Climate windows of intra-annual growth and post-drought recovery in Mediterranean trees

Abstract

Forests store large amounts of carbon as wood, but this storage potential depends on seasonal radial growth and how it is driven by climate. Therefore, we need a better understanding on how intra-annual radial increment rates determine growth responses to climate variability. There is a large gap of knowledge on the climate windows, i.e. the effective climatic time-window for tree growth, and predictors of intra-annual growth, particularly in seasonally dry biomes such as Mediterranean forests where growth may show several seasonal peaks. We described the radial increment rates of five tree species inhabiting mesic (Quercus ilex, Quercus faginea, Arbutus unedo) and xeric (Pinus halepensis, Juniperus thurifera) sites using dendrometers. Then, we related those rates and tree-ring width to climate data using correlations and model selection. All species presented bimodal patterns of radial increment rates with a major peak in spring and a minor peak in autumn, being this pattern most marked in Q. ilex, A. unedo and J. thurifera. Differences in climate-rates relationships were greater between species than between sites. Wet and cool conditions in winter and spring increased spring rates, but the climatic time-windows were longer in some species (Q. ilex, J. thurifera) and shorter in others (Q. faginea, P. halepensis). Similarly, wet and cool conditions also enhanced autumn rates in the xeric site, but warm conditions did it in the mesic site. Rainy autumn conditions reduced A. unedo rates. Climate-growth associations at intra- and inter-annual scales were consistent in species showing long intra-annual climatic time-windows such as Q. ilex. Our findings confirm the importance of wet winters and cool springs for radial growth in some species, and the relevance of autumn growth in A. unedo. Similar studies on intra-annual radial increment rates and climatic time-windows of forest growth and productivity can reveal which will be the species most impacted by drought.