Integrating erosion control value of forest ecosystems into forest management planning process

Erosion-induced land degradation is considered to be one of the most important environmental problems in Turkey, as well as many parts of the world. Forest ecosystems play a crucial role in solving the problem if properly managed. Improving this role is closely related to integrating the ecological values of forests –such as erosion control− into forest management plans prepared under the Ecosystem-based Multi-functional Forest Planning (EBMFP) concept. The main objective of this study is to integrate the erosion control value of forests into the EBMFP system used in Turkey. To this end, the aims were to; (i) quantify and map the annual potential soil loss and erosion control value, (ii) determine the forest areas allocated for erosion control in forest management plans, (iii) develop useful performance indicators for the integration process, and (iv) determine optimal forest forms minimizing soil losses in Veliköy and Olur Forest Planning Units (FPUs). Within these FPUs, growing stock and increment inventory was performed on 250 sample plots. In addition to typical inventory parameters; litter thickness, undergrowth height, and surface roughness were measured on the ground. Besides, topsoil samples were collected from each plot. Erosion risk maps were generated using the Revised Universal Soil Loss Equation (RUSLE) with very-high-resolution aerial photographs. Two scenarios were developed for quantifying the erosion control value. Thus, the amount of maximum, potential, and prevented erosion, as well as the soil protection performance index (SPPI), were calculated for the case study areas. Finally, the erosion control value was quantitatively related to each stand's biophysical structure. Thanks to the erosion control value of forests, 2.59 and 5.08 Mt yr-1 of soil were retained in place in Veliköy and Olur FPUs, respectively. Productive forests (canopy cover>10%) could reduce erosion rates by as much as 95% compared to the bareland conditions. In terms of soil protection performance, the best stand types were GD, GLD, and LA among uneven-aged forests, while Çsc3, Çscd3, and LGÇscd3 were prominent among even-aged stands. There was almost no soil loss on lands covered by those stand types. Despite the protective effects of all land cover types in the FPUs, the average annual soil losses were predicted to be 7.8 and 15.8 t ha-1 yr-1 for Veliköy and Olur, respectively. Given the erosion risk maps, the forest lands currently suffering from intolerable soil losses (>5 t ha-1 yr-1) were allocated to erosion control and no wood production activity was planned for those forests. On the other hand, the forest lands previously allocated to the nature protection value, but showing no erosion risk, were detected and some of them were assigned to wood production. Thanks to the new arrangement, potential soil losses were reduced while periodic (20-year) allowable cut amounts increased by 12.3% and 1.8% for Veliköy and Olur FPUs, respectively. Thus, we conclude that the functional land allocation criteria currently used in the Turkish forest management guideline need to be revised. Overall, an uneven-aged management system should be preferred for maximizing the erosion control value provided by forest ecosystems. If this is impossible due to poor site conditions, the establishment of multiple-layered, dense, and pure coniferous stands should be aimed. No matter which stand type is preferred, the forest's canopy cover ratio must be as high as possible. The optimal rotation age is 100−120 years for Scots pine forests allocated for erosion control. Potential soil loss gradually increases after 120 years, particularly on steep sites (slope>30%) of Scots pine. Finally, a stand basal area of around 55 m2 ha-1 seems to be optimal for these forests. The performance indicators, models, and maps presented in this study are expected to be essential data sources for forest management planners and practitioners. These may also help in scientific decision-making by serving as a baseline for national decision support systems to be activated in the future. Thus, Turkey will likely move towards more effective implementation of the EBMFP on the ground, like many developed countries.