Plant succession in perennial grass strips and effects on the diversity of leafhoppers (Homoptera, Auchenorrhyncha)

Abstract

The biodiversity of agroecosystems may be enhanced by increasing species richness and structural diversity of vegetation by creating perennial strips. Aims of the study were (1) to describe the plant succession of perennial strips in northern conditions; (2) to clarify the difference in insect fauna between cereal fields and perennial strips; (3) to determine the effect of succession on leafhoppers in perennial strips; and (4) to compare the leafhopper fauna of perennial strips with that of other uncultivated biotopes. Three perennial grass strips (12 m wide, 420 m long) were sown in the middle of cereal fields (15 ha) in 1991 with a seed mixture of timothy ( Phleum pratense), meadow fescue ( Festuca pratensis), red clover ( Trifolium pratense) and white clover ( Trifolium repens). The perennial strips were not mown or renewed after the establishment. In 1992 and 1993 barley and in 1994 spring wheat were grown in the surrounding fields. The composition of plant cover in the grass strips changed over four seasons. The total number of plant species decreased from 23 species in 1992 to 10 in 1995. The change resulted from the dramatic decrease of annual weeds after the first year. Furthermore, the total plant cover declined slightly. The cover of P. pratense increased, whereas that of T. pratense and T. repens decreased. The plant species typical of early succession were annual weeds including Tripleurospermum inodorum and Thlaspi arvense. In the last year, perennial weeds such as Cirsium arvense and Elymus repens became common. Leafhopper abundance and species number were higher in perennial grass strips than in cereal fields. Furthermore, the species composition varied between habitats. Year-to-year fluctuations in leafhopper catches were large. Leafhopper abundance and diversity (Shannon index) were highest in 1993 when 192 sweep net samples contained a total 4680 specimens belonging to 37 species. The plant species richness of the grass strips did not correlate with the abundance and species richness of leafhoppers, which seemed to be more dependent on other factors. Although the plant species number in grass strips decreased clearly during succession, changes in species richness of leafhoppers were not so great. Factors affecting the leafhopper community are discussed.