Effects of different site preparation methods on soil carbon and nutrient removal from Eastern beech regeneration sites in Turkey's Black Sea region

摘要

In terms of wood production, eastern beech (Fagus orientalis Lipsky) is one of the most important Turkish tree species. The main forestry operation in the Black Sea region (BSR) is the harvesting of natural beech stands. These stands are naturally regenerated. A dense rhododendron (Rhododendron spp.) understorey prevents eastern beech (F. orientalis Lipsky) seed-tree regeneration in the Turkish BSR. Our study objective was to investigate the forest ecosystem effects of different woody vegetation control methods on forest floor organic matter (OM), soil organic carbon (SOC), soil physical and chemical properties and nutrients on beech regeneration sites in this region. In 2006, rhododendrons were cleared from treatment plots using hand labour by grubbing (GR), prescribed fire (PF), or machine preparation (MP) with a rake-equipped bulldozer. Untreated plots served as controls. The woody vegetation understorey, forest floor OM and mineral soil (0-20cm) were sampled, and their biomass, SOC and nutrient content were estimated for each treatment. While effective in preparing sites for beech regeneration, the MP treatment resulted in highly compacted soil (mean=1.5gcmpd) compared to the other treatments (1.1gcmpd). It also showed the largest ecosystem losses of C (45%), N (30%), and P (55%) from the forest floor and mineral soil (0-20cm). Furthermore, the MP treatment induced large ecosystem losses of soil K (72%) and Ca (58%). Both the GR and PF treatments increased soil pH and cation exchange capacity (CEC) relative to the controls, while their ecosystem C (25%) and N (22%) losses were moderate. In conclusion, the MP site preparation method removes more OM and soil nutrients, resulting in a lower soil CEC capacity compared to the other rhododendron control practices, including prescribed fire. Using heavy machinery during site preparation compacts the soil, increasing soil density to a level that may restrict plant growth. In contrast, grubbing and prescribed fire increase the soil pH and plant nutrient availability without compacting the soil. Therefore, these two methods should be promoted as effective and sustainable rhododendron control techniques for long-term productivity of eastern beech forests.