EPOW - Ecology Picture of the Week

Left:  Pristine mopane woodland, Lupande Game Management Area.
Right:  Mopane forest degraded by elephants, South Luangua National Park.
Both photos from eastern Zambia.

Explanation:  Elephants are amazing creatures in so many ways.  Few other animals can so completely alter the structure and composition of entire forests. This week is a tribute to such amazing "key ecological functions" that African elephants perform in their ecosystems.  

Study the above two photos.  The left photo is of a pristine woodland of mopane trees (Colophospermum mopane) in Lupande Game Management Area of eastern Zambia.  Elephant numbers have been controlled in this area.

The right photo above is of a part of the adjacent South Luangua National Park, where an uncontrolled overpopulation of elephants in the 1960s-70s resulted in much of the native mopane forest being destroyed.  The current landscape is still recovering and in secondary successional stages with Acacia, Combretum,  and other shrub and tree species, with no mature mopane trees remaining.  

The elephants had taken down the mopane trees for food, creating openings of 1-5 acres (0.4- 2 hectares), and have since maintained the openings by continuing to eat the young shoots of the seedling mopane trees.  Burning also contributes now to maintaining the openings, which are used as latrine sites by native ungulates such as puku (Kobus vardonii) and other species.  

The pristine mopane forest harbors a number of mopane-specific wildlife species not found in the altered forest, such as the birds Racket-tailed Roller and Arnot's Chat.  The chat is actually an obligate secondary natural-cavity user in mopane forest; they occupy cavities often hammered out first by woodpeckers which are also absent in the altered forest. 

Thus, elephants are truly "ecosystem engineers" and, in sufficient numbers and densities, can radically alter the very structure and composition of their forests and influence which wildlife species occur there.  If left unchecked, either by natural or artificial factors, the elephants likely will continue to reduce the mature mopane forest cover (Duffy et al. 1999).  

References

Duffy, K.J., B.R. Page, J.H. Swart, and V.B.Baji.  1999.  Realistic parameter assessment for a well known elephant–tree ecosystem model reveals that limit cycles are unlikely.  Ecological Modelling 121(2-3):115-125.

Lewis, D., G.B. Kaweche, and A. Mwenya.  1990.  Wildlife conservation outside protected areas - lessons from an experiment in Zambia.  Conservation Biology 4(2):171-180.