Objective Based on 12 years of continuous fixed-position monitoring, this study investigates the long-term effects ofthinning intensity on the forest quality of a secondary broad-leaved Korean pine forest. It aims to construct a scientific forest quality evaluation system, clarify the recovery patterns of stand quality under differentthinning intensities, and provide a theoretical basis and technical references for the sustainable management of this forest type.
Method A 4-hectare secondary broadleaved Korean pine forest plot in the Jiaohe Forestry Experiment Bureau, Jilin Province, served as the research site. Fourthinning treatments were established: control (CK, 0%), lightthinning (LT, approximately 15%), moderatethinning (MT, approximately 30%), and heavythinning (HT, approximately 50%). A forest quality evaluation system was constructed by selecting 21 indicators across five dimensions: forest productivity, structure, regeneration, species diversity, and health. The analytic hierarchy process (AHP) was used to determine indicator weights. Forest quality was assessed before thinning and 12 years post-thinning to analyze changes under different intensities and identify the optimal thinning threshold for forest recovery.
Result Twelve years afterthinning, the forest quality indices for the four treatments were 0.808, 0.888, 0.860, and 0.793. The forest quality index of the LT treatment was the highest, representing a 14.7% increase compared to the pre-logging level. The LT treatment also showed the highest mean annual volume increment, the lowest proportion of deadwood, and superior performance in forest regeneration, species diversity, and health indicators compared to the CK treatment. The MT treatment increased the volume proportion of target tree species by 8.95%, but its forest productivity score was relatively low, with forest quality recovering to the pre-logging level approximately 10 years post-logging. The HT treatment caused significant disturbance to the forest ecosystem, making short-term recovery difficult, although it promoted forest regeneration, with quality recovering to the pre-logging level after 12 years.
Conclusion Lightthinning (around 15%) can significantly enhance the comprehensive quality of secondary broad-leaved Korean pine forests, representing the optimal ecological restoration effect. A lightthinning intensity of approximately 15% is recommended as an appropriate tending intensity for managing these forests in northeast China.
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