Assessment of Soil Fertility Changes Over 7 Years after Strip Clearcutting and Afforestation ina Low-Quality Forest Stand in China

In order to change the low-quality forest stands into qualified forest stands with desirable productivity and other ecological benefits, it is necessary to adjust the stand structure and functions. In this study, a low-quality forest stand after strip clearcutting in the Lesser Khingan Range of China was investigated, and the principal component analysis and membership functions were combined to evaluate the integrated soil fertility in different experimental strips (horizontal strips: S1-6 m×100 m, S2-8 m×100 m, S3-10 m×100 m, S4- 15m×100 m; Vertical strips: H1-6 m×100 m, H2-8 m×100 m, H3-10m×100 m, H4-15 m×100 m). Results showed that most soil fertility indexes of the experimental strips showed moderate variation over time, the variation coefficient of soil pH was relatively smaller, and that of total phosphorus was the largest. The integrated soil fertility index (IFI) of different strips generally decreased at the initial period and then increased over time with the lowest value appeared after planting for 3 years. After afforestation for 7 years, the order of the IFI for the horizontal clearcutting strips is: S2>S3>S4>S1, while that
of the vertical clearcutting strips is H1>H2>H4>H3. The integrated soil fertility index of S2 was the highest, which was also significantly higher than that of the year of harvest, showing the best effect. The soil fertility of some experimental strips (S2, S3, H1) was improved, however most of the clearcutting strips were remained at moderate level. Compared to vertical strips, the horizontal clearcutting strips showed better improvement in soil fertility. It is recommended that the 8 m×100 m horizontal clearcutting strip can be applied in forestry practice due to the significant improvement in soil fertility. However, soil fertility change is a long-term process, therefore long-term and consecutive observation in combination with scientific and effective study methods is still needed in order to accurately assess the changes of soil fertility in the clearcutting strips.