either selective or high intensity logging. Seedfall of P. malaanonan, was reduced in logged forest compared to primary forest. Despite insect seed predation being higher in primary forest, there was still successful recruitment during a non-mast year. Parasitism of insect-predated seeds was found to be inversely density dependent, and was higher in logged forest where seed predation was lower. 7. The results of this thesis suggest that the forests of Sabah appear to be being logged under a management system that is compatible with sustainable timber management, but not necessarily sustainable forest management. Low intensity selective logging seems to preserve much of the original forest structure, biodiversity and ecosystem functioning compared to logging at higher intensities. However, ecosystem processes were variable in their response to logging, suggesting that management decisions should be based on the consideration of multiple taxa and processes.

Great Basin bristlecone pine (GBBP) (Pinus longaevaBailey) is one of the longest-lived organisms on Earth, and is one of the most highly fragmented high elevation conifer species. Throughout the Great Basin of the Intermountain West, GBBP are being impacted by changing disturbance regimes, invasive species, and climate change. To better understand the effects of climate variability and ecological disturbances in GBBP systems, three studies were designed and implemented. The first characterized the distribution of forest fuel in stands of GBBP and predicted how fuels may change under future climate scenarios. Using the Forest Inventory Analysis (FIA) plot variables of tree species, height, diameter at breast height (DBH), canopy base height (CBH), coarse (CWD) and fine (FWD) woody debris across elevational gradients, this study examined the effects of changes to fuel loading on predicted changes in fire behavior and severity. All classes of FWD decreased with elevation, and only 1000-hr fuels remained constant across elevational transects. This, combined with lower CBH and foliar moisture and increasing temperatures due to climate change, suggested increased fire potential at the GBBP treeline. The second study examined the role of volatile organic compounds (VOCs) and tree chemistry and their response to the environment. VOCs and within needle chemistry were collected and analyzed along elevational gradients near the northern and southern limits of GBBP. Random Forest analysis distinguished elevation using VOCs, with 83% accuracy, and identified the compounds most important for classification. Ordination revealed that temperature, heat load index, and relative humidity were each significantly correlated with VOCs. Within-needle chemistry provided less predictive value in classifying elevation (68% accuracy) and was correlated only with heat load index. These findings suggest that GBBP VOCs are highly sensitive to the environment. The final study explored the role of VOCs in host selection of mountain pine beetle (MPB). Mountain pine beetles oriented toward VOCs from host limber pine (Pinus flexilis James) and away from VOCs of non-host GBBP using a Y-tube olfactometer. When presented with VOCs of both trees, females overwhelmingly chose limber pine over GBBP. While there were only a few notable differences in VOCs collected from co-occurring GBBP and limber pine, 3-carene and D-limonene were produced in greater amounts by limber pine. There was no evidence that 3-carene is important for beetles when selecting trees, however, addition of D-limonene to GBBP VOCs disrupted the ability of beetles to distinguish between tree species. Climate change will impact how forests are managed and this research could provide insight into the mechanisms underlying the incredible longevity of this iconic tree species.

The objective of this thesis was to validate the dynamic model SAFE (Soil Acidification in Forested Ecosystems) in a small deciduous watershed of southern Quebec. SAFE could then be used to: (1) identify which processes are governing acidification, and (2) assess the rates of acidification according to various forest conditions.
Soil and soil solution chemistry between unburned and burned zones following fire disturbance seventy-five years ago was examined within the watershed. Results showed two major, statistically significant, differences: (1) higher base status, and (2) lower soil solution N in the burned zone. High quality leaf litter of aspen and birch (burned zone) relative to that of sugar and red maple (unburned zone) has contributed to the enrichment of base cations in the forest floor. The enrichment of the forest floor did not however impoverish the B horizon as seen in other studies. Rather, fire enriched the soil in base cations and buffered the effect of forest regrowth in the B horizon.
The MAKEDEP model was used to reconstruct the time-series input files needed to run SAFE. In MAKEDEP, the availability of N determines tree growth which in turn, affects most of the processes involved in nutrient cycling. Regressions of measured deposition at the Hubbard Brook Experimental Forest and that of simulated deposition at the study site suggest MAKEDEP is suitable to model the deposition trends of all elements except Na.
SAFE was calibrated for the unburned and burned conditions at the study site. Fire disturbance and forest regrowth have produced different soil chemical composition within the zones as discussed above. SAFE was therefore validated at the study site as a function of its ability to reproduce soil chemistry under unburned and burned conditions. The simulated soil chemistry was in close agreement with the measured unburned soil conditions, but some processes would have to be clarified or accounted for with greater accurately, e.g., biological N fixation and N immobilization by myccorhizal fungi, to reproduce more accurately the measured burned soil chemistry. Simulated soil chemistry in the unburned zone reinforced nevertheless the conclusions of a few historical soil chemistry studies supporting the hypothesis that acid-sensitive forest sites of the United States underwent significant acidification during 1930--1980 during major input of acidity from the atmosphere. Model output suggests that cation nutrient deficiencies could occur in the long-term, but future Al phytotoxic responses are unlikely to occur due to a relatively high projected pH. (Abstract shortened by UMI.)

Apesar da reconhecida importância da fragmentação no balanço de carbono (C) das florestas tropicais, a maior parte do conhecimento a cerca deste assunto provém de estudos conduzidos na floresta Amazônica e desconsidera processos relacionados à influência da configuração da paisagem. Em particular, estimativas precisas da emissão de CO2 devido à fragmentação devem levar em consideração efeitos aditivos de borda e a idade das bordas. Nós investigamos estes efeitos sobre parâmetros estruturais de florestas (densidade, altura e área basal das árvores) e no estoque de C em oito fragmentos florestais (13 a 362 ha) antigos (>=70 anos), cercados de pastagens, em uma região de Mata Atlântica. Amostramos 5297 troncos, divididos em quatro tratamentos em cada um dos fragmentos: interior dos fragmentos; bordas antigas (>50 anos) em quina; bordas antigas retas; bordas novas (<50 anos) retas. Calculamos a biomassa acima do solo (BAS) através de equações alométricas que consideram a altura do tronco e seu diâmetro à altura do peito (DAP) e convertemos esse valor em carbono estocado na vegetação. O estoque de C foi altamente variável entre tratamentos, abrangendo valores entre 6.61 Mg ha-1 até 87.96 Mg ha-1 (média= 29.55 ± 14.97 Mg ha-1). As áreas de interior continham um estoque de C maior, bem como maior área basal, densidade de árvores e árvores mais altas do que as de borda. No entanto, a seleção de modelos não detectou influência da idade ou de efeitos aditivos no estoque de C. Nossos resultados sugerem que os padrões de efeitos de borda para a Mata Atlântica são diferentes dos observados em florestas tropicais fragmentadas mais recentemente, como é o caso da Amazônia. A Mata Atlântica tem um longo histórico de perturbação humana e uma dinâmica complexa de desmatamento e regeneração, que pode levar a uma condição de degradação generalizada, posto que até áreas mais distantes das bordas em manchas remanescentes de Mata Atlântica já perderam quantidades significativas de carbono. Nestas paisagens antrópicas, os efeitos de borda que atuam sobre a mortalidade de árvores e na redução da BAS podem ser mais abrangentes do que inicialmente estimado pelos modelos construídos para a floresta Amazônica.
Despite the importance of fragmentation for tropical forest carbon (C) balance, most of our knowledge comes from few sites in the Amazon and disregard underlying processes that relates landscape configuration with C stocks. Particularly, accurate estimation of CO2 emission from fragmentation must account for additive edge effects and edge age. Here we investigated those effects on carbon stock and forest structure (density, height, basal area) in eight old-growth forest (>=70 years) fragments (13 to 362 ha), surrounded by pasture, in the Brazilian Atlantic forest region. We sampled 5,297 stems in four distinct treatments, distributed in each fragment: fragment interiors; old (> 50 years) corner edge; old straight edge; and new (< 50 years) straight edge. Aboveground biomass (AGB) was estimated from tree height and diameter at breast height (DBH), and converted to carbon. C stock was highly variable between treatments, scoring from 6.61 Mg ha-1 up to 87.96 Mg ha-1 (average of 29.55 ± 14.97 Mg ha-1). Interior treatments had higher C stock, basal area, tree stem density and taller trees than edges. We found no significant effects of edge age or additive edge effects on C stocks. These results suggest that edge effects in the heavily-disturbed Atlantic rainforest may differ than those observed in more recently fragmented tropical forests, such as the Amazonian forest. In heavily human-modified landscapes, edge effects on tree mortality and reduction on AGB may contribute to overall higher levels of degradation across entire forest fragments, reducing the observed difference between edge and interior habitats, and suggesting that existing Amazonian forest models may underestimate the true impacts of tropical forest fragmentation for C storage.

Investigations into the effects of anthropogenic disturbance on greenhouse gas emissions from tropical peatlands are relatively well documented. However, the effects of such disturbance on fluvial carbon (C) losses has, thus far, been overlooked and remains unaccounted for in these ecosystem C budgets. Here, three land-cover classes in Central Kalimantan, Indonesia, were investigated in order to determine the effect of tropical peatland disturbance on fluvial organic C budgets. Intact peat swamp forest (IPSF), moderately disturbed and severely disturbed peat swamp forest (DPSF1 and 2) catchments were monitored for one year. Results demonstrate a trend of increasing annual total organic carbon (TOC) yields with increasing drainage severity, from 63 in IPSF to 105 and 131 g C m-2 y(1 in DPSF1 and 2, respectively. Including this routinely-ignored fluvial C loss component in the disturbed peatland ecosystem C budget increases the estimated total C loss by 30%. Radiocarbon analysis of dissolved organiC carbon (DOC) reveals that whilst DOC leaching from IPSF was derived from recent primary production, DOC leaching from the two disturbed sites was comprised of much older C, originating from deep within the peat column. The TOC flux from the Sebangau River basin was estimated to be 0.46 teragrams y(1, which upon regional extrapolation indicates that Indonesian rivers account for 10% of the global annual riverine DOC export to the ocean. There were no significant differences between sites in the quality of the organic C lost, but DOC lost from disturbed sites was generally less aromatic than from the intact site. It is recognized that a large portion of this labile C will be emitted to the atmosphere via biotic decomposition. Since 1990, peatland disturbance has resulted in a 53% increase in fluvial organic C export from Southeast Asia, an increase that alone approximates the entire annual fluvial organic C flux from European peatlands.

Doutoramento em Ciências do Mar
A pesca de arrasto de fundo é considerada a atividade antropogénica mais difundida e destrutiva que atualmente ameaça os ecossistemas de mar profundo. Geralmente, esta atividade está associada à redução da abundância e biomassa de organismos bentónicos, alterações na estrutura das comunidades e perda de biodiversidade em habitats de substrato rochoso (nomeadamente montes submarinos e recifes de coral de águas profundas), onde taxas de recuperação ocorrem tipicamente num período de várias décadas. No entanto, é nas regiões de fundos sedimentares, nomeadamente no talude continental e canhões submarinos, onde se concentram a maior parte dos pesqueiros e a maior pressão por parte dos arrastões de profundidade. No entanto, os efeitos sobre a biodiversidade e o funcionamento dos ecossistemas são pouco conhecidos, inclusive na margem Ibérica Oeste, uma das regiões Europeias mais impactadas por artes de arrasto de fundo. Como tal, a presente tese teve como objetivo principal investigar os efeitos da perturbação física induzida pelos arrastões de profundidade na composição, diversidade e estrutura trófica das comunidades bentónicas, bem como na manutenção de funções essenciais dos ecossistemas mediadas pela fauna (por exemplo, transformação da matéria orgânica, reciclagem de nutrientes, respiração e produção secundária). No total, foram selecionadas para o presente estudo três áreas de interesse, representativas de vários graus de perturbação física (não arrastado, e baixa e alta pressão por arrasto) na transição da plataforma para o talude continental da margem Sudoeste Portuguesa. Estas áreas foram estabelecidas a partir de dados de sistemas satélite de monitorização de embarcações (VMS). Foram realizados levantamentos de vídeo através de um veículo de operação remota (ROV) e amostradas sete estações dentro das três áreas de interesse, que permitiram a comparação das comunidades bentónicas, em termos de abundância, biomassa total, composição e diversidade (taxonómica e trófica), incluindo os grupos de meiofauna, macrofauna e mega-epifauna. Além disso, foi também realizado um trabalho experimental de curta duração (5 dias) com sedimentos colhidos em dois locais sujeitos a diferentes níveis de perturbação por arrasto. Aos sedimentos colhidos foram adicionadas algas marcadas com 13C, de forma a investigar vários proxys de funções tipicamente mediadas por comunidades bentónicas, nomeadamente mineralização de carbono por comunidades microbianas, biomassa bacteriana total (através da absorção do 13C e estimada a partir de ácidos gordos derivados de fosfolipídios específicos de bactérias - PLFAs), bioturbação (através da absorção do 13C no sedimento) e bioirrigação (analisada a partir da variação das concentrações de amónia no sedimento). Além disso, taxas de respiração e a respiração total da fauna foram utilizadas como proxy para a função metabólica do ecossistema. No geral, os resultados da presente tese demostraram que a pesca de profundidade por artes de arrasto de fundo resulta na degradação da integridade dos fundos marinhos (por exemplo, áreas perturbadas demonstraram uma topografia aplanada, pouca evidência de bioturbação e marcas de portas e redes de arrasto). As componentes da fauna de maior dimensão (mega-epifauna e macrofauna) apresentaram composições distintas nas áreas investigadas. Em condições de elevada perturbação física, observou-se a diminuição da riqueza taxonómica induzida pela perda de espécies raras e sensíveis à perturbação (por exemplo, organismos filtradores ou suspensívoros). Acresce que, no geral, a baixa dissimilaridade entre as áreas de pesqueiro e áreas adjacentes sujeitas a baixa perturbação, sugere que os efeitos negativos detectados podem estender-se para além das áreas directamente afectadas (por exemplo, resultados indirectos associados a plumas de sedimentos em suspensão). Correlações negativas significativas foram detectadas entre vários índices de diversidade da megaepifauna e esforço de pesca, bem como com a abundância, riqueza especifica e riqueza de grupos tróficos de macrofauna. No entanto, não foram detectadas correlações entre esforço de pesca e outros índices de diversidade estimados para macrofauna (Shannon-Wiener e a equitabilidade de Pielou), apesar de diferenças na composição das comunidades evidentes através da análise multivariada e na interpretação das comunidades nucleares (compostas por espécies características, dominantes ou frequentes). Estes resultados sugerem que alguns índices de biodiversidade tipicamente utilizados em estudos de impacto ambiental podem não ser suficientemente sensíveis para identificar alterações das comunidades sob perturbação física. Apesar das alterações na composição da macrofauna, a complexidade trófica foi no geral mantida (presença de todos grupos tróficos em todas as áreas). No entanto, a redundância trófica (número médio de espécies por grupo trófico) diminuiu, pelo que cada função (representada por cada grupo trófico) passou a ser assegurada por um menor número de espécies ou até mesmo uma única espécie. Esta alteração traduz-se numa maior vulnerabilidade a perturbações adicionais e/ou continuadas que induza novas extinções locais de espécies. Os resultados experimentais sugerem que as práticas de pesca de arrasto de profundidade na área de estudo parecem não afectar a biomassa bacteriana, nem a composição e a diversidade de organismos da meiofauna. A deplecção de várias funções realizadas pelos ecossistemas nas áreas sujeitas a de alta perturbação por pescas de arrasto, inclusive fluxos de energia e matéria nos sedimentos, foram relacionadas com alterações relevantes na composição da macrofauna, bem como alterações no espectro de tamanhos corporais dos organismos (prevalência de espécies de menor tamanho sob condições de perturbação generalizada). Tanto a produção secundária bacteriana, como a bio-irrigação e bioturbação apresentaram uma redução em sedimentos obtidos nas áreas de arrasto intenso. Adicionalmente, foi observada uma correlação positiva entre a respiração total e a riqueza específica da macrofauna, sustentando a nossa hipótese de que funções fundamentais do ecossistema podem sofrer depleções sob condições de perturbação física por arrasto de profundidade. Em resumo, a presente tese demonstrou que as atividades de arrasto de profundidade têm efeitos prejudiciais nas comunidades bentónicas de habitats sedimentares, em particular na mega-epifauna e macrofauna. Estes efeitos manifestam-se numa redução de funções regulatórias essenciais do ecossistema, normalmente mediadas pela fauna afetada. Estes resultados sugerem que a exploração continuada dos recursos biológicos ao longo da Margem Portuguesa, estão atualmente a pôr em risco os ecossistemas de mar profundo, e em particular as suas comunidades bentónicas. É importante salientar que os efeitos negativos detectados podem nem sempre ser identificados pelos actuais indicadores utilizados na avaliação dos impactos e programas de monitorização em sistemas marinhos e, portanto, deverão ser acompanhados por outros indicadores da composição das comunidades, condição do ecossistema e vulnerabilidade, de modo a adequadamente determinar o estado ambiental de ecossistemas de mar profundo ao longo das margens Europeias.
Bottom-trawling fisheries are considered the most pervasive and destructive anthropogenic activity presently threatening deep-sea ecosystems. In general terms, this activity is associated with the reduction of the benthos standing stocks, alterations of the benthic community structure and loss of fauna biodiversity in hard substrate habitats (i.e. seamounts and cold-water coral reefs), where recovery rates are estimated to be within decades. Yet, it is within the soft sediment regions, such as the continental slopes and submarine canyons, where a large amount of the trawling pressure is presently concentrated, and the effects on biodiversity and ecosystem function derived from this practice are barely known. This is particularly applicable for the West Iberian Margin, one of the most disturbed regions by bottom trawlers in Europe. Hence, this research aimed to investigate the effects of the longterm induced physical disturbance by bottom trawlers on the deep-sea softsediment benthic assemblages composition, diversity and trophic structure, and how this was translated into the maintenance of essential ecosystem functions (e.g. organic matter transformation and nutrient cycling, secondary production, ecosystem metabolism). Three main areas were selected based on various degrees of disturbance (no, low, and high trawling pressure) along a continental slope area off the SW Portuguese margin, established from Vessel Monitoring Systems (VMS) data. Remotely Operated Vehicle (ROV) video surveys and a total of seven stations within these three areas were sampled to compare the benthic assemblages, in terms of total standing stocks (abundance and biomass), composition and diversity (both taxonomic and trophic), including meiofauna, macrofauna and mega-epifauna groups. Additionally, an onboard short-term pulse-chase experiment (5 days) was performed on sediment cores obtained from two selected locations, and enriched with 13C labeled algae, to investigate several proxies of ecosystem functions in the sediment typically promoted by the benthic assemblages. These included carbon mineralization and production by bacteria communities and their total biomass (13C uptake estimated through bacteria specific phospholipid-derived fatty acids – PLFAs), bioturbation (13C sediment uptake profile with sediment depth) and bioirrigation (ammonia concentrations in the sediment depth profile). Additionally, infauna respiration rates and total respiration were used as a proxy for ecosystem metabolic function. Overall, the main results of the present thesis showed an evident compromise of the seabed integrity at the highly disturbed area (e.g. often flattened topography, low bioturbation evidence, and numerous trawl scars). Furthermore, the larger sized component of the benthic biota (megafauna and macrofauna) showed distinct assemblages between the areas investigated, and a lower morphospecies/species richness under conditions of high trawl disturbance, due to the loss of rare and trawl sensitive groups (e.g. sessile filter feeding fauna). Besides, a lower dissimilarity between assemblages were found in the main fishing ground areas (high trawled) and the adjacent lowdisturbance locations, suggesting that the potentially negative effects of trawling are extended beyond the main targeted areas (e.g. by the plumes of re-suspended sediments). Significant negative correlations were generally detected between various mega-epibenthic diversity indices and trawling pressure, as well for macrofauna abundance, species/trophic guild richness. However, diversity indices related with macrofauna community structure (Shannon-wiener and Pielou’s evenness) failed to detect the observed differences in community structure observed by the multivariate analysis and the structure of the core assemblages (i.e. characteristic, dominant or frequent taxa). We suggest that such indices may not be sensitive enough to identify changes under conditions of physical disturbance. Besides, even though alterations of macrofauna community composition were not reflected in an impoverished trophic complexity (all feeding guilds present in all areas), as a result of an increase trawling pressure, macrofauna trophic redundancy (average number of species per trophic guild) declined, reflecting a higher vulnerability under conditions of disturbance, as each function (trophic guild) was insured by a low number of species. Contrariwise, trawling practices seemed to have little effect on either bacterial biomass or meiofauna standing stocks and composition. A depletion of important ecosystem functions, such as energy and matter fluxes in the sediments at the high trawling pressure areas was particularly linked with changes in macrofauna assemblages and size structure, towards a dominance of smaller sized species under conditions of permanent disturbance. Both bacterial production and bioirrigation/ bioturbation (e.g. the higher build-up of ammonia at the sediment deeper layers), was reduced in high trawled sediments. Furthermore, the general decline in macrofauna species richness across the study region was correlated with the depletion of macrofauna total respiration, supporting our hypothesis that the depletions of fundamental regulatory ecosystem functions occur under high trawling disturbance regimes. In summary, this thesis demonstrated that trawling activities have deleterious effects on soft-sediment benthic assemblages, mainly within mega-epifauna and macrofauna, and are linked with the depletion of essential regulatory ecosystem functions normally mediated by the affected biota. These suggest that the exploitation of the deep-sea natural resources in the SW Portuguese Margin, one of the most disturbed regions by bottom trawlers in Europe, is currently endangering its benthic habitats. Finally, the deleterious effects on the benthic habitats associated with trawling disturbance may not be perceived by the current routinely used monitoring tools for impact assessment and monitoring programmes in marine systems (e.g. univariate indices of diversity) and therefore should be accompanied by other indicators of community composition, ecosystem condition and vulnerability to adequately determine and achieve a Good Environmental Status is deep-sea areas within the European margins.

This study focused on the long-term cycling of radiocaesium in pine forests at Boundary Plantation (Sherwood Forest, England), Chernobyl (Ukraine) and Wat Ban Chan in northern Thailand, each of which received markedly different levels of contamination due to radiocaesium deposition from the atmosphere under different circumstances. Systematic studies were made of stable and radiocaesium, potassium and rubidium in soil horizons, tree stems, needles and throughfall (the latter only at Boundary Plantation). Measurements of total concentrations were complemented with determinations of exchangeable fractions as well as the isotopic exchangeability of radio- and stable caesium. Data from Boundary Plantation and Wat Ban Chan were used to test, validate and calibrate the RIFE (Radionuclides in Forest Ecosystems) model for long-term forecasts of radiocaesium behaviour in forest ecosystems. Finally, modelling of 137Cs migration in forest soils was carried out to describe the relationship between the depth of the forest soil profile and the year of litterfall, to better understand the migration of fallout 137Cs. Boundary Plantation, a forest of semi-natural Corsican pine (Pinus nigra), receives chronic atmospheric fallout from nuclear weapons tests in the 1960s. Forest samples were collected every three months from June 2014 to March 2015 at a 24 randomly located sampling sites. The forest soil has a well-developed surface organic horizon while the mineral soil is composed almost entirely of quartz with no identifiable clay minerals. About 65% of nuclear-weapons fallout 137Cs is distributed within the organic layer (upper 9 cm) and maximum of vertical distribution is 12.9% at 8 cm depth. The accumulation of well-decomposed organic matter in the middle of the organic layer is strongly related to the migration of 137Cs in the soil; modelling describes the relationship between the depth of organic matter accumulating in the upper part of the forest soil profile and the year of litterfall indicates that fallout 137Cs deposited in 1963 has migrated in tandem with organic matter at the same rate of migration from the surface. Soil pH also appears to play a key role in controlling the mobility of Cs isotopes, with the most acidic layers within the soil organic horizons holding the highest 137Cs activity concentrations and having the highest exchangeable 133Cs concentrations. Wat Ban Chan in Thailand is a native tropical forest of Pinus kesiya (or Three-needled pine) which received chronic distribution of atmospheric fallout from nuclear weapons tests in the 1960s. Samples were taken from this site in late February 2016 at six randomly located co-ordinates. The forest soil is typical of similar forest soils in the tropical zone. The organic matter, even at the surface, is much less abundant than in temperate forest soils while the mineral soil is composed almost entirely of quartz with no identifiable clay minerals. About 84% of nuclear weapons fallout 137Cs is distributed within the upper 3 cm and the maximal distribution is 37.6% at 2 cm depth. Even though the organic matter content in the upper 2 – 3 cm of the soil profile is low it probably still plays an important role in the vertical distribution of 137Cs. The variation of soil pH throughout the upper 13 cm of the soil profile is less than 1 pH unit and thus is unlikely to influence the vertical distributions of 137Cs and 133Cs in the soil. K and Rb are strong competitors of Cs during cycling within the forest ecosystems at Boundary Plantation and Wat Ban Chan. K is present in the exchangeable fraction in soil at much higher concentration than Rb and especially Cs. The overall degree of translocation from soil to needles is in the order of 39K > 85Rb > 133Cs. Forest sites surrounding the Chernobyl nuclear power plant in Ukraine received acute and localised deposition of nuclear fallout during the Chernobyl reactor accident in April and May 1986. Samples were taken from four Scots pine (Pinus sylvestris L.) plantations close to Chernobyl in early September 2015. Tree cores were taken at all four sites (Red Forest, North Trace, Kopachi and Bourakovka). Soil cores were also collected at Kopachi where 137Cs behaviour appears similar to 133Cs as indicated by Tag values of 133Cs and 137Cs. Scots pine at the Red Forest and the North Trace sites were exposed to extremely high and acute radiation doses (more than 5.0 mGy/h) in the very early stages of the Chernobyl accident. The surviving Scots pine trees sampled in 2015 show a transient decrease in growth rate for several years after 1986, and then show signs of accelerated growth possibly due to a reduction in competition from surrounding trees (an effect known to foresters as ‘growth release’). Calculations of present day 137Cs distributions using the RIFE model for Boundary Plantation and Wat Ban Chan calibrated with inter-compartmental half-times from seven European (‘SEMINAT’) forest sites proved surprisingly accurate, although the model consistently under- and over-predicted the percentage of the total 137Cs inventories retained in the organic and mineral soil layers, respectively. Site-specific calibrations of the RIFE model were made using newly acquired data for nuclear weapons 137Cs deposited in 1963 at Boundary Plantation and Wat Ban Chan. It is considered that these calibrations are more applicable for long-term predictions of radiocaesium cycling in forests than the SEMINAT calibrations which were based on measurements made less than 10 years after the Chernobyl accident in 1986. Finally, measured unsupported 210Pb activities in forest soil profiles were modelled to describe the relationship between the accumulating depth of organic matter in the forest soil profile and the year of litterfall, to improve understanding of the migration of fallout 137Cs at Boundary Plantation (Sherwood Forest, UK) and in the relatively organic-poor soil at Wat Ban Chan in Thailand.

The impact of natural and anthropogenic disturbances on catchment hydrological and biogeochemical dynamics are difficult or impossible to capture through experimentation or observation alone. Process-based simulation models can address this need by providing a framework for synthesizing data describing catchment responses to climate, harvest, fire, and other disturbances. However, existing models are either too simple to capture important process-level hydrological and biogeochemical controls on ecosystem responses to disturbance, or are too computationally expensive to simulate the local dynamics over large watershed areas, or require a high level of expertise to implement. To this end, a spatially distributed, physically based, eco-hydrological model (VELMA: Visualizing Ecosystems for Land Management Assessments) that is both computationally efficient and relatively easy to implement is developed. VELMA is a state-of-the-art model with real-time visualization tools that shows temporal and spatial patterns of state and flux variables, and is used to address the effects of changes in climate, land-use, and other interacting stressors on multiple ecosystem services such as timber production, carbon sequestration, regulation of water quality and quantity and reduction of greenhouse gases at scales relevant to formulating management decisions. In this study, VELMA was applied to the H.J. Andrews Experimental forest, an intensively studied watershed with observed daily temperature, precipitation, streamflow, and nutrient losses data. VELMA was first used to explore the factors that controls catchment response to forest harvest. Specifically, elucidate how forest harvest factors such as harvest location and amount control watershed hydrological and biogeochemical fluxes. Thereafter, VELMA was used to reconstruct and analyze the impact of two significant disturbance events − a stand replacing fire and a 100% clearcut − on vegetation and soil carbon and nitrogen dynamics. Finally, VELMA was used to explore the potential impact of climate change on catchment hydrological regime, site productivity and carbon and nitrogen dynamics at high spatial resolution relevant to formulating management decision. The main insights from this study include: (1) streamflow, nutrient losses to the stream, and gaseous carbon and nitrogen losses to the atmosphere are strongly sensitive to the location of harvest as a result of the spatial variation in soil water content, plant nitrogen uptake, soil organic carbon decomposition, nitrification, and denitrification within the watershed, (2) forested riparian buffers reduce water and nutrient losses to the stream through plant transpiration, plant nitrogen uptake, soil storage, and soil microbial decomposition, (3) following fire and harvest, losses of N from the terrestrial system to the stream are tightly constrained by the hydrological cycle and driven mainly by wet-season rain events large enough to generate hydrologic connectivity and flushing of nutrients along hillslopes, (4) climate change strongly impacts the hydrological regime in the Pacific Northwest as a result of less snowpack, earlier snowmelt, higher winter streamflow, lower summer streamflow, and soil moisture deficit, and (5) climate change increases plant and soil biomass accumulation as a result of longer growing season and higher soil organic decomposition, reduce water quality by increasing the amount of nutrients that reach the stream, and transforms the ecosystem into a net source of carbon to the atmosphere.

Field ecology has generally focussed on the quantification of patterns in the distribution of biota and attempted to explain these by comparison with variations in habitat conditions. This approach generates hypotheses about causal mechanisms which can be tested experimentally. Such approaches have been used in stream ecology and these have highlighted the role that natural physical disturbance may have in determining patterns in the distribution and abundance of taxa among streams of different regions. In recent years, there has been a great increase in effort to understand factors controlling the distribution and abundance of stream periphyton communities. Awareness has grown of the importance of these communities as food for invertebrates (and thus as a fundamental energy base for streams), as excellent indicators of environmental change, and on a less positive note as causes of degradation in water quality and aesthetic values. The importance of flood disturbance as a determinant of periphyton development has been clearly shown in many early studies (see Chapter 1). In-fact from first principles alone it can easily be argued that streams with a high frequency of flood disturbances are unlikely to suffer from enrichment and nor are their communities going to be subject to heavy invertebrate grazing control. Conversely, nutrients and grazers are likely to become increasingly important with time since the last disturbance event and thus require long interdisturbance stability to be a significant determinant of community development. It is highly possible that the disturbance regime is the most important determinant of community development in streams of the temperate region. However, much of the research undertaken between 1989 and 1995 has focussed on grazing and nutrient enrichment processes in hydrologically stable, continental, streams. Only a limited number of studies have extended our understandings of the importance of disturbance as a major factor controlling periphyton community structure, biomass and production in streams. The goal of the following set of studies was therefore to more clearly define the role of hydraulic disturbance in determining the development of periphyton in streams, and to provide a physical basis upon which disturbance intensity and frequency could be defined. Using this approach I hoped to obtain a much clearer understanding, and ultimately to produce a predictive model, to explain why periphyton communities of streams in one region can be so different from those in another. Following a general review of patterns in periphyton development in natural streams, and an elucidation of the potential importance of hydraulic disturbance in determining these patterns (Chapter 1), I describe a broadscale study of 16 New Zealand streams which investigates the importance of differing disturbance frequencies in controlling average periphyton biomass over a whole year. The contribution, and interactive effects, of nutrient resource supply in determining this pattern are also investigated (Chapter 2). In the third chapter, I describe an experiment designed to determine what shear stresses are required during flood events to dislodge different types of periphyton communities, and thus also determine removal kinetics and resistance properties. In Chapters 4 and 5, I investigate community redevelopment as functions of spatial variation in hydraulic conditions in a stream. Hypotheses are tested regarding differential colonisation, growth and sloughing dynamics in relation to time since a disturbance, and the interaction of these dynamics with hydraulic conditions on the falling stage of the hydrograph. In Chapter 6, I attempt to establish a conceptual basis for understanding the effects of disturbance on periphyton community development and to explain how this interacts with limiting resource supply and invertebrate grazers as major components of the habitat matrix of stream periphyton. This conceptual model is tested using both field (Chapter 7) and experimental (Chapter 8) studies. The field study involved monitoring periphyton development at multiple locations which varied in disturbance and nutrient supply regimes within a single catchment. Average development over a two year period was then compared with predictions made under the disturbance - resource supply - grazer conceptual model. In the experiment, periphyton communities were grown under varying degrees of light and nutrient resource stress, and the effects of a single, simulated disturbance measured in terms of community resistance, resilience and mean biomass. These results are compared with the predictions of the conceptual model. The chapters in this thesis are presented in the form of manuscripts that have been, or will be, submitted to various scientific journals. Inevitably, this has resulted in some repetition of material (particularly review material in the Introductions), and some differences in format including the citation of references. Nevertheless, I have attempted to standardise the layout of chapters as much as possible, and have provided some continuity to the thesis by including linking sections in the form of short prefaces before each chapter.

Stated preference and revealed preference are two commonly conducted non-market value evaluation methods which can also be applied to make evaluation of forest ecosystem. In the application of these evaluation methodologies, there always exists limitation from the data collection and empirical analysis. In the dissertation here, I extend the traditional evaluation methods with novel design or statistical analysis approaches to solve the practical problem we met in evaluation of forest ecosystem. The first and second chapters are based on stated preference methods. The first chapter employ both the mail survey and on-site survey to investigate the preference for attributes of low-impact timber harvesting programs. In the second chapter, we recruit three interest groups for on-site survey and compare their preference for the low-impact timber harvesting programs. In these first two chapters, choice modeling method is employed to elicit the respondents' preferences, and I also use bootstrap method to get robust estimation results for small sample size data. The last chapter employed revealed preference method to evaluate the economic losses from hemlock damages caused by forest pest. Three different interpolation methods are employed to scale-up the analysis from sites to states. Based on the findings of all three chapters, we can see that these survey design and statistical methods help to overcome the limitations in empirical analysis of forest ecosystem and make more robust inferences for design forest protection policies.
Ph. D.

This project was designed to examine the stability of stream ecosystems in response to forest disturbance and subsequent succession. Stability was defined as the ability of streams to retain particulate organic matter and nutrients during storms. I hypothesized that forest streams are least stable during the intermediate stages of forest succession because particulate organic matter accumulations in streams are lowest at that time. This hypothesis was tested by examining stream stability in relation to forest succession. Stream surveys indicated fewer debris dams and organic matter accumulations in streams draining early and intermediate successional forests compared to reference sites. The abundance of large wood declined within 10 years of forest disturbance and continued to decline for at least 30-40 years through the intermediate stages of forest succession. Comparisons of inputs with standing stocks of organic matter indicated that streams draining early and intermediate successional sites receive less litter from their watersheds and processed it faster. Decreases in stream obstructions combined with changes in litter inputs and processing resulted in relatively high storm transport of fine organic matter from disturbed streams. Storm organic matter export from disturbed streams averaged 4.22 g AFDW/m² and from reference streams averaged 1.83 g AFDW/m². Storm nutrient budgets, constructed by measuring nutrient inputs (soil water, throughfall) and outputs (stream discharge) during individual storms indicated that streams draining early and intermediate successional forest were less retentive of nitrogen and phosphorus than reference sites. Nitrogen loss from disturbed streams averaged 58.04 mg/m²/storm and from reference streams averaged 16.52 mg/m²/storm. Phosphorus loss from disturbed streams averaged 32.52 mg/m²/storm and from reference sites averaged 7.14 mg/m²/storm. A majority of the nitrogen and phosphorus loss was in association with organic particles. There was no difference between disturbed and reference streams in potassium, calcium, or sulfate retention during storms. However, disturbed streams tended to lose more particulate organic potassium and calcium than reference sites. These results indicate that forest disturbance has a Iong-term impact on stream ecosystems by reducing their stability for many years following forest clearing.
Ph. D.

Natural habitat in the eastern United States has diminished over the past century because of the effects of invasive species. Both plant and animal invaders can alter habitat structure and may decrease survival of native species. The degree to which an invasive species alters ecosystem function depends on the functional characteristics of affected species and the resulting cascading effects. The loss of important native species, such as foundation species, can potentially influence the structure and distribution of animal communities because of the foundation species' unique ecosystem roles. The foundation species concept is relatively new to the terrestrial ecology and the impact on animal communities resulting in the loss of terrestrial foundation species is generally unknown. Eastern hemlock (Tsuga Canadensis), a foundation species in the eastern United States, is declining in abundance due to the invasive sap-sucking insect, hemlock woolly adelgid (Adelges tsugae, Annand). The loss of hemlock may impact the distribution and microhabitat associations of dependent species such as small mammals. I hypothesized that the distribution, population size, community composition, and microhabitat associations of small mammal species differ in response to canopy disturbance from the effects of logging and invasive species. In this dissertation, Chapter One provides an exploration of the past research conducted on 1) invasive species and how they affect habitat structure, 2) foundation species and how they affect ecosystem function, 3) small mammal habitat associations and population cycling, 4) occupancy modeling and its usefulness and limitations in the analysis of local occupancy, colonization rates, and extinction rates. Chapter Two presents a large-scale experiment on how the hemlock woolly adelgid impacts distribution and community assembly of small mammals. Chapter Three presents how forest disturbance, food resources, and habitat structure effects local colonization and extinction patterns of southern red-backed voles. Chapter Four presents how a paper published in 2005 brought the foundation species concept to terrestrial research and how the foundation species concept can be misleading in research.

Forest models are tools for explaining and predicting the dynamics of forest ecosystems. They simulate forest behavior by integrating information on the underlying processes in trees, soil and atmosphere. Bayesian calibration is the application of probability theory to parameter estimation. It is a method, applicable to all models, that quantifies output uncertainty and identifies key parameters and variables. This study aims at testing the Bayesian procedure for calibration to different types of forest models, to evaluate their performances and the uncertainties associated with them. In particular,we aimed at 1) applying a Bayesian framework to calibrate forest models and test their performances in different biomes and different environmental conditions, 2) identifying and solve structure-related issues in simple models, and 3) identifying the advantages of additional information made available when calibrating forest models with a Bayesian approach. We applied the Bayesian framework to calibrate the Prelued model on eight Italian eddy-covariance sites in Chapter 2. The ability of Prelued to reproduce the estimated Gross Primary Productivity (GPP) was tested over contrasting natural vegetation types that represented a wide range of climatic and environmental conditions. The issues related to Prelued's multiplicative structure were the main topic of Chapter 3: several different MCMC-based procedures were applied within a Bayesian framework to calibrate the model, and their performances were compared. A more complex model was applied in Chapter 4, focusing on the application of the physiology-based model HYDRALL to the forest ecosystem of Lavarone (IT) to evaluate the importance of additional information in the calibration procedure and their impact on model performances, model uncertainties, and parameter estimation. Overall, the Bayesian technique proved to be an excellent and versatile tool to successfully calibrate forest models of different structure and complexity, on different kind and number of variables and with a different number of parameters involved.

Les comunitats fúngiques dels sòls juguen un paper vital en molts processos ecosistèmics forestals, així com en el manteniment de les poblacions d'espècies vegetals. Amb l'aparició de noves tècniques moleculars és possible estimar la diversitat i composició d'aquestes comunitats de forma més precisa i conèixer la seva resposta a pertorbacions com la gestió forestal o els canvis en el clima. L'objectiu principal d'aquesta tesi va ser descriure l'efecte de dos factors en les comunitats fúngiques de sòls forestals: la gestió forestal (concretament les aclarides) i el clima. A més, hem desenvolupat un mètode per analitzar la diversitat i composició d'espores de fongs a l'aire, així com els seus canvis en el temps i en l’espai. Aquesta tesi doctoral es va realitzar sobre un dispositiu experimental consistent en 28 parcel·les forestals localitzades en el Paratge Natural d’Interès Nacional de Poblet i dominades per Pinus pinaster de 60 anys, on es van aplicar aclarides de diverses intensitats. Mitjançant l'ús de diverses tècniques moleculars com la PCR en temps real (qPCR), seqüenciació massiva d'ADN (PacBio RS II, Illumina MiSeq) i l'extracció d'ergosterol, hem descrit les dinàmiques de biomassa i composició fúngica d'aquests sòls forestals, així com de la comunitat aèria (espores). Les dades obtingudes s'han analitzat en un gradient d'humitat i temperatura del sòl, així com també en les aclarides realitzades l’any 2009. Pel que fa a la part metodològica d'aquesta tesi, observem com liofilitzant els sòls es va recuperar el màxim d'ADN i es va evitar el creixement de floridures. Un cop establert el millor tractament d'assecat, es va observar com la sequera d'estiu afectava negativament la biomassa fúngica del sòl i causava importants canvis funcionals i estructurals en les comunitats de fongs. Entre les espècies més resistents a la sequera figuraven els fongs ectomicorízics, probablement per la seva relació simbiòtica amb arbres hoste. Els màxims valors de biomassa fúngica en sòl es van observar a la tardor, coincidint amb majors abundàncies de fongs ectomicorízics, molt probablement a causa d'una redistribució del carboni al sòl per part de la planta hoste. D'altra banda, la majoria de fongs sapròfits es van veure afavorits sota condicions d’alta humitat i baixes temperatures al sòl. A diferència dels factors climàtics, les aclarides realitzades l’any 2009 no van afectar a la composició de fongs als sòls, possiblement degut a que es va deixat un nombre d’arbres suficients per mantenir la comunitat. Finalment, les comunitats d'espores en l'aire variaven a escala espaial però sobretot a escala temporal. Les variacions temporals d'aquesta comunitat es veien condicionades en gran part per la fenologia de la comunitat de bolets. Moltes espècies que produïen cossos fructífers van poder ser detectades a les trampes d'espores, i per tant aquesta tècnica es podria utilitzar per detectar l'emergència de bolets. En base a aquests resultats es pot concloure que 1.- La liofilització és el mètode d'assecat que millor preserva l'ADN de fongs específics i evita el creixement de floridures. 2.- El cicle anual de certes espècies de fongs es pot veure modificat en un context de canvi climàtic, amb menor biomassa fúngica a l'estiu però major biomassa durant l’hivern i primavera. 3.- Les condicions climàtiques afecten les comunitats de fongs segons els seus trets funcionals, essent els fongs ectomicorrízics els que suporten millor les condicions de sequera estiuenca. 4.- Increments d'humitat afavoreixen la proliferació de sapròfits i fongs degradadors de miceli. 5.- Les aclarides no afecten de manera significativa les poblacions de fongs del sòl si es deixen en peu el nombre suficient d'arbres. 6.- Mitjançant l'ús de tècniques moleculars i trampes d'espores, és possible estudiar la comunitat d'espores a l'aire, essent aquesta altament afectada per la fenologia dels cossos fructífers de fongs i mostrant variabilitat espaial i temporal.
Las comunidades fúngicas de los suelos juegan un papel vital en muchos procesos ecosistémicos forestales, así como en el mantenimiento de las poblaciones de especies vegetales. Con la aparición de nuevas técnicas moleculares es posible estimar la diversidad y composición de estas comunidades de forma más precisa y conocer su respuesta a perturbaciones como la gestión forestal o los cambios en el clima. El objetivo principal de esta tesis fue describir el efecto de dos factores en las comunidades fúngicas de suelos forestales: la gestión forestal (concretamente las claras forestales) y el clima. Además, hemos desarrollado un método para analizar la diversidad y composición de esporas de hongos en el aire, así como sus cambios espacio-temporales. Esta tesis doctoral se realizó sobre un dispositivo experimental consistente en 28 parcelas forestales localizadas en el Paraje Natural de Interés Nacional de Poblet y dominadas por Pinus pinaster de 60 años, en las que se aplicaron diferentes intensidades de claras. Mediante el uso de varias técnicas moleculares como la PCR en tiempo real (qPCR), secuenciación masiva de ADN (PacBio RS II, Illumina MiSeq) y la extracción de ergosterol, hemos descrito las dinámicas de biomasa y composición fúngica de estos suelos forestales, así como de la comunidad aérea (esporas). Los datos obtenidos se han analizado en un gradiente de humedad y temperatura del suelo, así como también en las claras realizadas el año 2009. En cuanto a la parte metodológica de esta tesis, observamos como liofilizando los suelos se recuperó el máximo de ADN y se evitó el crecimiento de mohos. Una vez establecido el mejor tratamiento de secado, se observó como la sequía de verano afectaba negativamente la biomasa fúngica del suelo y causaba importantes cambios funcionales y estructurales en las comunidades de hongos. Entre las especies más resistentes a la sequía figuraban los hongos ectomicorrízicos, probablemente por su relación simbiótica con los árboles huésped. Los máximos valores de biomasa fúngica en suelo se observaron en otoño, coincidiendo con mayores abundancias de hongos ectomicorrízicos, muy probablemente debido a una redistribución del carbono en el suelo por parte de la planta huésped. Por otro lado, la mayoría de hongos saprófitos se vieron favorecidos en condiciones de alta humedad y bajas temperaturas en suelo. A diferencia de los factores climáticos, las claras realizadas en 2009 no afectaron a la composición de hongos en suelos, posiblemente debido a que se dejó un número de árboles suficiente para mantener la comunidad. Finalmente, las comunidades de esporas en el aire variaban a escala espacial, pero sobre todo a escala temporal. Asimismo, comprobamos como las variaciones temporales de estas comunidades se veían condicionadas en gran parte por la fenología de la comunidad de setas. Muchas de las especies que producían cuerpos fructíferos pudieron ser detectadas en las trampas de esporas, y por lo tanto creemos que esta técnica podría ser utilizada para detectar la emergencia de setas. En base a estos resultados se puede concluir que 1.- La liofilización es el método de secado de muestras de suelo que mejor preserva el ADN de hongos específicos y previene el crecimiento de mohos. 2.- El ciclo anual de ciertas especies de hongos se puede ver modificada en un contexto de cambio climático, con menor biomasa fúngica en verano, pero mayor durante invierno-primavera. 3.- Las condiciones climáticas afectan a las comunidades de hongos según sus rasgos funcionales, siendo los hongos ectomicorrízicos los que soportan mejor las condiciones de sequía estival. 4.- Incrementos de humedad favorecen la proliferación de saprófitos y hongos degradadores de micelio. 5.- Las claras no afectan de manera significativa las poblaciones de hongos del suelo si se dejan en pie el número suficiente de árboles. 6.- Mediante el uso de técnicas moleculares y trampas de esporas, es posible estudiar la comunidad de esporas en el aire, siendo esta altamente afectada por la fenología de los cuerpos fructíferos de hongos y mostrando una elevada variabilidad espacio-temporal.
Fungal communities inhabiting soils play a vital role in many forest ecosystem processes, as well as in the maintenance of plant species. With the emergence of new molecular techniques, it is possible to estimate the diversity and composition of these communities more precisely and study their responses to disturbances such as forest management or changes in climate. The main objective of this thesis was to describe the effect of two factors in the soil fungal communities: forest management (specifically forest thinnings) and climate. In addition, we have developed a method to study the diversity and composition of airborne fungal spores, as well as their spatio-temporal changes. This doctoral thesis was carried out in an experimental set-up consisting of 28 forest plots located in the Natural Park of Poblet, dominated by 60-year-old Pinus pinaster trees, where thinnings were applied under different intensities. Using several molecular techniques such as real-time PCR (qPCR), high-throughput DNA sequencing (PacBio RS II, Illumina MiSeq) and ergosterol extraction, we have described the fungal biomass dynamics and fungal composition of these forest soils, as well as from the airborne community (spores). The data obtained have been analyzed in a gradient of soil moisture and temperature, as well as in the forest thinnings made in 2009. Regarding the methodological part of this thesis, we observed how maximum DNA recovery and lowest growth of molds occurs under freeze-drying treatments. Once the best drying treatment was established, we observed how summer drought negatively affected the soil fungal biomass and caused important functional and structural changes in the fungal community. Ectomycorrhizal fungi were the most resistant species to drought, probably because of their symbiotic relationship with host trees. The maximum soil fungal biomass was observed in autumn, coinciding with higher abundances of ectomycorrhizal fungi, most likely due to a redistribution of soil carbon by the host plant. On the other hand, most saprotrophic fungi were promoted under conditions of high soil moisture and low temperatures. Unlike climatic factors, the forest thinnings made in 2009 did not affect the soil fungal community, likely because a sufficient number of trees were left to support the community. Finally, the airborne spore community changed at spatial scale, but especially at temporal scale. We verified how the temporal variations of these communities were largely determined by fruiting body emergence. Many of the species that produced fruiting bodies could be detected in the spore traps, and therefore this technique could be used to detect fruiting body emergence Based on these results, it can be concluded that 1.- Freeze-drying is the method that best preserves the DNA of specific fungi and prevents the growth of molds. 2.- The annual cycle of specific fungal species can be modified in a context of climate change, with predicted lower fungal biomass in summer, but higher biomass during winter-spring. 3.- Micro-climatic soil conditions affect fungal communities according to their functional traits, with ectomycorrhizal fungi being the ones that better resist summer drought conditions. 4.- High soil moisture promote the proliferation of saprotrophs. 5.- Forest thinnings does not affect significantly the soil fungal communities if enough trees are left standing. 6.- It is possible to study the airborne spore community using spore traps and molecular techniques, being these communities highly affected by the phenology of the fruiting bodies and showing spatio-temporal variability.

Thesis (Ph.D.)--Indiana University, School of Public Environmental and Affairs, 2008.
Title from PDF t.p. (viewed on Jul 28, 2009). Source: Dissertation Abstracts International, Volume: 69-12, Section: B, page: 7386. Adviser: James C. Randolph.

Abstract Climate change and its warming effects on vegetation and soils are a widely recognized phenomenon. In addition to warming, the understorey vegetation in northern environments has been subjected to several environmental changes, such as increasing nitrogen (N) and other disturbances. This thesis examines the effects of N-fertilization and disturbances on the vegetation biomass and abundance, plant community composition and plant, soil and microbial N and C pools. Seedling establishment of the most common dwarf shrubs (deciduous Vaccinium myrtillus, evergreens V. vitis-idaea and Empetrum nigrum ssp. hermaphroditum) was investigated after artificial disturbance treatments (vegetation and soil removal). These studies were conducted in the boreal and subarctic ecosystems and in the forest-tundra ecotone in northern Finland. N-fertilization and disturbances enhanced the amount of graminoids in plant communities, and the recovery ability of graminoids was enhanced after N-fertilization, which homogenized the vegetation and resulted in a new stable state in the plant community. The recovery ability of evergreen dwarf shrubs was low after disturbances. Disturbances created habitats for seed germination, but the seedling establishment of dwarf shrubs studied was still limited by seed availability. N-fertilization had no effect on microbial biomass. Instead, microbial biomass decreased with disturbance treatment in the boreal forest. However, the concentration of N increased in above-ground vegetation, both after N-fertilization and disturbance without any indication of N immobilization, suggesting that plant species captured the available N effectively for their recovery. The study shows that the likely outcome of N enrichment, when combined with disturbances, is the enhanced growth of graminoids. The seedling establishment does not compensate for the reduction of the vegetative recovery of evergreen dwarf shrubs, which makes evergreen dwarf shrubs sensitive to environmental changes. As the understorey is more resilient to perturbations in the boreal forest than in the subarctic ecosystem, these results emphasize the sensitivity of the vegetation to simultaneous environmental changes in the northernmost ecosystems. Moreover, microbial properties are more resilient to environmental changes than is above-ground vegetation
Tiivistelmä Ilmaston muutos ja siitä aiheutuvan lämpenemisen vaikutus kasvillisuuteen ja maaperään on laajasti tunnustettu ilmiö. Lämpenemisen lisäksi pohjoisten alueiden aluskasvillisuuteen kohdistuu useita muutospaineita, kuten lisääntynyt typpipitoisuuden nousu ja kasvillisuutta muokkaavat häiriöt. Tässä tutkimuksessa mitattiin lisääntyneen typpipitoisuuden ja häiriöiden vaikutus kasvillisuuden biomassaan ja runsauteen sekä yhteisörakenteeseen, sekä kasvilajeihin, maaperään ja mikrobibiomassaan sitoutuneen typen ja hiilen määrään. Lisäksi tutkittiin yleisimpien varpukasvien (lehtensä pudottava mustikka, ikivihreät puolukka ja variksenmarja) siemenellistä lisääntymistä kokeellisen häiriön (kasvillisuuden tai maaperän poisto) jälkeen. Tutkimukset tehtiin boreaalisessa ja subarctisessa ekosysteemeissä sekä metsänrajaympäristössä Pohjois-Suomessa. Typpilannoitus ja häiriöt lisäsivät heinien määrää kasviyhteisöissä. Lisäksi typpilannoitus edisti heinien kasvullista palautumiskykyä häiriön jälkeen, joka johti kasvillisuuden homogenisoitumiseen ja kasviyhteisön uuteen tasapainotilaan. Häiriöt heikensivät ikivihreiden varpujen kasvullista palautumista häiriön jälkeen. Häiriö loi sopivia elinympäristöjä siementen itämiselle, mutta tutkittujen lajien siementen määrä rajoitti siemenellistä lisääntymistä. Typpilannoitus ei vaikuttanut mikrobibiomassaan, mutta häiriö vähensi mikrobibiomassaa boreaalisessa ekosysteemissä. Kuitenkin kasvien typen pitoisuudet lisääntyivät sekä lannoituksen että häiriön jälkeen ilman viitteitä typen sitoutumisesta mikrobibiomassaan. Tämä viittaa siihen, että kasvit käyttävät maaperän typen tehokkaasti häiriön jälkeiseen palautumiseen. Väitöskirjan mukaan typen lisääntyminen häiriöiden yhteydessä edistää heinien esiintymistä. Koska ikivihreiden varpujen siemenellinen lisääntyminen ei kompensoi häiriöstä kasvulliselle palautumiselle aiheutuvaa haittaa, ovat ikivihreät varvut erityisen herkkiä häiriöille. Aluskasvillisuus on vastustuskykyisempi ympäristön muutoksille boreaalisessa kuin subarktisessa ekosysteemissä, mikä korostaa pohjoisimpien alueiden herkkyyttä yhtäaikaisille ympäristön muutoksille. Maaperän olosuhteet ovat kasvillisuutta kestävämpiä ympäristön muutoksille

Abstract The effect of biodiversity loss and change on the functioning of ecosystems is one of the key questions in ecological research. For stream ecosystems, compelling evidence indicates that species diversity may enhance ecosystem functions. However, ecosystem functions are often regulated by the same environmental factors that also shape diversity; thus, a major challenge for ecologists is to separate the effects of biodiversity loss on the ecosystem functions from the direct effects of human induced disturbance. In this doctoral thesis, I studied how decomposer communities and ecosystem functions respond to human disturbances (nutrient enrichment, acidification) and a natural stressor (naturally low water pH). I also studied how human disturbances and natural stressors affect the phylogenetic structure of stream fungal communities. I showed that human disturbance had a strong impact on species dominance patterns by reducing species evenness. Species dominance patterns also explained the variation in decomposition rates. Changes in abiotic variables also had a direct effect on leaf decomposition rates. In the naturally acidic sites, human impact (land drainage) further decreased water pH and increased metal concentrations, thereby reducing leaf decomposition rates, whereas high nutrient concentrations enhanced leaf decomposition. Naturally low pH had no effect on decomposition rates. Decomposer community similarity was higher in drainage-impacted sites, but only in naturally acidic, not in circumneutral, streams. Human induced disturbance also modified the phylogenetic similarity of fungal decomposer communities, with communities in disturbed sites consisting of more closely related species when compared to those in circumneutral reference sites. Leaf litter decomposition showed greater temporal variation in human disturbed sites than in reference sites, whereas fungal community variability was similar in disturbed and reference sites. Thus, temporally replicated monitoring may be needed for a reliable assessment of human disturbance in streams. My thesis emphasizes that using both functional and taxonomic measures allows a more comprehensive assessment of biological responses to human disturbance
Tiivistelmä Biodiversiteetin väheneminen ja siitä seuraava ekosysteemin toiminnan heikkeneminen on eräs keskeisimmistä ekologisista kysymyksistä. Ekosysteemin toiminnot ovat kuitenkin monesti yhteydessä ympäristöolosuhteisiin, joten on vaikea erottaa vähentyneen biodiversiteetin ja ympäristöolojen suhteellista merkitystä ekosysteemien toimintoihin. Tässä väitöskirjatyössäni tutkin, kuinka virtavesien hajottajayhteisöt ja ekosysteemin toiminnot (lehtikarikkeen hajotus) muuttuvat valuma-alueen ihmistoimintojen myötä. Tutkin myös, kuinka luontainen stressi (matala pH) vaikuttaa yhteisöihin ja ekosysteemin toimintoihin. Tarkastelen myös akvaattisten sienten fylogeneettistä rakennetta ihmistoiminnan muuttamissa vesiympäristöissä. Osoitan tutkimuksissani, että ihmistoiminnoilla on vaikutuksia hajottajayhteisöiden kokonaisrunsauden jakautumiseen lajien kesken. Muutamien runsaiden lajien dominoimissa yhteisöissä lehtikarikkeen hajoaminen on tehokkaampaa kuin yhteisöissä, joissa lajien runsauserot ovat pienempiä. Myös ympäristöoloilla on vaikutus lehtikarikkeen hajotukseen. Luontaisesti happamissa puroissa metsäojituksen seurauksena lisääntynyt veden metallipitoisuus ja alhainen pH vähentävät hajotuksen määrää. Toisaalta joen korkea ravinnepitoisuus lisää hajotusta. Lehtikarikkeen hajotus vaihtelee enemmän vuosien välillä ihmistoimintojen muuttamissa virtavesissä kuin luonnontilaisissa vesissä. Toisaalta sieniyhteisöt pysyvät koostumukseltaan samankaltaisina vuosien välillä ihmistoiminnan muuttamissa paikoissa ja referenssipaikoissa. Tämä työ osoittaa, että toiminnallisten ja yhteisöihin perustuvien indikaattorien yhteiskäyttö antaa kokonaisvaltaisimman kuvan ihmistoimintojen vaikutuksesta virtavesien ekosysteemeihin

In the work described in this thesis I studied how increases in nitrogen (N) inputs may affect plant community structure in boreal forest understorey vegetation. These phenomena were investigated in N fertilization experiments and along a national N deposition gradient. After five years of N additions, large changes in understorey vegetation composition were observed in the fertilization study. In plots that received 50 kg N ha'1 year"1 (N2), the abundance of the dominant species, Vaccinium myrtillus, decreased on average by 32 %. No decrease was observed in control plots during the same period. In contrast, the grass Deschampsia flexuosa responded positively to increased N input, being on average more than five times as abundant in the N2 treatments as in controls. Also an increase was seen in the incidence of disease caused by the parasitic fungus Valdensia heterodoxa on leaves of V. myrtillus following N additions. The parasite was on average nearly twice as abundant in N2 plots than in control plots. This could be explained by increased N concentrations in host plant tissue. Disease incidence also increased following experimental additions of glutamine to leaf surfaces of V. myrtillus, suggesting a causal connection between plant N concentration and performance of the fungus. The parasite also played a key role in the observed changes in understorey species composition. D. flexuosa was more abundant in patches in which V. myrtillus was severely affected by V heterodoxa. This suggests that V heterodoxa mediates the increased abundance of D. flexuosa following increased N additions. The fungus mediates changes in the composition of understorey vegetation mainly by increasing light availability via premature leaf loss of V. myrtillus. The incidence of disease due to the parasite was on average higher in large than in smaller N-treated plots, indicating that the response to N fertilization is spatially scale dependent. This shows that using small plot sizes in experiments that simulate changed environmental conditions may be problematic, as important interactions may be underestimated. Comparison of the occurrence of understorey species between regions with different rates of N deposition revealed that the occurrence of the two dwarf shrubs V. myrtillus and V. vitis- idaea was lower in regions with high N deposition compared to regions with low deposition. The opposite pattern was found for V heterodoxa. This is consistent with expectations from N fertilization experiments. For D. flexuosa no differences in occurrence were found between the different regions investigated. The effects on vegetation and mycorrhizal fungi observed following N additions were also found to be long lasting. Nine years after termination of the fertilization, no signs of recovery were detected, and nearly 50 years after termination characteristic signs of N fertilization were found among bryophytes and mycorrhizal fungi. This suggests that the time needed for re-establishment of the original biota following N-induced changes may be substantial.

Diss. (sammanfattning) Umeå : Umeå universitet, 2002, härtill 5 uppsatser

digitalisering@umu

Forests provide a number of ecosystem services which sustain and enrich the wildlife, human societies, and the environment. However, many disturbances threaten forest ecosystems, making it necessary to monitor their health for optimal management and conservation. Although there are many indicators of forest health, changes in biogeochemical cycling, loss of species diversity, and invasive plants are particularly useful due to their vulnerability to the effects of climate change and intensive agricultural land use. Thus, this work evaluates the use of imaging spectroscopy to monitor forest nutrient status, species diversity, and plant invasions in the Mid-Atlantic region. The research is divided into four separate studies, each of which evaluated a unique application for imaging spectroscopy data at a different scale within the forest. The first two studies examined loblolly pine nutrient status at the leaf and canopy scales, respectively. The first study determined that loblolly pine foliar macronutrient concentrations can be successfully modeled across the Southeastern US (R2=0.39-0.74). Following on these results, the second study focused on the relationship between physical characteristics, reflectance, and nutrients. Reflectance values and W scattering coefficients produced successful nitrogen models across loblolly pine plots at the canopy scale. Regression models showed similar explanatory power for nitrogen, although W scattering coefficients were significantly correlated with nitrogen at multiple wavelengths and reflectance variables were not. However, the direction of some of the correlations with W and the unusually high directional area scattering factor values indicate a need for further experimentation. The third study found that several imaging spectroscopy algorithms were moderately successful in identifying wavyleaf basketgrass invasions in mixed deciduous forests (overall accuracy=0.35-0.78; kappa=0.41-0.53). Lastly, the fourth study used a novel imaging spectroscopy/lidar fusion to identify canopy gaps and measure species diversity of understory vegetation. The lidar algorithm identified 29 of 34 canopy gaps, and regression models explained 49 percent of the variance in gap species diversity. In conclusion, imaging spectroscopy can be used to evaluate ecosystem health through forest nutrient status, nitrogen models, species diversity estimates, and identification of invasive plant species.
Ph. D.

Kyoto University (京都大学)
0048
新制・課程博士
博士(農学)
甲第11615号
農博第1471号
新制||農||905(附属図書館)
学位論文||H17||N4008(農学部図書室)
23258
UT51-2005-D364
京都大学大学院農学研究科地域環境科学専攻
(主査)教授 武田 博清, 教授 二井 一禎, 教授 東 順一
学位規則第4条第1項該当

Doutoramento em Engenharia Florestal e dos Recursos Naturais - Instituto Superior de Agronomia. Universidade de Lisboa
This work focuses on innovating forest ecosystem management planning and on enhancing its contribution to the provision of ecosystem services. A web-based forest decision support system was developed to support public and private forest managers, involving operational research methods. First, all work related to database management and the integration of data was carried out. Databases were created with PostgreSQL, which on the one hand facilitated the development of multi-criteria linear programs, and on the other met all the data and information needs of a forest decision support system, not only for data processing and information presentation, but also as a source to be consulted and analyzed by forest decision makers. The wSADfLOR, a forest web-based decision support system, integrates one analytic tool to visualize interactive decision maps showing the decision space and trade-offs among the criteria in Pareto frontiers, according to forest users’ management options. Taking advantage of constant improvements in the Interactive Decision Maps tool in wSADfLOR, a second article was developed regarding a web-based approach to show interactive decision maps with Pareto frontiers. Based on these interactive decision maps and jointly with some decision support systems available in the EMDS platform (Criterion DecisionPlus and NetWeaver), a hybrid decision methodology for cases in which there is no consensus among the solutions chosen by different (groups of) forest decision makers was developed, enabling them to choose a unique strategic decision plan
N/A

Forest disturbance is expanding in rate and extent and is affecting many montane catchments critical to water resources. Western North America is experiencing an epidemic of mountain pine beetle (MPB) that has affected 20 million hectares of forest in Canada and the United states. This epidemic may have long-lasting consequences for coupled cycles of water, energy, and biogeochemicals. While impacts of forest disturbance by fire and harvest have been studied for more than a half-century, insect-driven mortality differs from these events in the timing and accompanying biophysical impacts. In this work, we quantified catchment hydrologic and hydrochemical response to severe MPB infestation in a lodgepole pine ecosystem. Observations were organized laterally in a nested fashion from soil observations to nested headwater catchments. Vertical observations encompassed what is often termed the critical zone, from atmospheric interactions at the top of the forest through the ground surface and the rooting zone to the interface with groundwater. We quantified responses manifest in snowpack, the primary hydrologic input to this montane ecosystem, in water partitioning between vapor flux and streamflow, and in biogeochemical patterns across the landscape. Key findings of this study include 1) Loss of shelter from the atmosphere caused compensatory sublimation of snowpack to offset decreased interception losses after MPB-driven canopy loss; 2) Vaporization at multiple scales increased over time and in comparison to control forest, reducing water available for streamflow; 3) Nitrogen (N) concentrations were elevated in hillslope groundwater, but attenuation in the riparian zone protected streams from major N influx; and 4) headwater streams rapidly attenuated dissolved carbon (C) and N inputs. Collectively these results demonstrate compensatory negative feedbacks which help explain the lack of strong response to streamflow and stream chemistry observed in the recent MPB epidemic.

Forest ecosystems are being altered by climate change, invasive species, and additional stressors. Our ability to detect these changes and quantify their impacts relies on detailed data across spatial and temporal scales. This dissertation expands the ecological utility of long-term satellite imagery by developing high quality forest mapping products and examining spatiotemporal changes in tree species abundance and phenology across the northeastern United States (US; the ‘Northeast’). Species/genus-level forest composition maps were developed by integrating field data and Landsat images to model abundance at a sub-pixel scale. These abundance maps were then used to 1) produce a more detailed, accurate forest classification compared to similar products and 2) construct a 30-year time-series of abundance for eight common species/genera. Analyzing the time-series data revealed significant abundance trends in notable species, including increases in American beech (Fagus grandifolia) at the expense of sugar maple (Acer saccharum). Climate was the dominant predictor of abundance trends, indicating climate change may be altering competitive relationships. Spatiotemporal trends in deciduous forest phenology – start and end of the growing season (SOS/EOS) – were examined based on MODIS imagery from 2001-2015. SOS exhibited a slight advancing trend across the Northeast, but with a distinct spatial pattern: eastern ecoregions showed advance and western ecoregions delay. EOS trended substantially later almost everywhere. SOS trends were linked to winter-spring temperature and precipitation trends; areas with higher elevation and fall precipitation anomalies had negative associations with EOS trends. Together, this work demonstrates the value of remote sensing in furthering our understanding of long-term forest responses to changing environmental conditions. By highlighting potential changes in forest composition and function, the research presented here can be used to develop forest conservation and management strategies in the Northeast.

We are currently faced with the global challenge of conserving biological diversity while also increasing food production to meet the demands of a growing human population. Land-use change, primarily resulting from conversion to production land, is currently the leading cause of biodiversity loss. This occurs through habitat loss, fragmentation of remaining natural habitats, and resulting edge effects. Land-sparing and land-sharing approaches have been discussed as alternative ways to engineer landscapes to mitigate biodiversity loss while meeting production objectives. However, these represent extremes on a continuum of real-world landscapes, and it will be important to understand the mechanisms by which adjacent land use affects natural remnant ecosystems in order to make local land-management decisions that achieve conservation, as well as production, objectives. This thesis investigates the impact of juxtaposing production and natural forest on the community-wide interactions between lepidopteran herbivores and their parasitoids, as mediated by parasitoid spillover between habitats. The first and overarching objective was to determine whether herbivore productivity drives asymmetrical spillover of predators and parasitoids, primarily from managed to natural habitats, and whether this spillover alters trophic interactions in the recipient habitat. The study of trophic interactions at a community level requires understanding of both direct and indirect interactions. However, community-level indirect interactions are generally difficult to predict and measure, and these have therefore remained understudied. Apparent competition is an indirect interaction mechanism thought to be very important in structuring host-parasitoid assemblages. However, this is known primarily from studies of single species pairs, and its community-wide impacts are less clear. Therefore, my second objective was to determine whether apparent competition could be predicted for all species pairs within an herbivore assemblage, based on a measure of parasitoid overlap. My third objective was to determine whether certain host or parasitoid species traits can predict the involvement of those species in apparent competition. My key findings were that there is a net spillover of generalist predators and parasitoids from plantation to native forest, and that for generalists, this depends on herbivore abundance in the plantation forest. Herbivore populations across the edge were linked by shared parasitoids in apparent competition. Consequently, an experimental reduction of herbivore density in the plantation forest changed parasitism rates in the natural forest, as predicted based on parasitoid overlap. Finally, several host and parasitoid traits were identified that can predict the degree to which host or parasitoid species will be involved in apparent competition, a finding which may have extensive application in biological control, as well as in predicting spillover edge effects. Overall, this work suggests that asymmetrical spillover between production and natural habitats occurs in relation to productivity differences, with greater movement of predators and parasitoids in the managed-to-natural forest direction. The degree to which this affected species interactions has implications for landscape design to achieve conservation objectives in production landscapes.