Developing the risk map of winter storm hazard using GIS based fuzzy logic method

Abiotic and biotic factors causing damages on forest tress also threat sustainability of forest resources. The wind damage is one of the most effective factors among the abiotic factors such as forest fires, wind, snow, avalanche, and drought. In Turkey, there is very limited number of studies conducted on wind damage. However, wind causes serious impacts on various tree species and damages in many regions. In order to prevent or minimize wind damage, it is crucial to determine the factors that affect wind damage and to develop risk maps for the forested areas with wind risk. In this thesis, risk map of wind damage was developed by using GIS based mathematical model (Fuzzy Logic). Tree species, tree age, crown density, site quality, topographical features (elevation, slope, aspect), climatic parameters (wind, precipitation), and soil depth were considered as the factors that influence the magnitude of wind damage on forest tress in the model. Alabarda Forest Enterprise Chief within the borders of Tavşanlı Forest Enterprise Directorate was selected as the study area due to high occurrence of storm damages in the region during winter 2015. For model verification, risk map of wind damage was compared to areal distribution of wind damage determined by the Enterprise Directorate. Model developed based on Fuzzy Logic approach indicated that slightly more than half of the study area (52.49%) was under wind damage risk at very low degree. On the other hand, 28.12% of the study area was under low wind damage risk while 19.19% was classified as risky zone. Very small land in the study area (39.47 ha) was classified as very risky zone. According to the wind damage map generated based on the amount of irregular production recorded by Tavşanlı Forest Enterprise Directorate, there was very low wind damage in 45.77% of the area while 30.20% encountered very low wind damage. It was specified that 23.72% of the area was subject to high wind damage. There was very high wind damage in the area of 60.13 ha. When weighting the risk factors to analyze their relative effects on overall wind damage risk, it was revealed that the most effective factors were wind direction and speed, followed by slope and site quality factors. In the study, some silvicultural, management, and technical suggestion measures were provided in order to minimize wind damage. The results indicated that GIS based mathematical models can be effectively and accurately used to generate risk map of wind damages.