The tree’s coverage in the lowlands of Baringo County rose from 882 hectares in 1988 to 18,792 hectares in 2016, according to a study by Mbaabu and colleagues published in Remote Sensing . We have all been there where we tried solving one problem but created a much larger one. That is what has happened in parts of Kenya. The mathenge tree was planted to hold back desertification. For herder John Lmakato, the spread of mathenge trees indirectly cost him most of his livestock, as he tells it.
In the Mbaabu study, the tree was introduced in Baringo district in the 1980s. The damage goes beyond lost grass. John Lmakato lives at Lerata, a village at the base of Mount Ololokwe in Samburu County. He recalls a time when the rangelands were covered with grass, and his animals roamed free. And so his animals had to travel farther for grass. A few years ago, his cattle wandered into a conservation area in Laikipia, an area known for conflicts over land access between Indigenous pastoralists and commercial ranchers. The trees did not kill the animals directly; the search for grass is what pushed his herd into that conflict zone. The authors describe it as a key driver of those changes. Many animals die after feeding on the weed. Mathenge has sharp thorns that can injure animals’ feet, and its seeds can damage their teeth. For families dependent on livestock, these problems add up fast.
He lost 193 cattle. Only seven of the 200 he once owned are still around. Researchers analyzed Landsat satellite images taken every seven years from 1988 to 2016. Its cover increased from 882 to 18,792 hectares, more than 20 times its original size. The study’s satellite record ends in 2016, so these figures do not show the tree’s current spread. They also found the tree responsible for over 30% of the negative land cover changes in the study area. The Kenya Forestry Research Institute estimates that mathenge has encroached on about 2 million hectares across Kenya, spreading by up to 15% a year. Modeling by researchers puts the invaded area lower, at 7,000 to 12,000 square kilometers (0.7 to 1.2 million hectares), so estimates differ. Its deep roots, which can reach up to 35 meters underground, deprive other plant life of water.
Now, he says, the land is overgrown with mathenge trees and cattle cannot eat them. Some of his cows, he says, were shot dead.
University of Bern researchers estimate that about three-quarters of Kenya, roughly 450,000 of 580,000 square kilometers (closer to 77 percent by those figures), has conditions suitable for mathenge. A 2020 Ecosphere study by Eckert and colleagues points in a similar direction. One project in Samburu, where more than 95% of people use firewood or charcoal for cooking, turns mathenge wood into briquettes.
Its models revealed that large areas of Eastern Africa not yet invaded by the tree are suitable now, or will become suitable with climate change. Risk does not mean the tree already grows everywhere; it means conditions there could support it. The authors also say that the tree may have begun to adapt to new climate conditions. That’s a possibility, not a certainty. The Baringo study authors say the tree needs more integrated management. Eckert and colleagues add that their methods can help inform policy and management. Some groups are also trying to turn the problem into an opportunity. This eases pressure on native trees and creates a new source of income. The larger lesson is simple. Quick fixes can create new problems, so long-term planning matters.
