Beyond Proxies: Towards ecophysiological indicators of drought resistance for forest management

Abstract

AbstractAs drought-induced mortality increases globally in forest biomes, it becomes necessary for foresters to have access to reliable predictors of species vulnerability to drought and mortality risk under different climatic scenarios. On the one hand, there exist several “operational” indicators of drought resistance, which are based on observations, expert knowledge and species bioclimate (e.g.Ellenberg, Rameau, ClimEssences). On the other hand, as traits can now be measured at high throughput, functional traits (such as plant hydraulic traits) have been increasingly used to assess species’ vulnerability to hydraulic failure, a key process of tree mortality under drought. However, this mechanistic approach has never been compared to the operational approach. In this study, we review if indicators commonly used by foresters provide information onAbiesspecies’ vulnerability to hydraulic failure. We measured a set of traits in a common garden experiment of closely related MediterraneanAbiesspecies. These traits were used as inputs to the SurEau model to compute a single indicator of vulnerability (Time to Hydraulic Failure -THF) and to assess mortality risk in future climate. We found that among circum-Mediterranean firs, a highTHFwas mainly due to high water losses after stomatal closure. Some operational indicators are good proxies ofTHF, however they are not available for all species, reduce a species to a single value and have the same limitations as species distribution models. We argue that the ecophysiological approach could help foresters in species selection and in estimating the risk faced by forest tree species in a changing climate. While accounting for the variability of traits, hydraulic models can be forced with different climatic scenarios allowing hydraulic failure risk assessment by the end of the century.HighlightsIntegrating ecophysiological traits in a process-based model allows the computation of an accurate indicator of vulnerability: the Time to Hydraulic Failure (THF).ForAbiesspecies, ”operational” indicators,i.e.indicators used by foresters and land managers, are mutually consistent and can be simplified proxies of the vulnerability to hydraulic failure.More research on intra-specific variability is needed to assess the evolutionary potential of Euro-MediterraneanAbiesspecies.