Invader bush and the Namibian savanna

Wave a magic wand and nasty weeds become an energy crop. What's wrong with this picture?


Andrew Leonard
April 4, 2007 2:58AM (UTC)

Biopact informs us that Namibia has an innovative plan to deal with the "plague" of "invader bush" encroaching on the country's southwest African savanna pasturelands. Government officials hope to harvest the woody biomass as fuel for power generation, potentially restoring the savanna ecosystem and providing for all of Namibia's electricity needs in one masterstroke.

Biopact helpfully links to a 250-page study of the problem of Namibian "bush encroachment," funded by the Finnish government. The "Report on Phase I of the Bush Encroachment Research, Monitoring and Management Project" contains an astonishing amount of detail about Namibia's savanna ecosystems and the nasty, thorny, water-hungry bushes and trees that are sucking the lifeblood from the land. But there's one thing missing from the Biopact summary that is emphasized over and over again in the report: the identity of the culprits that made the dreaded bush invasion possible.

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A double whammy of over-grazing by cattle farmers in conjunction with the suppression of naturally occurring fires gave the invaders their opening. Typically, invasive species like the acacia varieties black thorn, blue thorn and (my favorite) false umbrella thorn make inroads on the savanna during drought years, capitalizing on the superior ability of their root systems to extract water from semi-arid land. But until midway through the last century, periodic high-intensity fires, whether started by lightning or indigenous peoples, cleared out the brush and allowed savanna grasses to reestablish themselves. But shortly after WWII, the government began aggressively engaging in fire suppression. Cattle farmers then responded by overstocking the land with livestock.

Why is this point worth highlighting? Because while I share Biopact's optimistic hopes that developing nations can invigorate their economies via judicious cultivation of energy crops, and I understand the attraction of transforming a nasty weed into an enlightening power source, we shouldn't lose sight of the depressing reality that it was human intervention that screwed up the eco-balance in Namibia, and unless we're extraordinarily careful, our "solutions" to the problems we've caused will only make matters worse. Suppose, for example, the electricity generation plan is a huge success, and there is suddenly a strong economic incentive to hack down all the acacia bushes currently making life so hard for cattle. Complete eradication of the invader bush, declares the bush encroachment report, would further destabilize the savanna.

Maintaining the right ratio of bush to savanna appears to be quite the tricky process, especially when the plan is to integrate the achievement of that balance with the maximum-possible level of commercial exploitation.

The good news, as one can discern from reading the bush encroachment study, is that we now know an amazing amount about how the savanna works. Scientists are unlocking the secrets of how different plant and animal species interact, their varying thirst for water and nutrients, and the mysteries of how climate, vegetation and humans interact (oh, and guess what, thorny invader bushes love greenhouse gases). In a perfect world, careful scientists working together with responsible government officials might be able to figure out just how much human commercial activity the savanna could bear, and put into effect policy recommendations that kept everything hanging together.

The report:

The potential wood available for harvesting varies between 10 and 20 tonnes per hectare in the different districts, and total yield is largely influenced by the prevailing invader species. Care needs to be taken that these considerations will not become more important than ecological considerations. Thus, harvesting should take place in accordance with ecological principles.

We can do it. We have the data. But can we be trusted to act accordingly?

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Andrew Leonard

Andrew Leonard is a staff writer at Salon. On Twitter, @koxinga21.

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