Omni-directional distribution patterns of montane coniferous forest in the Helan Mountains of China

Slope aspect has significant effect on the development and distribution of montane forest, especially in arid and semiarid regions. This paper, using SPOT5 images and 1:50,000 DEM, digitally extracts and analyzes the spatial information of montane coniferous forest (mainly Qinghai spruce), and thereby explores how the upper and lower limits and the altitudinal range of coniferous forest vary and how the area of coniferous forest is related with annual insolation with all aspects in the Helan Mountains. The results show that: 1) In the eastern flank, the lower limit of coniferous forest is between 1,600 m and 2,000 m a.s.l., and the upper limit between 2,800 m and 3,000 m a.s.l.; in the western flank, the lower limit of coniferous forest is between 2,000 m and 2,300 m a.s.l., and the upper limit between 2,800 m and 3,100 m a.s.l. 2) The altitudinal ranges of coniferous forest are 806 similar to 1,435 m, 438 similar to 1,140 m for eastern flank and western flank, respectively. 3) The area of coniferous forest takes on a normal distribution with aspect, and it has a close relationship with annual insolation. This distribution model developed in this paper quantitatively reveals the significant effect of slope aspect on the distribution of coniferous forest in arid and semi-arid land.