Long-Term Effect of Thinning and Creating Gaps on Tree Regeneration and Understory Vegetation in Larch Plantation

The influences of different management operations on tree regeneration and understory vegetation were tested 20 years after thinning in larch plantations in the Loess Plateau of China. Five treatments were conducted: unthinned, uniform light, moderate, heavy thinning, and creation of gaps. Creating gaps noticeably enhanced tree regeneration and understory vegetation development. In contrast, the effect of light and moderate thinning on tree regeneration was slight. Shade-tolerant species dominated seedling communities in unthinned and lightly and moderately thinned stands, while the importance value of shade-intolerant species increased with the intensity of thinning. These results suggest that creating gaps in larch plantations can be an effective way of improving tree regeneration and increasing the diversity of shrubs and herbs in the long-term. However, the results also suggest that uniform light and moderate thinning are probably too slight to improve either of these outcomes. Thus, periodically variable density thinning should be considered for both biodiversity conservation and timber production in larch plantations.