A 2024 study analysed the drought adaptation strategies of 12 tropical rainforest tree species, combining field observations with modelling (SurEau model). This work sheds crucial light on the functional traits (life traits, LTs) governing tree responses to water stress.
The study confirms that the mobilisation of carbohydrate reserves constitutes a widespread tolerance mechanism: 11 of the 12 species examined showed conversion of starch stocks into soluble sugars, lowering leaf osmotic potential and delaying cell dehydration. This mechanism is nonetheless contingent on the prior availability of reserves, as repeated droughts may progressively exhaust them.
A key finding of the study is that once roots become disconnected from the soil, the primary determinant of the time to hydraulic failure (THF) is not xylem vulnerability to embolism, but rather the rate of residual dehydration — that is, uncontrollable water losses through leaf surfaces and bark following stomatal closure. Protective leaf shedding, documented across all simulated species (near-complete defoliation at the point of THF), emerges as a primary adaptive mechanism, mediating the trade-off between hydraulic safety and the capacity for post-stress growth recovery.
These findings have direct implications for forest managers: in the context of global warming, which is intensifying atmospheric evaporative demand, tree survival depends on the ratio between internal water reserves (capacitance) and irreducible water losses. The research areas identified — effects of defoliation on carbon balance, and the role of capacitance across functional types — represent as many potential levers to explore in adapting silvicultural practices to future droughts.