Linking biophysical models with LiDAR-based vegetation mapping to evaluate thermal refugia at a landscape scale in the Kruger National Park

Abstract

Increases in global air temperatures have provided the impetus for extensive research into how thermal constraints impact species behaviour and vulnerability to climate change, with recent heat-related mortality events underscoring the need for such research. The role of vegetation in creating cooler microsites that buffer organisms against high temperatures has received attention in the past, yet few studies have assessed the availability of cool, shaded microsites for small animals at a landscape level. Here, I combined tree canopy height and density values derived from remote sensing (LiDAR) products with biophysical models to predict operative temperatures for black bulbs within tree canopies at a landscape scale in the Kruger National Park, South Africa. The accuracy of the biophysical models was evaluated by comparing the outputs to the operative temperatures (Te) recorded by deploying Te thermometers across the thermal landscape. For most of the trees (64%), Te values predicted by the biophysical models were not significantly different (p > 0.05) to those measured by black bulbs. I mapped values of Te predicted by the biophysical model to quantify thermal refuges potentially available to different-sized model organisms that approximate the size of different bird species, using the canopies while inactive on hot days. My results reveal that exposure to extreme heat events (defined as Te > 40 °C) varies with canopy height and density. Of the subset of trees sampled during this study, Kigelia africana provided the greatest degree of buffering from high temperatures, whereas Combretum hereroense provided the least protection against exposure to high Te. For example, organisms seeking refuge in Kigelia africana can experience ~ 50 fewer days per summer where they are exposed to high daily maximum Te, compared to those making use of exposed sites. Furthermore, tree canopies can reduce the intensity and frequency of animals’ exposure to sustained heat events by up to 10-fold per summer, when compared to exposed microsites. This study demonstrates how combining remote-sensing technology and biophysical models can provide a better understanding of thermal landscapes and inform decisions regarding the vegetation management in protected areas.