Older forests function as energetic and demographic refugia for a climate-sensitive species

Area of Science:

• Ecology
• Climate Change Biology
• Conservation Biology

Background:

• Extreme heat waves pose significant threats to climate-sensitive species.
• Older forests with complex structures can create microclimates that buffer against heat stress.
• The mechanisms by which forest refugia mitigate physiological and population-level heat impacts are not well understood.

Purpose of the Study:

• To assess how older forest characteristics buffer individual California spotted owls (Strix occidentalis occidentalis) from heat.
• To examine the value of older forests as refugia for core and peripheral owl populations.
• To understand the population-level consequences of heat exposure in relation to forest structure.

Main Methods:

• Utilized fine-scale movement data and doubly labeled water to measure individual energy expenditure.
• Analyzed two decades of demographic data for California spotted owl populations.
• Compared owl populations in the Sierra Nevada (core) and San Bernardino Mountains (periphery) with varying forest characteristics.

Main Results:

• California spotted owls conserved energy by reducing movement during warmer periods, with tall canopies aiding daytime roosting energetics.
• In the core population with prevalent tall canopies, temperature anomalies did not impact territory occupancy dynamics.
• Peripheral populations with less older forest experienced higher site abandonment after warm summers, indicating reduced thermal buffering.

Conclusions:

• Older forests provide essential energetic buffers for California spotted owls against heat stress.
• Forest structure significantly influences population resilience to climate change-induced temperature anomalies.
• Conservation of older forests is critical for mitigating the negative energetic and demographic consequences of heat exposure for sensitive species.