| By investigating the secondary forest topography,vegetation types,community structure,soil conditions,hydrology and other resource and environmental information in Fuyang District,Hangzhou,this project analyzed community characteristics,assessed the species diversity,quantity and health quality of different types of stands,and revealed the law of interaction between different types of stands and soil,terrain and other environments.It provides theoretical basis for the protection and sustainable management of secondary forest resources.The following conclusions are drawn from the investigation.(1)Plant resources and floraThere are 267 species of vascular plants belonging to 77 families and 165 genera,including 6 families and 6 genera and 8 species of ferns,6 families and 11 genera and 12 species of gymnosperms,and 65 families and 148 genera and 247 species of angiosperms,with 20 families and 42 genera containing single species.From the composition of families,among the 77 families,those containing more species are Camphoraceae(20species)and Rosaceae(21 species).From the composition of genera,among 165 genera,the genus containing more species is Ilex(10 species)of Holly.According to the "Flora of China" Chinese fern zoning method,ferns are mainly of world distribution,Old World tropical distribution,tropical Asia and tropical America intermittent distribution.The types of seed plant distribution areas in the study area are wide,mainly belonging to tropical and temperate zones,and the main vegetation types of forests are: warm coniferous forests,mixed evergreen deciduous broad-leaved forests,evergreen broad-leaved forests,bamboo forests and scrub and grasses.(2)Soil physical and chemical propertiesMost of the soil types in the study area belong to red loam soil.It mainly belongs to three sub-categories: red loam,yellow red loam and young red loam.Red loam has the largest distribution area and is basically distributed throughout the region,yellow red loam is distributed in high hilly areas,and young red loam is distributed in areas with steep slopes or areas formed by artificial land preparation after pushing out the surface layer.Soil thickness is mostly between grade III-IV,soil erosion intensity is grade II,which is slight erosion,and rock exposure is mostly between grade I and II,with an area of 5.74km2,which together accounts for about 72.3% of the total area.The area of rock gravel content grade I accounts for 2.9% of the total area,and other grades of soil are evenly distributed in space,all around 20%.The sum of soil organic layer thickness grades IV and V accounted for 64.8%,with a larger proportion,and the combined soil physical index grades in grades III and IV accounted for more.The average contents of total nitrogen,hydrolytic nitrogen,fast-acting potassium,fast-acting phosphorus,and organic matter in the whole study area were generally average,and the soil nutrient conditions were average,with an average fertility grade of 3.18,which was at a medium and slightly lower level.The problem of potassium deficiency and phosphorus deficiency is prominent.Five indicators of total nitrogen,hydrolytic nitrogen,fast-acting potassium,fast-acting phosphorus and organic matter were analyzed by dimensionality reduction,two principal components were obtained,and the principal component coefficients were used as weights to calculate the index scores and synthesize the comprehensive fertility index CFI,and the results were basically consistent with the order of the size of the average grouped index values.(3)Importance values and diversity of forest species in different vegetation typesThe importance values of balsam fir,wetland pine and fir were higher than those of other species in the plantation forest,and in the secondary forest,the importance value of mullein was the highest,followed by fringe shrub,holly and stone oak.The species with higher importance value in the regeneration layer was bitter chink,in the succession layer was fringe,and in the main forest layer was balsam fir and mullein respectively.By forest type,the highest IV value of deciduous broad-leaved mixed forest was Liriodendron,the evergreen broad-leaved forest was Mullein,the broad-leaved mixed forest was Balsam fir,the coniferous forest was Fir,and the coniferous mixed forest was Wetland pine.In terms of plant diversity in different stand layers,the overall species diversity of plantation forests in the regeneration layer was higher,the species diversity index of secondary forests in the succession layer was higher,and the species richness and evenness of plantation forests were higher.The overall species diversity of plantation forests in the main forest layer was higher,and the species richness and evenness were also higher,and the species distribution of mixed coniferous forests was more even.(4)Correlation of community characteristics indicatorsFour indices,Vi mixedness,Hgci competition index,Si stand index and Ki openness index,were highly correlated with the biodiversity index.Among them,Si was only highly significantly correlated with Alatalo(r=0.309),while the other indices were not significantly correlated with biodiversity.vi was paired with P,Zi with p H,N and ori content,Si with N and ori,Ki with p H,and Uaci with nutrient formation of top soil.As soil gravel content decreased,N,P,and ori decreased,species abundance decreased,and biodiversity and evenness increased.Stand health and high stand quality increased with the number of stands,decreased with Zi and Vi,increased with Si and Hgci indices,and decreased with biodiversity;increased with soil organic matter and p H,and decreased with the elevated surface of P nutrients.Evergreen deciduous ratio and topness increased with the progress of forest succession,and with the increase of Si and Uaci.Similarity between forest strata was positively correlated with biodiversity measured by frequency.(5)Distribution of tree species and environmental effectsAccording to the clustering of sample sites,it was found that the forest types in the whole study area could be divided into seven categories,planted pure forest type,silviculture type,mixed type,lightly disturbed type,and special natural forest type.After the hierarchical clustering,it was found that the forest types in the study area could be divided into 6 categories,artificial pure forest type,afforestation type,interforest type,lightly disturbed type,and near natural forest type.The clustering was found to be consistent with the changing trend of forest origin types,in the order of logging afforestation-replanting afforestation-interforestation shrubland-interforestation naturalization-natural forest,with a high probability that forest stands of the same origin are clustered together,and the more similar the origin order is,the more likely they are to intersect with each other.The more similar the order of origin,the greater the probability of interlocking.However,the clustering is not identical to the origin type.The clustering breaks the clear boundary of the origin type and produces interlacing between them,indicating that there is a tendency for different origin stands to converge in structure and composition after more than 20 years.The results of tree species classification in the survey area showed that 166 tree species were classified into four types: i,j,h and k.The tree species in the main forest layer and the understory could also be classified into the above four categories according to the order of clustering,of which 81 species were contained in the main forest layer and 157 species in the understory.The distribution of tree species is similar to that of the whole forest layer above,and the change trend is consistent.(6)Spatial distribution and environmental impacts of different disturbance types of forest communitiesA total of 38 environmental indicators that may affect the distribution of sample sites and tree species were selected as explanatory variables,and the results of the environmental impact study on the distribution of sample sites and species in the whole forest layer showed that the first canonical axis of RDA was mainly influenced by the disturbance intensity,soil thickness,soil erosion intensity,elevation,and p H,which can be called the disturbance factor axis;the second axis was mainly related to soil cfi,P4,and K2,which can be called the soil axis.Different disturbance types and constituent tree species were clustered in different quadrants and distributed according to the environmental gradient,among which tree species of category j and k were the most widely distributed,mostly in the median area of the environmental gradient.The distribution of indicators,sample plots and tree species was similar for the two canonical axes of the main forest layer and the understory,with the understory being more influenced by the vegetation environment.Based on the RDA analysis at the sample site and stand level,28 key environmental indicators affecting the distribution of sample sites and species were screened.(7)A stand structure optimization model was proposed to select six structural indices that were typical,relatively independent,and significantly different among stand types to construct a comprehensive spatial structure evaluation index,including angular scale Zi,mixedness Vi,openness Ki,stand layer index Si,intersection angle competition index Uaci,and stand spatial density index di. |
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