Drought timing, intensity, and consecutiveness have more influence on Douglas fir growth response than site conditions and stand density in European temperate climate

14 S.

e-journal

200211950

Douglas fir is a largely introduced species in Europe and is often presented as a promising alternative to more drought-sensitive species. However, the observed and predicted increase in drought frequency and intensity could undermine its ability to cope with drought. This study aims to investigate the radial growth response of Douglas fir to drought in its climatic optimum in Europe, considering a number of drought characteristics (in terms of timing during the growing season, intensity, and consecutive occurrence), site conditions (average climatic water balance, maximal extractable soil water), and stand densities. Using growth data from 360 trees sampled across 24 sites in Wallonia (Belgium), we fitted linear mixed models to investigate the influence of drought, site, and stand characteristics on three commonly used resilience indices, as well as on an integrated index comparing observed resilience with a theoretical full resilience reference. On average, radial growth was reduced during droughts regardless of drought characteristics and site conditions. Trees always recovered to some extent, but not always to full resilience.
Keywords: Pseudotsuga menziesii; Drought response; Tree ring; Resilience; European forest