Thinning can increase shrub diversity and decrease herb diversity by regulating light and soil environments.

Area of Science:

• Forest ecology
• Understory vegetation dynamics
• Silviculture impacts

Background:

• Tree thinning influences forest understory light, nutrient cycling, and species diversity.
• The specific responses of understory vegetation to thinning intensity and short-term effects in temperate broadleaf-conifer mixed forests remain unclear.

Purpose of the Study:

• To investigate the effects of different thinning intensities on understory vegetation diversity in a temperate mixed forest.
• To analyze the relationships between light environment, soil nutrients, and species diversity using structural equation modeling (SEM).

Main Methods:

• Established four permanent plots (4 hm²) with varying thinning intensities: 20% (light), 35% (medium), 55% (heavy), and unthinned (control).
• Measured photosynthetically active radiation (PAR), light quality (R/FR), soil nutrients (TN, TP, OM, NN, AN, pH), and understory species diversity.
• Employed structural equation modeling (SEM) to assess the relationships between environmental factors and vegetation diversity.

Main Results:

• Thinning significantly increased PAR and R/FR, while decreasing soil nutrients and pH compared to the control.
• Optimal light conditions (PAR and R/FR) were observed at 55% thinning intensity.
• Soil nutrients showed a negative correlation with light conditions and a positive correlation with herbaceous diversity but a negative correlation with shrub diversity.

Conclusions:

• Short-term thinning leads to soil nutrient loss, reduced herb diversity, and increased shrub diversity.
• Understory vegetation diversity, particularly for shrub and herb layers, is more sensitive to soil nutrient availability than light conditions.
• Forest management practices like thinning require careful consideration of their short-term impacts on understory ecosystems.