Influence of slope position stand type and rhododendron (rhododendron ponticum) on litter decomposition rates of oriental beech (Fagus orientalis Lipsky.) and spruce [Picea orientalis (L.) Link]

Oriental beech (Fagus orientalis Lipsky.) and Oriental spruce [Picea orientalis (L.) Link] are the two most common tree species in northeast Turkey. Their distri- bution, stand type and understorey species are known to be inXuenced by topographical landforms. However, little information is available as to how these changes aVect litter decomposition rates of these two species. Here, we investi- gated the eVects of slope positions (top 1,800 m, middle 1,500 m and bottom 1,200 m), stand type (pure and mixed stands) and purple-Xowered rhododendron (Rhododendron ponticum) on litter decomposition rates of Oriental beech and spruce for 4 years using the litterbag technique in the Weld. Among these three factors, stand type had the stron- gest inXuence on litter decomposition (P < 0.001, F = 58.8), followed by rhododendron (P < 0.001, F = 46.8) and slope position (P < 0.05, F = 11.6). Litter decomposition was highest under mixed beech/spruce forest, followed by pure beech and spruce forest. Beech and spruce litter decom- posed much faster in mixed bags (beech–spruce) than they did separately under each stand type. Purple-Xowered rho- dodendron signiWcantly reduced litter decomposition of Oriental beech and spruce. Beech and spruce litter decom- posed much slower at top slope position than at either bot- tom or middle position. DiVerential litter decomposition of Oriental beech and spruce was mainly due to adverse con- ditions in spruce forest and the presence of rhododendron on the ground which was associated with lower soil pH. Higher elevations (top slope position) slowed down litterdecomposition by changing environmental conditions, most probably by decreasing temperature as also other factors are diVerent (pH, precipitation) and no detailed investiga- tions were made to diVerentiate these factors. The adverse conditions for litter decomposition in spruce forest can be eVectively counteracted by admixture of beech to spruce monoculture and by using the clear-cutting method for controlling rhododendron