THICKET FORMATION IN ABANDONED FRUIT ORCHARDS - PROCESSES AND IMPLICATIONS FOR THE CONSERVATION OF SEMIDRY GRASSLANDS IN CENTRAL GERMANY

Abandonment of traditional agricultural practices in fruit orchards on hillsides in Central Germany results in successive changes in vegetat ion. We examined three hypotheses relating to these changes: (I) thick ets of fleshy-fruited plants develop around planted trees as a result of ornithochory and local soil and site amelioration, (2) woody plants have long-term effects on soil fertility, and (3) thicket development reduces the plant-species diversity of semi-dry grassland between the trees. Field observations and nursery experiments supported the first and second hypotheses. Increased soil fertility, a seed rain of flesh y-fruited shrubs, and shrub establishment occurred mainly around plant ed fruit trees. Soils from old tree-planting sites remained fertile af ter the trees had died and disappeared. The third hypothesis was rejec ted because no decrease in species' richness or diversity occurred dur ing the initial stages of thicket formation. Nevertheless, herbaceous plant species characteristic of the Festuco-Brometea community were ab sent from the vegetation and seed bank of shaded, nutrient-enriched si tes. Conservation of semi-dry grasslands following orchard abandonment will therefore require active control of woody plants.