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.
Highlights
IntroductionA feasible solution to resolve these problems is the conversion of pure coniferous plantations into mixed forests with a more complex stand structure through natural regeneration of broadleaved tree species [3,10]
The establishment and growth of broadleaved tree species is a crucial step in the natural regeneration processes [11], and it is strongly restricted by environmental factors, e.g., the light environment and soil nutrients [12,13]
The specific questions we would like to address are as follows: (1) what is the temporal response of canopy openness and soil stoichiometry to thinning? and (2) how do regenerated broadleaved trees adjust their leaf nutrient status to respond to the soil nutrients and light conditions of larch plantations over different terms after thinning? we developed two hypotheses for the study: (1) canopy openness will decrease, and soil C, N, and P concentrations will increase, but C:N:P ratios will decrease with time after thinning; and (2) based on the first hypothesis, leaf C, N, and P concentrations will increase with the changing environments along the thinning term
Summary
A feasible solution to resolve these problems is the conversion of pure coniferous plantations into mixed forests with a more complex stand structure through natural regeneration of broadleaved tree species [3,10]. The complex stand structure and species composition could contribute to higher biodiversity, multiple canopy layers, and various litter compositions, which are favorable for the enhancement of ecosystem services and the maintenance of the sustainable development of plantations. The establishment and growth of broadleaved tree species is a crucial step in the natural regeneration processes [11], and it is strongly restricted by environmental factors, e.g., the light environment and soil nutrients [12,13]. Understanding the alterations of nutrient stoichiometry to varying environmental factors might help predict the development of regenerated broadleaved trees in coniferous plantations
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