Effects of thinning on soil respiration and microbial respiration were examined over a 2-year period (2010-2012) in a coppice-originated European hornbeam (Carpinus betulus L.) stand in Istanbul, Turkey. Four plots within the stand were selected; tree density was reduced by 50% of the basal area in two plots (thinning treatment), and the other two plots served as controls. The study focused on the main factors that affect soil respiration (R-S) and microbial respiration on the forest floor (R-FFM) and in soil (R-SM): soil temperature (T-S), soil moisture (M-S), soil carbon (C), soil nitrogen (N), soil pH, ground cover biomass (GC), forest floor mass (FF), forest floor carbon (FFC) and nitrogen (FFN), and fine root biomass (FRB). Every 2 months, soil respiration was measured using the soda-lime method, and microbial respiration was measured with the incubation method separately for the soil and forest floor. Results were evaluated yearly and over the 2-year research period. During the first year after treatment, RS was significantly higher (11%) in the thinned plots (1.76 g C m(-2) d(-1)) than in the controls (1.59 g C m(-2) d(-1)). However, there were no significant differences in either the second year or the 2-year study period. In the thinned plots during the research period, R-S was linearly correlated with GC, T-s and FRB. Thinning treatments did not affect R-SM, but interestingly, they did affect R-FFM, which was greater in the control plots than in the thinned plots. R-SM had a significant and positive correlation with soil N and soil pH, while R-FFM was linearly correlated with FFC and C/N ratio of the forest floor in both thinned and control plots during the research period.