| Broadleaf evergreen forest is the most important vegetation type in the subtropical region,but due to human interference,most of the existing vegetation is dominated by secondary forests which is restored naturally by the remaining virgin forest.Natural regeneration is an important way for forest self-restoration and a fundamental way of sustainable development of secondary forests.The Liankangshan National Nature Reserve in Henan Province is located at the northern edge of the north subtropical zone of China,preserving natural evergreen broad-leaved secondary forests with less anthropogenic disturbance.The study of natural regeneration characteristics and its influencing factors in this area can help to understand the dynamic process of forest communities.This is important for the scientific formulation of artificial promotion of natural regeneration strategies and forest management methods.In this study,the evergreen broad-leaved secondary forest in Liankangshan National Nature Reserve of Henan Province was taken as the research object.By laying 50 fixed plots,the characteristics of stand structure and site factors were defined,and the composition,diversity,diameter class structure and ecological niche of natural regeneration species were studied.The effects of topography,soil,spatial structure of stand and non-spatial structure of stand on regeneration density and species diversity were analyzed,and the key influencing factors of natural regeneration on stand condition and forest structure were clarified,in order to provide basis for sustainable management of evergreen broadleaved secondary forest in this area.The main findings were as follows:1.There were 37 species(25 families and 33 genera)in the tree layer of the evergreen broad-leaved secondary forest in the reserve,and 51 species(31 families and 45 genera)in the regeneration species.Quercus glauca was absolutely dominant in the tree layer(IV=72.58%).Loropetalum chinense was the most dominant in regeneration species,which had the largest importance value(IV=57.25%)and ecological niche width(B(L)=35.52).The regeneration species Symplocos sumuntia,Quercus glauca and Ilex chinensis were the dominant evergreen species in the understory.2.The stand spatial structure uniform angle index(CV,12.89%),mingling degree(CV,27.69%),Hegyi competition index(CV,47.76%),opening degree index(CV,25.86%),storey index(CV,22.74%)and spatial density index(CV,14.76%)all belonged to moderate variability,and only the neighborhood comparison(CV,4.31%)belonged to weak variability.Uniform angle index(0.61)belonged to the reunion distribution,neighborhood comparison(0.52)was at a disadvantage,mingling degree(0.58)was intensity mingling,the competition index(99.44)was large,the openness(0.17)was seriously insufficient,and only the spatial density index(0.62)was the closest to the best state.3.The regeneration density of the study area was as high as 7375 stems·hm-2.The Shannon index,Simpson index,richness index and Pielou evenness index of regeneration species were 2.02,0.81,15 and 0.77,respectively.The Shannon index,Simpson index,richness index and Pielou evenness index of tree layer were 1.93,0.79,13 and 0.76,respectively.The size-class structure of evergreen tree species Quercus glauca,Ilex chinensis and Symplocos sumuntia showed inverted “J” shape.The size-class structure of Ilex latifolia followed a unimodal distribution,and Lithocarpus glaber was a fluctuating representative species.4.The effects of stand structure characteristics and site condition factors on regeneration density showed that mingling degree(R2=0.143),Hegyi competition index(R2=0.123),mean DBH(R2=0.203),richness index of tree layer(R2=0.181),Pielou evenness index of tree layer(R2=0.087)had significant regression fitting relationship with regeneration density(P<0.05).There was a significant negative correlation between regeneration density and altitude,soil organic matter,total nitrogen and available phosphorus(P<0.05).With the increase of mingling degree,richness index of tree layer and Pielou evenness index of tree layer,and the decrease of Hegyi competition index,the regeneration density showed an increasing trend.With the increase of the mean DBH,the regeneration density initially increased slowly.When the mean DBH exceeded 8.78 cm,the regeneration density decreased obviously.The results of one-way ANOVA method in different slope-aspects with regeneration density showed that there was a significant difference between the regeneration density of semi-shady slope,semisunny slope and sunny slope(P<0.05).Among them,the order of regeneration density in different slope-aspects was shady slope > sunny slope > semi-sunny slope.5.Pearson correlation analysis of stand structure characteristics,site condition factors and regeneration species diversity showed that the Shannon diversity index of regeneration species was significantly positively correlated with mingling degree,Shannon diversity index of tree layer and slope(P<0.01),and significantly negatively correlated with available potassium(P<0.01).The Simpson dominance index of regeneration species was positively correlated with mingling degree(P<0.01),and negatively correlated with stand density,altitude and available potassium(P<0.01).The richness index of regeneration species was positively correlated with the degree of mixing and Shannon diversity index of tree layer(P<0.01),and negatively correlated with altitude and available potassium(P<0.05).The Pielou evenness index of regeneration species was only negatively correlated with stand density(P<0.05).6.According to the redundancy analysis(RDA)results of stand structure characteristics and site condition factors on the composition of regeneration species,elevation(20.12%),mingling degree(7.49%),total phosphorus(5.57%),slope(2.33%)and mean tree height(2.06%)had significant explanatory power on the composition of regeneration species in the study area(P<0.05).Elevation was the critical factor affecting the composition of regeneration species.The results of RDA on natural regeneration of stand structure characteristics and site condition factors showed that the interpretation ability of natural regeneration was significant(P<0.05)for mingling degree(19.90%),mean DBH(16.37%),altitude(9.78%),total phosphorus(3.86%)and Simpson dominance index of tree layer(2.44%),and the mingling degree was the most critical factor affecting natural regeneration.7.Using four groups of topographic factors,soil factors,stand spatial structure factors and stand non-spatial structure factors as explanatory variables,variation partitioning analysis for the composition of regeneration species and natural regeneration respectively.The results showed that the four groups of factors explained 38.4% and 52.5% of the variation in the regeneration species composition and natural regeneration,respectively.The topographic factor was the most important factor in explaining the change of regeneration species composition(11.20%),followed by the common contribution of the spatial structure and nonspatial structure of the stand(7.61%).The common contribution of stand spatial structure and non-spatial structure contributed the most to natural regeneration(26.45%). |
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