Simulation of the spatial distribution of thinning area under different silvicultural subsidy systems in Japanese plantation forests

The aim of this study was to simulate the effect of spatial thinning on the distribution of non-industrial private forests (NIPFs) and predict the thinning area under different subsidy systems in Hokkaido prefecture, Japan. The simulated thinning area is based on a Geographic Information System (GIS) and an algorithm that considers the stand condition and applicability of different subsidies for conducting thinning. The accuracy of the simulations was checked by comparing observed and predicted thinning area data. In Shimokawa municipality the thinning area was significantly smaller than in Furano municipality, where the rules governing subsidy allocations are more relaxed. The coefficients of determination (R2), which were calculated by comparing the estimated and observed jointly implemented thinning areas, defined as areas in which thinning occurred in several adjacent subcompartments, were 0.88 and 0.89 in Furano and Shimokawa, respectively. Although our algorithm slightly overestimated the jointly implemented thinning area, the estimated average thinning area was within the two-sided 95% confidence interval for the observed area. By applying the model and linking our simulation results to the GIS, the total potential distribution of jointly implemented thinning area was visualized in two geographic areas that have different subsidy systems.

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