海南尖峰岭热带山地雨林2种夹竹桃科植物的空间分布格局与关联性 / Spatial distribution patterns and association of two Apocynaceae plants in the tropical mountain rainforests of Jianfengling, Hainan Island, China
根类药用植物在生产栽培过程中常产生连作障碍, 原因之一是其容易产生化感作用, 而化感作用是密度制约产生的主要原因之一。夹竹桃科植物是重要的药用植物, 也是热带植物区系的主要科。为探究自然条件下密度制约是否存在于根类药用植物中, 本文以海南尖峰岭60 ha森林动态监测样地中两种常见的夹竹桃科根类药用植物盆架树(Alstonia rostrata)和尖蕾狗牙花(Tabernaemontana bufalina)为研究对象, 采用点格局分析的成对相关函数Ripley’s g(r), 结合完全随机零模型和异质泊松零模型, 分析了它们的空间分布格局、种内和种间空间关联, 并采用Berman-test方法分析了地形因子对其种群分布的影响。结果表明: (1)盆架树和尖蕾狗牙花在0-100 m的研究尺度上主要表现为聚集分布, 但随着尺度的增大, 聚集程度降低, 逐渐变为随机分布。(2)盆架树和尖蕾狗牙花各龄级的分布特征类似: 幼树和中龄树个体在较大尺度范围内为聚集分布, 而成年树个体在0-100 m尺度上为随机分布或均匀分布。(3)在小尺度上, 盆架树的幼树与中龄树呈空间正关联, 与成年树呈空间负关联, 而中龄树与成年树空间无关联。尖蕾狗牙花各龄级间在0-65 m的尺度范围内以空间正关联为主。(4)在0-49 m尺度内盆架树与尖蕾狗牙花呈显著空间正相关。盆架树的中龄树和成年树与同龄级的尖蕾狗牙花都表现为空间无显著关联, 而幼树与尖蕾狗牙花幼树存在明显的空间正关联。(5)盆架树和尖蕾狗牙花幼树的分布与海拔、凹凸度显著正相关, 中龄树的分布与凹凸度显著正相关, 而成年树中只有盆架树的分布与海拔正相关。从现有格局推断: 生境异质性和扩散限制影响盆架树和尖蕾狗牙花空间格局的形成, 相对于尖蕾狗牙花, 密度制约对盆架树空间格局形成的影响更显著。
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.