An evaluation of the impact of scattering limestone powder on acidified soil surface on the growth of young trees of Schima superba under crowns of a Pinus massoniana plantation (three years and four months after treatment) were made by a long-term field fixed position experiment, which was conducted in the Tieshanping Forest Farm of Chongqing City in 2004. The randomized complete block experiment had five treatments and three replicates: the doses of one-time scattering of 0 (control), 1, 2, 3 and 4 t·hm-2 finely ground limestone respectively. The effect was significant: surface limestone could ameliorate health condition of the young trees of S. superba and among them the optimum dose was 2 t·hm-2. The mean canopy thickness, crown size, height and diameter of the base at 20 cm above the ground of the young trees of S. superba treated by 2 t·hm-2 increased by 96.84%, 52.68%, 77.47% and 61.19% respectively (P<0.05) compared to the control.
In order to test the accuracy of the usually-used fixed calibration factor of the canopy scanner of LAI-2000 for measuring the leaf area index (LAI), a Larix principis-rupprechtii plantation was chosen in the small watershed of Xiangshuihe located at the Liupan Mountains of Ningxia Hui Autonomous Region of NW China, the LAI was measured in October 2010, a period from full canopy to the total fall of needles, by using both the LAI-2000 and litter-fall collection method. Then, a comparison was made between the LAI values determined by the litter-fall collection and that calculated based on the figures read from LAI-2000 and the fixed calibration factor (1.49). It showed that the average of LAI measurements of the 2 methods was very close, with a difference of only 5%. However, the calculated LAI from LAI-2000 was obviously higher than the true values determined by litter-fall collection when the canopy was full of needles; and obviously lower than the true value when the canopy was sparse after needle falling. The reason may be that LAI-2000 takes the projection of twigs as needles. So, a dynamic calibration factor is needed, especially in the seasons when the needle amount and the percentage of twigs projection in crown projection change quickly. Therefore, a statistic relation in a quadratic polynomial form between the 2 series of LAI data was well fitted. This relation can be used for a more accurate estimation of LAI based on the data read from the easily-used canopy scanners like LAI-2000.