Patterns of seedling survival in the tropical African tree Milicia excelsa
Patterns of seedling survival in the tropical African tree Milicia excelsa
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热带非洲树 Milicia excelsa 幼苗的存活模式
DOI：
10.1017/s0266467499000942
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发表时间：
1999
影响因子：
1.4
通讯作者：
J. Cobbinah
中科院分区：
文献类型：
--
作者：
J. Nichols;V. Agyeman;F. B. Agurgo;M. Wagner;J. Cobbinah
研究了非洲热带乔木Milicia excelsa冠层树和幼苗生命阶段的空间格局，以检验Janzen-Connell假说（逃逸假说）。Janzen-Connell假说指出，同一物种的种子和幼苗的死亡率在成年树附近最高，并随着远离成年树而下降。这一假说认为，这种效应是维持热带森林高树种多样性的部分原因。太阳辐射和水果传播进行了调查，作为可能的解释所观察到的模式在幼苗分布。胸径≥30 cm的糜子树呈随机分布，密度≤1 hm 2。Milicia excelsa幼苗位于母树之间的小丛中，距离母树150 m，平均密度为65株幼苗ha−1。在雌树下有大量的水果（地面上有超过9000个）。天然幼苗所在位置的光照水平为全辐照度的2-29%。种植的幼苗没有遭受更大的死亡率更接近成年同种，并在2-37%的全辐照度之间的光照水平下存活。商陆属，在任何天然或种植的幼苗上都没有观察到在大开口和种植园中的米利西亚幼苗中引起高死亡率的形成瘿的木虱，尽管在优势树木的树冠中存在瘿。
The spatial patterns of canopy tree and seedling life stages in the African Tropical Tree Milicia excelsa were examined to test the Janzen–Connell hypothesis (escape hypothesis). The Janzen–Connell hypothesis states that the mortality of seeds and seedlings is highest near the adult tree and declines with distance away from the adult tree of the same species. This hypothesis argues that this effect is partially responsible for maintaining the high tree species diversity of tropical forests. Solar radiation and fruit dispersal were investigated as possible explanations of observed patterns in seedling distribution. Milicia excelsa trees ≥30 cm DBH were found to be randomly dispersed and occurred at a density of ≤1 ha. Milicia excelsa seedlings were located in small clumps between parent trees and up to 150 m from parents at a mean density of 65 seedlings ha−1. Fruits were in abundance (>9000 on the ground) beneath female trees. Light levels at locations of natural seedlings ranged from 2–29% of full irradiance. Planted seedlings did not suffer greater mortality closer to adult conspecifics, and survived at light levels between 2–37% of full irradiance. Phytolyma spp., gall-forming psyllids which cause high mortality in Milicia seedlings in large openings and plantations, were not observed on any natural or planted seedlings, although galls were present in the crowns of dominant trees.