Establishment of Fitted Models for Topographical Factors and Coexisting Plants Influencing Distribution of Natural Wild Jujube

Fitting mathematical models to describe the influence of topographic factors and coexisting plants on wild jujube distribution was performed to provide a scientific basis for wild jujube forestation. Investigation quadrats, with straight-line distances between adjacent quadrats of longer than 100 m, were set up in areas of wilderness or low human disturbance, which were rich in wild plant species. Data concerning altitude, slope aspect, slope position and slope degree of each investigation quadrat, as well as the type and number of coexisting wild plants, were collected. Based on this, correlations with the average number, occurrence probability and density of wild jujube and these variables were analyzed, and data models were established. Results of analyses show that topographic factors such as altitude, aspect, gradient, slope and position, play an important role in the distribution of wild jujube; and that Vitex negundo var. heterophylla (Franch.) Rehd. coexistence is related to wild jujube distribution. Both average number and occurrence probability of wild jujube conform to a GaussAmp model with altitude. The highest average number was recorded at 581.24 +/- 13.78 m above sea level, and the highest occurrence probability at 462.53 +/- 36.67 m above sea level. Average number and occurrence probability of wild jujube were fit to a linear model with slope aspect-with mathematical slope 0.49 +/- 0.16-indicating that wild jujube is a light-loving and drought-tolerant plant. Average number and density of wild jujubes were fit to GaussAmp models with slope position. The highest average number and the highest density of wild jujube appears on the upper part of the middle slope. Wild jujube occurrence probability was correlated to slope degree in a quadratic equation model. With an increase in slope degree, the distribution number of wild jujube increased sharply. The survey data of slope position and slope degree further reinforced the observed drought-resistance qualities of wild jujube. Average number and density of wild jujubes were correlated to the number of Vitex negundo var. heterophylla by quadratic equation models. No other plants investigated conformed to a statistically significant relationship with wild jujube distribution. Our results suggest altitude, slope aspect, slope position and slope degree play an important role in wild jujube distribution, and that Vitex negundo var. heterophylla is an important coexistent plant species for wild jujube.