Species-specific weather response in the daily stem variation cycles of Mediterranean pine-oak mixed stands

Climate change forecasts are particularly severe for the western Mediterranean Basin, where rising temperatures and decreased precipitation could increase the frequency of drought events. Understanding the specific weather drivers of radial variation in Mediterranean mixed forest stands will allow us to better predict the ecological and production alterations that may result from climate change. Here, we studied species differences in stem daily radial variation cycles and daily radial increment of Mediterranean pine-oak (Pinus pinaster-Quercus pyrenaica) mixed stands over three climatically contrasted years (2012-2014) at two sites with dissimilar drought conditions. Our aim was to uncover differences in the weather drivers of daily radial variation for the two co-existing species. High-resolution point dendrometers were installed in dominant oak and pine trees, so that daily radial variation cycles were analyzed. Linear mixed models were fitted to analyze species-specific response to weather. Air temperature leads to radial stem-size changes in daily variation cycles with different species responses. Precipitation increased daily radial variation and cycle duration in the same way for both species. Daily radial increment and number of cycles with increment phase during spring was mostly higher for pine than oak, and water availability was the most important control factor for the phase mentioned. Differences in species response to weather conditions may offset the usual low production of pure oak coppice Mediterranean stands and highlight the role of mixed forests as a possible adaptation strategy for climate change.