Invasion of Savannas by Prosopis Trees in Eastern Africa: Exploring Their Impacts on Lulc Dynamics, Livelihoods and Implications on Soil Organic Carbon Stocks

Abstract

Abstract. Trees of the genus Prosopis from the Americas, were introduced in Eastern Africa in the 1970s to mitigate land degradation and its associated disservices. However, over time these trees have spread and invaded valuable grasslands and croplands and consequently led to significant land use and land cover (LULC) changes and livelihood stress. Early detection of invasive species is essential for formulating effective management strategies to prevent further spread into non-invaded lands and for monitoring the outcome of management interventions. We mapped the spatio-temporal evolution and dynamics of Prosopis invasion, its impacts on LULC and livelihoods in Baringo, Kenya by applying a Random Forest classifier on Landsat satellite data over seven-year intervals from 1988 – 2016. We then linked the LULC changes to soil organic carbon (SOC) stocks that we had measured for the different LULCs and also to socio-economic data on annual costs of clearing Prosopis from farmlands. By 2016, Prosopis had invaded 18,792 ha of land, spreading at a rate of 640 ha/yr, while all other land uses and land cover declined, each by over 40% of its original coverage in 1988. Through LULC specific SOC measurements, and relating the changes to annual costs of clearing Prosopis, we found that Prosopis removal and restoration to grassland is more effective for climate change mitigation compared to Prosopis “cultivation” while also avoiding trade-offs with other ecosystem services and livelihoods. Therefore, future management of this species in Kenya and Eastern Africa should be based on a more collaborative and integrated approach.

Management Strategies of Prosopis juliflora in Eastern Africa: What Works Where?

“…Besides Prosopis wood being a source of fuel, mature pods can be a valuable source of carbohydrates and proteins for livestock [80], and they can be processed to flour for human consumption. Studies by [41] showed positive relationships between Prosopis and soil properties. Thus, dense stands of Prosopis are associated with increases in soil carbon pools and increase soil phosphorus contents [73].…”

“…Within approximately 50 years, the shrub has invaded about 12% of the land in the Afar Region of Ethiopia [37] and over 550,000 ha of the land area in Somaliland [33,40]. The invaded area around Lake Baringo in Kenya has increased more than 200-fold between 1988 and 2016 [41]. In South Africa, Ref.…”

“…Prosopis can have a positive effect on some soil parameters. Thus, Prosopis can increase the availability of soil P, the amounts of K, Ca and Mg, possibly by nutrient pumping [59], total soil N by plant nitrate uptake from groundwater, N addition by biological N 2 fixation [49], and organic C from leaf litter fall [41]. Likely, implications of such soil improvement for potential future land uses remain elusive but require further research.…”