Scrub encroachment into species-rich limestone grassland: recruitment, herbivory and the threat from incipient scrub

Abstract

Background: 'Scrub-grassland' mosaics are valued owing to their notable biodiversity. However, they are dynamic and difficult to manage, largely because of our incomplete knowledge of vegetation boundary shifts. Aim: Increase our understanding of the ecological processes involved in woody plant establishment at scrub-grassland ecotones and assess whether current management practices in a reserve (Cressbrook Dale, UK) are controlling scrub encroachment. Methods: Vegetation structure, seed deposition and seedling density were studied for woody species across the scrubgrassland interface. Seedlings of successful colonisers were planted in the grassland to assess their palatability and susceptibility to grazers. Results: Vegetation structure changed radically at the scrub-grassland interface. Woody plant canopy cover decreased more sharply than did the density of woody species. Seed deposition was much higher within the scrub than in the grassland (71.3 vs. 9.0 seeds m −2 year −1 ). Corylus avellana and Crataegus monogyna were the most successful grassland colonisers, with Corylus being less palatable but less resistant to grazing. Conclusions: Although the current grazing regime is stopping scrub encroachment, there is a notable density of stunted woody plants in the grassland adjacent to the scrub, their growth suppressed by grazers. This incipient scrub could rapidly become closed scrub if grazing pressure were relaxed.

Mapping scrub vegetation cover from photogrammetric point clouds: A useful tool in reserve management

“…for wildlife, scrub can become undesirable when it encroaches and dominates priority habitats (Laborde & Thompson, 2015). Scrub management through grazing or manual removal is a challenging task for land managers in the UK, particularly in finding the right balance of maintaining scrub for biodiversity and ensuring protection of priority habitats or ecological features.…”