Alternative Vegetation States in Tropical Africa: the Search for Consistent Signals in Diverse Remote Sensing Datasets
Abstract
Globally, the spatial distribution of vegetation is driven primarily by climatological factors, interacting locally with disturbances including fire, herbivory and other anthropogenic activities. Depending on the nature of feedbacks, disturbances may trigger alternate states under otherwise similar climatic and edaphic conditions. Previous studies have noted existence of pronounced bimodality (interpreted as alternate vegetation states) in tree cover estimated within regions of similar rainfall across Africa. Several of these studies used the MODerate Resolution Imaging Spectroradiometer (MODIS) vegetation continuous fields satellite products (VCF). However, recent studies have also shown that the MODIS VCF product may over-estimate bimodality due to algorithm limitations and hence may be unreliable for detection of alternate states. In this study, we explore the presence or absence of alternate vegetation states across Africa using a suite of independently derived remotely sensed products, based on the argument that major discontinuities in vegetation structure should manifest in a range of remote sensing products (e.g. albedo, surface temperature, fire frequency) and not only in estimated tree cover.Comparative analysis of the MODIS VCF data set with MODIS active fire, albedo and other land surface products over the entire African continent, stratified by long-term (30 year) rainfall, is presented and discussed. While results confirm previous observations of alternate vegetation states in the MODIS VCF, such states are not always evident in the distributions of other remotely sensed observations over the same precipitation regime. Furthermore, analysis of spatial coherence among multiple remote sensing data types allows much stronger inference of vegetation pattern that is less sensitive to potential bias in any one product. Similar analysis across different spatial scales and inclusion of other remotely sensed independent variables related to tree cover is required confirm or negate the existence and extent of alternate vegetation states.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.B51G1883S
- Keywords:
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- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 0476 Plant ecology;
- BIOGEOSCIENCES;
- 1615 Biogeochemical cycles;
- processes;
- and modeling;
- GLOBAL CHANGE;
- 1813 Eco-hydrology;
- HYDROLOGY