Temporal Effects of Thinning on the Leaf C:N:P Stoichiometry of Regenerated Broadleaved Trees in Larch Plantations

Abstract

The shift from natural mixed broadleaved forests to pure coniferous plantations results in soil degradation and the unsustainable development of plantations due to the simple stand structure and low species diversity. Thinning can practically sustain the forest structure and promote the regeneration and growth of broadleaved trees in these pure coniferous plantations. The growth of regenerated broadleaved trees is closely related to leaf ecological stoichiometry, which is strongly restricted by environmental factors such as light, soil moisture, and nutrients after thinning. However, the temporal effects of thinning on leaf C:N:P stoichiometry are still not well understood, which constrains our understanding of implementing thinning in coniferous plantations to promote the regeneration and growth of broadleaved species, and further forming the mixed larch-broadleaf forests. Here, we compared canopy openness (i.e., light availability) and the soil and leaf stoichiometry for regenerated broadleaved trees in larch (Larix keampferi) plantations in short-term (1–3 years), medium-term (4–9 years), and long-term (≥10 years) periods after thinning, taking natural mixed broadleaved forests as a control in Northeast China. The results showed that the temporal effects of thinning were not significant with respect to soil C concentrations, but significant with respect to soil C:P and N:P ratios. The regenerated broadleaved trees adjusted their leaf N concentrations and C:N ratios in response to the changed environmental conditions after thinning over time. The responses of soil and leaf stoichiometry to thinning and their significant correlation indicated a strong interaction between the soil and understory regeneration following thinning. Thus, thinning affects the soil and leaf stoichiometry of regenerated trees over time. These findings provide new insights into the conversion of pure coniferous plantations into mixed larch-broadleaf forests by controlling thinning intervals.