Long-term effect of thinning from above on forest-floor in Scots pine stands in Southern Moravia (Czech Republic)

One of the preconditions of the sustainable forest management is maintaining the production capacity of the site. In Southern Moravia (Czech Republic), Scots pine stands are managed by a clear-cutting system with relatively intensive soil preparation before planting. As a result, an important part of the forest ecosystem - humus horizons - must be re-created during each rotation period. We observed the long-term effect of management (thinning by positive selection from above) on production characteristics and site conditions in stands of Scots pine on nutrient-poor sandy sites. The research was conducted on experimental series established during 1962 in 33-year-old pine stands. After the third experimental treatment (1972), the basal area of the control and thinned plots differed significantly (41 and 27 m(2)). Twenty years later, these differences disappeared due to post-windstorm salvage cuts on the control treatments. In 2008, about 9-10 t ha(-1) of dry mass was stored in the forest-floor L (litter) horizon under both stands, with no significant differences between treatments. In the F (fermented) horizon, we found about 18-19 t of dry mass per hectare. The highest amount of dry mass was found in the H (humus) horizon (31-58 t ha(-1)). Comparison of the control to the thinned treatment showed significantly greater dry mass under unthinned stands (by 85 %). Our results suggest that the studied thinning regime resulted in a decreased amount of accumulated humus and, consequently, of carbon in the H horizon under the treated pine stands compared to that under the controls.