DIGITALNA ARHIVA ŠUMARSKOG LISTA
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|ŠUMARSKI LIST 1-2/2015 str. 41 <-- 41 --> PDF|
distance was calculated from these irregular located points to the nearest forest roads using Analysis Tools™ in ESRI® ArcGIS. The shortest mean extraction distance (SDs) is the arithmetical mean of the values obtained for each forest management unit. The SDs derived with this method was dependent on the extracted volume of timber and hence it was weighted with the volumes of the allowable cut from each forest stand.
Grid point method – Metoda pravilne mreže točaka
Segebaden (1964) introduced the concept of regular system of points for calculating the SDs of a given area as the arithmetical mean of the shortest distances from each point of the grid system to the nearest forest road. The accuracy of this method depends on: the accuracy of measuring these distances, the number of points in the grid system and the size of the area. In this study, the project area is the same for all scenarios and the accuracy of distance measurement is extremely high due to vector format computations in GIS. Hence, the only factor influencing the accuracy is the number of points from each grid point set.
The SDs was computed using five different sets of regular grid points for each infrastructure scenario, in order to determine which grid point set provides the most reliable results. The grid point sets were defined using Data Management Tools™ in ESRI® ArcGIS (Figure 2) and described rectangular cells of: 10x10 m (method G10), 50x50 m (G50), 100x100 m (G100), 500x500 m (G500), and 1000x1000 m (G1000), respectively. The shortest distances from each point of the grid to the closest forest road were calculated.
Automation of the grid point method focused on establishing the grid point sets and calculating simultaneously the SDs for each scenario and grid point set. The model was created and executed using multiple inputs in Batch processing tool of Model Builder™. This tool allows choosing more input files or parameter values in order to create multiple outputs (Allen 2011). A list of the input datasets (e.g. traffic infrastructure scenarios) was compiled and used as a batch variable in the model for iterating through scenarios.
Buffer strips method – Metoda omeđenih površina
This method relies on the approach of Backmund (1966) and the method presented by Hentschel (1999). Buffer strips with a width of 100 m around the forest roads were established using automation models in GIS (Figure 3). The SDs of a buffer strip was given by the distance from its