How forests drink: hydroclimatic adaptation and tropical forest survival

How forests drink: Hydroclimatic adaptation as the key to tropical forest survival under climate change

Not all tropical forests face climate change equally. Some forest types and regions show remarkable resilience to shifting rainfall and temperature regimes — maintaining their structure and function even under significant hydroclimatic stress. Others appear far more vulnerable, at risk of rapid degradation or transition to savanna-like states if water stress intensifies. This paper, published in Global Change Biology, investigates what makes some tropical forests more resilient than others, with a focus on the role of hydroclimatic adaptation — how forests adjust their water uptake strategies in response to changing conditions.

The key insight is that forests differ dramatically in their rootzone water storage capacity — the amount of water accessible to vegetation through deep root systems. Forests with larger rootzone storage buffers are better equipped to maintain transpiration and carbon uptake during dry seasons and drought periods, as they can draw on deeper soil water reserves when shallow soil moisture is depleted. Using a global dataset of rootzone storage capacity alongside satellite-derived metrics of vegetation stress, we show that hydroclimatic adaptation — the degree to which forests can access and utilise deep water reserves — is a strong predictor of resilience across tropical biomes.

These findings have important implications for projecting forest futures under climate change scenarios. Forests in regions where both warming and increased dry-season length are projected — such as eastern Amazonia and parts of Central Africa — face compounding stresses that may overwhelm even well-adapted forests. The results also suggest that deforestation, by removing deep-rooted trees and replacing them with shallow-rooted crops or pastures, destroys adaptive capacity that took millennia to develop.

A forest's resilience to drought is not just about how much it rains — it is about how deep its roots reach and how effectively it can store and access water across seasons. Protecting these hidden hydraulic capacities is as important as protecting the canopy above.