Effects of thinning on soil respiration and microbial respiration of forest floor and soil in an oak (Quercus frainetto) forest

The effects of tree thinning on soil respiration and microbial respiration in a Hungarian oak (Quercus frainetto Ten.) forest were examined over a 2-year period (2010-12). Tree density was reduced to 50% of the basal area. The research focus was on the main factors influencing the soil respiration (R-S) and microbial respiration in the forest floor (R-FFM) and in the soil (R-SM): soil temperature, moisture, carbon (C), nitrogen (N), and pH; groundcover biomass (GC); forest floor mass, carbon and nitrogen; and fine root biomass. R-S was measured twice monthly with the soda-lime method, and the incubation method was used to measure R-SM and R-FFM separately. The results were evaluated annually and over the 2-year research period. Correlation and stepwise regression analyses were used for statistical evaluation. Annual mean R-S was significantly higher in thinned plots (1.92gCm(-2)day(-1)) than in the control plots (1.79gCm(-2)day(-1)). Over the 2-year research period, R-S was higher in the thinned plots, and had linear correlations with GC, soil temperature and fine root biomass. GC was found to be the main factor that determined R-S. The control plots had significantly higher R-SM in first year, whereas the thinned plots had significantly higher R-SM in second year; no significant difference was found over the 2-year research period. R-FFM was significantly higher in the control plots than in the thinned plots, by 84% in the second year and by 34% over the 2-year study period. R-SM had a linear correlation with soil N content and soil pH, whereas R-FFM had linear correlations with C concentration and the C:N ratio of the forest floor in the thinned plots.