Environmental limitation contributes to the differential colonization capacity of two forest herbs

Question: The recovery of forest plant communities in post‐agricultural landscapes is largely determined by dispersal constraints, but can environmental legacies of former land use additionally limit the recolonization of recent forests by forest herbs? Location: Ancient forest and recent forest on former heavily fertilized agricultural land (Muizenbos, northern Belgium). Methods: Seeds and adults of two forest herbs with similar life‐history traits, but contrasting colonization capacity – the fast‐colonizing Geum urbanum and the slow‐colonizing Primula elatior – were introduced into both ancient and recent forest sites. Soil conditions and plant tissue nutrient concentrations were measured to characterize habitat quality. To determine whether the introduced species could successfully establish and persist, we monitored recruitment, longevity and adult performance during 8 years in permanently marked plots. Results: Phosphorus availability was ten times higher in recent forest soils and was also reflected in the plant tissue samples. Species longevity was clearly lower in recent forest sites indicating higher turnover. The fast‐colonizing G. urbanum counterbalanced this lower longevity by new establishment, while the slow‐colonizing P. elatior dropped below the number of originally introduced individuals. Additionally, G. urbanum performed better in recent forest sites in contrast to P. elatior . Conclusions: Even when dispersal constraints of the slow‐colonizing forest herb P. elatior are eliminated through introduction, environmental conditions in recent forest sites additionally restrict its recruitment, longevity and performance. These experimental results suggest that environmental constraints may strengthen the differences in colonization capacity among forest herbs if slow dispersers also tend to be less likely to establish.