Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5742532 | Acta Oecologica | 2017 | 10 Pages |
The hypothesis that African elephants may cause the local extirpation of selected woody species was evaluated in a medium-sized, semi-arid reserve following their reintroduction at low density. Mortality, state-change, and regeneration of 25 tree and 17 shrub species were studied between 1997 and 2010. Annual mortality of shrub species ranged from 0.2 to 8.0%, with six species experiencing 6-8%. Eight shrub species lost more than half their adult population (range 10-94%). Annual tree mortality ranged from 0.2 to 10.5%. The two dominant dryland tree species experienced <1% annual mortality, 18 species lost more than half their tree population, and one was eliminated. Elephants accounted for >63% and stress-related agents >20% of tree deaths. The manner in which elephants induced tree death depended on species. The proportion of individuals of a species killed by pollarding or uprooting ranged from 0 to 74%, and by debarking from 0 to 100%. Complete uprooting was a common cause of death for three shrub species. Regeneration ranged from zero for six tree and one shrub species to a seedling every 7Â m2 for Colophospermum mopane and 23Â m2 for Dichrostachys cinerea in riparian habitat. Three shrub and eight tree species were identified as vulnerable to local extirpation owing to a combination of high mortality and poor regeneration that is likely to result in a considerably simplified system. Reintroduction of elephants into medium-sized reserves without regulation of their numbers may not be a desirable action.