Multiyear drought-induced morbidity preceding tree death in southeastern U.S. forests

Area of Science:

• Forest Ecology
• Dendrochronology
• Climate Change Impacts

Background:

• Recent forest diebacks and future drought threats necessitate understanding tree mortality causes.
• Chronic declines in tree health, accumulating over years, may have pervasive impacts, alongside catastrophic events.
• Increasing drought stress raises concerns about forest composition shifts in many regions.

Purpose of the Study:

• To investigate long-term growth declines in trees exposed to drought.
• To determine the relationship between pre-mortality growth reduction and subsequent tree death.
• To assess the influence of local moisture availability and species-specific drought tolerance on mortality patterns.

Main Methods:

• Utilized long-term, whole-stand inventory data from southeastern U.S. forests.
• Analyzed multiyear growth trends before and after severe drought events.
• Calculated drought-induced morbidity as the difference in cumulative growth post-drought compared to surviving trees.

Main Results:

• Trees exposed to drought exhibited multiyear growth declines preceding mortality.
• 72% of trees failing to recover pre-drought growth rates after a severe drought died within 10 years.
• Drought-induced morbidity varied by species and correlated with drought tolerance, mediated by local moisture.

Conclusions:

• Tree mortality following drought is predictable based on pre-existing growth declines.
• Findings support trees' ability to avoid immediate death but indicate potential for long-term, multi-decadal shifts in forest composition.
• Incorporating multiyear drought-induced morbidity into models and management is crucial for forest resilience.