Quantifying forest structure effects on microclimate buffering across a climatic gradient in temperate Australia

Abstract

Forest structure, through its three-dimensional arrangement of foliage and wood, moderates the climate, creating a microclimate that is more stable than the climate outside the forest in a process known as microclimate buffering. This study aimed to improve understanding of the relationship between forest structure and microclimate buffering of daily maximum temperature (T_max.) and vapour pressure deficit (VPD_max.) in temperate evergreen forests. Forest structure assessments and microclimate monitoring across eight sites in temperate Australia revealed significant variation in microclimate buffering, primarily driven by canopy closure, leaf area index (LAI), and tree stem density (≥10-cm diameter). Compared to open sites, closed forests (>70 % canopy cover) reduced mean T_max. by 1.8 ± 0.08°C to 4.1 ± 0.09°C, and open forests (30–70 % canopy cover) by 0.2 ± 0.08°C to 0.4 ± 0.06°C. Only closed forests reduced mean VPD_max., by 0.15 ± 0.01 kPa to 0.43 ± 0.02 kPa, while mean VPD_max. in open forests and woodlands was 0.04 ± 0.01 kPa to 0.38 ± 0.02 kPa higher than open sites respectively, indicating net drying. Across the forest structure gradient, canopy closure, LAI and stem density had significant negative relationships with microclimate offsets of daily T_max. and VPD_max. Over the assessed forest structure range, T_max. offsets were negative (buffering) above 35 % canopy closure, 137 stems ha⁻¹, and LAI 0.36, while VPD_max. offsets were negative above 59 % canopy closure, 485 stems ha⁻¹, and LAI 0.82. These findings emphasize the role of forest structure in microclimate buffering and potential climate resilience.