Restoration of degraded grasslands, but not invasion by Prosopis juliflora, avoids trade-offs between climate change mitigation and other ecosystem services

Abstract

Grassland degradation and the concomitant loss of soil organic carbon is widespread in tropical arid and semi-arid regions of the world. Afforestation of degraded grassland, sometimes by using invasive alien trees, has been put forward as a legitimate climate change mitigation strategy. However, even in cases where tree encroachment of degraded grasslands leads to increased soil organic carbon, it may come at a high cost since the restoration of grassland-characteristic biodiversity and ecosystem services will be blocked. We assessed how invasion by Prosopis juliflora and restoration of degraded grasslands in a semi-arid region in Baringo, Kenya affected soil organic carbon, biodiversity and fodder availability. Thirty years of grassland restoration replenished soil organic carbon to 1 m depth at a rate of 1.4% per year and restored herbaceous biomass to levels of pristine grasslands, while plant biodiversity remained low. Invasion of degraded grasslands by P. juliflora increased soil organic carbon primarily in the upper 30 cm and suppressed herbaceous vegetation. We argue that, in contrast to encroachment by invasive alien trees, restoration of grasslands in tropical semi-arid regions can both serve as a measure for climate change mitigation and help restore key ecosystem services important for pastoralists and agro-pastoralist communities.

Prosopis juliflora management and grassland restoration in Baringo County, Kenya: Opportunities for soil carbon sequestration and local livelihoods

“…The flats are dominated by rangeland and deciduous shrubland-a woody mixture of indigenous Vachellia species and exotic species. The main livelihood strategies in the study are pastoralism, agro-pastoralism, farming and charcoal production (Linders et al, 2020).…”

“…Cumulative SOC content in the top 1m was determined in 10-17 plots in each of the five LULC categories (63 plots in total) as described by Mbaabu et al (2020; Appendix S1 in Supporting Information for details). In short, four 1-m deep soil cores were taken in one 15 × 15 m plot per location (Kutsch et al, 2009; Lal, no date).…”

“…The costs of manual Prosopis removal and grassland restoration by sowing of native grasses, as well as the resulting benefits in terms of changes in SOC and cattle number and income from charcoal F I G U R E 1 Prosopis invasion between 1995 and 2016 in nine sublocations in Baringo County, Kenya TA B L E 1 Mean and standard error (SE) of SOC measured to 100 cm depth (Mbaabu et al, 2020) . Land size was not considered in the budget as land tenure in the region is mixed and many households do not own, use or manage a defined piece of land.…”

“…The results of two recent studies suggest that restoration or protection of grasslands is likely to benefit SOC content, fodder availability and biodiversity, and, consequently, peoples' livelihoods (Bekele, Haji, Legesse, Shiferaw, et al, 2018;Linders et al, 2020). The studies further revealed that people were very willing to invest money or time in managing Prosopis (Bekele, Haji, Legesse, Shiferaw, et al, 2018).…”

“…Impacts on stakeholders differ, depending on their main livelihood and on the ecosystem services they rely on. However, by reducing the availability of grassland, Prosopis invasion is threatening the traditional way of living of large numbers of people (Linders et al, 2020). These and other trade-offs associated with Prosopis invasion must be considered when assessing its impacts and implications for its management and related policies.…”