Cattle grazing increases plant species richness of most species trait groups in mesic semi-natural grasslands

The effects of cattle grazing on plant species trait groups were studied by comparing three kinds of mesic semi-natural grasslands in southern Finland: old (continuously cattle grazed), new (cattle grazing restarted 3-8 years ago) and abandoned pastures (grazing terminated > 10 years ago). Two spatial scales were studied: 1 m(2) and grassland patch (0.25-0.8 ha). Species richness was higher among most species trait groups in old than in abandoned pastures and showed some recovery in new pastures. More pronounced differences were found per m(2) than per grassland patch. Richness of perennial and biennial plants was in order old > new > abandoned pastures both per m(2) and per grassland patch, but richness of annual plants was significantly higher only per grassland patch. Grazing increased the richness of hemicryptophytes and chamaephytes and decreased that of geophytes both per m(2) and per grassland patch. Richness of small and medium-sized plants was higher in grazed than in abandoned grasslands. Only richness of the tallest species (height > 80 cm) was lower in grazed grasslands. The proportion of species trait groups, in which species richness was higher in grazed than in abandoned grasslands, was higher than in previous studies. This may be due largely to the differences in the grassland type (mesic vs. dry or wet). It is proposed that species trait responses to grazing may be related to how effectively natural factors (e.g., drought, flooding) limit plant growth. In mesic grasslands natural factors limit plant growth less than in dry or wet grasslands. Because of this the number of groups of species with different species traits benefitting from grazing is higher in mesic than in dry or wet areas.