Study On Plant Diversity And Community Succession Trend Of Degraded Forest Of Pinus Armandii In Shennongjia

The Pinus armandii,a species of pine tree,is widely distributed in northern,eastern,and southern regions of China.The invasion of pine bark beetles and the occurrence of extreme environmental disturbances have led to a significant number of Pinus armandii deaths and the gradual degradation of forest areas in the Shennongjia Forest District.As a result,the stability and functionality of the ecosystem have been severely impacted.Therefore,studying the plant diversity and successional trends of degraded Pinus armandii forests is of great theoretical and practical significance for the restoration and management of this ecosystem.This study focused on degraded Pinus armandii forests in the Shennongjia Forest District in Hubei Province.Based on investigations of plant species and community structure in typical degraded forest plots,it analyzed the species composition,plant diversity,community successional trends,and changes in soil physicochemical properties in three types of Pinus armandii degraded forests:mid-altitude beetle-infested degraded forests(A),high-altitude beetle-infested degraded forests(B),and mid-altitude waterlogged degraded forests(C),under different altitudinal gradients and disturbance conditions(insect infestation and waterlogging).The aim was to provide a theoretical basis for the transformation and conservation of degraded Pinus armandii forest ecosystems.The main research findings are as follows:(1)In the survey plots of degraded Pinus armandii forests,a total of 53 tree species belonging to 36 genera and 20 families were found,along with 47 shrub species from 28 genera and 18 families,and 176 herb species from 126 genera and 56 families.The most abundant families in the survey plots were Asteraceae and Rosaceae,with 35 and 24 plant species,respectively.P.armandii and Betula utilis were the dominant tree species in the degraded forest’s tree layer,while Rubus inopertus and Berchemia sinica were the dominant species in the shrub layer,and Dipsacus asperoides,Fragaria orientalis,and Parathelypteris nipponica were the dominant species in the herb layer.(2)There were no significant differences in plant diversity indices of the tree layer among different disturbance conditions and altitudinal gradients in the degraded Pinus armandii forest plots.However,significant differences(P<0.05)were observed in the Shannon-Wiener and Simpson indices of the shrub layer among different disturbance conditions,with higher values found in beetle-infested degraded forests compared to waterlogged degraded forests.Significant differences(P<0.05)in the Simpson index of the herb layer were observed among different altitudinal gradients,with lower values in high-altitude degraded forests compared to mid-altitude degraded forests.Thus,natural disturbances and increasing altitudinal gradients to some extent reduced the plant diversity in the shrub and herb layers of the community.(3)Successional trend analysis of the degraded Pinus armandii forests in Shennongjia showed that P.armandii had insufficient regeneration and would become a declining species in the community.Litsea pungens,Crataegus wilsonii,and Symplocos macrophylla were identified as progressive species in the community.Therefore,the recent successional trend of degraded Pinus armandii forests is towards a deciduous broad-leaved forest dominated by C.wilsonii,L.pungens,and S.macrophylla.Specifically,the successional trend of mid-altitude beetle-infested degraded forests(A)in Shennongjia will shift from P.armandii-Cunninghamia lanceolata mixed forests to Carpinus turczaninowii-Bothrocaryum controversum-L.pungens mixed forests.The successional trend of high-altitude beetle-infested degraded forests(B)will shift from(P.armandii-Salix wilsonii-B.utilis mixed forests to C.wilsonii-Malus kansuensis f.calva-Malus hupehensis mixed forests.The successional trend of mid-altitude waterlogged degraded forests(C)will shift from P.armandii-Larix kaempferi mixed forests to Ligustrum molliculum-Litsea cubeba-Symplocos macrophylla wet mixed forests.(4)There were significant differences in total nitrogen,hydrolyzable nitrogen,total potassium,available phosphorus,and organic matter content of the soils in degraded Pinus armandii forests among different altitudinal gradients.The total potassium and available phosphorus of the soils in mid-altitude degraded forests were higher than those in high-altitude degraded forests.Significant differences were also found in the total nitrogen,hydrolyzable nitrogen,total phosphorus,total potassium,and available phosphorus of the soils in degraded forests under different disturbance conditions,with higher values in waterlogged degraded forests compared to beetle-infested degraded forests.The soils in the degraded Pinus armandii forests of Shennongjia were acidic to strongly acidic,with higher acidity at higher altitudes.Low-lying waterlogged areas had neutral soil conditions.Overall,the soils in the degraded Pinus armandii forests had high organic matter and nitrogen content,indicating good soil conditions favorable for community succession.The Shannon-Wiener diversity index and Simpson diversity index of the shrub layer were significantly negatively correlated(P<0.05)with the total phosphorus and available phosphorus content in the soil,and they were also highly negatively correlated(P ≤ 0.001)with the total potassium content in the soil.The Simpson diversity index of the herb layer was highly negatively correlated(P<0.01)with the total nitrogen,hydrolyzable nitrogen,and organic matter content in the soil.In comparison to the shrub layer,the herb layer showed a stronger correlation with soil nutrients.