Variation in seed rain from Widdringtonia whytei growing in different conditions on Mulanje Mountain in Malawi

Abstract

Mulanje Mountain is one of the examples of tropical montane landscapes with plant populations varying in size from small fragments of less than 1 ha to riverine strips and stands of more than 100 ha. Seed availability is a potential limiting factor in vegetation recovery in such landscapes. Field observation on seed rain and seed limitation was conducted in 2008 and 2009 in three sizes of forest fragments at three sites on the mountain to investigate: (1) whether size of Widdringtonia whytei forest patches influences seed-rain density; (2) whether W. whytei seed rain occurs in a specific season; and (3) if seed limitation differs from within forest patches to the adjacent non-forest patch habitats. The results showed that there was a distinct difference in seed-rain density among fragments where large fragments (>20 trees) collected higher seed-rain density (10.4 ± 0.9 seeds m^-2 y^-1) than small fragments (1.1 ± 0.4 seeds m^-2 y^-1). The seed-rain density differed significantly between 2008 (2.1 ± 0.6 seeds m^–2 y^-1) and 2009 (6.1 ± 1.1 seeds m^-2 y^-1). Seed rain was recorded every month of the year but the densities were not significantly different among months. Seed-rain density was highest inside the forest fragments (12.04 ± 2.3 seeds m^-2 y^-1) and decreased drastically and very significantly at the edges (1.0 ± 0.8 seed m^-2 y^-1) and outside the forest fragments (0.11 ± 0.1 seed m^-2 y^-1). Seed limitation was strong (0.98) on all sites; 0.95 in large fragments and 0.99 in medium and small fragments, respectively. Therefore, it can be concluded from this study that the presence and retention of more seed trees ensures the continued availability of W. whytei seed on the forest floor within the context of limited seed dispersal.

Keywords: Widdringtonia whytei, Mulanje Mountain, seed rain, seed limitation

Southern Forests 2011, 73(3&4): 123–129