Forest Tree Persistence, Elephants, and Stem Scars

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.