# Growth Performance Is Driven by Site Conditions and Moderated by Functional Trait Plasticity in Quercus robur and Prunus avium

## TL;DR

The growth of oak and cherry trees is mainly influenced by site conditions, with some traits like leaf area and leaf-out date showing small changes in response to climate.

## Contribution

The study quantifies phenotypic plasticity and genetic differentiation in functional traits of two tree species under varying climate conditions.

## Key findings

- Growth performance is primarily determined by site conditions, with specific leaf area being the most significant trait.
- Prunus avium shows modest provenance-level variation in traits, while Quercus robur shows variation mainly in leaf-out timing.
- High inter-individual variability suggests potential for acclimation and adaptation to climate change.

## Abstract

Functional traits mediate plant‐environment interactions, yet their plasticity and genetic variability remain poorly quantified in long‐lived tree species. We examined provenance trial (common garden) data from one growing season of
Quercus robur L. and
Prunus avium L. across six sites spanning a ~2°C climate gradient to evaluate phenotypic plasticity and genetic differentiation in specific leaf area (SLA) and spring leaf‐out, and their effects on growth. We applied mixed‐effects models to separate provenance, family, and site effects, and to test trait‐growth relationships under contrasting water availability and temperature conditions. Growth performance from planting to between 16 and 8 years of age, respectively, was primarily determined by site conditions (modeled as a trial random effect, which includes climate, soil, and other local factors), with SLA emerging as the most significant functional trait across both species. As for the functional traits themselves,
P. avium
showed modest provenance‐level variation in both traits (R
2 ~ 7%), while in
Q. robur
only leaf‐out varied (R
2 ~ 19%) across provenances and families, indicating in both cases the presence of genetic differentiation. Plasticity in SLA and leaf‐out was detectable in response to climate variables but was generally small relative to inter‐individual variability (plasticity explained < 10% of trait variance). In
P. avium
, however, leaf‐out timing was strongly climate‐sensitive, consistent with its role as a short‐lived, pioneer species, whereas
Q. robur
(a long‐lived, dominant species) showed weaker plastic responses but slightly higher genetic structuring of traits. For all traits studied, a large proportion of the observed trait differences cannot be explained by climate or genetics, indicating high levels of individual variability (R
2 ~ 70%). This high inter‐individual variability, together with the modest but significant plasticity observed, suggests that the studied species possess the genetic potential (aided by plasticity) needed for acclimation and adaptation to climate change.

Growth performance in Quercus robur and Prunus avium is strongly influenced by site conditions, but also by functional traits (Specific Leaf Area, spring leaf‐out date), which show moderate plasticity in response to climate. These traits differ among provenances of the same species, and there is variability in trait values within the provenances. The observed plasticity and inter‐individual variability suggest potential for acclimation and adaptation to climate change.