The perfect storm: Land use change promotes Opuntia stricta's invasion of pastoral rangelands in Kenya

The process of alien plant invasion is complex and multidimensional. Opuntia stricta (var stricta), is one of the world's most invasive plants but evidence for the invasion process is limited to historical reconstruction and experiments. Here, we present data on the landscape spread of O. stricta into a high altitude dry savanna on the Laikipia Plateau of Kenya. Factors like species characteristics, ecosystem dynamics, habitat susceptibility, and system context are implicated. We propose that the current invasion, 50 years after the plant arrived in the area, is not the result of a lag phenomenon but instead is a response to recent changes in land use primarily sedentarization of pastoralists. Subsequent continuous heavy livestock grazing produced an ecological state transition to degraded rangeland which created the opportunity for the invasion. Thereafter, the special characteristics of O. stricta, the number of mammalian consumers, and additional anthropogenic changes fueled the process. These data strengthen existing evidence that change in land use provides opportunities for alien plant invasions. This Kenyan case illustrates the challenges posed by humanization of ecosystems and suggests why it is important to look at the underlying causes of alien plant invasions, not just deal with the symptoms. (C) 2015 Elsevier Ltd. All rights reserved.