Tree water balance drives temperate forest responses to drought

Area of Science:

• Ecology
• Forestry
• Environmental Science

Background:

• Intensifying drought is a major driver of global forest diebacks.
• Quantifying tree moisture access and depletion is challenging, limiting understanding of drought vulnerability.
• Forest moisture depletion primarily occurs through tree water use (transpiration).

Purpose of the Study:

• To develop a predictive model for drought impacts on tree fitness and demographic performance.
• To quantify how species and size differences influence tree moisture availability across landscapes.
• To link individual tree moisture deficit to biomass growth and reproductive output.

Main Methods:

• Developed a hierarchical state-space framework to estimate tree moisture reservoir as a mass balance.
• Applied the model to seasonal droughts using tree transpiration measurements.
• Tracked individual moisture reservoir depletion over drought periods.

Main Results:

• Drought impacts on tree fitness and demographic performance can be predicted by tracking the moisture reservoir.
• Species and size modulate moisture availability, influencing vulnerability across landscapes.
• Individual moisture deficit was successfully linked to biomass growth and reproductive output.

Conclusions:

• A mass balance approach effectively tracks tree moisture reservoirs and predicts drought vulnerability.
• This method provides insights into individual tree moisture deficit and demographic performance.
• The approach can forecast drought vulnerability in forest stands using sample tree data.