Abstract:

Field surveys have been conducted by using a Li-cor LAI-2000 plant canopy analyzer in a small sub-alpine dark coniferous forested catchment in western Sichuan Province during the period from July to September,2005.This study is to quantify LAI of the four different fir stands composed mainly of Abies faxoniana and LAI seasonal patterns,and to explore the relationship between LAI and topographical factors in terms of altitude and aspects,and spatial variability of LAI at catchment scale and at stand scale.The results showed that single peak curve of LAI seasonal change pattern occurred in sub-alpine dark coniferous forest during growing season,with the peak value of 5.82±1.32 in the middle ten days of August.There were significant differences in LAI among the four stands(p<0.001),with the mean LAI value of 5.44±0.83.The highest LAI occurred in the moss,Fargesia nitida,Bashania fangiana and A.faxoniana stand,followed by the grass,F.nitida,B.fangiana and A.faxoniana stand and the grass,Rhododendron spp.and A.faxoniana stand,while the lowest LAI value was in the moss,Rhododendron spp.and A.faxoniana stand.With increasing altitude,LAI increased subtly at first,but then decreased continuously when the elevation exceeded 3 000 m.The relationship between LAI(y)and altitude(x)can be commendably expressed as the following regression equation:y=-22.408 6+0.019 6x-0.000 003 360 1x²(R²= 0.999 6,p<0.001,n=12).LAI at northeast-aspect was larger than that at southwest-aspect,with the significant difference in LAI between the two aspects(p<0.05).The coefficient of variability(CV)of LAI at catchment scale(19.79%～22.80%)was approximately twice larger as that at stand scale(10.02%～12.22%).At the different altitudinal gradients,the highest CV(23.09%)was at the elevation of 3 800 m,while the lowest(7.64%)was at 3 500 m.The CV at northeast-aspect(16.58%)was higher than that at southwest-aspect(13.44%).

Key words: sub-alpine, dark coniferous forest, vegetation, LAI, spatial variation