The effects of weeding methods on the survival and height growth of naturally regenerated Pinus densiflora saplings

The effects of weeding methods on the survival and height growth of naturally regenerated Pinus densiflora saplings were examined in an experimental site 5 years after clear-cutting in Shizukuishi Town, Iwate Prefecture. The weeding treatments were strip weeding with a width of 1 meter and lateral weeding of the reserved central part with width of 1 meter, and conducted annually from 2002 to 2007. There was no significant difference in the survival rates of P. densiflora saplings between the experimental plots where strip weeding and lateral weeding took place from the control group on the upper slope. The upper slope is a suitable regenerating site for P. densiflora saplings, and the mean heights of P. densiflora saplings also were higher than those of the shrub community in control plots on the upper slope by 2007. In contrast, the survival rates of the P. densiflora saplings in the experimental plots where the two weeding treatments took place were significantly higher than those in control plots on the lower slope. This finding reveals that interspecies competition on the lower slope would be more severe than on the upper slope, and the mortality of P. densiflora saplings suppressed by the shrub community would increase on the lower slope. The survival rates of P. densiflora saplings in the strip weeding plots were significantly higher than that in the lateral weeding plots on the lower slope. This finding reveals that the difference in weeding intensity would affect the difference in the survival rates of P. densiflora saplings between the strip weeding and the lateral weeding plots on the lower slope. The mean heights of P. densiflora saplings in the weeding plots were higher than that in control plots by 2007 regardless of slope position, and the height difference among weeding and control plots increased with time. Therefore, the annual weeding for 6 years would decrease the growth reduction in the height of P. densiflora saplings caused by interspecies competition. The decreasing effect of the growth reduction in the height of P. densiflora saplings was approximately the same between the strip weeding and the lateral weeding plots in the same slope position. The lateral weeding is simple and effective in decreasing the growth reduction in the height of P. densiflora saplings on the upper slope. On the other hand, the strip weeding was limited in how it decreased the growth reduction in the height of P. densiflora saplings on the lower slope because of severe interspecies competition.