The Applied Research Of Estimating Aboveground Biomass Of Grassland Communities Based On Measuring Plates

Aboveground biomass is an important indicator of grassland community.Direct harvesting has a great damage to the fragile ecosystem.In order to estimate the aboveground biomass of several communities,including white clover grassland,aegilops tauschii dominant forbs community and green bristlegrass grassland communities,more effectively without destroying herbaceous communities,various handmade measuring plates were used to study the community height and aboveground biomass of communities in Yangling,Shaanxi.Measuring plates used for trials were made of circular or square thin aluminum-plastic,whose thickness is 0.3 cm and density 1.24 g/cm2,or polymer plates,whose thickness is 0.3 cm and density 0.94 g/cm2.Circular diameters were made of 10 cm,20 cm,30 cm,35 cm,40 cm five specifications and square sides were made of 10 cm,20 cm,30 cm,40 cm four specifications.Multiple regression equations were established with aboveground biomass of corresponding area as dependent variable,community height below the measuring plate as independent variable.Finally,correlation analysis were made,such as biomass variation coefficient,determination coefficient(R~2),F-test,total relative error(RS)and mean absolute value of relative error(RMA),and the best estimate model was verified.Based on above,the optimum measuring plate size and the best estimate model of aboveground biomass was selected for this type of grassland community.Field samplings were conducted in flat,relatively marvelous terrain,where the plant growth looked to be uniform.The plate was laid flat on the community crown,at random sites in the survey area,until the measuring plate smoothly stop,as far as possible to ensure the measurement plate level,and the height of plant community from ground level to the plate was measured and recorded,and measurements were repeated 20 times for every specification of plate.Then the plants of whole areal part below the measuring plate were cut to ground level in corresponding quadrat.Put the sample into the sample bag,mark it and bring it back to the lab,and the biomass was obtained after oven-drying at 65°C until the weight was constant and weighing.Then the mathematical models were established and the correlation analysis were carried out.The results showed that:1.Multiple regression equations were established with aboveground biomass of corresponding area as dependent variable,community height below the measuring plate as independent variable,where independent variable was positively correlated with dependent variable and the determination coefficients,R~2,ranged from 0.29 to 0.94.2.The best measuring plate of Trifolium repens community from April to May was circular aluminum-plastic plate with diameter of 35 cm,and its best regression model was y[biomass in(DW g·m-2)] = 1.6460 x [height of plate from the ground level(cm)]-3.3462,where the R~2 was 0.76 and the prediction accuracy was 92.1%.3.The best measuring plate of the dominant grass community in Gramineae was from April to May circular polymer plate with diameter of 35 cm,and its best regression model was y [biomass in(DW g·m-2)] = 0.8645 x [height of plate from the ground level(cm)]-6.5262,where the R~2 was 0.81 and the prediction accuracy was 93.3%.4.The best measuring plate of Setaria viridis grassland community from August to September was circular aluminum-plastic plate with diameter of 40 cm,and its best regression model was y [biomass in(DW g·m-2)] = 4.8564 x [height of plate from the ground level(cm)]-23.134,where the R~2 was 0.83 and the prediction accuracy was 94.2%.