[Estimating aboveground biomass of Trifolium repens community using 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 Trifolium repens community more effectively without destroying herbaceous community, various handmade measuring plates were used to study the community height and aboveground biomass of T. repens community in Duzhai Village, Dazhai Town, Yangling Zone, Shaanxi Province. Measuring plates used for trials were made of 17 kinds of specifications of aluminum-plastic and polymer plates. The plate was laid flat on the community crown, the height of plant community from ground level to the plate was measured and recorded, and measurements were repeated 20 times for each specification of plate. Then the plants of whole areal part below the measuring plate were cut to ground level from the corresponding quadrat, and the biomass was obtained after oven-drying and weighing. Finally, the modeling and correlation analysis were made, and the best estimate model was verified. The results showed that multiple regression equations were established with aboveground biomass of corresponding area as dependent variable, and community height below the measuring plate as indepen-dent variable. The independent variable was positively correlated with the dependent variable, and the determination coefficients, R², ranged from 0.37 to 0.76. Compared with the polymer plates, the aluminum-plastic plates performed better on coefficients of variation of biomass, determination coefficients of regression equations, R², and degree of accuracy. The best measuring plate was circular aluminum-plastic plate with diameter of 35 cm, and its best regression model was y=1.6460x-3.3462, where the R² was 0.76 and the prediction accuracy was 92.1%.