Data and code from: Phenotypic plasticity masks evolutionary change in grassland plant traits in response to land use abandonment

Traditionally-managed grasslands are among the most biodiverse habitats in
Europe, but are threatened by land use abandonment. While the negative
impacts of grazing and mowing cessation on species richness are well
documented, little is known about potential evolutionary changes within
species. Yet, intraspecific functional diversity is critical for
successful grassland restoration and ensuring adaptive potential to future
climate change. To disentangle the heritable and non-heritable components
of population-level response to land use change in semi-natural
grasslands, we examined 22 populations of a common grass, Briza media,
from grazed sites and sites where grazing was abandoned, with resulting
tree and shrub encroachment. We measured a range of traits under field
conditions and following clonal propagation under common garden
conditions. Field surveys revealed that abandonment resulted in litter
accumulation, greater shading by woody and herbaceous vegetation, and
lower temperature and moisture fluctuations compared with grazed sites.
Plants responded to conditions at abandoned sites with phenotypic
plasticity in traits that enhanced competitive ability for light (greater
height and specific leaf area) but reduced tissue protection against
stress (lower dry matter content). However, when the same genotypes were
measured after clonal propagation in common conditions, countergradient
variation was apparent, with heritable shifts towards increased tissue
protection in populations from abandoned sites. When measured under field
conditions, trait diversity was higher in sites with higher levels of
shading and productive sites with higher variation in light conditions.
However, high heritable trait diversity was instead characteristic of
grazed sites with high densities of flowering B. media individuals. These
findings demonstrate that land use change can cause evolutionary shifts
and changes in heritable trait diversity that are masked in the field by
phenotypic plasticity. Hence, the assessment of functional trait variation
based on field observations is not a reliable way to assess the genetic
variation essential for population adaptive potential.