Relationship Between Community Coverage With Species Composition And Aboveground Biomass Production Of Farming-withdrawn Grasslans In Loess Hilly-gully Region

Coverage and aboveground biomass are important parameters that reflect the status and characteristics of vegetation growth,and they are also important indicators in evaluating the construction and restoration of vegetation.To clarify the relationship between coverage,species composition and aboveground biomass of farming-withdrawn grasslands in loess hilly-gully region is helpful to understand the change characteristics of grassland communities during the succession process after withdrawing from farmland,and to provide guidance for the evaluation and improvement of grassland communities.In this paper,the grassland communities of 5,10,15,20,and 30 years after farming-withdrawn were studied.During the key growth period?June-September?,on the basis of community survey,the aboveground biomass was measured by species division and layered mowings,and combined with photo analysis,the monthly characteristics of community coverage,species composition,and aboveground biomass were studied.The relationship between species composition and stratified coverage and also the aboveground biomass were analyzed.The main results are as follows:?1?With the increase of farming-withdrawn years,grassland community coverage and aboveground biomass generally showed an increasing trend,but decreased at the time of 20years.Coverage and aboveground biomass were higher in July and August and lower in September.There was no significant difference in species richness and diversity index between grassland communities in different farming-withdrawn years,and they were all higher in August.There were differences in dominant species of different grassland communities.The dominant species in the farming-withdrawn 5^th years were Setaria viridis,Lespedeza davurica and Heteropappus altaicus,and in the 10^th and 15^th years were Artemisia gmelinii and L.davurica,and in the 30^th years were Artemisia gmelinii and Stipa bungeana.There was a monthly variation in the dominant species of the community,and the coverage and aboveground biomass of different species varied with the growth period.The changes of layered coverage and aboveground biomass of grasslands in different farming-withdrawn years were basically consistent with the growth trend.The coverage was the highest in the0¹0 cm layer,the lowest were in the>50 cm and 40⁵0 cm layers,and there was no significant difference in the other layers.The aboveground biomass on the layers was generally the highest in the 0¹0 cm layer and the lowest in the>50 cm layer.?2?There was no significant correlation between the coverage and the species richness and diversity index.And there was a significant negative correlation between the coverage and species richness in 0¹0 cm,20³0 cm,and 40⁵0 cm layers?R²=0.13,0.13 and 0.14?;the correlation of coverage and species richness of 10²0 cm layer were significant positive?R²=0.14?.There was no significant correlation in the 30⁴0 cm and>50 cm layers between coverage and species richness.There was a significant negative correlation in the 0¹0 cm layer between coverage and diversity index;coverage in the 20³0 cm layer was significant positive with the diversity index?R²=0.11 and 0.12?.There was no significant correlation between the coverage of 10²0 cm,30⁴0 cm,40⁵0 cm and>50 cm layers and the diversity index.?3?The coverage of farming-withdrawn grasslands showed a rapid increase with the increase of aboveground biomass,followed by a trend of stabilization.The aboveground biomass was the highest at 313.28 g m^-2,and the coverage reached the maximum.The range of aboveground biomass per unit coverage of different species varied from 0.04 to 6.31%.There was a significant positive correlation between the coverage of dominant species and their aboveground biomass in the farming-withdrawn grasslands.There was a significant positive correlation between coverage and aboveground biomass in the 0⁵0 cm layer of farming-withdrawn grassland.And there was no significant correlation between coverage and aboveground biomass in the>50 cm layer.The highest coefficient of determination R² was30⁴0 cm layer?0.55?,and the lowest was 0¹0 cm layer?0.24?.