Dale MayleaChinese pine (Pinus tabuliformis Carr.) is a major afforestation species in northern China, playing a crucial role in restoring forest ecosystems and preserving soil and water. However, these plantations face ecological challenges, such as low understory plant diversity and difficulty in natural regeneration. A new study by Yang and colleagues in the journal Forest Ecosystems indicates that thinning may be an effective management technique to address these issues.
Thinning is a forestry practice involving the selective removal of trees to improve the growth and health of the remaining trees. It also enhances light, water, and nutrient availability, promoting understory plant diversity and regeneration.
Yang and colleagues conducted a meta-analysis of 22 publications, which reported on the effects of thinning on the species richness of understory plants. They also examined 15 publications which investigated the effects of thinning on the regeneration of Chinese pine in plantations.
The results show that, compared to unthinned control stands, thinning increased the species richness of shrubs and herbs by an average of 25.3% and 26.5%, respectively. Among varying thinning intensities, moderate thinning (30%–50%) had the most positive effect on the density of regenerating Chinese pine seedlings and saplings (60.2%).
The scientists observed the highest species richness of understory plants 14 years after thinning, with a 36.3% increase compared to unthinned stands. Regarding regenerating Chinese pine seedlings and saplings, their density reached a maximum after 11 or more years of thinning, with a 76.5% increase compared to unthinned stands.
Thinning in half-mature plantations had the most significant impact on understory shrub richness (44.1%) and the density of regenerating Chinese pine seedlings and saplings (86.5%). Yang and colleagues found both single and multiple thinning events significantly improved understory plant diversity and Chinese pine regeneration. The positive effects of thinning were more pronounced in areas with a humidity index (HI) of less than 30 compared to those with an HI of 30 or greater. HI measures water availability in a given area, considering factors such as precipitation, temperature, and evaporation.
The study identified age group, planting density, and recovery time as the main factors affecting the species richness of understory plants. On the other hand, slope, HI, and recovery time were the dominant controls of the density of regenerating Chinese pine seedlings and saplings, highlighting the differential effects of thinning on these two aspects.
Yang and colleagues say in their article:
This result implies that the responses of the species richness of understory plants and the density of regenerating Chinese pine seedlings and saplings to these key factors were different after thinning. Therefore, we suggest that if plantation forests focus on ecological restoration, such as soil and water conservation, a reasonable restoration interval after thinning should be controlled for different forest development stages to maximize the species diversity of understory plants. If the purpose of cultivation is to achieve sustainable development by utilizing the natural regeneration capacity of plantations, we should first consider the decisive influence of climatic conditions (such as the HI) and stand conditions (such as the slope) on the density of regenerated seedlings. Then, some positive measures, such as soil loosening, moderate clearing and gap expansion, should be supplemented after thinning to promote the occurrence and survival of natural regeneration.
Yang et al. 2023
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Yang, H., Pan, C., Wu, Y., Qing, S., Wang, Z. and Wang, D. (2023) “Response of understory plant species richness and tree regeneration to thinning in Pinus tabuliformis plantations in northern China,” Forest Ecosystems, 10(100105), p. 100105. Available at: https://doi.org/10.1016/j.fecs.2023.100105.
Chinese Pine cover image by Shang Ning / Flickr
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