The impact of 36 years of grazing management on soil nitrogen (N) supply rate and Salix repens N status and internal cycling in dune slacks

Aims: To determine the impact of long-term rabbit and sheep grazing on Salix repens N status (green and abscised leaf N content and C:N ratio), internal N dynamics and soil N supply rate in dune slacks. Methods: Herbivore exclosures were erected in dune slacks at Ainsdale Sand Dunes NNR, creating three grazing treatments: rabbit grazing; rabbits excluded for 36 years; rabbit grazing followed by sheep and rabbit grazing for 18 years. Soil N supply rate was analysed using ion exchange membranes; leaf N dynamics of S. repens were measured over one summer. Results: Soil N supply rate was higher in ungrazed plots. There was no difference in green leaf NMASS or C:N ratio between treatments, but N dynamics differed. Adding sheep to existing rabbit grazing reduced S. repens N resorption efficiency (REFF) from 67 to 37 %; excluding rabbits had no impact. Litter NMASS was lower and C:N ratio higher in ungrazed plots. Conclusions: Grazing can impact significantly on leaf N resorption, but this impact depends on the grazing regime

The impact of 36 years of grazing management on vegetation dynamics in dune slacks

Grazing mammals are often used to maintain and restore high conservation value plant communities, but the evidence base for management is lacking long-term studies. We erected grazing exclosures in dune slacks to determine the impact of three different grazing regimes on the plant community: (1) rabbits and sheep excluded for 36 years, (2) continued rabbit grazing for 36 years and (3) rabbit grazing for 17 years followed by rabbit and sheep grazing for 19 years. We monitored plant community composition inside and outside the exclosures. All of the plant communities changed over time, moving away from the original high-value system and losing some characteristic species. Grazing slowed succession, reduced woody perennial cover and increased graminoid and forb cover and species diversity. The impact of adding sheep grazing to the existing rabbit grazing was additive at the functional group scale, but both complementary and additive (depending on the species) at the plant species scale. Synthesis and applications. At the levels of grazing present in this study (2·5 sheep ha year), sheep had similar impacts on dune slack plant communities to rabbits, making them suitable for replacing or augmenting rabbit grazing for conservation management. At the intensity present in this study, long-term grazing can help to maintain a species-rich dune slack community but is not sufficient for successful restoration