RESTORATION OF BUTTERFLY AND MOTH COMMUNITIES IN SEMI-NATURAL GRASSLANDS BY CATTLE GRAZING

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The effects of restorative grazing on species composition and community structure of butterflies and moths were studied in mesic semi-natural grasslands differing in their management history: (1) old continuously grazed pastures, (2) restored pastures with -5 yr of reinitiated grazing, and (3) abandoned former pastures. Butterflies and moths were counted with a transect method during 1999 and 2000 in 33 study sites in southwest Finland. In a multivariate ordination (NMDS), the studied grasslands were separated from each other on the basis of their species composition so that the actively grazed pastures differed from abandoned pastures. The first ordination axis represented most (73%) of the variation in species composition, and it was strongly correlated with variables describing the current grazing intensity. Species richness and total abundance were highest in aban- doned pastures, both for all species and for grassland-preferring species. In contrast, relative diversity (N,, N2, and a) and evenness (Alatalo's evenness index) were in most cases highest in old pastures and lowest in abandoned pastures. Generalized linear models (GLM) were constructed for four response variables: total species richness, grassland species richness, abundance of all species, and abundance of grassland species. The derived models explained 78-84% of the total variation for species richness and 92-93% for abundance, and the type of grazing history explained the largest proportion of variation. Mean vegetation height was included in the abundance models as a quadratic function, which indicated that but- terflies and moths were most abundant at an intermediate level of grazing intensity, as predicted by the dynamic equilibrium model. The results suggest that grazing manage- ment is a useful tool in the restoration of insect communities of abandoned semi-natural grasslands. In order to enhance the survival of species suffering from continuously high grazing intensity, the existing management instructions should be developed toward con- struction of regional networks of semi-natural grasslands, which would allow differing grazing intensities or rotational grazing on the patch level, but simultaneously ensure con- tinuity of varying management regimes on a regional level.