Impacts of stand density on diversity of understory plant and soil seed banks in a Pinus massoniana plantation.

Abstract

Stand density is a critical factor impacting the diversity of understory plants. We analyzed the diversity of understory plants and soil seed banks, as well as their relationship by setting up three planting densities in a Pinus massoniana plantation, including low density (1575 trees·hm-2, D1), medium (2474 trees·hm-2, D2), and high (3550 trees·hm-2, D3). It aimed to provide a scientific basis for the implementation of the multi-objective sustainable development of plantations. The results showed that there were 70 species of herbs and shrubs belonging to 42 families and 62 genera. D1 was dominated by heliophiles, whereas both the D2 and D3 were dominated by shade-tolerant species. The Margalef (M), Shannon (H), Simpson (D), Pielou (Jsw), and Altalo (Al) indices of the herbs and shrubs exhibited a downward trend with increasing stand den-sity. In the herb layer, D1 and D3 showed significant difference in H, D, Jsw and Al. There were significant differences of Jsw and Al in the shrub layer among the three stand densities, but no diffe-rence of H and D. H, D, Jsw and Al in the soil seed bank first decreased and then increased with increasing stand density, with species richness and diversity being the highest in D1. The similarity coefficient of Jaccard and Sorensen among different stand densities was low. In the herb layer, M was positively correlated with Jsw. The correlations between stand density and H, D, Jsw and Al were greater in the shrub layer than in the herb layer. There was significant negative correlation between stand density and Jsw both in the shrub and herb layers. The stand density of 1575 trees·hm-2 was comparatively beneficial for the development of understory, plant diversity, and sustainability of P. massoniana plantation.