Calcareous grassland restored by clearance and subsequent sheep grazing show fast recovery of plant functional traits – Results from a 25-year-long experiment

Abstract

In this study, the long-term restoration success of calcareous grasslands was investigated using a functional trait approach. The study site is located in the Swabian Alb, Germany, where a former calcareous grassland patch was restored in the 1990s by clearance of a spruce (Picea abies (L.) H. Karst.) afforestation and subsequent reintroduction of sheep grazing as mobile dispersal vector. Vegetation development was monitored over a period of 25 years, both on the restored and an adjacent never afforested ancient grassland which is still managed by traditional sheep grazing. Changes in the functional composition of fifteen ecological meaningful traits were investigated by comparing the respective attribute expressions of the restored with the ancient reference grassland for each year of observation. A RLQ-analysis was conducted in order to identify plant functional groups. The comparison of attribute expressions showed that differences between restored and ancient grassland decreased rapidly over time. The greatest differences were found in persistence-related traits (e.g., life span and growth form) while dispersal- and establishment-related traits recovered faster. The clustering of plant functional groups showed similarities with Grime’s CSR-strategy, as cluster analysis grouped species with either ruderal, competitive or stress-tolerant trait attributes. 20 years after restoration, stress-tolerators dominated, while the ruderal cluster could not longer be detected and only a small group of competitive, mostly woody species remained. In 2018, RLQ analysis revealed no differences in the functional composition between restored and ancient grassland. The quick functional recovery is most likely attributed to the reestablishment of the traditional low-intensive grazing management but also to the close vicinity of the ancient grassland as no spatial isolation prevented dispersal of plant species. Hence, the functional trait approach showed that restoration by clearance and subsequent sheep grazing was a suitable management in our study.