South American Tropical Lowland Cloud Forest (TLCF) under Climate Extremes:Fog Dynamics, Refugial Areas and Microclimate Modelling
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Philipps-Universität Marburg
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Abstract
Fog affects human lives and the environment in many ways. In addition to economic effects, for example on road and air traffic, fog also fulfils important ecological functions. It is widely known, for example, that in montane tropical forests there are special conditions due to frequent fog input that favour a high level of epiphyte diversity. In the valleys of the tropical lowlands, nocturnal fog can also represent a special form of water supply for organisms such as epiphytes, which obtain supply from the fog water while they have no direct root connection to the ground for their water supply. Although the general existence of such tropical lowland cloud forests (TLCF) in French Guiana is known and has been extensively researched, their spatial extent on a continental scale in South America is still unknown.Knowledge of the distribution of these species-rich TLCF is of particular ecological interest, as these areas play important local ecological and mesoscale climatological roles. The first aim of this dissertation is to derive the potential distribution of TLCF on a continental scale for the entire Amazon lowlands based on long-term fog frequency maps.Satellite data have proven to be an effective means of classifying the frequency of fog events in the mostly inaccessible areas of the tropical forests. The work in this study is based on infrared image data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board the Aqua weather satellite, which is in a polar, sun-synchronised orbit. Two spectral bands were extracted from the MODIS data, which are often used to derive nebula signals due to their optical properties. Based on validated predictions of the presence and absence of fog, fog frequency maps were calculated for the entire tropical lowland forest of South America. The frequency maps determined in the first part were then statistically analysed to derive the extent to which fog frequency is related to terrain shape and whether fog frequency over concave landforms is less regressive than over convex landforms during atmospheric dryness. Knowledge of the potential distribution of TLCF can thus be extended to include knowledge of the distribution of hygric climate change refugia (HCCR), which are located particularly in valleys. Since the modelling of identified fog-rich areas enables an exact quantification and small-scale identification of TLCF (niche species) and HCCR (refugium species), the last part of this dissertation analysed to what extent existing algorithms can be used to model nocturnal cold air outflows and the resulting temperature inversions in valley areas of tropical lowland forests. It was demonstrated that existing algorithms need to be modified and re-calibrated for use in the tropics. Based on the findings of this dissertation, it is possible to precisely identify and classify particularly valuable areas of the Amazonian lowlands, classified as tropical lowland cloud forests, which may serve as hydric climate change refugia in the future. Moreover, their ecological functions may be quantified based on further developed algorithms, and these areas can be recommended as regions deserving special protection privileges.
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Created: 2025Issued: 2025-12-03Updated: 2025-05-22
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Fachbereich Geographie
Publisher
Philipps-Universität Marburg
Language
eng
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DoctoralThesis
DFG-subjects
NebelFernerkundung, fog, low-stratus, FLS, tipping element, climate change, epiphNaturwissenschaftenAmazonasEpiphytenTropenSatellit
DDC-Numbers
910
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Pohl, Marius: South American Tropical Lowland Cloud Forest (TLCF) under Climate Extremes:Fog Dynamics, Refugial Areas and Microclimate Modelling. : Philipps-Universität Marburg 2025-12-03. DOI: https://doi.org/10.17192/z2025.0214.