Tropical forest ecohydrology

Tropical forests have a significant impact on global carbon balance and this impact varies from negative (sink-) to positive (source) as a function of water availability.   Soil water availability for root water uptake (RWU) has been shown to have a key role on tropical forest T flux but the specific response of tropical ecosystem to drought is not well understood yet.  In Brazil, deep-RWU has been considered as the main responsible for maintaining elevated T rates during the dry season in the Amazon. However, despite their supposed access to deep soil-water reservoirs due to their deeper roots, larger and taller trees have been shown to have the highest mortality rates during natural and induced (i.e., rainfall exclusion experiments) droughts. Besides, in the Amazon, shallow roots are far more abundant than deep roots. These findings challenge the deep-RWU as a mechanism of forest resilience to severe droughts. Together with the fact that most Earth System models fail to reliably represent dry season T in the Amazon,  it reveals some gaps in our understanding of the primary sources of water transpired by Amazonian trees, which undermines our ability to predict tropical forest climate feedbacks to global warming. Given the prospects of increased dry-season length and severity, improved knowledge on the soil-vegetation water interactions in the rapidly changing Amazon is urgently needed.

While most studies suggest that high forest T rates would lead to a decrease in surface and subsurface water sources, recent studies suggest that an adequate forest cover could favor the storage of water in the soil, which is required for plant metabolic activities and atmospheric demands, and groundwater recharge. This question is of particular importance in the Atlantic Forest in Brazil, where forest conservation and recovery actions have been taken, as for instance the Mata Atlântica Connection Project, an initiative of the Global Environmental Facility (GEF) and Brazilian Ministry of Science and Technology and Innovation (MCTI), in partnership with the Environment Secretariat of the State of São Paulo.

Several master theses are possible around these topics:

• how does soil type impacts forest resilience against drought?

• how does forest change soil functionning?

• How soil-plnat intercat and how reforestation does affect water and carbon cycles?