ABSTRACT
Drainage of mid-field small wetlands or small ponds leads to the simplification of the agricultural landscape structure. According to prevailing opinion, agricultural activity eliminates many wild plant and animal species and is among those human actions that impoverish living resources. The fields where animals were eliminated by harmful agents can be recolonized from unaffected refuges situated in the mosaic landscape. Thus one can suppose that the main factors counteracting biodiversity decline caused by agriculture are the mosaic structure of landscape and dispersal properties of species. Diversification of plant cover structure in landscape influences the richness of weed communities. The main attention of botanists has been directed to protected areas, such as national parks, or to more or less natural forest and grassland landscapes. The Turew landscape is located in the Wielkopolska region, where the intensity of agricultural production is greater than in most other areas of Poland.
