Abstract: Secondary forest formed by natural restoration and artificial forest are the most typical forest types with the largest distribution in the mountainous areas of southwest China. This study focuses on the naturally restored secondary forests as well as the Pinus armandii and Pinus tabuliformis plantations in the Dagou Watershed of Maoxian County, western Sichuan. We examined changes in the species composition and structure of tree community under different restoration pathways during 2005-2015, aiming to provide a scientific basis for forest management. The results showed that tree density and the range of tree diameter class and height distribution increased in Pinus tabuliformis forest along with forest succession. The seedling regeneration of tree layer species was weak and the number of largediameter individuals increased, indicating stable community succession. Tree density in Pinus armandii and secondary forests decreased firstly and then increased, while the distribution of tree diameter class and height showed increased firstly and then decreased with an increase in abundance of young trees. The number of tree layer species in all three forest types showed an increasing trend, especially in Pinus armandii forest, which increased from 12 to 23. The importance value decreased in the planted tree species and increased in the remaining native broad-leaved tree species in the retention belt, which drove the shift of Pinus armandii forest from coniferous forest to coniferous and broad-leaved mixed forest. High planting density in Pinus tabuliformis forest inhibited the regeneration and growth of native broad-leaved species, with forest gap being the main factor driving succession. In secondary forest, the importance value of native tree species increased from 35.48% in 2005 to 81.12% in 2015. Native broad-leaved species including Quercus aliena var. acutiserrata were the dominant species, which was the main factor driving the succession of secondary forest. The richness and diversity in Pinus tabuliformis forest were significantly lower than that of secondary forest. The diversity in Pinus armandii forest significantly increased with time, quite close to the secondary forest. In the long term, the effect of Pinus armandii forest with low density “contour-staggered configuration afforestation model” was similar to that of natural restoration in terms of biodiversity restoration.

Key words: secondary forest, afforestation model, community succession, forest plantation, natural restoration.