ABSTRACT:The original natural forest ecosystems of the Ore Mountains (Norway spruce, silver fir, and beech forests) have been destroyed by overcropping since the 11 th century. In the 19 th century spruce afforestations on large areas were intended to meet the steadily increasing demand for timber. They led to the introduction of planned forestry by building up spruce age-class forests. Efforts of a few forest specialists to establish an ecologically adapted silviculture failed before long due to economic necessities. The paper presents the results of a complex experimental plot system aiming at the forest conversion in the Ore Mountains. Answers are given particularly to problems of the upper stand treatment for regeneration and of appropriate ways of soil preparation and planting. A network of forest climate stations and a broad variety of ecophysiological and yield investigations provide the basis for conclusions on light, temperature, soil, and water demand by regenerated tree species.Keywords: substitute tree species stands; pure spruce stands; species composition conversion; Ore Mountains Mts.; Germany JOURNAL OF FOREST SCIENCE, 51, 2005 (11) About 48% of this area were reforested with immission-tolerant, non-indigenous coniferous species such as larch, blue spruce, Serbian spruce and lodgepole pine. These species are suitable for planting on large clear-cut areas. They were also acceptable for reforestation under high loads of SO 2 . The aim was to preserve the forest as an ecosystem with all ecological functions such as soil protection, regulation of water regime and shelter.Norway spruce was planted on 31% of the area, especially in lower mountain ranges. Stands of birch (Betula spec.) and European mountain ash (Sorbus aucuparia L.) arose from succession on 8% of the area. Broad-leaved trees like beech or sycamore (Acer pseudoplatanus L.) could not survive under the extremely difficult climatic conditions typical of the large clear-cut areas.Spruce stands have only survived in the western parts of the mountains and, in addition, at medium and lower altitudes. However, their canopy was opened up, and many stands suffered from severe bark peeling by red deer. Due to dense overgrowing with grass and strong game population, natural regeneration almost came to an end. Current situationThe situation of air pollution has changed during the last years. Sulphur input has considerably fallen whereas nitrogen input has increased. Thus, the acidification of forest soils is becoming a problem. Therefore, soils are limed; about 160 sq. km of Saxon forests are treated every year.The forest stands which are composed of the so-called substitute tree species are in good shape. However, they are artificial and ecologically unstable ecosystems. Therefore, the long-term target consists in restoring ecologically stable mixed forests with a substantial proportion of tree species of natural forest ecosystems. The stands of substitute tree species create conditions favourable for the successful reintroduction of original tree s...