Variation in early fitness traits across European populations of silver birch

Climate change models predict drier and warmer summers for Mediterranean regions in the next decades. In Central Europe, increases in temperature and considerable contrasts in precipitation between dry and wet seasons are predicted. As a consequence, plant species distribution ranges and demographics might be considerably altered. There is a need to assess the levels of intraspecific genetic variation in fitness-related traits, and its environmental determinants, in order to evaluate the potential for, and the drivers of adaptive evolution to climate change. Specific questions are raised related to intraspecific variation in early growth traits, including (1) does seed origin imply differences in early fitness traits? (2) can environmental factors compromise the first stages of the regeneration process? (3) do seed origin (genotype) and the germination environment interact? And (4) do emergence success and early growth follow clinal patterns in widely distributed species?

Emerged *Betula pendula* seedlings from a Lithuanian population sown in the Spanish common garden. Coloured pins were used to track individual seedlings within each experimental cell. Image credit: Solé-Medina *et al.*

In their new study published in AoBP, Solé-Medina et al. attempt to answer these questions by examining the extent to which populations of Betula pendula, a widely distributed tree species in Europe, differed in early fitness traits under contrasting environmental conditions. Their results from common garden experiments across Europe suggest that the answer to all these questions is ‘yes’. Overall, genetic, environmental and demographic factors seem to influence the observed high levels of variation in early fitness traits among B. pendula populations. Their study also highlighted the limited regeneration capacity of this species under dry environments. The results of the study, along with high among-year variation in seed production and germination, highlight the difficulty of achieving general conclusions concerning tree early fitness traits. The authors hope that further studies under sufficiently replicated environmental conditions will help to test for plastic responses, ideally using seeds collected in different years, to improve our understanding on the potential regeneration niche and vulnerability of forest trees species such as B. pendula to climate change.

This study was published as part of the AoBP Special Issue entitled The Ecology And Genetics Of Population Differentiation In Plants.