Abstract
AbstractAimDistribution ranges of temperate tree species are shifting poleward and upslope into cooler environments due to global warming. Successful regeneration is crucial for population persistence and range expansion. Thus, we aimed to identify environmental variables that affect germination and seedling establishment of Europe's dominant forest tree, to compare the importance of plasticity and genetic variation for regeneration, and to evaluate the regeneration potential at and beyond the southern and northern distribution margins.LocationEurope.Time period2016â2018.Major taxa studiedEuropean beech (Fagus sylvatica (L.)).MethodsWe investigated how germination, establishment and juvenile survival change across a reciprocal transplantation experiment using over 9,000 seeds of beech from 7 populations from its southern to its northern distribution range margins.ResultsGermination and establishment at the seedling stage were highly plastic in response to environmental conditions. Germination success increased with warmer and declined with colder air temperature, whereas establishment and survival were hampered under warmer and drier conditions. Germination differed among populations and was positively influenced by seed weight. However, there was no evidence of local adaptation in any trait.Main conclusionsThe high plasticity in the early lifeâhistory traits found irrespective of seed origin may allow for shortâterm acclimatization. However, our results also indicate that this plasticity might not be sufficient to ensure the regeneration of beech in the future due to the low survival found under dry and hot conditions. The future climatic conditions in parts of the distribution centre and at the rear edge might thus become limiting for natural regeneration, as the likelihood of extreme heat and drought events will increase. By contrast, at the cold distribution margin, the high plasticity in the early lifeâhistory traits may allow for increasing germination success with increasing temperatures and may thus facilitate natural regeneration in the future.
Highlights
Distribution ranges of species are projected to shift polewards or upwards in elevation (Lenoir et al, 2008; Parmesan, 2006; Sykes et al, 1996), whereas populations at the rear edge are threatened due to global warming (Thomas et al, 2004; Thuiller et al, 2005)
In the case of strong local adaptation, assisted gene flow within a species range, that is the transplantation of genotypes from origins climatically similar to the expected future conditions of a given site, or assisted migration, that is the transplantation of genotypes outside of a species range, might be considered as an adaptation strategy by forest managers to ensure sustainable forest ecosystem services under rapid change in climatic conditions (Aitken & Bemmels, 2016; Williams & Dumroese, 2013)
Plastic responses to changing environmental conditions could allow for short-Âterm acclimatization and might buffer the impact of climate change
Summary
Distribution ranges of species are projected to shift polewards or upwards in elevation (Lenoir et al, 2008; Parmesan, 2006; Sykes et al, 1996), whereas populations at the rear edge are threatened due to global warming (Thomas et al, 2004; Thuiller et al, 2005) These predictions from species distribution models generally neglect the potential for in situ responses of organisms to changing environmental conditions through phenotypic plasticity, local genetic adaptation and demographic processes (Aitken et al, 2008; Savolainen et al, 2007; Scherrer et al, 2020; Valladares et al, 2014). We aimed: (a) to identify which environmental variables of the transplant site or the population origin affect these earliest life stages; (b) to directly compare the importance of plasticity and genetic variation for germination, seedling establishment and survival of juvenile trees. We expected local environmental conditions to dominate the outcome, that is a prevalence of plasticity over genetic adaptation; and (c) to explicitly evaluate the potential for regeneration at and beyond the southern and northern distribution margins
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