In the new Collective Forest Management Plan System in Japan, introduced in 2012, a formula similar to the Austrian formula is used to define the maximum clearcutting volume,andthe standard cutting cycle is considered anadjustment period. However,if the current stand volume exceeds the assumed normal growing stock, the allowable clearcutting volume is less than the expected harvest volume that decreases the stand volume to the standard volume within the adjustment period. This is because the end of the adjustment period is deferred in the calculation of the allowable clearcutting volume after the first planning period. This rule constrains the maximum clearcutting volume after the first planning period. The constraint is relatively severe in clearcutting of broadleaved stands where the standard cutting cycle is short(short adjustment period) and the relative current stand volume is higher than the normal growing stock.

The purpose of this paper was to analyze changes of thinning tendencies in the term 2003-­2012 based on thinning records summarized by local governments in prefectures, particularly focusing on the years from 2010 to 2012 before and after the new direct payment system of thinning subsidy was enforced. The following three indices were calculated : 1. total thinned area, 2. thinned area or volume with log extraction and 3. ratio of thinned area or volume with log extraction to total thinned area or volume. The average values of indices for the prefectures in 2012, when the direct payment system became widespread, were compared with those from 2003 to 2011. As a result, the index 1 was smallest and the indices 2 and3 were largest in the term,particularly compared with the values in 2010 when the direct payment system was not enforced yet, the index 1 decreased to 0.726, the 2 and 3 increased to 1.491 and 2.317 respectively. Moreover, the indices 1 and 2 in 2012 became statistically significant as a result of the Steelʼs multiple tests to the preceding years. These significant changes were considered to be caused by the spread of the direct payment system : The spread brought out both desirable and undesirable aspects of thinning tendencies such as the promotion of log extraction and the regression of stand improvement.