The response of tropical rainforests to drought-lessons from recent research and future prospects

Abstract

Key message: We review the recent findings on the influence of drought on tree mortality, growth or ecosystem functioning in tropical rainforests. Drought plays a major role in shaping tropical rainforests and the response mechanisms are highly diverse and complex. The numerous gaps identified here require the international scientific community to combine efforts in order to conduct comprehensive studies in tropical rainforests on the three continents. These results are essential to simulate the future of these ecosystems under diverse climate scenarios and to predict the future of the global earth carbon balance.

Context: Tropical rainforest ecosystems are characterized by high annual rainfall. Nevertheless, rainfall regularly fluctuates during the year and seasonal soil droughts do occur. Over the past decades, a number of extreme droughts have hit tropical rainforests, not only in Amazonia but also in Asia and Africa. The influence of drought events on tree mortality and growth or on ecosystem functioning (carbon and water fluxes) in tropical rainforest ecosystems has been studied intensively, but the response mechanisms are complex.

Aims: Herein, we review the recent findings related to the response of tropical forest ecosystems to seasonal and extreme droughts and the current knowledge about the future of these ecosystems.

Results: This review emphasizes the progress made over recent years and the importance of the studies conducted under extreme drought conditions or in through-fall exclusion experiments in understanding the response of these ecosystems. It also points to the great diversity and complexity of the response of tropical rainforest ecosystems to drought.

Conclusion: The numerous gaps identified here require the international scientific community to combine efforts in order to conduct comprehensive studies in tropical forest regions. These results are essential to simulate the future of these ecosystems under diverse climate scenarios and to predict the future of the global earth carbon balance.

Keywords: Carbon; Climate; Drought; Global change; Growth; Mortality; Soil; Tropical; Water.

Fig. 1

a, b Satellite-derived standardized anomalies for dry season rainfall for the two most extensive droughts of the twenty-first century in Amazonia. c, d The difference in the 12-month (October to September) maximum climatological water deficit (MCWD) from the decadal mean (excluding 2005 and 2010), a measure of drought intensity that correlates with tree mortality. a, c The 2005 drought; b, d the 2010 drought. Reproduced from Lewis et al. (2011) with authorization from the corresponding author

Fig. 2

The rainfall exclusion experiment in Caxiuanã National Forest Reserve, Brazil (credits L. Rowland)

Fig. 3

The 55-m high eddy flux tower set up in 2003 in French Guiana (Bonal et al. 2008) (credits D. Bonal). Equipment installed on top of the tower (above the canopy) allows to continuously monitor the gas exchange (CO₂, H₂O) between the atmosphere and the considered ecosystem (around 50–100 ha)

Fig. 4

Installation of an automatic weather station in the tropical rainforest in French Guiana (credits B. Hérault). Long-term monitoring of environmental conditions in remote forest inventory plots is a prerequisite to understand the effect of seasonal or extreme drought on tree and ecosystem functioning and simulate future changes