Heterogeneity and diversity of orchard grassland vegetation in Central Germany: role of tree stock, soil parameters and site management

Abstract

Orchard grasslands in Central Europe are highly valued due to their contribution to the biodiversity of agricultural landscapes. Little is known about the factors that control the phytodiversity of orchards and the role of small scale vegetation heterogeneity. In our study, we address the role of (1) tree stock, (2) soil parameters and (3) site management on orchard grassland heterogeneity and diversity. For this purpose, we investigated species diversity in 32 orchards covering a broad range of orchard types in Central Germany. Each study site comprised 9 × 1 m2 plots, of which three were located beneath a tree canopy (trunk), three in the transition zone between canopy and open grassland (ecotone) and three in the open grassland (open). Results show (1) increasing vegetation heterogeneity induced by trees. On average, the ecotone and open hosted significantly larger species richness than the trunk. They also differed from the trunk in vegetation species composition. (2) Increasing phosphorous content and potassium contents > 20 mg/100 g showed negative effects on species richness. Species richness generally increased with a soil pH until about pH 6.5. (3) We could not prove that grazing as compared to non-grazing increased vegetation heterogeneity; yet, the species composition was different. Species composition was further affected by vegetation height, which also showed a negative effect on high nature value species richness. To preserve orchard vegetation diversity, we recommend reducing the soil nutritional status of enriched soils by mowing or grazing in combination with night penning early in the vegetation season.