Effects of interannual weather on understory plant traits in old-growth beech forests

Luciano Ludovico Maria De Benedictis , Stefano Chelli, Roberto Canullo, Carlos Pérez Carmona, Marco Cervellini, Enrico Tordoni, James Lee Tsakalos, Giandiego Campetella

We aimed to estimate the effects of annual mean temperature and precipitation on understory plant traits and trait diversity in old-growth beech forests. We combined sub-canopy and open-field measurements from local weather stations with data on aboveground and belowground traits.
Relationships and potential confounding effects within the system were analysed using a causal model. The resulting statistical model estimated the response of traits to interannual weather fluctuations within a site, exploiting the longitudinal data from a 12-year monitoring program.
Overall, temperature effects were uncertain, while precipitation effects were more precisely estimated but small. Aboveground traits and trait diversity showed a positive response to temperature, while belowground traits a negative response to precipitation, highlighting the importance of considering distinct functional compartments and different sets of traits when assessing plant responses to environmental variability.
More than half of the variation in trait diversity occurred among neighbouring sub-plots, rather than among sites and years. This fine-scale heterogeneity suggests that micro-environmental factors and biotic interactions might have a larger effect on the coexistence of different functional strategies than broader-scale variation, environmental or otherwise.
We conclude that interannual weather variability, especially in precipitation amount, has limited effects on the functional properties of understory plant communities in undisturbed beech forests. However, this apparent functional stability may be threatened by more frequent climatic extremes or altered seasonal weather patterns.