Distribution and socio-ecological impacts of the invasive alien cactus Opuntia stricta in eastern Africa

Ross T Shackleton,Francis M Piroris,Brian W Van Wilgen,Arne B R Witt

doi:10.1007/s10530-017-1453-x

Ross T Shackleton, Francis M Piroris + Show 2 more

Open Access

https://doi.org/10.1007/s10530-017-1453-x

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Abstract

Many cactus species have been introduced around the world and have subsequently become major invaders, inducing social and ecological costs. We recorded the distribution of Opuntia stricta in eastern Africa, and conducted 200 household interviews using semi-structured questionnaires to assess local perceptions of O. stricta in Laikipia County, Kenya. Opuntia stricta was widespread and abundant in parts of Kenya, Tanzania and Ethiopia and present at low densities in Uganda. In Laikipia County, pastoralists identified that O. stricta had been present for more than 10 years, and were of the opinion that it was still spreading and increasing in density. Two-thirds of respondents estimated that 50–75% of valuable grazing land had been invaded, and all felt that it contributed to the ill-health and death of livestock. Other negative impacts included reductions in native plant populations, rangeland condition, human health, and mobility of humans and animals. These negative impacts resulted in economic losses of US$ 500–1000 per household per year for 48% of households. Only 20% of respondents reported actively managing O. stricta, yet all respondents believed a reduction in the abundance of this weed would improve well-being. Management interventions are needed to reduce negative impacts.

Highlights

General introductionThousands of plant species have been introduced to countries around the world, both accidentally and intentionally for a host of reasons, including agriculture, forestry, and ornamental purposes (Mack 2003)
Opuntia stricta was found to be present in Ethiopia, Kenya, Tanzania, and Uganda but was not found in Rwanda (Fig. 1; Table 1)
Opuntia stricta var. stricta was found to be widespread and abundant in eastern Ethiopia, especially between and around Alemaya and Jijiga, where it was often found to be growing in semiarid rangelands and on rocky outcrops in association with O. ficus-indica (L.) Mill

Summary

Introduction

General introductionThousands of plant species have been introduced to countries around the world, both accidentally and intentionally for a host of reasons, including agriculture, forestry, and ornamental purposes (Mack 2003). It is estimated that there are over 751 invasive trees and shrub species globally (Rejmanek and Richardson 2013) These biological invasions are a major component of global change, and they cause numerous negative impacts on biodiversity, ecosystem services, and human well-being (Pimentel 2002; Simberloff et al 2013). The impact of invasive alien species can often be reliably gauged through an assessment of local knowledge (Chalmers and Fabricius 2007; Sundaram et al 2012) Such assessments can be valuable in areas where information on impacts is virtually absent, for example in Africa and Southeast Asia (Nunez and Pauchard 2009). More than 25% of people identified that the three primary areas that O. stricta invades are near rivers, homes and on hills/mountains (which are the most valuable grazing areas), while

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