The biodiversity of birch stands in agricultural landscapes of Estonia is associated with past land use, restoration approach, site and landscape variables

Questions Abandonment of agricultural land followed by tree planting or natural regeneration has increased forest area in Europe. We asked how restoration approach, past land use, site and landscape variables affected the richness and composition of vascular plants (field and shrub layers), bryophytes and lichens in middle-aged forests. Location Thirty-three birch stands in Estonia. Methods Data were collected from stands on former agricultural land that originated from plantations (PL-A) or natural regeneration (NR-A), and for reference, from native forest land (NR-F). In every stand a 10 m x 10 m survey plot was established. Generalised Linear Mixed Models were used to test the effect of restoration approach, past land use, soil, light, stand and landscape variables on species richness estimates. Compositional patterns were analysed using Non-metric Multidimensional Scaling, permutational multivariate analysis of variance and indicator species analysis. Results Altogether 215 vascular plant, 70 bryophyte and 63 lichen species were found. The effects of restoration approach, past land use, and site and landscape variables on the species richness varied depending on the taxonomic and ecological groups of species. The richness of shrubs and bryophytes was higher in NR-A than in PL-A, and both variables were also related to soil properties. The richness of the field layer was related to past land use because previous croplands hosted fewer forest species than previous grasslands and stands on forest land. Higher current forest cover around the studied stands increased the richness of lichens, which were also affected by light and soil conditions. Species composition differed among the three stand types; however, the previous land use (agriculture vs forest) had a stronger effect than the restoration approach. Conclusions Although natural forest regeneration promoted biodiversity the most, plantations also supported the recovery of biodiversity at abandoned agricultural sites. Therefore, on a regional scale both restoration approaches are recommended.