Analysis on mountain forest distributional variation with slope aspects in the northern flank of the central Tianshan Mountains

Abstract:

Slope aspect has an important effect on spatial distribution of forest. As for forest on Tianshan Mountains, previous studies have focused mainly on the simple comparison between northern flank and southern flank in macro scale. However, there is little quantitative analysis on the distribution of mountain forest varying with slope aspects in local scale in northern flank. This paper explores how the upper and lower limits of altitude and the area of mountain coniferous forest vary with aspect in the northern flank of the central Tianshan Mountains. The spatial information of mountain coniferous forest and slope aspects are extracted respectively from SPOT5 image and 1:50,000 DEM. The results are shown as follows: (1) 98.6% of coniferous forest distribute from 1500 to 2700 meters above sea level. The average upper and lower limits of altitude of mountain coniferous forest are respectively 2730m and 1519m. The forest area has a U shaped pattern along 0-360˚ slope aspects. The area of forest on the shady slope is largest while on the sunny slope is smallest and this distribution is similar to that in macro scale. The area of forest on the western slope is larger than on the eastern slope. (2) The upper and lower limits of altitude of mountain coniferous forest vary little with aspects. The upper limit of altitude is slightly higher on the eastern slope and slightly lower on the western slope. The highest upper limit of altitude of forest is 2790m on the eastern slope while the lowest upper limit of altitude is 2691m on the western southwestern slope. There is no significant exposure effect on treeline elevation in local scale, which is different from that in macro scale.(3) The forest area near the climatic tree line also has a U shaped pattern along 0-360˚ slope aspects, but there is a difference that the area of forest near tree line on the eastern slope is larger than on the western slope, which suggests eastern slope is more suitable for treeline update.