Species Diversity And Above-ground Biomass Of Woody Plants Of Karst Secondary Forest And Their Correlation In Central Guizhou

Karst rocky desertification is an important barrier for ecological construction in southwest my country.Due to the unreasonable development and utilization of human beings,the forest has been destroyed,and vegetation restoration has become the main governance measure in this area.Studying the species diversity and aboveground biomass of karst secondary forests can provide a certain reference for vegetation restoration and protection in karst areas.This paper takes the plant community in Puding County,central Guizhou as the research object,and uses the monitoring data of the sample plots in 2012,2015 and 2020 to analyze the composition of the community structure,species diversity and above-ground biomass changes at different scales and The impact of the environment on both,the results of the study are as follows:（1）The important values of different layers（tree and shrub layers）of woody plants from 2012 to 2020 were calculated as follows: During the 8years,the main species in the tree layer did not change significantly,Lithocarpus confinis was always the constructive species,Zanthoxylum dimorphophyllum,Pittosporum brevicalyx,Carpinus pubescens and other species increased,while the important values of Cinnamomum bodinieri,Platycarya longipes,Itea yunnanensis,and Machilus cavaleriei decreased.Fagaceae,Juglandaceae and Lauraceae were the main dominant families;The composition of the main species in the shrub layer did not change.Most of the saplings were trees,and the saplings of the narrow-leaf Lithocarpus confinis were absolutely dominant.The important values of,Mahonia fortunei,Lindera communis and Itea yunnanensis increased,Machilus cavaleriei,Stachyurus obovatus,Rhamnus heterophylla and other species important values decrease.Lauraceae,Fagaceae and Stachyuraceae were the main dominant families.During the process of succession,the status of mesophyte,shady species and transitional species rose,and Lithocarpus confinis was still the main dominant species in succession.The shrub layer gradually declined,and the tree layer showed a positive development trend.（2）The overall change of species diversity in time was small,only the shrub layer was relatively significant,but the species diversity of the tree and shrub layer on a small scale（≤20 m）was obvious: 1)The species diversity index difference of the tree layer in 8 years not obvious,only the Pielou evenness index was significantly different at small scales（≤20 m）,but not at 50 m scale.The coefficient of variation of the species diversity index between years was small;The species diversity index of the shrub layer showed obvious performance from 2012 to 2015,especially at the 10 m scale.The Margalef richness index and Pielou evenness index differed significantly between the 20 m and 50 m scales.The coefficient of variation of the species diversity index in 2015 and 2020 was larger;2)With the expansion of the scale,most species diversity indices in the tree and shrub layer increased and the coefficient of variation decreased,and the variability of species diversity at small scales was high.The coefficient of variation of the shrub layer was higher than that of the tree layer only at the 10 m scale;3)The spatial distribution of the species diversity index was different at different scales.But on the whole,the high value of species diversity index in the tree layer was mainly concentrated in the middle of the plot,and the distribution in the shrub layer was relatively uniform.（3）The above-ground biomass of the tree layer increased year by year,while the shrub layer showed a fluctuating change.On small scales（≤20 m）,the above-ground biomass of the tree and shrub layers had a high degree of variability and the spatial distribution was generally consistent:1)With the succession of time,the above-ground biomass of the tree layer gradually increased steadily,while the shrub layer showed a trend of first decreasing and then increasing.In 2015,the coefficient of variation of the above-ground biomass of the tree and shrub layer was large;The above-ground biomass of the karst secondary forest in the study area was low,in which the tree layer dominated and was an important leader of the forest ecosystem function;2)With the expansion of the scale,the above-ground biomass of the tree-shrub layer increased and the coefficient of variation decreased,and the coefficient of variation of the shrub layer was higher than that of the tree layer;3)The spatial distribution of above-ground biomass at small scales（≤20 m）was generally uniform,but at 50 m scales,there were differences in tree and shrub layers;Affected by the diffusion mechanism,the spatial distribution of the extreme values of the above-ground biomass in the tree and shrub layers was similar.（4）The relationship between species diversity and above-ground biomass had no obvious regularity in time,only the degree of correlation in the shrub layer gradually decreases,but on small scales（≤20 m）,the tree and shrub layers were mostly significantly positively correlated: 1)Trees Layers showed no regularity.In 2012,only the Margalef richness index was significantly negatively correlated with above-ground biomass（P<0.05）,and in 2015,most species diversity indexes were significantly positively correlated with above-ground biomass（P<0.05）,which were concentrated at 10 m and 20 m scale.The 50 m scale was not significant;The correlation degree of the shrub layer gradually decreased,and most species diversity indices were significantly（P<0.05）and extremely significantly（P<0.01）positively correlated with above-ground biomass in the years and concentrated at the 10 m scale.20 m and 50 m scales were not significant;2)The tree layer was significantly positively correlated at the 20 m scale,and the shrub layer was significantly positively correlated at the 10 m scale.As the scale increases,this significant relationship fades and was mostly negative.（5）Slope,soil thickness and soil moisture content were the main factors affecting species diversity and above-ground biomass.In the tree layer,the slope was significantly negatively correlated with the Pielou evenness index（P<0.05）.Soil thickness was positively correlated with Simpson advantage index,Shannon-Wiener index,Pielou evenness index,and above-ground biomass significantly（P<0.05）,extremely significant（P<0.01）.Soil moisture content was positively correlated with Margalef richness index,Pielou evenness index,Simpson advantage index and Shannon-Wiener index（P<0.05）,extremely significantly（P<0.01）,and was significantly negatively correlated with above-ground biomass（P<0.05）;In the shrub layer,slope was significantly negatively correlated with Margalef richness index,Simpson advantage index and Shannon-Wiener index（P<0.05）.Soil moisture content was significantly positively correlated with Margalef richness index,Shannon-Wiener index and Simpson advantage index（P<0.05）and extremely significantly positive（P<0.01）.Most soil nutrients had no significant correlation with species diversity indices and above-ground biomass,except for soil hydrolyzable nitrogen,which was significantly negatively correlated with Pielou evenness index in tree layer and Simpson advantage index in shrub layer respectively（P<0.05）.Soil effects on both were more physical than chemical.