How do Droughts and Wildfires Alter Seasonal Radial Growth in Mediterranean Aleppo Pine Forests?

Abstract

Climate models project increasing temperatures, evapotranspiration, and droughts for the Mediterranean Basin, which will trigger more frequent and dangerous fire events. Here, we evaluate the combined effects of drought and wildfire on seasonal tree growth on Aleppo pine stands at the intra- and inter-annual level. Indexed earlywood width (EWI), latewood width (LWI), and latewood proportion (LWPI) series were obtained from unburned and burned stands located at four sites along a precipitation gradient in southeastern Spain. The combined effect of drought in 1994 and 1995 and wildfire in August 1994, negatively impacted seasonal growth in the short term (1994–1999 period) at the site with higher water availability. At the driest site, however, no significant effects were found. We found fewer negative pointer years at the wettest burned stand than at the wettest unburned stand during the post-fire 1994–2012 period, and the opposite pattern was found at the driest site, i.e. more negative pointer years at the driest burned stand than at the driest unburned stand. This result indicates that the drier sites were more sensitive to cumulative impact of drought and wildfire disturbances in the long term, whereas the wetter sites were more sensitive in the short term. Our results demonstrate the seasonal growth plasticity of Aleppo pine to combined disturbances depends on site water availability. This study will help forest managers to implement climate change strategies, such as prescribed fires (controlled low-medium severity fires) to prevent wildfire hazards more efficiently in Aleppo pine stands with high water availability.