Rapid adaptive evolution in restored populations of a perennial plant

Abstract

Restored plant populations often face novel environmental challenges because degraded restoration sites typically differ from natural habitats. The success of ecosystem restoration may therefore depend on whether restored plant populations can adapt rapidly to these novel conditions. Yet, rapid adaptive evolution during restoration remains rarely studied. Here, we tested for rapid adaptation in Galium wirtgenii, a perennial herb, within restored alluvial grasslands. Sites were restored 20 years ago by transferring hay from nearby ancient semi-natural meadows. Compared to the semi-natural donor meadows, restored sites are more productive and are mown two to three months earlier. We collected seeds from 571 mother plants from 48 restored and 18 semi-natural sites and grew their offspring in a common garden over three years. To test for differences in regeneration after mowing, we included a clipping treatment when plants were in full blossom. Plants from restored sites flowered earlier than plants from semi-natural sites, and this difference persisted across all three years, consistent with a heritable evolutionary response to earlier mowing allowing plants at restored sites to complete reproduction before mowing. Plants from restored sites also grew more slowly in early life stages, but this effect disappeared later, suggesting maternal effects rather than genetic differentiation. We did not detect differences in regeneration after clipping, likely because regrowth rarely results in viable seeds, providing little fitness advantage. In summary, we found evidence for rapid adaptation to novel environmental conditions in restored sites, likely contributing to successful establishment of Galium wirtgenii populations in the restored grasslands.