Intact Forest Canopies Can Protect Tropical Organisms from Severe Climate Warming

Abstract

As undisturbed tropical forests become increasingly rare, the importance of logged and recovering forests for the conservation of biodiversity has gained much attention. Disturbed forests can, however, have hotter microclimates, which may exacerbate the effects of future climate change on biodiversity and alter ecosystem processes. We used thermal imaging to capture surface temperatures along a gradient of logging intensity in Sabah, Malaysian Borneo, and compared these to the upper thermal limits (CTmax) of over 5000 individual invertebrates from 129 taxa collected from the same forests. We found that reducing canopy closure by 5% led to an increase in mean and maximum surface temperatures during the hottest parts of the day by 1 °C and 4.1 °C, respectively. Maximum surface temperatures were recorded that exceeded the CTmax of all invertebrate groups once forest canopy was reduced beyond 76%. Total available surface niche space was reduced by up to 22% for the most sensitive taxa in the most heavily disturbed forests, and this doubled following simulated warming, with a reduction in surface niche space of 42% in highly degraded patches. In contrast, sites that retained 80% forest canopy or higher were able to sufficiently buffer all available thermal surfaces for all groups even following severe warming. We demonstrate a very narrow threshold of forest disturbance beyond which the capacity for microclimate buffering is significantly diminished. These findings illustrate the crucial importance of conserving and restoring high canopy cover forests, which may be unique in their ability to protect tropical biodiversity in a hotter future.

Keywords: Tropical Forests, Microclimates, Insects, Logging, Restoration, Climate Change, Land-Use Change