Impact of Prosopis juliflora on Kenya's semi-arid and arid ecosystems and local livelihoods

Abstract

Prosopis juliflora or prosopis is a small, fast growing, drought-resistant, evergreen, tree of tropical American origin. Its pods can be used as livestock food and are fed upon by native herbivores. It has good timber and shade and quickly turns bare arid environments green. These qualities rendered it an attractive candidate for aridland environmental rehabilitation programmes. In the 80s and early 90s it was a preferred species in afforestation, fuel-energy and fodder programmes in Kenya's Turkana and Baringo districts and North Eastern Province. Prosopis however produces masses of pods containing small tough smooth seeds. When pods are eaten by livestock, seeds pass easily through the gut. Once in the soil, seeds can lie dormant for long, till good conditions return. Prosopis is deep-rooted and coppices well when cut above ground. These factors make it highly invasive and hard to control once established. Research was carried out to determine the spread of Prosopis juliflora over time in Kenya and its effect on livelihoods and biodiversity. It was evident that barely three decades since the first herbarium specimen was collected in 1977 from Coast Province, the species was now found in seven of Kenya's eight provinces. It was more aggressive in aridlands of the north where it formed thorny impenetrable thickets especially along water courses, flood plains, roadsides and in inhabited areas. It was encroaching upon paths, dwellings, irrigation schemes, crop farms and pastureland, significantly affecting biological diversity and rural livelihoods. Three sites, Baringo in the Rift Valley, Garissa between Coast and North Eastern Provinces and Loiyangalani in Eastern Province were chosen for detailed studies covering economic importance, perceptions, effect on biodiversity and what it would take to manage the spread of prosopis. Of the 18 positive attributes mentioned, charcoal making and fodder were most important. 24 negative attributes were mentioned. Of these, invasion of pastureland, cropland and homesteads was ranked first followed by the harmful effects of the thorns. The significance of each attribute however varied across and within the sites. In all three sites, there was significantly more plant diversity outside prosopis thicket than within it. The average labour cost of clearing a prosopis thicket 3-4 yrs old in a plot 10x10 m was found to range from Ksh 1000 (US$ 13) in Loiyangalani and Ksh 1200 in Baringo to Ksh 2,800 in Garissa. It was evident that in areas where prosopis was well established, it was beyond the community's ability to control its expansion. Prosopis invasion had reduced the capacity of pastoralists to keep large herds of livestock in affected areas. The impact among pastoralist communities has led to frequent lawsuits, pitting communities in Baringo District against government. Their source of livelihood undermined, they had turned to the very prosopis as a source of income, mainly poles, charcoal and pods. On perception, an overwhelming majority in all sites (64% in Garissa, 78.6% in Loiyangalani and 67% in Baringo) said life would be better without prosopis. Despite the stand of the affected local communities, the environmentalists, scientists and development workers were still divided on prosopis matters. Future scenarios indicated further expansion that will not only affect people's livelihoods but also key sectors of the economy such as tourism. It is evident that Kenya's vast arid and semi-arid lands totalling 80% of land area are at risk and the longer the wait, the more difficult it will be to control or eradicate the species. A comprehensive policy on prosopis is proposed.