Tesi sul tema "Tropical cloud forest"

Light spectra distributions were measured in two different montane forests: temperate and tropical. Spectral light measurements were made in different sized canopy gaps in the conifer forest at H. J. Andrews Experimental Forest in Oregon, USA. Researchers at Oregon State University created these gaps of 20 m, 30 m, and 50 m in diameter. In the tropical cloud forest, spectral light measurements were made in two plots that were permanently established at La Mucuy Parque Nacional in Venezuela, in collaboration with researchers at Universidad de Los Andes. In both studies, spectra and distributions of physiologically active light were analyzed: red, far-red, R/FR ratio, and blue light.

Many tropical trees do not form reliable annual growth rings, making it a challenge to develop tree-ring width chronologies for application to paleoclimatology in these regions. Here, I seek to establish high-resolution proxy climate records from trees without rings from the Monteverde Cloud Forest in Costa Rica using stable isotope dendroclimatology. Neotropical cloud forest ecosystems are associated with a relatively narrow range of geographic and hydroclimatic conditions, and are potentially sensitive to climate variability and change at time scales from annual to centennial and longer. My approach takes advantage of seasonal changes in the d18O of water sources used by trees over a year, a signature that is imparted to the radial growth and provides the necessary chronological control. A rapid wood extraction technique is evaluated and found to produce cellulose with d18O values indistinguishable from conventional approaches, although its application to radiocarbon requires a statistical correction. Analyses of plantation-grown Ocotea tenera reveal coherent annual d18O cycles up to 9 permil. The width of these cycles corresponds to observed basal growth increments. Interannual variability in d18O at this site is correlated with wet season precipitation anomalies. At higher elevations within the orographic cloud bank, year-to-year changes in the amplitude of oxygen isotope cycles show a relationship with dry season climate. Longer d18O chronologies from mature Pouteria (Sapotacae) reveal that dry season hydroclimatology is controlled at interannual time scales by variability in the eastern equatorial Pacific (ENSO) and the Western Hemisphere Warm Pool (WHWP), which are correlated with trade wind strength and local air temperature. A change in the late 1960s toward enhanced annual d18O amplitude may reflect low frequency changes in the Atlantic and Pacific ocean-atmosphere system. This study establishes the basis for cloud forest isotope dendroclimatology and demonstrates that the local climate of neotropical cloud forests is sensitive to interannual, and perhaps, multidecadal changes in important large-scale modes of climate variability.

Thesis (M. S.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2009.
Committee Chair: Rong Fu; Committee Member: Robert Dickinson; Committee Member: Robert X. Black. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Tropical montane cloud forests (TMCF) are one of the most fascinating, but least understood ecosystems in the world, and the interest in the carbon (C) cycle of TMCFs with regard to carbon sequestration and storage practices has increased rapidly in recent years. One feature that prevails in all TMCFs is a decrease in aboveground net primary productivity (ANPP) and standing biomass and leaf area index (LAI) with increasing altitude, together with the stunted growth form of the trees. This thesis focuses on the input part of the TMCF C-cycle, and investigates the controlling factors on photosynthesis on a leaf, canopy, and ecosystem level in the Kosñipata valley in south east Peru, on the eastern slope of the Andes (13º11’28’’S / 71º35’24’’W). Leaf traits are known to relate to foliar C-exchange, and compared with other altitudinal transect studies of TMCFs, the studied sites had similar altitudinal trends for foliar nitrogen (N) content (though not for phosphorus) and leaf mass per area (LMA), with N content decreasing and LMA increasing with altitude. N concentrations were relatively high and LMA values relatively low, but this observed relationship was consistent with those found in global leaf trait surveys. Examining plant stoichiometry (i.e. N:P ratios), the data suggests that unlike the general hypothesis, the Kosñipata forests are not N limited, except for the study site at 2990 m a.s.l. At the 2990 m a.s.l. site, which is the focal study site of the thesis, photosynthetic parameters Vcmax (the carboxylation efficiency of the Rubisco protein) and Jmax (the electron transport efficiency) proved to be similar to those found in lowland tropical rainforest leaves when expressed on an area basis and standardised to 25 °C (55.6 ± 2.6 and 106.5 ± 5.2 mmol m-2 s-1, for Vcmax and Jmax, respectively). However, when standardised to the mean ambient TMCF temperature of 12.5 °C, both photosynthetic parameters were much lower than ambient tropical rainforest Vcmax and Jmax values. The TMCF Jmax -Vcmax relationships were steeper than found in other tropical biomes, indicating a possible adaptation to the lower light availability in TMCFs because of frequent cloud cover, or a consequence of little atmospheric evaporative demand, which is also due to the humid conditions in this forest type. Although N-Vcmax relationships were significant (P<0.05), the fit was not very strong and the relationship between nitrogen use efficiency (NUE) and Vcmax indicates that TMCF species can be regarded as a different plant functional type compared with other tropical forest types. Diurnal measurements of net photosynthesis (A), stomatal conductance (gs) and leaf water potential (Yleaf) showed that different TMCF species experienced non-contrasting diurnal patterns of Yleaf and gs in the dry season. The observed patterns suggest that some TMCF species can be classified as isohydric species, while others behave anisohydrically. Additionally, in situ gs was not very responsive to these to the range of experienced photosynthetically active radiation (PAR), vapour pressure deficit (VPD) or soil water content (SWC), leading to the conclusion that in the studied TMCF, drought stress does not play a role in C-uptake. When using the measured photosynthetic parameters for up-scaling C-uptake to stand scale with a Soil-Plant-Atmosphere model, simulated annual gross primary productivity (GPP) was 16.24 ±1.6 T C ha-1 yr-1, which is about half the GPP observed in neotropical lowland rainforests. Analyses of the modelled results showed that GPP in this TMCF is mostly controlled by temperature, PAR and leaf area index (LAI) and when increasing these three factors to values found in tropical lowland forest, GPP increased up to 75%. In addition, the modelled results indicate that hydraulic limitations on TMCF C-uptake are very unlikely under current climatic conditions. The modelled results also showed that increases in radiation as a result of less cloud cover do not translate to straightforward increases of GPP. The cloudy conditions of TMCFs, which reduced incident PAR in TMCFs, should therefore not be regarded simply as a negative control on TMCF GPP. Instead, the increase in fraction of diffuse radiation partially offsets the decrease in GPP following the reduction in PAR. Overall, the results of this study show that leaves of Andean TMCF forests have similar C-uptake capacity to tropical lowland rainforests when standardized to similar temperatures, but that for in situ C-uptake temperature, radiation and LAI are the key controls.

This research considers human impacts on three components of biodiversity (composition, spatial structure and function). Given the relict character and unusual biogeochemical balance of tropical montane cloud forests in Mexico, logging poses a pressing threat to their survival. Specifically, this thesis explores the effect of selective logging and above-ground secondary succession on the biogeochemical cycling and soil macroinvertebrate community in a cloud forest in Oaxaca, Mexico. The research investigates: (1) whether the above-ground chain of successional changes in tree dominance, litterfall, litter diversity and soil microenvironmental conditions are coupled with a below-ground succession of soil nutrient availability and macroinvertebrate communities, (2) the role of spatial structuring of environmental conditions and litter resources as determinates of the nutrient availability and macroinvertebrate taxa abundance, (3) the implications of successional changes for decomposition and (4) whether the local influence of single trees explains the spatial structure of macroinvertebrate communities in late successional forests. The work was carried out in three chronosequences (c.15, 45, 75 and 100 year-old stages) of high altitude (1500-2000m) tropical montane cloud forest, two recently logged sites and two pristine sites. the macroinvertebrates in the litter and mineral soil were hand sorted from monoliths. Parametric statistics and canonical correspondance analysis were used to determine mean successional trends, and Spatial Analysis by Distance Indices and geostatistical methods were used in combination to determine spatial patterns. Two decompositional experiments were performed to explore the relationship between decompositional rate, litter quality and macroinvertebrate community higher taxa composition in different successional stages and under the canopy of different tree species. The research showed that: 1. The macroinvertebrate community composition in both recently logged sites and pristine forests were distinct compared to secondary successional stages. A decrease in soil temperature and nutrient availablity but increase in litter diversity and soil organic matter recorded through succession were accompanied by an increase in the number of macroinvertebrate taxa in the soil. For exampl, Collembola were most abundant in recently logged sites and earthworms (Megascolecidae) were almost excluvely found in pristine forests. 2. The oldest secondary forest (100 year-old) showed the highest frequency of aggregation in the abundance of individual macroinvertebrate taxa, and the highest and most uniform value of Shannon's diversity. This suggests that high levels of diversity in litter resources and soil chemistry in late succession are associated with complex spatial structuring of highly diverse macroinvertebrate communities. 3. The leaves of a late successional species (Persea americana)decomposed at a slightly slower rate than an early successional species (Pinus chiapensis) in all successional stages, yet the number and Shannon's diversity of macroinvertebrate taxa that invaded decomposing P.Americana leaves was consistently higher. The preference of macroinvertebrate taxa for the late-successional leaves was ultimately explained by differences in leaf quality during decomposition. P.americana leaves had higher concentrations of cations throughout decomposition and their concentration of lignin and nitrogen became higher. 4. In the 100-year-old forest, the effect of seasonal variation on soil microenvironmental conditions and litter availability was different under the canopy of different tree species. Furthermore, the chemical evolution of the same leaf type (e.g. Oreopanax xalapensis) was differentwhen decomposing under different canopies. The highly diverse and spatially complex macroinvertebrate community found in late succession (and experimental litter) was largely explained by the interactive effects of seasonal variation, tree species, litter quality and availability of the decomposing leaf type. The results provide the first analysis of the relationship between soil biodiversity and the tight biogeochemical cycling in this relict ecosystem type. Overall the results indicate that mature cloud forests sustain a diverse and spatially heterogenous macroinvertebrate community. The compositional and spatial components of soil biodiversity are compromised by logging and full recovery may take mopre than 100 years.

Orientador: Rafael Silva Oliveira
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia
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Resumo: Matas nebulares montanas tropicais (MNMT) são ecossistemas frequentemente inundados por neblinas, o que influencia quase todos os aspectos de seu funcionamento. MNMTs são extremamente importantes devido aos serviços ecossistêmicos que provêm, principalmente hidrológicos, e devido a sua alta biodiversidade. Com mudanças climáticas e de uso de terra já acontencendo há urgência em compreender o funcionamento de MNMTs para o desenvolvimento de estratégias de conservação e restauração. O objetivo deste trabalho é analisar e quantificar os efeitos da neblina no microclima e funcionamento foliar de MNMTs. Medimos a ocorrência de neblina, variáveis microclimáticas, parâmetros fotossintéticos e usamos uma nova metodologia para medir a capacidade de absorção foliar de água de cinco espécies abundantes de uma MNMT na região de Campos do Jordão, Brasil. Utilizamos esses dados para estimar os efeitos da neblina na disponibilidade hídrica, na demanda de água da atmosfera, na fotossíntese potencial, na absorção foliar de água e no balanço térmico foliar de MNMTs. A neblina teve um forte efeito no aumento da disponibilidade hídrica do solo e na redução da demanda atmosférica de água. A neblina apresentou um efeito negligível na redução da fotossíntese potencial das espécies estudadas. Nós apresentamos, pela primeira vez, estimativas do efeito da neblina no balanço térmico foliar mostrando que ela possui um importante papel em amenizar as temperaturas foliares médias durante o dia, reduzindo-as em 0.5oC por cada hora de ocorrência de neblina. Nós encontramos que a absorção foliar de água constituí uma fonte importante de água para as espécies estudadas, com a neblina noturna possuindo o potencial de reidratar as folhas de duas das espécies estudadas das suas condições mais secas até hidratação total em mais de 50% das noites. Diferenças na capacidade de absorção foliar de água das espécies estudadas sugere que a absorção foliar é um nicho importante de recursos com o potencial de selecionar características foliares relacionadas à eficiência de absorção foliar de água em espécies de MNMTs
Abstract: Tropical montane cloud forests (TMCFs) are ecosystem with frequent fog immersion influencing almost all aspects of its functioning.TMCFs are extremely important both due to the ecosystem services it provides, particularly hydrologically, and because of its high biodiversity. With climate and land use changes already happening there is urgency on understanding TMCFs functioning to devise conservation and restoration strategies. The objective of this work is to analyze and quantify fog effects on the microclimate and leaf functioning of TMCFs. We measured fog occurrence, microclimatic variables, photosynthetic parameters and used a new methodology to measure foliar water uptake capacity of five abundant TMCFs tree species in the region of Campos do Jordão, Brazil, We used these data to estimate fog effects on water availability, atmospheric water demand, potential photosynthesis, leaf water uptake and leaf thermal balance of TMCF. Fog had a pronounced effect on increasing soil water availability and reducing atmospheric water demand. Fog had a negligible effect on reducing potential photosynthesis of the studied species. We provide for the first time estimates of fog effects on leaf thermal balance showing it has an important effect on buffering mean daytime leaf temperatures by reducing it 0.5oC for each hour of fog occurence. We found that foliar uptake of fog water constitutes an important water source for the studied species, with nocturnal fog having the potential to rehydrate leaves of two of the studied species from its driest conditions to fully rehydration more than 50% of the nights. Differences in foliar water uptake capacity in the studied species suggests leaf water uptake is an important resource niche with potential of selecting leaf water uptake related traits in TMCFs species
Mestrado
Ecologia
Mestre em Ecologia

Tropische Nebelwälder gehören zu den am meisten bedrohten Ökosystemen der Erde. Neben dem Schutz ist für den Erhalt des Lebensraumes tropischer Nebelwald dringend die Restauration ehemaliger, degradierter Nebelwaldflächen nötig. Leider sind die bisher erprobten Verfahren zu allgemein gehalten, um am jeweiligen Restaurationsstandort erfolgreich angewendet werden zu können. Zudem ist das derzeitige wissenschaftliche Erkenntnisvermögen über den Sukzessionsablauf und die Wuchseigenschaften der vorkommenden Baumarten unbefriedigend. Ziel der Untersuchung war daher eine Bewertung der Eignung von Baumarten und waldbaulichen Verfahren zur Anlage von Restaurationsflächen im montanen Eichennebelwald Costa Ricas. Das Untersuchungsgebiet lag in den Waldungen des Cloudbridge Reservates nahe dem Ort San Gerardo de Rivas. Als Versuchsflächenstandort wurde eine 1,05 Hektar große, auf einer Höhe von 1.828 bis 1.891 Meter gelegene, um 35 Grad geneigte Hangfläche mit einer Ausrichtung von Nordost bis Nordwest ermittelt. Es wurden 20 quadratische Parzellen mit einer Seitenlänge von 18 Metern errichtet, auf denen vier waldbauliche Verfahren und zwölf Baumarten mit Hilfe der statistischen Verfahren Regressionsanalyse und Kruskal-Wallis-Test bewertet wurden. Nach Feststellen der Degradationsstufe wurden die Restaurationsverfahren Framework Species (Verfahren 1) und Nurse Trees (Verfahren 2) ausgewählt. Weiterhin wurde eine Kombination der beiden Verfahren (Verfahren 3) und die natürliche Sukzession (Verfahren 0) untersucht. Datengrundlage bildeten die in den Jahren 2008, 2009, 2010 und 2012 aufgenommenen Werte für Baumhöhe, Wurzelhals- und Brusthöhendurchmesser, Kronenradius, Bodenbedeckung, Stammfußposition, Beschattung und Vitalität. Die Verfahren 1, 2 und 3 weisen bereits in den ersten vier Wuchsjahren gute Bedingungen für die natürliche Etablierung von Baumarten auf. In Verfahren 0 siedelten sich keine naturverjüngten Baumarten an. Verfahren 0, in dem die natürliche Sukzession ablaufen kann, ist für eine zügige Restauration im Untersuchungsgebiet aufgrund fehlender Naturverjüngung restaurationsrelevanter Baumarten ungeeignet. Die Verfahren 1 bis 3 sind zur Anlage von Restaurationsflächen unterschiedlich gut geeignet. In Verfahren 2 werden die höchsten Wuchsleistungen erreicht. Es ist aber aufgrund der hohen Individuensterblichkeit und geringen Verdrängung von Gräsern und Farnen am wenigsten für die Anlage von Restaurationsflächen geeignet. Weniger Individuensterblichkeit, bessere Beschattungswirkung und höhere Anziehungskraft auf samenverbreitende Tierarten wurden bei Verfahren 1 beobachtet. Verfahren 3 kombiniert die guten Eigenschaften von Verfahren 1 und 2, weswegen es für die Restauration im Untersuchungsgebiet am besten geeignet ist. Gräser und Farne werden ausreichend verdrängt, eine hohe vertikale Bestandesstruktur wird erreicht und die Individuensterblichkeit ist geringer als in Verfahren 2, so dass mit diesem Verfahren eine gute Grundlage für die natürliche Etablierung restaurationsrelevanter Baumarten geschaffen wird. Voraussetzung für eine gelungene Restauration ist bei den Verfahren 1, 2 und 3 die Beachtung der Ansprüche der jeweiligen Baumarten an die Exposition und die Wasserversorgung. Bis auf die Baumart Gordonia fruticosa sind alle weiteren untersuchten Baumarten für die Anlage von Restaurationsflächen geeignet. Vorteilhaft ist in jedem Fall die Pflanzung in Baumartenmischung. Die Baumart Cecropia polyphlebia sollte gruppenweise in Mischpflanzungen eingebracht werden. Alle weiteren Baumarten bevorzugen oder vertragen eine einzelbaumweise Mischung. Alnus acuminata und Inga oerstediana sind selbst schattenunverträglich und müssen daher mit langsamer wachsenden Baumarten, wie Quercus rapurahuensis oder Billia hippocastanum, kombiniert werden. Für die Position Senke sind alle Baumarten, mit Ausnahme von Alnus acuminata und der oben genannten Baumart Gordonia fruticosa, geeignet. Einschränkungen gibt es für die Positionen Nordosthang und Nordhang, an denen nur die Baumarten Alnus acuminata, Billia hippocastanum, Inga oerstediana, Quercus rapurahuensis und Ulmus mexicana gepflanzt werden sollten. Viburnum costaricanum kann ebenfalls am Nordhang eingesetzt werden. Unter sehr hohem Pflegeaufwand ist auch die Pflanzung von Sapium pachystachis an Nordost- und Nordhang möglich. Um Restauration im montanen Eichennebelwald Costa Ricas in Zukunft zielführend umzusetzen, wurden Pflanzschemata entwickelt, die auf Verfahren 3 basieren und die die Ansprüche der einzelnen Baumarten an Exposition und Wasserversorgung berücksichtigen. Die Pflanzung nach diesen Schemata bewirkt möglichst geringe Individuensterblichkeiten, hohe Wuchsleistungen und Vitalitäten. Ebenfalls wird dadurch eine hohe vertikale Struktur und Kronenüberdeckung des Bodens erreicht, um gute Voraussetzungen für das Anwachsen von Naturverjüngung zu gewährleisten.

Orientador: Rafael Silva Oliveira
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia
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Resumo: Diversos modelos climáticos predizem mudanças no regime hídrico e secas extremas nos mais variados ecossistemas, dentre esses, as florestas tropicais nebulares (FTNs), que são apontadas como ambientes sensíveis às mudanças no clima. Nas FTNs a frequência e intensidade de neblina são determinantes na composição da vegetação. As predições são de que o aquecimento terrestre causará um deslocamento da área atual de ocorrência de neblina para altitudes maiores, acima da maioria das FTNs do mundo. Com diminuição da neblina nesses ambientes é provável que ocorra um aumento da evapotranspiração e estresse hídrico da vegetação, podendo haver mortalidade das plantas. Em nosso estudo investigamos as relações hídricas de duas coníferas que ocorrem em FTNs A. angustifolia e P. lambertii, além disso avaliamos se o ponto de perda de turgor (?tlp) é um bom preditor de mortalidade para essas espécies. Para compreendermos os efeitos da neblina no status hídrico de A. angustifolia avaliamos duas populações em altitudes diferentes, sendo elas, montanha (1950 m) e vale (1500 m). Os indivíduos localizados na montanha mantiveram potenciais hídricos menos negativos do que os localizados no vale, durante todo o período de monitoramento. Conduzimos um experimento em casa de vegetação para avaliar a resistência a seca de A. angustifolia e P. lambertii. Também avaliamos a importância da absorção de água da neblina pelas folhas (AAF) e do aporte hídrico diretamente no solo na recuperação do status hídrico dessas espécies depois de submetidas à secas em que seu potencial hídrico foliar (?Folha) chegou ao ponto de perda de turgor (?tlp). As duas espécies apresentaram diferentes estratégias de manutenção do status hídrico, A. angustifolia foi mais resistente à seca, sobrevivendo por até 17 semanas de seca P. lambertii sobreviveu a 12 semanas de seca, no entanto, esta espécie apresentou maior capacidade de manutenção do ?Folha quando a única fonte de água foi à neblina. O ?tlp foi um bom preditor de mortalidade para essas duas espécies
Abstract: Several climate models predict changes in the water regime and extreme droughts in a wide variety of ecosystems. Among these ecosystems, there are the tropical montane cloud forests (TMCFs), pointed as sensitive environments to climate changes. Frequency and intensity of fog are crucial to the composition of vegetation in TMCFs. Predictions are that global warming will cause a shift in fog occurrence from the current area to higher altitudes, above most TMCFs in the world. With the fog decrease in these areas it is likely to occur an increase in the evapotranspiration and water stress of the vegetation, which may result in plant mortality. In this research we look into water relations of two conifers that occur in TMCFs, A. angustifolia and P. lambertii. Furthermore, it is evaluated if the turgor loss point (?tlp) is a good mortality predictor for these two species. To comprehend the fog effects in A. angustifolia's water status we evaluate two populations in different altitudes: mountain (1950m) and valley (1500m). Individuals located in the mountain kept water potentials less negative than the ones located in the valley throughout the monitoring period. An experiment was conducted in greenhouse to evaluate the resistance to drought of A. angustifolia and P. lambertii. Were also evaluated the importance of fog water uptake by leaves (LWU) and of water input directly into the ground in the water status recovery of the species after being subjected to drought in which their leaf water potential (?Leaf) reached the turgor loss point (?tlp). Both species presented different strategies of water status maintenance. A. angustifolia was more resistant to drought, surviving for up to 17 weeks of it, while P. lambertii survived for 12. However, P. lambertii showed higher capacity of ?Leaf maintenance when the only source of water was fog. Turgor loss point was a good mortality predictor for these two species
Mestrado
Biologia Vegetal
Mestra em Biologia Vegetal

La Guyane est un territoire d’outre-mer, situé en zone intertropicale (ZIT). Cette zone est le lieu de phénomènes de convections intenses. De ce fait, l’énergie solaire incidente au sol est très variable ce qui constitue un frein à son exploitation à grande échelle. La question de recherche étudiée dans ce manuscrit est : comment peut-on améliorer les estimations et prédictions de rayonnement au sol en ZIT de façon à augmenter le taux de pénétration dans le réseau électrique de cette énergie renouvelable intermittente ? Afin de répondre à cette question, nous avons utilisé deux outils. Le code Héliosat-II (HII) et le modéle de prévisions météorologiques Weather and research forecast (WRF). Nous avons utilisé ces outils de manière à améliorer les estimations et prévisions de rayonnement global au sol (IGH) dans la ZIT. La première partie de ce manuscrit présente le contexte de la thèse. La seconde présente une modification d’H-II permettant d’améliorer les estimations d’IGH par une modélisation explicite de l’absorption de nuages. Ces estimations améliorées donnent ainsi des outils décisionnels permettant de situer au mieux une centrale solaire en fonction du potentiel solaire du site et des systèmes services avoisinants. La seconde partie traite dans un premier temps de la précision des prévisions des modèles globaux IFS et GFS (i.e integrated forecast system, global forecast system GFS) en ZIT. Ces produits téléchargés sont validés par comparaison avec des mesures in situ de trois pays situés dans la ZIT et caractérisés par des climats tropicaux. Cette étude permet de combler un vide dans l’étude des prévisions d’IGH des modèles globaux en ZIT. Nous proposons ensuite une méthode générique permettant de calibrer le modèle WRF en ZIT. Cette méthodologie vise à limiter le nombre de simulations à effectuer en sélectionnant et en faisant varier uniquement les paramètres ayant le plus d’influence sur le rayonnement au sol en ZIT. Pour valider cette méthodologie nous avons comparé les prévisions d’IGH du modelé WRF calibré avec celle du modelé AROME ainsi qu’avec des mesures in situ en Guyane. La quatrième partie présente l’utilisation d’une méthode hybride ensembliste variationnelle d’assimilation de donnée permettant d’améliorer les prévisions de rayonnements en ZIT. Cette méthode initialement utilisée pour améliorer la description de phénomènes convectifs extrêmes tels que prévision de la trajectoire des cyclones est pour la première fois appliquée pour améliorer les prévisions d’IGH. Cette méthodologie appliquée à la ZIT fournie alors des prévisions améliorées d’IGH permettant ainsi une gestion améliorée de centrale solaire
French Guiana is a French territory located in the inter-tropical zone (ITZ). The ITZ is an area with highly variable dynamic in which we encounter significant amounts of convective clouds. Consequently the solar energy available at the ground is highly variable. This variability causes economical and technical challenges to fully exploit this resource. This thesis dissertation aims to answer the following scientific issue: How could the solar irradiance be assessed and forecast accurately in the ITZ to increase the penetration rate of this intermittent renewable energy into the electricity grid? To answer this scientific issue, we use two tools: Heliosat-II (H-II) and Weather and research forecast (WRF). We used these tools in order to produce improved GHI estimates in the inter-tropical zone. The first chapter introduces the thesis and the research issue. The second chapter presents a modification to H-II; with this modification H-II can account for cloud absorption. The GHI estimates from modified H-II provide therefore tools for decision making in the ITZ. These tools allow one identifying the most suitable locations to install solar facilities in the ITZ with respect to both solar potential and surrounding facilities that favor grid stability. In the third chapter we study first the accuracy in the ITZ of the GHI forecasts from integrated forecast system (IFS) and global forecast system (GFS) numerical weather prediction model (NWP). We validate the accuracy of these downloaded products by comparison with ground measurements from three countries located in the ITZ that have tropical climate. This study aims to fill the gap with regard to the accuracy of global NWP model in the ITZ. Second we propose a methodology to calibrate WRF to produce improved GHI forecasts in the ITZ. The goal is to restrain and select the minimum number of simulations to run, to obtain improved GHI forecasts compared to a non-calibrated model. This methodology to calibrate WRF is validated in French Guiana by comparison with the GHI forecasts of AROME NWP model and ground measurements. The fourth chapter deals with the use of an hybrid 3D variational (3D-Var) ensemble transform Kalman filter (ENTKF) to further improve the GHI forecasts of calibrated WRF in the ITZ. This methodology originally used in the tracking of extreme convection events such as cyclones is applied for the first time for GHI forecasts. This methodology applied to the ITZ therefore allows obtaining improved GHI forecasts which makes easier monitoring the electricity production from solar facilities

La prévision de l'intensité des cyclones tropicaux est aujourd'hui un enjeu scientifique majeur. Parmi de nombreux facteurs multi-échelle, l'impact de la microphysique nuageuse et des aérosols sur les variations d'intensité a été récemment mis en évidence. Cette problématique a motivé l'évaluation du schéma microphysique à 2-moments LIMA en milieu tropical et le développement d'un couplage avec le schéma d'aérosols ORILAM au sein du modèle atmosphérique Meso-NH. L'intérêt de ce développement numérique est d'inclure l'émission des aérosols marins en fonction des vents cycloniques et des paramètres océaniques. L'application de ce couplage aérosols-microphysique à la simulation du cyclone tropical Dumile (2013) montre que le modèle couplé tend à améliorer la représentation de l'intensité, la trajectoire, la structure microphysique du cyclone tropical et les précipitations associées, en comparaison avec les observations. La production secondaire des cristaux de glace est également un thème de recherche actif en microphysique nuageuse. Ainsi, une paramétrisation du processus de rupture collisionnelle de la glace a été implémentée dans le schéma microphysique LIMA. L'impact de ce processus a été testé sur le développement d'un orage des moyennes latitudes et sur le cyclone tropical Dumile. Les deux cas d'étude ont des réponses similaires vis-à-vis de ce processus : une augmentation de la concentration et de la masse des cristaux de glace et une diminution des cumuls de précipitations. La poursuite de ces travaux pourrait permettre de déterminer si ce processus de formation secondaire peut améliorer la modélisation de la couverture cirriforme des cyclones tropicaux
Intensity forecast of tropical cyclones is a major scientific issue. Among many factors, the impact of cloud microphysics and aerosols on intensity variations has been recently underlined. This issue motivated the evaluation of the 2-moment microphysical scheme LIMA in a tropical context and the development of a coupling with the aerosol scheme ORILAM into the atmospheric model Meso-NH. The interest of this numerical development is to represent the emission of sea salt aerosols depending on cyclonic winds and oceanic parameters. The application of this aerosols-microphysics coupling to the simulation of tropical cyclone Dumile (2013) shows that the coupled model tends to improve the representation of the intensity, the track, the microphysical structure of the tropical cyclone and the associated precipitation, when comparing with observations. The secondary production of ice crystals is also an active research topic in cloud microphysics. A parameterization of the collisional ice break-up process is thus implemented into the microphysical scheme LIMA. The impact of this process has been analyzed on a mid-latitude storm and on tropical cyclone Dumile. Both case studies display similar results regarding this process: an increase of ice crystals concentration and mass, and a decrease of precipitation. The continuation of this work could allow to determine if this process of secondary formation could improve the cirrus modelling in tropical cyclones

Disturbance in a forest’s canopy, whether caused by treefall, limbfall, landslide, or fire determines not only the distribution of well-lit patches at any given time, but also the ways in which the forest changes over time. In this dissertation, I use a 25 year record of treefall gap formation find a novel and highly patterned process of forest disturbance and regeneration, providing a local mechanism by examining the factors that influence the likelihood of treefall. I then develop a stochastic cellular automaton for disturbance and regeneration based on the analysis of this long term data set and illustrate the potential of this model for the prediction and detection of patterned forest dynamics in general. Finally, I investigate the spatial structure of a population of one of the most common gap colonist species in this forest, Didymopanax pittieri, and illustrate the effect of local aggregation of treefalls and on the population dynamics of D. pittieri in the process.