Forest tree persistence, elephants, and stem scars
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Sheil, D., Salim, A. 2004. Forest tree persistence, elephants, and stem scars . Biotropica 36 (4) :505-521. ISSN: 0006-3606.
Permanent link to cite or share this item: http://hdl.handle.net/10568/19089
External link to download this item: http://www.cifor.org/nc/online-library/browse/view-publication/publication/1654.html
Sixteen percent of tree stems 10 cm diameter or greater recorded in seven 1 ha plots in Rabongo Forest, Uganda had stem damage attributable to elephants (Loxodonta africana). We propose four strategies that may help tree species persist under these conditions: repellence, resistance, tolerance and avoidance. We sought and found evidence for each strategy. Large, shade-tolerant Cynometra alexandri dominated basal area (often >50%) and showed severe scarring. Nearly 80 percent of stems were small pioneer species. Scarring frequency and intensity increased with stem size. Stem-size distributions declined steeply, implying a high mortality to growth rate ratio. Tree species with spiny stems or with known toxic bark defenses were unscarred. Epiphytic figs escaped damage while at small sizes. Mid-successional tree species were scarce and appeared sensitive to elephants. Savanna species were seldom scarred. Taking stem size effects into account by using a per-stem logistic modeling approach, scarring became more probable with slower growth and with increasing species abundance, and also varied with location. Pioneer and shade-bearer guilds showed a deficit of intermediate-sized stems. Evidence that selective elephant damage is responsible for monodominant C. alexandri forests remains equivocal; however, elephants do influence tree diversity, forest structure, and the wider landscape.
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