Variability of the climate-radial growth relationship among Abies alba trees and populations along altitudinal gradients

- The climate-radial growth relationship of fir is studied along altitudinal gradients.
- Summer drought of current and previous years is the main factor limiting fir growth.
- Spring drought of the previous year is correlated with higher growth.
- The climate-growth relationship varies among fir stands but not among trees.
- The recent climate change has not altered the fir growth response to climate.

Tree ring widths provide very useful information to assess factors controlling tree radial growth and to estimate future growth trajectories under climate change. Radial growth variability has already been largely studied among tree populations that experience different environmental conditions and was most recently analyzed among individuals within populations.In the present study we assessed, over the 1960-2011 period, the growth response of silver fir (Abies alba Mill.) individuals originating from ten populations located along two altitudinal gradients (1000-1600 m a.s.l.) in the south east of France. Tree ring increments were estimated from wood cores collected from 129 adult trees. Results showed that (i) 30% of the growth variance among individuals was explained by competition; (ii) the climates of both the current and previous years were correlated with growth. Most of the climatic variables affecting growth were consistent with those identified in previous studies and with the known physiology of the species: negative effects of summer drought of the current and past years as well as a positive effect of the spring temperature of the current year. However in our study, fir growth was also enhanced by previous year spring droughts. The growth responses to precipitation, temperature, and, relative humidity of the current and previous years varied between sites and/or altitudinal levels, reflecting population acclimation by plasticity or genetic adaptation to local conditions. By contrast, only summer rainfall induced variable responses between individual trees, result attributed to the edaphic micro local heterogeneity. The recent climate change did not significantly alter the fir growth response to climate.