Effects of changes in agricultural land-use on landscape structure and arable weed vegetation over the last 50 years

Agricultural dynamics and associated changes in the structure of habitat patches affect species composition and distribution in the landscape. Land-use, landscape changes and vegetation changes of weeds were analysed in a 4 km(2) area in Central Germany (Saxony-Anhalt) from 1953 to 2000. This period includes the collectivisation (1952-1968), the agricultural industrialisation (1969-1989) and the privatisation of agricultural land following the political changes in East Germany in 1990. For the analyses, historic and current aerial photographs and vegetation data were used. Landscape indices and the average amount of mineral fertilizers were used as indicators for landscape structure and land-use intensity. Intensification of agriculture and the collectivisation in East Germany in the fifties and sixties led to a decline of the spatial heterogeneity of the landscape matrix (arable fields). The average number and cover of weed species, especially archaeophytes, decreased significantly since 1957. However, the total number of weed species increased. There was a remarkably high number of species with an average cover below 0.05%, called "chance" species in 2000. Out of 17 tested landscape indices only mean patch size and mean patch fractal dimension were significantly correlated with the average number of weed species. The average amount of the mineral fertilizer potash used as land-use intensity indicator was significantly negatively correlated with the total number of weed species. However, there was an increase in the number of farms after 1990 without changes in landscape structure and arable weed vegetation. The results suggest that structural variability of the landscape and habitat quality are the principal correlates of plant species diversity. (c) 2005 Elsevier B.V. All rights reserved.