Prosopis upsurge in Kenya: Cause and effects

African dry lands were severely degraded by the prolonged sahelian droughts of 1970’s and rehabilitation through tree planting prioritized. In Kenya, species from the Prosopis genus were enlisted for screening because they had shown potential in rehabilitation of quarry mines (Maghembe et al 1983).

Project description

The introduced species included Prosopis chilensis (Mol.) St., Prosopis juliflora, Prosopis cineraria (L.) Druce., Prosopis pallida (Humb. & Bonpl. ex Willd.) Kunth and Prosopis tamarugo Phil. (Barrow 1980, Herlocker et al., 1980, Maghembe et al., 1983). From these and other efforts, P. chilensis and P.juliflora emerged as the most promising (Barrow 1980, Herlocker et al. 1980) and their seeds were sporadically exchanged across the country (Paetkau 1980), without a trace of provenance origins.

Introduction and distribution of Prosopis germplasm did not take cognisance of the invasive traits of the species’ as manifested in prolific seeding, seed dispersal through livestock and prolonged viability of seeds in the soil seed bank (Otsamo et al.,1993, Shiferaw et al., 2004), hybridization (Pasiecznick et al., 2001, Vega and Hernandez, 2005, Landeras et. al., 2006), allelopathy (Goel et al., 1989, Al-Humaid and Warrag, 1998, Rizvi et. al., 1999, Nakano et al., 2003) and root plasticity (Elfadi and Luukkanen, 2006). Prosopis invasions started becoming a reality, when the weedy potential of P julilora was first observed in the Tana Riparian Ecosystem in 1985, but its control was considered expensive and almost impossible because of its prolific seeding and seed dispersal by livestock (Otsamo et al.,1993). This lead to planting restriction in the Tana region but planting in other parts of Kenya continued unchecked. For example, in Turkana District, extensive planting of P.chilensis and P. juliflora continued up to early 90s, when rehabilitation projects were active. This and other related efforts in the country contributed to widespread planting of the species’ that are now considered problematic outside the rehabilitation areas (Choge et al., 2002), with the wetlands being single most critical ecosystems that are under threat.

Riparian ecosystems are the most common wetlands in drylands and are highly valued for socio-economic and ecological factors. National statistics project that drylands supports over 80% of the livestock, 90% of the wild game and 30% of the human population which are dependent on riparian ecosystem directly or indirectly. Surveys on Prosopis invasion have revealed potential malfunctions of these ecosystems through loss of pastures, farms, fishing grounds and replacement of indigenous plants (Ngunjiri and Choge, 2004, Anderson, 2005, Mwangi and Swallow, 2005). However, local communities have contrasting views on Prosopis invasion, with some perceiving it as a resource, while others consider Prosopis as problematic plants that should be eradicated.

This study would address invasion concerns by determining the diversity of Prosopis populations in Kenya, the attendant ecological and socio-economic impacts and develop methods for ascertaining the invasion extents. The study will contribute to current Prosospis initiatives in Kenya where policy is inclined towards management by utilization because of the obvious eradication constraints and the potential role of the species in the initial introduction objectives in specific areas.