Study On Extinction Characteristics And Heat Balance Of Plantations In Semi-arid Region On Loess Plateau

Based on the date of solar radiation, net radiation, reflect radiation above canopy and under canopy of 11 stands contained 6 tree species, combined with the observation of the dynamic changes of leaf area index in growing season, the paper studied extinction characteristics and heat balance of some plantations. The dissertation involved following aspects:1. The dynamic changes of reflectivity of different plantations in growing seasons were observed and regression equations of reflectivity were established.2. In growing season, the change of leaf area index of Pinus tabulaeformis and Platycladus orientalis were gently. Shrubs reach peak point at August and trees at September. The individual leaf area decrease with the increase of stand density but the stand leaf area added. 4th curve can reflect the dynamic changes go leaf area index in growing season.3. Extinction coefficients was low in beginning, increased gradually, became stable in July and decreased rapidly in the last stage of the growing season. Daily extinction coefficient of Robinia pseudoacacia, Ulmus pumila, Hippophae rhamnoides, Caragana korshinskii, Pinus tabulaeformis, Platycladus orientalis individually changed in the range of: 0.267-0.372, 0.427-0.525, 0.401-0.491, 0.42-0.522, 0.231-0.243, 0.598-0.675; The solar altitude decided the changes of instantaneous extinction coefficient and leaf area index effected the changes of the daily extinction coefficient. A model simulating the value of instantaneous extinction coefficient was established.4. In different depth of all plantations'canopy, the cumulative distribution curves of LAI were S-shape; Leaves in the high density plantations which is more thick than low were mainly distributed in top canopy; the radiation absorptivity above middle parts of the average canopy; the extinction capacityof Robinia pseudoacaci in middle was lower distinctly than the other parts, but the variance a canopy of Platycladus orientalis is not obvious.5. During the growing season, the amounts of gross solar radiation reaching the canopy layer were 2632.27 MJ/m2; the amounts of gross net radiation intercepted by the canopy of Pinus tabulaeformis, Platycladus orientalis with the density of 1.5×2, Shrubs of Hippophae rhamnoides and Caragana korshinskii stands were 1 576.14 MJ/m2, 1 500 MJ/m2 and 1 200 MJ/m2 respectively.