Abstract:

Medicinal root plants often produce a continuous crop obstacle due to allelopathy during cultivation. Apocynaceae plants are important medicinal plants belonging to tropical flora. Allelopathy is one of the major causes of density dependence. To explore whether density dependence likely exists in root type medicinal plants under natural conditions, we analyzed the species distribution and spatial intraspecific and interspecific correlations of two root medicinal plants of Apocynaceae (Alstonia rostrata and Tabernaemontana bufalina), using a point pattern analysis of pair correlation function Ripley’s g(r) method with complete spatial randomness (CSR) and heterogeneous Poisson (HP). The impacts of topographic factors on the distributions of the two species were analyzed using a Berman-test. Results showed that the spatial patterns of the A. rostrata and T. bufalina were mainly aggregated at 0-100 m scales, while the former’s spatial pattern was still aggregated and the latter became a random pattern within this scale. The spatial patterns of A. rostrata and T. bufalina changed similarly with increases in age stage, as young and middle-aged trees showed aggregated distributions within a larger scale, while adult trees became randomly or uniformly distributed. The spatial association between different age classes individuals of A. rostrata showed that the relationship between young and middle-aged trees was positively associated at the small scale, while it was negatively associated between young and adult trees, and there was no association between middle-aged and adult trees. Positive associations were found between different age classes individuals of T. bufalina within the larger scale (0-65 m), which indicated that different DBH class individuals were consistent with environmental selection. Interspecific associations between A. rostrata and T. bufalina showed positive associations at 0-49 m scale. The spatial association between middle-aged, adult trees of A. rostrata and similarly aged trees of T. bufalina showed no significant correlation, while obvious positive spatial correlation was found between young trees of these two species. Significant positive correlation was found between young trees of these two species and elevation and convexity. We also found significant positive correlations between convex and middle-aged trees of these two species, while only adult trees of A. rostrata showed positive correlation with the degree of slope. We inferred that environmental heterogeneity and diffusional limitation played important roles in the formation of current spatial patterns of woody Apocynaceae in the tropical montane rainforest of Jianfengling, while compared to T. bufalina, density dependence plays a more significant impact on the spatial patterns of A. rostrata.

Key words: Alstonia rostrata, Tabernaemontana bufalina, root medicinal plants, allelopathy, interspecific association, Jianfengling