Effects of sowing and management on vegetation succession during grassland habitat restoration

The impact of sowing a seed mixture to recreate a semi-natural community in combination with six cutting and/or grazing treatments on the vegetation that developed on former agricultural land was examined over 6 years. Introducing seeds significantly increased the number and cover of sown species persisting. Summer grazing by cattle maintained the number, but not cover, of sown species. Few sown species persisted when grazed by sheep, although those that did maintained high cover. Sorenson's qualitative similarity index (based solely on species presence or absence data) revealed that pairs of sown and non-sown plots within a management treatment did not appear to converge during succession. However, using Sorenson's quantitative similarity measure (based on both species occurrence and abundance) pairs of plots became increasingly similar after the first year. The sown plots became less similar to each other using the qualitative similarity measure, but this was less marked using the quantitative measure. In contrast, the non-sown plots became less similar to each other with the quantitative measure, but no changes were observed with the qualitative measure. The vegetation in the sown plots became more like that in the non-sown plots as sown species failed to persist. In contrast, the non-sown plots became more like the sown plots as the sown grasses Agrostis capillaris and Festuca rubra increased in abundance. The exception to this was the cattle-grazed sown plots, which retained more sown species, however, succession in this treatment also converged towards the non-sown plots because the non-sown species Trifolium repens and Ranunculus repens increased in abundance in this treatment. The addition of seeds of a desired grassland community appeared to have less effect in directing the trajectory of succession than did the vegetation management. (C) 2002 Elsevier Science B.V. All rights reserved.