Invasive wood put to good ecological use

The attractive wood of an aggressive alien invasive tree – the prosopis – is used for decking at Wilderness Safari camps throughout Namibia.

“This is not only extremely eco-friendly, but also provides a strong incentive to other lodges to seek alternative wood for floors and decking rather than use the traditional hardwoods harvested from diminishing forests around the world,” said a Wilderness spokesperson recently.

“You can walk over a prosopis decking with a clear ecological conscience, and lodge owners will be promoting the use of a destructive alien rather than other precious indigenous wood resources. The durability of prosopis decking is also likely to exceed that of decking made from traditional wood, which means that replacement intervals will be longer.”

This is a small start, says Wilderness, but with decking in such great demand, lodge builders will be encouraged to use the wood of this aggressive invasive tree. This, in turn, will decrease the destruction of many thousands of other trees that the planet so desperately needs.

Prosopis glandulosa, also known as the mesquite or honey locust, is a common and abundant alien tree in Namibia. Many even think that it’s an indigenous tree. However, mesquite grows in Namibia at a huge cost to the natural flora. It is, in fact, a highly aggressive alien invasive. The tree favours watercourses, disturbed soil around water points and farmsteads, roadsides and moist areas around natural fountains. In these areas the tree out-competes natural fauna and in central Namibia it displaces especially the camel-thorn, Acacia erioloba, and the sweet-thorn, Acacia karroo. Despite its invasive nature, this tree also has features that make it useful: It grows extremely rapidly, provides very dense shade, produces seedpods in great abundance, which are eaten by both animals and humans, and because of its rapid growth, produces a great deal of wood that has been used primarily as firewood to date.

However, the downside of this tree is that it literally strangles other natural plants out of existence. River courses in the central highlands and the linear river systems that carve westwards through the Namib become choked with prosopis at huge expense to slow-growing trees like the camel-thorn. The seeds that are ingested by almost all wildlife in the area are deposited around natural seeps, where the new prosopis growth literally sucks the seeps dry within a few months. In the Khan and Swakop rivers, this has changed the natural ecology of the dry watercourses and resulted in a shift of wildlife populations.

Prosopis does, however, have one other positive feature. Its wood is extremely stable, relatively hard and very attractive when cut. All this explains why it makes such good firewood, producing coals that rival those of any acacia wood. Large prosopis trees, many probably the ancestors of the alien invasive prosopis, also have large enough trunks and branches for planks. Herein probably lies the best use for this tree.

This article appeared in the Aug/Sep ‘07 edition of Travel News Namibia.