Intact island forest in the desert

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Lawrence Wagura weighing a bird caught in a mist net on the Mathews Range. Photo/Rupi Mangat

Lawrence Wagura weighing a bird caught in a mist net on the Mathews Range. Photo/Rupi Mangat 


Posted  Friday, November 1   2013 at  15:29

In Summary

  • Little-known mountain range in northern Kenya home of long term research in forest dynamics.

I accompany Dr Luca Borghesio into the mountain range the local Samburu called Ol-Doinyo Lenkiyieu — now called the Mathews Range.

Dr Borghesio, a biologist and an associate researcher with the National Museums of Kenya, has been studying mountain forests including globally threatened species of birds for the past two decades in Kenya, Tanzania and Ethiopia.

Interested in forests, Borghesio is carrying out a long term study on changes in the Mathew Range forests. He’s been recording data in the range for six years. The range has no access roads beyond the forest at 5,000 feet, and is little touched by human hand, making it one of the most intact forests left in Kenya – virtually an island forest in the desert.

Strolling through one of the plots marked for monitoring, with mist nets strung across it, Borghesio points to the endemic cycad, Encephalarctos tegulaneus, dubbed the “living fossil.” This ancient plant can withstand fire, and growing barely five millimetres a year, a 15-foot-cycad is several hundreds of years old.

The Mathews Range also boasts the only species of cactus indigenous to Africa, Rhipsalis baccifera, and in a departure from the normal cactus, this one grows like an epiphyte on the higher branches of trees.

“People tend to think of forests as never changing,” said Borghesio. “But forests change a lot and quite fast.”

Sunlight pours through gaps created by ancient trees crashing at the end of their lives, bringing down other trees with them. Voracious safari ants march through the litter of leaves and dead trees. Elephant dung shows a healthy population, but the black rhino — the last known free ranging ones of the north — died out in the late 1990s.

“A century ago, this was more open because the elephant and rhinos ate the bush. With the demise of the herbivores, the land that was more grassland is more bush now,” Borghesio said.

He begins his narration of the forest with a time in the distant past, when it was more open, stimulating the germination of light-demanding trees such as Cordia and Croton.

More than a century later, these trees have grown to remarkable sizes. “Based on this, we can speculate that the forest at that time was kept more open by higher densities of wildlife,” he said.

Soaring to the heavens, the towering Croton trees seem healthy, but the scientist and his team of field assistants and Samburu aides recognise the signs of stress and the major die-back caused by the drought of 2009.

“The trees survived the drought, but in the following years we saw the death of large trees at a rate above normal. The effect of drought can go on for many years,” continues Borghesio.

Northern Kenya is mostly arid with little rainfall. “There were droughts in 2004, 2009, 2010 and 2011. What we’re seeing is increasing droughts in the past 10 years whereas prior to that the droughts occurred once every 10 years.”

Lawrence Wagura, the field assistant, carefully untangles a Yellow-whiskered Greenbul from the mist net to record the ring around its foot. From the data collected over the past six years, bird numbers have been fluctuating.

“With frugivores like Yellow-whiskered Greenbul, numbers will fluctuate from year to year depending on the availability of fruit,” explains Borghesio. “These are not new birds because we’re seeing them after two years. But for the Abyssinian ground-thrush, which is very territorial and moves little inside the forest, things are tough, showing an 80 per cent decrease in eight years. What we’re seeing now are non-forest bird species increasing in number, like the Grey-backed Camaroptera, a widespread bird outside the forest whose population has increased following a series of droughts.

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