Post-dispersal fate of hazel (Corylus avellana) nuts and consequences for the management and conservation of scrub-grassland mosaics

Granivorous rodents and birds are both predators and dispersers of the nuts produced by many woody plants. This study examines the role of granivores as predators and dispersers of Corylus avellana L. and the consequences of this interaction for Corylus regeneration and scrub encroachment into grassland. In the Cressbrook Dale nature reserve (Derbyshire, UK), Corylus nuts were buried in the grassland at two distances (<15 and >70 m) from scrub vegetation (the main source of nuts, and habitat of the granivores) to estimate the rate of seed removal over 3 years, assessing also the success of dispersal and seedling establishment in the grassland. The rate of nut removal at close sites (<15 m from scrub) was consistently higher than at far sites (>70 m) over the 3 years. All sown nuts were removed over 2 years at close sites, while at the far sites around 20% of the sown nuts were still present the following spring. Grassland close to the scrub had the highest intensity of nut predation but also had the highest density of Corylus seedlings. Sciurus carolinensis was the most important disperser of hazelnuts into the grassland. This squirrel scatter-hoarded 10–12 thousand hazelnuts in 1.5 ha of grassland adjacent to scrub. In this reserve, two vertebrates – both non-native – are largely responsible for maintaining the dynamic balance between the scrub and grassland habitats. American grey squirrels disperse hazelnuts into the grassland and sheep slow the encroachment of scrub by repeated browsing.