Patterns of seedling survival in the Tropical African tree Milicia excelsa

1999

English

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 O 30
cm DBH were found to be randomly dispersed and occurred at a density of o 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.

Nichols, J. D.; Agyeman, V. K.; Agurgo, F. B.; Wagner, M. R.; Cobbinah, J. R.