Long-Term Temporal Divergence in Post-Drought Resilience Decline Between Deciduous and Evergreen Tree Species

Area of Science:

• Forest Ecology
• Climate Change Biology
• Dendrochronology

Background:

• Forests face increasing threats from severe drought, impacting resilience, productivity, and distribution.
• Understanding the historical evolution of tree drought resilience is crucial for predicting future forest dynamics.

Purpose of the Study:

• To analyze temporal and spatial patterns of tree drought resilience in Canadian forests over the past century.
• To investigate the influence of leaf habit, prior drought exposure, and site/tree factors on drought response (resistance and recovery).

Main Methods:

• Utilized a comprehensive tree-ring database from 40,147 trees across 4558 plots and 23 Canadian species.
• Assessed growth resistance and recovery metrics to quantify overall drought resilience.
• Examined the impact of environmental factors like temperature, moisture, and elevation on tree drought responses.

Main Results:

• Most Canadian tree species exhibit low and declining drought resilience, with deciduous species showing significant 20th-century declines in recovery and resilience.
• Evergreen species maintained stable but low resilience and recovery, while summer droughts disproportionately affected deciduous species.
• Prior drought exposure demonstrated a mitigating effect on negative drought responses, indicating some adaptive capacity.

Conclusions:

• Declining deciduous resilience and low evergreen resilience signal significant future changes for Canadian forests, including reduced productivity and altered species composition.
• Older forests unaccustomed to severe droughts are particularly vulnerable, potentially leading to biodiversity loss.
• Proactive forest management is essential to preserve forest productivity and biodiversity under climate change.