MAN-INDUCED CHANGE OF THE FLORA OF AGROFORESTRY COMPLEXES IN MIDDLE TAIGA LANDSCAPES OF GLACIOLACUSTRINE PLAINS

Abstract

The study was carried out in one of the most common types of geographical landscape of the middle and southern taiga subzones in the Northwest of European Russia. In areas with a long agrarian land use history boreal ecosystems are replaced by agroforestry complexes, which represent a mosaic of arable land, hayfields and meadows, together with fragments of forest of different generations, covering extensive territories. These forests can be of the 'copse' type (with the overstorey predominated by a most varied mixture of deciduous species, including those typical of understorey) and ordinary secondary forests (coniferous, coniferous-deciduous, and deciduous stands aged on average from 40 to 80 years). A comparative analysis of species lists for meadows (meadow flora), copses (copse flora) and forests (forest flora) showed that copse flora features a higher level of species diversity, and high shares of meadow and wetland species. These features were due to high coenotic distinctness, relative spatial isolation (distance from the forest edge), direct contact with meadow communities and, as a rule, small size of such forest patches. The investigated floras are arranged along the disturbance gradient in the following order: forest flora - copse flora - meadow flora. Synanthropism of the communities with the tree layer is achieved mainly owing to the apophytic component, and in meadow communities it is owing to both apophytes and adventitious species. Having compared the coenotic structure of these three floras we found a stepwise increase in the number of meadow species along synanthropism gradient, a relatively high persistence of forest species (trees, shrubs, herbaceous apophytes) within meadow communities, a notable contribution of species pertaining to very wet habitats to copse and meadow floras. According to cluster analysis, the rate at which the natural vegetation recovers is largely defined by the scope of disturbance. Although forest communities in our study were considerably transformed by human activities, there occurred species that are naturally rare or relatively rare in the middle taiga of Karelia: Dryopteris cristata, Ranunculus subborealis, Stellaria longifolia, Rubus humulifolius and Urtica galeopsifolia, as well as a rare inhabitant of secondary forests Galium triflorum.