Spatial distribution and species composition of tree seeds and seedlings under the canopy of the shrub, Chromolaena odorata Linn., in Ghana

Abstract

The spatial distribution and species composition of tree seedlings and seeds under the canopy of the shrub, Chromolaena odorata Linn., were investigated at a 4 ha disturbed site that was surrounded by natural forests on two sides. For the seedling study, one hundred and eight 5 m 2 circular plots were established systematically (at 20 m intervals) with a random start point. For the seed bank study, soil samples were taken from 0.25 m 2 plots adjacent to 50% of the seedling plots at two depths (0–2 and 2–4 cm) and were germinated in a germination house. The study was conducted after the end of the seed dispersal season for tree species in the area. There were 11,780 seedlings ha −1 of 55 tree species growing under the woven canopy of C. odorata and 72% of the seedlings were economically valuable species. Tree seedlings as a whole were relatively uniformly distributed across the area but the distribution of individual species was very uneven. Some of the species were present only in 1% of the plots. Viable seeds of seven tree species were found in the soil seed bank with an average density of 46,000 seeds ha −1. The spatial distribution of tree seeds was very uneven across the site and only 39% of the plots contained tree seeds. C. odorata seeds in the soil seed bank were over 1600 times more abundant than tree seeds. No clear relationships were found between the density and species richness of tree seedlings or seeds and the distance (up to 260 m) from adjacent forest stands in the direction of prevailing wind during the seed dispersal season. The data suggest that the stock of tree seedlings represented an accumulation of seedlings established over several years.