Vegetation dynamics and livestock performance in system-scale studies of sheep and cattle grazing on degraded upland wet heath

Upland wet heaths in the UK are of international conservation significance but high grazing pressure by sheep has caused widespread degradation. Restoration by reducing sheep numbers is not always successful if competitive grasses such as Molinia caerulea become dominant. Cattle can reduce grass biomass but their utility as a conservation tool is also dependent on economic viability. This study assessed the effect of two sheep-only and two mixed cattle-plus-sheep grazing regimes on vegetation and livestock performance over 4 years at a system scale on a 103 ha heterogeneous degraded wet heath. Grazing regimes were sheep all year at 1.5 or 0.66 ewes ha(-1) with 25% removed in winter, with or without dry Continental cross suckler cows at 0.75 cows ha(-1) for up to 10 weeks in summer. In mixed grazing paddocks, M. caerulea cover declined substantially in vegetation types where it was abundant. Calluna vulgaris declined slightly in the mixed grazing paddocks, primarily because of localised trampling. M. caerulea increased in the sheep-only paddocks and C. vulgaris declined slightly despite low grazing indices. Other changes in plant community composition were minor. Cow daily liveweight gains were adequate to regain body condition prior to calving, but these and ewe mating weights and lamb weaning weights were lower in paddocks with 1.5 than 0.66 ewes ha-1. Ewe and lamb performance were similar in mixed and sheep-only paddocks at each ewe stocking rate. Cows can be grazed with sheep to remove M. caerulea biomass without detriment to livestock performance, although the stocking levels used in this study would not be sustainable every year. Despite reduction of M. caerulea biomass, there was no evidence that heathland vegetation was being restored after 4 years. Restoration by grazing alone probably requires longer timescales and agri-environment schemes should avoid prescribing stocking levels regardless of livestock species. (c) 2008 Elsevier B.V. All rights reserved.