Disentangling Relationships between Habitat Conditions, Disturbance History, Plant Diversity, and American Black Cherry (Prunus serotina Ehrh.) Invasion in a European Temperate Forest

Whether non-native plant invasions are causes, consequences, or independent of the low species diversity in recipient ecosystems remains a debated question. We tried to test these three hypotheses in the special case of the American black cherry (Prunus serotina Ehrh.), a gap-dependent tree species, which is invading European temperate forests. We compared plant communities, soil properties, and disturbance history between P. serotina-invaded and uninvaded paired-stands in a managed mixed forest. Relationships between invasion, disturbances, plant communities, and environmental conditions were investigated using redundancy analyses with variation partitioning. Several soil characteristics differed between paired stands, but were rather components of stand invasibility than invasion effects, except for topsoil available phosphorus. The disturbance history was similar among paired stands except for the amount of storm-induced tree falls, which correlated with the invader's density. Wild boar-disturbed soil areas were more important beneath P. serotina canopies, suggesting a positive feedback on its own establishment. Overall, species assemblages in invaded and uninvaded stands were similar; their ecological inconsistency suggested a management-sustained non-equilibrium. Habitat conditions and disturbances explained most of the variation in both plant diversity and P. serotina density, the last two factors exhibiting a weak direct association. We conclude that in managed forest ecosystems where plant communities are mainly driven by non-interactive factors and immigration processes, non-native plant species can naturalize without being directly influenced by measured features of the plant community in the receiving environment on the short term.