Academic literature on the topic 'Ecotones'

Thesis (M.S.)--University of North Carolina at Chapel Hill, 2009.<br>Title from electronic title page (viewed Jun. 26, 2009). "... in partial fulfillment of the requirements for the degree of Masters of Science in the Department of Biology." Discipline: Biology; Department/School: Biology.

Con questa tesi di dottorato si è applicato un approccio multi-scala per l'analisi delle dinamiche spazio-temporali di specie arboree negli ecotoni di treeline di origine antropica nell'Europa meridionale, nel contesto dei cambiamenti di uso del suolo e climatici in atto. In primo luogo, abbiamo analizzato la posizione e la composizione specifica delle treeline negli Appennini, cercando di definire su più scale spaziali in che modo il cambiamento climatico, la topografia e l'impatto dell'uomo avessero influito ed influissero sui cambiamenti della copertura del suolo, sulla quota della treeline e sulla composizione delle specie arboree dominanti. In secondo luogo, abbiamo studiato le recenti dinamiche di innalzamento della treeline antropogena, che sono una caratteristica comune nei paesaggi montani in tutta Europa e in particolare nelle aree ad alta quota del bacino mediterraneo. Abbiamo analizzato questo processo in quattro siti negli Appennini centrali (Italia), i quali hanno in comune la presenza di popolamenti di pino nero europeo (Pinus nigra Arn.). Il passo successivo è stato quello di valutare il verificarsi di dinamismi simili in altre treeline che ospitano diverse specie di pino autoctono. Abbiamo confrontato il processo di ricolonizzazione di quattro diverse specie (Pinus heldreichii, Pinus peuce, Pinus sylvestris e Pinus uncinata) in nove ecotoni di treeline antropogene. L'ultimo capitolo della tesi è un approfondimento su una nuova applicazione di telerilevamento (Laser scanner ALS), che permette la definizione di altezza e posizione delle singole piante; questa tecnologia risulterebbe applicabile anche in ambienti di limite del bosco, riducendo costi e tempo di rilievo, affiancata alle tecniche tradizionali di campo.<br>This research is aimed to apply a multi-scale approach to the analysis of the spatial-temporal dynamics of forest tree species at anthropogenic treeline ecotones in Southern Europe, within the context of land-use and climate changes. Firstly, we explored the position and species composition of the treelines in the Apennines. We searched how climate, topography and human impact affected land cover changes, elevation of treelines and dominant tree species composition at multiple spatial scales. Secondly, we investigated the recent dynamics of human-shaped treelines, which are a common feature in mountain landscapes across Europe and particularly in secularly managed Mediterranean high-elevation areas. We explored this process in four anthropogenic treeline ecotone sites in the Central Apennines (Italy) populated by European black pine (Pinus nigra Arn.). The following step was to assess the occurrence of similar dynamic processes in other human-shaped treelines hosting native pine species. We compared the recolonization process of four different pine species (Pinus heldreichii, Pinus peuce, Pinus sylvestris and Pinus uncinata) at nine anthropogenic treeline ecotones. The last chapter of the thesis is a new technology application for the detection of tree heights and of treeline position and dynamics at landscape scale. Airborne laser scanning-based (ALS) and traditional field-based survey methods for tree heights estimation in forest stand are assessed by using one hundred felled trees as reference dataset.

Alpine treeline ecotones (ATE) are the transition zones between contiguous subalpine forest and open alpine tundra. Because of their transitional natures formed by different ecosystems in high mountain areas, there are a variety of acute interactions between different species, between vegetations and environmental factors, and between ecological pattern and process. These interactions, or feedbacks, are often nonlinear in nature and make alpine treeline ecotones sensitive to environmental change, especially climate change. Feedbacks or nonlinear interactions between pattern and process create a variety of distinctive yet sometime surprising alpine treeline patterns. These nonlinear interactions between pattern and process and their resultant various patterns are defined as spatial complexity. In this study, the research framework of complexity theory was adopted. Dynamical simulations of alpine treeline ecotone is used as basic research method, and local nonlinear interactions, or more specifically, positive feedbacks are considered the key mechanism driving alpine treeline dynamics. A cellular simulation was created with tree/no-tree states that change as a function of probabilities of tree establishment and mortality which are functions of the neighborhood and an underlying gradient; the former changes in space and time endogenously; the latter can change in space and time exogenously. Three research projects were conducted for this dissertation that explore the endogenous and exogenous aspects of alpine treeline dynamics. First, the endogenous dynamics of alpine treeline ecotones was examined, which indicates that local positive feedbacks originated from interactions between trees can create fractal spatial dynamics in space and time. Second, the impacts of geomorphologic factors that impose an exogenous spatial structure on alpine treeline dynamics, was examined, which shows that there is a geomorphic limit to the endogenous fractal alpine treeline dynamics. Third, the impacts of climate change that imposes an exogenous temporal structure on alpine treeline dynamics was examined, which suggests that the self-organization nature of alpine treeline dynamics will not be significantly affected by external climate change and the use of alpine treeline ecotones as potential indicator of climate change is called into question. Results of this study suggest further research using complexity theory is needed to improve our understanding of alpine treeline dynamics and their interactions with exogenous environmental factors.

Part of the intorduction: The task of writing a reliable and convincing paper on this topic is a very uneasy one because it is threefold: one has to know at least a bit about the agricultural sector, biology (or more precisely ecology), and about the sometimes beneficial but often distorting consequences of human activities. And all that has to be judged from the perspective of an economist who is aware of the steadily increasing uncertainties which are closely connected with post-modem sciences. Especially with regard to global, but also regional environmental issues, neither the conventional applied sciences nor the traditional professional consultancy deliver promising results. Today scientists have to tackle problems which are created by political necessities overwhelmingly caused by short-term human behavior, due in part to a serious lack of information on the longterm behavioral consequences. In these issues, typically, information stacks are high, scientific facts uncertain, individual as well as collective values disputed, and political decisions very urgent. "In general, the post-normal situation is one where the traditional opposition of 'hard'facts and 'soft' values is inverted. Here we find decisions that are 'hard' in every sense, for which the scientific inputs are irremediably 'soft'" (FUNTOWICZ/RAVETZ, 1991, p. 138).

In contrast to documented increases in woody plant dominance of former savannas and grasslands of North America, oak (Quercus L.) savannas that form lower treelines in the southwestern United States and northwestern Mexico have been relatively stable over the past millennium. This research identified potential biotic and abiotic constraints on seedling recruitment of Quercus emoryi Torr. (Emory oak) within the context of potential shifts in lower treeline. Field surveys were used to describe seedling distribution at and below lower treeline, and to determine the potential for acorn dispersal from lower treeline into adjacent grassland. Field and greenhouse experiments designed to determine constraints on seedling establishment included reciprocal soil transfers, nutrient amendment studies, provision of artificial shade, and manipulation of seasonal precipitation inputs. Results indicate that rates of Q. emoryi recruitment within grasslands below treeline are relatively low, and are constrained by low rates of seed dispersal coupled with a low probability of seedling emergence. Seedling recruitment rates were directly correlated with quantity of summer precipitation, but were independent of winter precipitation. Results of this and complementary research suggest that lower treeline in southern Arizona is stabilized by self-enhancing feedback mechanisms of overstory shade, seed dispersal, and seedling establishment coupled with strong abiotic constraints beyond the current ecotone. The observed shift in treeline in the last millennium was less likely the result of slow, spatial progression of autogenic safe sites than the result of episodic and infrequent allogenic processes that simulated, or negated the importance of, conspecific, biogenic safe sites. Increases in summer precipitation are one such process that would facilitate (historic or potential future) downslope shifts in lower treeline. This interpretation is consistent with observations that downslope shifts in lower treeline which occurred 700-1700 ybp coincided with a period of particularly high summer precipitation in the region (i.e., the "Medieval Warm" period, 645-1295 ybp).

We reconstructed historical fire regimes of montane forest-grassland ecotones in the ~40,000 ha Valles Caldera National Preserve, New Mexico. We used a targeted approach to sample ancient fire-scarred trees along the ecotone, and compared variations in historical fire occurrence within and among valles in the grassland-forest. The resulting tree-ring record extends from 1240-2008 C.E., comprised of 2,443 fire scars from 330 trees representing 238 fire years during the period of analysis, 1601-1902 C.E. Our results confirm pre-1900 historical occurrence of high-frequency, low-severity surface fires over multiple centuries in the ecotone. Mean fire intervals for all fires were 5.5-22.5 years (~6-123 ha) at individual sites, 2.7-10 years (~67-4955 ha) in individual valles, and 1.6 years (~10 386 ha) across the landscape. Synchronous fires burned extensively and occurred at ~10 year intervals during years with significantly low PDSI. Results will be useful in planning forest/grassland restoration actions and reinstituting fire regimes.