The Slope Variation And Scale Effect Of The Stand Structure And Radial Increment Of Larix Principis-ruprechtii Plantations Of Liupan Mountains

An obvious difference in forest structure exist among slope positions and thus there is a clear slope scale effect on the slopes of dryland region, as an integrated result of the changing site factors (such as topography, soil, weather and others) and the redistribution of water and nutrients along the slopes. In this paper the selection of Larix principis-rupprechtii in the semi-humid small watershed of Xiangshui of Liupan Mountains of Northwest China mainly distributed to:on the south (sunny) and southeast(semi sunny) slope, the level of slope length of 225 and 480 m. And setting the slope belt respectively with a series continuous sample area. Investigating the stand structure and the radial growth of the trees, and analysis the slope change of the growth of the trees and the difference with aspect of slope. And using the tree growth target from slope top to bottom level 100 m slope length as the unit of space scale effect calculation. Understanding and quantifying of such slope scale effect is necessary for providing a scientific basis to realize the fine management of forests and their ecological services, and understand the slope scale effect, to promote the forest ecology and eco-hydrological studies.(1) The slope changes and scale effect of the characteristics of stand structureThe stand structure indexes have obvious difference in two different slopes. In sunny slope, the slope average (variation range) of DBH, tree height and dominant height was 19.28 (17.92～20.93) cm,15.9 (14.9～17.0) m,19.3 (17.9～19.9) m, respectively. In semi-sunny slope, the slope average (variation range) was 20.42 (18.47～21.57) cm,16.9 (15.0～18.6) m,20.6 (19.4-22.0) m, respectively.The stand structure indexes and the slope change trend in two slope positions exists difference in different slope positions. In sunny slope the DBH, tree height and dominant height from top to bottom were performance the "increase - decrease -increase - decrease" of double wave change trend. In semi-sunny slope are presented for "increase - decrease" unimodal trends.In sunny slope, the spatial scale effect of DBH, tree height and dominant height increased 0.39 cm, increased 0.49 m and increased 0.82 m. In semi-sunny slope, the spatial scale effect of DBH and tree height needs to be segmented to describe, in the horizontal distance range of 0-200 m,200 to the bottom, the scale effect of DBH increased 0.33 cm, decreased 0.21 cm; In the horizontal distance range of 0-67 m、 67-305m、305 m to the bottom, the spatial scale effect of tree height decreased 1.12 m, increased 0.31 m, decreased 0.10 m; the spatial scale effect of average height of dominant trees increased 0.28 m.(2) The slope change and scale effect of stand volumeThe stand volume was different between sunny and semi-sunny slopes. The slope stand volume average slope was 216.48 m3·hm-2 for sunny slope,209.71 m3·hm-2 for semi-sunny slope, The variation range were 175.45～277.31 m3·hm-2 and 117.78～ 117.78 m3·hm-2, respectively.The changes of stand volume in the two slopes were firstly increased and then decreased with the increase of the slope. The spatial scale effect is also different at different slope. In sunny slope, at the horizontal distance from slope top of 0-74 m、74 m to the bottom of the slope, the spatial scale effects of stand volume increased 81.98 m3·hm-2 and decreased 20.81 m3·hm-2, respectively. In semi sunny slope, at the horizontal distance from slope top of 0-189 m、189 m to the bottom of the slope, the spatial scale effects of stand volume increased 49.41m3·hm-2 and decreased 11.34 m3·hm-2, respectively.(3) The correlation of the radial growth of trees and climate, and the slope changes and scale effect of annual ring widthThe radial growth of trees was affected by precipitation and temperature, and the correlation between the radial growth of trees and the precipitation is larger than that of the temperature, and a significant positive correlation with the previous year’s precipitation in December, and the year before September and the positive correlation coefficient is larger in October.Tree ring width index were different between two slopes, described with flat water years, wet years and dry year, respectively. In sunny slope, the slope averages of annual ring width index in the three different precipitation were 1.08,1.28,0.79, the variation range were 1.00～1.28,1.25～1.32,0.61～0.92. In semi-sunny slope the slope averages were 1.08、1.39、0.76, the variation range were 1.00～1.15,1.21～1.50, 0.65～0.93, respectively.On the two slope, there were differences in the width index of trees in different precipitation years. In flat water years and wet years, on two slopes, the radial growth of trees decreased with the increase of the horizontal distance from slope top, and the radial growth of the two slope at the dry year increased with the increase of the horizontal slope length.In different precipitation years, the spatial scale effects of the tree ring width index on the two slopes are also different. In the sunny slope, the ring width index of flat water years in the spatial scale effects of the slope decreased 0.10, the spatial scale effect of wet water years in the 0-130 m,130 m to the bottom of the slope at the level of the horizontal slope length respectively decreased 0.03 and increased 0.01, ring width index of dry year in the spatial scale effect of the whole slope increased 0.12; In the semi-sunny slope, the ring width index of flat water years in the 0-74m,74 m to the bottom of the slope at the level of the horizontal slope length decreased 0.01 and increased 0.04, respectively, the spatial scale effect of annual growth ring width index of wet year in the 0-192 m,192 m to the bottom of the slope at the level of the horizontal slope length respectively decreased 0.02 and increased 0.02, ring width index of dry year in the spatial scale effect of the whole slope increased 0.03.In summary, the forest grow of Larix principis-rupprechtii in sunny slope was better than semi-sunny slope in the northwest semi-humid region. The difference of slope positions spatial scale effect of stand structure index and radial growth were different in different slope, and the spatial scale effect was different in different slope section. The main reason is different years, different slope’s hydrothermal condition different, and the nutrient and water along the slope redistribution caused by tree growth difference, and in different slope positions relative to the size of the relationship between changes. This indicated the complexity of tree growth slope changes and spatial scale effect. The results of this study can improve the forest resources survey, evaluation and management of forest ecological service precision, and more in-depth understanding of the slope scale effect growth index of trees.