Abstract
Climate change and deforestation influence the rainfall patterns in the
tropics, thereby increasing the risk of drought-induced
forest-to-savanna transitions. Forest ecosystems respond to these
changing environmental conditions by adapting various drought coping
strategies driven by different magnitudes of water-stress (i.e., defined
here as a deficit in soil water availability inhibiting plant growth due
to change in rainfall patterns). A better understanding of forest
dynamics in response to the water-stress conditions is, therefore,
crucial to determine the rainforest’s present ecohydrological
conditions, as well as project a possible rainforest-savanna transition
scenario. However, our present understanding of such transitions is
entirely based on rainfall, which does not consider the adaptability of
vegetation to droughts by utilizing subsoil moisture in a quantifiable
metric. Using remote-sensing derived root zone storage capacity
(Sr) and tree cover, we analyze the water-stress and drought
coping strategies of the rainforest-savanna ecosystems in South America
and Africa. The results from our empirical and statistical analysis
allows us to classify the ecosystem’s adaptability to droughts into four
key classes of drought coping strategies: lowly water-stressed forest
(shallow roots, high tree cover), moderately water-stressed forest
(investing in Sr, high tree cover), highly water-stressed forest
(trade-off between investments in Sr and tree cover) and
savanna-grassland regime (competitive rooting strategy, low tree cover).
This study concludes that the ecosystems’ responses are primarily
focused on allocating carbon in the most efficient way possible to
maximize their hydrological benefits. The insights from this study
suggest remote sensing-based Sr as an important indicator
revealing important subsoil forest dynamics and opens new paths for
understanding the ecohydrological state, resilience, and adaptation
dynamics of the tropical ecosystems under a rapidly changing climate.