Effects of site preparation on emergence and early establishment of Larix olgensis in montane regions of northeastern China

Larix olgensis is one of the important commercial timber tree species in northeastern China, but it does not naturally regenerate in L. olgensis forests even after cutting. To identify the causes of the regeneration failure, the authors tested the effects of site preparation in a thinned stand and in a clearcut on the emergence and early establishment of L. olgensis seedlings. The results indicated that there was no correlation between cumulative emergence percentage (CEP) of L. olgensis seedlings and canopy openness, but the CEP was significantly affected by site preparation (P < 0.001). The average seedling survival rates after treatments consisting of removing both litter cover and understory vegetation cover were significantly higher in the clearcut than in the thinned stand (P < 0.001). Without site preparation, all seedlings in both the thinned stand and the clearcut disappeared within the first growing season, meaning that ground cover (understory vegetation cover and litter cover) was not beneficial to seedling survival. The average growth of seedlings exhibited significant differences between the thinned stand and the clearcut, and among the site preparations (P < 0.001). Intensely thinned stands without ground cover improved seedling growth. These results imply that light and ground cover might be the main factors limiting the early establishment of L. olgensis seedlings in managed plantation forests.