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<p>Understory afforestation is a key strategy in close-to-nature silviculture that can effectively transform monoculture plantations into mixed-species forests, and it is increasingly promoted for global forest restoration and biodiversity conservation. While most existing research has focused on seedlings, comparatively less is known about the light adaptation of young trees. In this study, we investigated survival, growth, biomass allocation, and leaf economic spectrum (LES) traits of 11-year-old <i>Picea asperata</i> trees underplanted across five canopy transmittance gradients (CTGs; CTG1: 10%–20%, CTG2: 20%–40%, CTG3: 40%–60%, CTG4: 60%–80%, and CTG5: 80%–100%) in mature <i>Larix principis-rupprechtii</i> forests. Results showed that the survival rates of young <i>P. asperata</i> trees averaged 60%, with no significant differences across all CTG (<i>P</i> &gt; 0.05). The young <i>P. asperata</i> exhibited the maximum height (2.0&#xa0;m), crown projection area (6.4 m<sup>2</sup>), and crown volume (4.6 m<sup>3</sup>) under CTG2. Moreover, total, aboveground, and belowground biomass were significantly greater at CTG2 compared to other gradients. Young <i>P. asperata</i> in CTG1 showed significant biomass reallocation compared to CTG5, with an 18.0% decrease in leaf biomass and a 39.0% increase in root biomass (<i>P</i> &lt; 0.05). Canopy transmittance had a strong influence on LES traits, with most traits exhibiting significantly higher values in CTG5 than in lower light gradients. The comprehensive performance index (CPI) of young <i>P. asperata</i> peaked at CTG2 (0.56), while the lowest CPI was observed at CTG1 (0.31). These findings suggest that a minimum canopy transmittance of approximately 20% is necessary to sustain normal growth in young <i>P. asperata</i>, offering practical guidance for implementing under-canopy afforestation with shade-tolerant species in monoculture plantation conversion.</p> Graphical abstract <p></p>

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Optimizing understory afforestation of shade-tolerant conifer Picea asperata across canopy transmittance gradients

  • 期刊论文

  • 发表日期：

    2026年1月20日

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  • Jing Jin,
  • Haoran Wang,
  • Zhidong Zhang,
  • Yuan Gao,
  • Qiang Liu,
  • Lihua Fu,
  • Dongsheng Chen,
  • Lihu Dong,
  • Hongtao Xie,
  • Deliang Lu

摘要

Understory afforestation is a key strategy in close-to-nature silviculture that can effectively transform monoculture plantations into mixed-species forests, and it is increasingly promoted for global forest restoration and biodiversity conservation. While most existing research has focused on seedlings, comparatively less is known about the light adaptation of young trees. In this study, we investigated survival, growth, biomass allocation, and leaf economic spectrum (LES) traits of 11-year-old Picea asperata trees underplanted across five canopy transmittance gradients (CTGs; CTG1: 10%–20%, CTG2: 20%–40%, CTG3: 40%–60%, CTG4: 60%–80%, and CTG5: 80%–100%) in mature Larix principis-rupprechtii forests. Results showed that the survival rates of young P. asperata trees averaged 60%, with no significant differences across all CTG (P > 0.05). The young P. asperata exhibited the maximum height (2.0 m), crown projection area (6.4 m2), and crown volume (4.6 m3) under CTG2. Moreover, total, aboveground, and belowground biomass were significantly greater at CTG2 compared to other gradients. Young P. asperata in CTG1 showed significant biomass reallocation compared to CTG5, with an 18.0% decrease in leaf biomass and a 39.0% increase in root biomass (P < 0.05). Canopy transmittance had a strong influence on LES traits, with most traits exhibiting significantly higher values in CTG5 than in lower light gradients. The comprehensive performance index (CPI) of young P. asperata peaked at CTG2 (0.56), while the lowest CPI was observed at CTG1 (0.31). These findings suggest that a minimum canopy transmittance of approximately 20% is necessary to sustain normal growth in young P. asperata, offering practical guidance for implementing under-canopy afforestation with shade-tolerant species in monoculture plantation conversion.

Graphical abstract