Effects of Long-Term Thinning on Soil Nematode Communities in Pinus taiwanensis Plantations

Thinning, as a critical forest management practice, has multidimensional impacts on forest ecosystem environments. Soil nematode communities, which serve as sensitive bioindicators of ecosystem health, can effectively reflect the effects of different thinning intensities on forest ecosystems. Based on a long-term thinning experiment with varying intensities in a Pinus taiwanensis plantation, this study examines how thinning influences the structure and function of soil nematode communities. The results showed that the total abundance of soil nematodes changed significantly across varying intensities of thinning (p < 0.05). Different trophic groups exhibited distinct responses: bacterivorous nematodes achieved the highest relative abundance under light thinning (10% removal), plant-parasitic nematodes showed no significant change in relative abundance, while fungivorous and omnivorous-predatory nematodes were significantly enriched under moderate thinning (20% removal). The synergistic changes in the latter two groups reflected trophic cascading effects. Moderate thinning significantly enhanced nematode diversity indices (Shannon-Wiener index, evenness index), increased the proportion of K-strategists, and strengthened the bacterial decomposition channel. These changes are attributed to moderate thinning better optimizing soil nutrient regimes and alleviating competitive exclusion through more rational allocation of food resources. Therefore, moderate thinning helps improve the structure of soil nematode communities and increases the complexity of belowground food webs. These changes further indicate improved ecosystem stability and support the healthy development of belowground ecosystems.