Aims The purpose of this study was to understand the effects of the second generation wild boar grazing on species diversity and soil physicochemical properties of coniferous-broad-leaved mixed forest in the Jiajin Mountain, and to provide reference for the maintenance of ecological stability and scientific grazing of the mixed coniferous and broad-leaved forest in this area.
Methods On the basis of comprehensive investigation, according to the number, area, behavior characteristics and activity range of wild boar, four grazing disturbance intensity (from strong to weak was followed by I, II, III, IV) were divided, and no disturbance state was set as control (CK) to explore species diversity and soil physicochemical properties under different grazing disturbance intensity.
Important findings (1) 172 species of vascular plants, belonging to 55 families and 117 genera, were recorded, with the families, genera and species of trees, shrubs and herbs reaching the highest under slight disturbance intensity (IV). (2) The responses of tree, shrub and herb diversity index to the disturbance gradient were basically the same, but the richness index (S), Shannon diversity index (H') and Simpson dominance index (D) reached the maximum under the IV level disturbance intensity, which were higher than those in CK. The diversity level tended to decline with the increase of disturbance intensity (IV-I). In addition, for Pielou evenness index (E), there was no significant difference among different disturbance intensity levels. (3) Compared with CK, soil water content, maximum water content and total nitrogen content decreased under wild boar grazing. The greater the grazing pressure, the greater the proportion of decline. The content of soil total porosity, total phosphorus, available phosphorus and organic matter content increased in the IV level of interference, and decreased significantly under the I-III level interference; the soil density increased with the increase of disturbance intensity. (4) Redundancy analysis showed that soil organic matter content, available phosphorus content, soil density, soil water content, soil porosity, total phosphorus content, total nitrogen content and diversity index were significantly correlated. The light disturbance intensity is beneficial to the richness of community species diversity, the improvement of soil fertility and soil structure, which is a positive factor for the maintenance of ecological stability of the mixed coniferous and broad-leaved forest in the Jiajin Mountain. The study provides a reference for the forest ecological environment protection and sustainable development in this area under the background of increasingly expanding grazing and animal husbandry and increasingly frequent disturbance of human activities.