Construction of deer fences restores the diversity of butterflies and bumblebees as well as flowering plants in semi-natural grassland

The abundance of both flower-visiting insects and flowering plants in semi-natural grasslands in temperate zones has declined as a result of overbrowsing by deer. The construction of deer fences is an effective method for biodiversity conservation because these fences prevent the invasion of deer. However, few studies have elucidated the biodiversity conservation effects of deer fences in semi-natural grasslands. Here we investigated the effects of the construction of deer fences on the diversity of butterflies, bumblebees, and flowering plants on the Kirigamine Plateau, Nagano Prefecture, Japan, which is covered by semi-natural grassland. The number of species of flowering plants inside the deer fences was higher than that outside the deer fences. The numbers of individuals and species of flower-visiting butterflies and bumblebees also tended to be higher inside the deer fences than outside the deer fences. On the other hand, there tended to be no difference in the number of individuals and species of non-flower-visiting butterflies inside and outside the deer fences. The diversity of flowering plants, butterflies, and bumblebees within the fenced areas was not substantially affected by the size of the fenced-off area. Our findings suggested that the construction of deer fences can contribute to the conservation of both flower-visiting insects and flowering plants in semi-natural grassland.