Buffering of climate extremes within riparian forest corridors: a theoretical study with practical applications

Riparian forests in tropical and temperate regions often act as climatic microrefugia for many species and taxa, buffering climate extremes relative to their surroundings. For example, during a summer heatwave, maximum air temperatures can vary by several degrees between the edge and the core of the riparian forest understory. This buffering of climate extremes within riparian corridors is well documented, but the processes behind it are not well understood because they involve complex turbulent air flows throughout the convective atmospheric boundary layer interacting with the forest canopy and landscape microtopography. To better understand how forest cover and microtopography influence the microclimate within and above riparian corridors, we performed in silico experiments using a 3-dimensional Large Eddy Simulation (LES) vegetation-atmosphere model to simulate air flows and microclimate below and above the trees, and across the entire convective boundary layer. Simulations were performed for different atmospheric stability conditions, and for different corridor widths. The tree species composition in the riparian corridor and its microtopography (slope, aspect) were chosen to be representative of an old-growth temperate riparian forest known to act as a climate refugium for European beech in south-west France. In this context, we first investigated the effect of microtopography alone on the air flows below and above the forest canopy during a typical summer heatwave. We also investigated the impact of replacing maritime pine plantations on the plateau with a strip of deciduous trees extending beyond the riparian corridor, with the aim to evaluate the minimum strip size required to mitigate climate extremes in the riparian understory.