| Leaf area index(LAI)is one of the most frequently used parameters for the analysis of canopy structure,it is lelated to forest photosynthesis, evapotranspiration, transpiration, water utilization and stand productivity, after more than 50 years of research on it, LAI has became an essential parameter for the growth analysis of plant populations and communities and was Widely used in agriculture and forestry, Fruit trees industry , forest ecology biology, etc.This paper chose black locust plantations as study object,which grew at Manliantan valley and Huaiping forestry centre of Yongshou county, Shaanxi province.we estimated LAI of values of the black locust plantations with different densities (925~1125/hm~2, 1375~1625 /hm~2, 1900~2300 /hm~2, 2775~3050 /hm~2) and different ages(1-10a, 11-15a, 16-20a, 21-30a, above 30a) by using LAI-2200 Plant Canopy Analyzer in the growing seasons. To analysed the changes of LAI to the different densities and ages of plantations and seasonal dynamics of LAI. Some conclusions have been drawn as the following:(1) LAI of the same sample plot was measured by LAI-2000 and WinSCANOPY-2005a, the result showed: LAI was estimated from LAI-2000 have no difference compared to the instrument of WinSCANOPY-2005a when was measured before sunrise and after sunset, however, the value of LAI by LAI-2000 was steady and has no different.Therefore, we suggest that LAI-2000 is more optimal instrument for a large number of sample plots.(2) The difference of LAI was significant among the different densities (P<0.05)which occurred in late May when leaf growth initial stage; the LAI values increased firstly and then decreased with the increasing of density; there were no obvious changes of the LAI values in the plot with the density of 1375~3050/hm~2; the minimum value of LAI occurred in the plots with densities of 925~1125/hm~2 in the whole growing seasons.(3)In the same stand age(19a),the values of various growth indexes in higher forest is lower lower density forest, such as tree height,crown width and DBH(Diameter at Breast Height), specially there was a significant difference on the DBH in different densities forest; while the value of canopy closure is higher than lower density forest.(4) It was suggested that age was one of important factors affecting the LAI variations,the difference of LAI was significant among the different ages(P<0.05). LAI increased and then decreased with increasing of the ages, the peak value of 4.37±1.26 appeared in half-mature plantations on the sunny slope, While LAI decreased with increasing of the ages on the shady slope. By variance analysis of LAI of black locust woods with different age, we known thatⅢ(16-20a)was a critical point, the difference of LAI had no significance afterⅢ(16-20a)and the value of LAI was steady.(5) The temporal dynamic of LAI at different aspects in growing season had maily same trend, the value of LAI increased firstly and then decreased in growing seasons, the peak value appeared in late June. The LAI of black locusts was higher on the shady slope than on the sunny slope from May to June, while it showed lower than on the sunny slope from late July to Auguest. The T test analysis of different aspects show that LAI at northeast aspect was similar to that at southwest aspect, with not significant difference between the two aspects. Therefore, it demonstrated that the aspect was not the main impatct factor for affecting on the LAI of black locusts.(6) There were obvious seasonal changes of LAI of black locust plantations in the whole growing seasons with peak value(3.88±1.02) occurring in late June or early July, the reason is directly related to the climate this year. |
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