Effects of Thinning on Litterfall Production and Leaf Litter Decomposition Rates of Karacabey Forested Wetlands, Bursa, Turkiye

The contribution of litterfall (dead leaves, twigs, etc., fallen to the ground) and forest floor (organic residues such as leaves, twigs, etc., in various stages of decomposition, on the top of the mineral soil) is fundamental in both forest ecosystem sustainability and soil greenhouse gases (GHG) exchange system with the atmosphere. A focus on forested wetlands is particularly important, as these systems account for a disproportionate amount of global carbon flux relative to their spatial coverage, and the decomposition of leaf litter is a major contributor. In this study, we aimed to investigate the effects of two different thinning treatments (low thinning-canopy closure 41-70% and intense thinning-canopy closure 10-40%) on litterfall, forest floor litter and leaf litter decomposition rates of alder (Alnus glutinosa) stands in Karacabey forested wetlands. The litterfall was monthly collected using open litterfall traps for 2 years from 2021 to 2022. The forest floor litter was also sampled 50 x 50 cm2 quadrates of 5 points in research plots of 20×20 m. The differences in leaf litter decomposition rates between the low and intense thinning stands were investigated using the litterbag method in the field for 18 months. The results indicated that the intense thinning significantly reduced the total litterfall production (7.24 ± 0.384 Mg ha-1) and the forest floor litter (2.78 ± 0.41 Mg ha-1) compared to the low thinning stand (10.8 ± 0.527 Mg ha-1 and (4.38 ± 0.82 Mg ha-1 respectively). Lower leaf litter decomposition rates were also seen in the intense thinning stands than in the lower thinning stands. At the end of the 18 months, the leaf litter mass loss was 83.6% in the intense thinning stands compared to the lower thinning stands (88.3%).