Paddock Tree Arrangement and Pasture Photosynthetic Heat Tolerance in a Temperate Tree-Pasture Grazing System Under Climate Change Scenarios

Abstract

Climate change and associated extreme heat events threaten productivity in agricultural systems. Integrating trees into grazing/pasture systems has the potential to enhance resilience to warming. However, the extent to which tree cover can buffer the impacts of climate change on pasture species is unclear. We examined how tree density and spatial configuration influence leaf nitrogen content, specific leaf area, and photosynthetic heat tolerance (T_crit) of dominant pasture species in a temperate Australian landscape. Traits were assessed across fine-scale spatial gradients from individual trees under different structural configurations. Future thermal safety margins (TSMs) were projected under two climate emission scenarios—the best-case scenario (SSP1-2.6) and the worst-case scenario (SSP5-8.5) using 28 earth system models. While leaf nitrogen varied with tree spatial configuration, T_crit and TSMs remained largely conserved. Projected warming substantially reduced TSMs without exceeding thermal thresholds, suggesting limited physiological capacity for heat tolerance adjustment. These results highlight the constrained role of tree cover in buffering climate impacts on pasture species and the need for broader adaptation strategies in agricultural systems.