Species diversity of forest islands in agricultural landscapes of southern Finland, Estonia and Lithuania

Abstract

Plant species diversity of woodland patches in the agricultural landscapes of different geographical regions (Finland, Estonia, Lithuania) have been studied. During the field studies (1990–1993) a total of 127 woodland patches was investigated (42 in Finland, 44 in Estonia and 41 in Lithuania). In each wood patch the following variables have been identified: number of tree and shrub species (in Estonia also herb species), area, age, disturbance, distance to the nearest woodland patch, and number of soil types (in Finland, the number of forest site types). On the basis of measured variables the coefficient of biotope heterogeneity, the coefficient of age and disturbance, the gamma-diversity (Whittaker, 1977) and the edge index have been calculated. A multiple regression model has been developed and compared with an analogous model designed by Rudis and Ek.The model describes comparatively well the tree, shrub and herb species richness of the woodlots in the Estonian study area. In Lithuania and southern Finland the correlation between variables was significant but relatively low. Therefore, no multiple regression model has been compiled for these study areas. The best correlation has been found with the number of species and the woodland patch area. There was no connection between the species number and isolation level in all three areas. The diversity of species increases considerably from north to south. Because of nitrogen loading in small woodlots of the Estonian study area nitrophilous herb species mostly dominate.