Tree growth responses to severe droughts for assessment of forest growth potential under future climate

Abstract

More frequently occurring droughts, related to climate change, lead to reduced growth and loss of vitality in trees. The recent drought of 2018 was extreme, long-lasting and resulted in high evaporative demands due to the concurrent high temperatures. The aim of this study was to compare the drought resilience of nine temperate tree species in the Netherlands, and to determine their responses to the severe drought of 2018 in comparison with five earlier drought events since 1970. To assess drought effects on tree species, we analysed tree-ring series of 678 trees in 45 plots throughout the Netherlands. Resilience indices were calculated based on growth reactions and growth recovery after drought. Furthermore, the impact of drought events on species productivity was quantified. We observed species-specific differences in growth responses to drought timing. All species in nearly all sites responded with growth reductions to drought, except sessile oak (Quercus petraea (Matt.) Liebl.). The most productive species in our study were found to be drought sensitive, with productivity losses of up to 30 % during drought in some sites. Productivity losses were highest on the driest soils. Resilience to the 2018 drought did not differ significantly from other drought years for six out of the nine studied species. However, 77.5 % of the individual trees of all studied species did not fully recover in growth within the following two years. Low post-drought growth remains poorly understood and should be taken into account in future studies to safeguard the health and productivity of the forest under climate change. We consider sessile oak a promising species for future forests in the Netherlands. Based on our results, we provide an outlook on future resilience and growth potential of the species studied under projected climate change for the Netherlands.