Abstract:

Topography is a primary factor that creates microenvironmental heterogeneity in a landscape. In previous studies, topographic factors, such as slope and aspect, were measured as discrete data and had limited use in analyses. In this paper, a digital elevation model (DEM) was used to analyze the influence of topographic heterogeneity on the distribution patterns of woody plants at the community level by calculating digital topographic values and creating a digital description of the landform. The establishment of a DEM can be generalized in three steps: 1) gathering the topographic data; 2) data adjustment & interpolation; and 3) displaying the data. To illustrate this process, a DEM was built based on a 0.96 hm 2 permanent forest plot in the Shennongjia area (31°19′4″ N, 110°29′44″ E). The forest was dominated by Fagus engleriana and Cyclobalanopsis oxyodon. Topographic data were gathered when the plot was established. A total of 425 sample points were mapped by elevation. An inverse distance weighted method was used to interpolate data between points. Using Arcview GIS software, the slope and aspect of all 425 points within the plot were calculated. The slope varied from 18.2 to 74.6 degrees in the 0.96 hm 2 plot. The precision of the DEM was 0.4 m. Using the DEM, the slope and aspect of every point within the permanent plot were calculated and these topographic factors were then used to analyze species distribution patterns. Twenty-four species were chosen to calculate their correlations with slope, aspect and position. The positive and negative correlations with the slope, aspect and position were 7, 7, 6, 3, and 8, 5 respectively. One problem of using a DEM at small scales is related to the difficulties associated with the collection of the original data. Under the forest canopy, it was difficult to gather topographic data using GPS, remote pictures or other automated tools. To achieve the required precision, all topographic data were acquired using a compass, which limited the scale at which the analysis could be conducted. Although improvements are needed in this method, the DEM provided a lot of information and was a convenient method for analyzing species distributions in relation to topographic factors. Because remote sensing cannot provide a detailed description of species distributions within forest communities, such research should be combined with the establishment of permanent plots.

Key words: Slope, Aspect, DEM, Species distribution, Shennongjia