Adaptive pattern of phenotypic plasticity and inherent growth reveal the potential for assisted transfer in sessile oak (Quercus petraea L.)

Abstract

Abstract Based on data published by Saenz-Romero et al. (Adaptive and plastic responses of Quercus petraea populations to climate across Europe, 2017), an alternative reanalysis of a continent-wide common garden experiment (provenance test) of sessile oak was performed. Population mean heights were analyzed with a focus on responses to drought and high summer temperatures projected for the future. The main aim was to assess the adaptive capacity of populations in the critical drying and warming domain of the distribution. A unilateral approach was applied to calculate response regressions (reaction norms) of individual populations. Regression parameters served to investigate the changing balance of growth potential, phenotypic plasticity and resilience among populations of different provenance. Among the reanalysis results, the most striking was the flat, quasi-linear response in the dry-warm niche domain reaching beyond the mimicked “local” conditions. Consequently, at climates equivalent to the population origins no maxima were found. Populations from humid-cool climates displayed higher climate sensitivity (plasticity) to changes toward drier and warmer climates. Populations of dry-warm provenance have shown higher resilience under changing climate. Inherent height growth potential of populations in climates similar to that at their origin (“virtual height”) diminished significantly with increasing aridity at provenance. Growth potential and resilience revealed a selection trade-off among populations and both appeared as traits under climatic (adaptive) selection. Thus, assisted transfer of sessile oak populations may improve resilience; however, at the expense of lower growth potential. This cautions against mixing differently adapted populations in artificial regenerations. The use of local provenances as a recommended adaptive measure indicates limited relevance for sessile oak. The present generation of forest trees meets the predicted rapid climate/habitat shifts in its lifetime. Therefore, phenotypic plasticity and resilience will play a central role in sustaining the fitness of extant populations. To determine these traits independently from local site effects, common garden data cannot be neglected and are worth reanalyzing. Notably, provenance tests provide real-time field information on the performance of populations in new climatic environments, applicable for assisted transfer initiatives.