Comparison of Decomposition Rates of Beech (Fagus orientalis Lipsky) and Spruce (Picea orientalis (L.) Link) Litter in Pure and Mixed Stands of Both Species in Artvin, Turkey

The decomposition of spruce, beech and mixed litters of spruce and beech was investigated over 3.5 years in beech, spruce and mixed (beech/spruce) stands using less than 1.5 mm mesh litter bags. Initially, carbon, nitrogen, lignin and cellulose concentrations, and C:N and lignin:N ratios were determined in beech and spruce litters. For all sampling intervals, mixed litters showed higher decay rates than individual beech and spruce litters in both pure stands and mixed stands. Spruce decomposed more rapidly than beech, and initial lignin concentration explained most of the variation in decomposition rates between beech and spruce. However, differences in decomposition rates between beech and spruce were most pronounced in the mixed stand, while they were intermediate in the beech stand and least pronounced in the spruce stand. This shows that adverse environmental conditions, mostly associated with a lower pH content of the soil under spruce stands, retard decomposition processes and individual litters appear to be more sensitive to this retardation than mixed litters. The results also indicate that abiotic and microbial factors in mixed stands could be better than those in pure stands of spruce and beech. Therefore, the establishment of mixed beech and spruce stands can counteract detrimental processes in decomposition associated with spruce monocultures.