Evaluating the cost-effectiveness of invasive alien plant clearing: A case study from South Africa Matthew M. McConnachie a,⇑ , Richard M. Cowling a , Brian W. van Wilgen b , Dominic A. McConnachie c a Restoration Research Group, Centre for Invasion Biology, Department of Botany, Nelson Mandela Metropolitan University, Port Elizabeth 6031, South Africa b Centre for Invasion Biology, CSIR Natural Resources and the Environment, PO Box 320, Stellenbosch 7599, South Africa c Technology and Policy Program, Massachusetts Institute of Technology, Cambridge, MA 02139, USA article info Article history: Received 21 January 2012 Received in revised form 1 June 2012 Accepted 5 June 2012 Available online 17 July 2012 Keywords: Ecological restoration Biological invasions Ecosystem services Adaptive management Pest control Public works abstract Conservation projects spend billions of dollars clearing invasive alien plants, yet few studies have mea- sured the cost-effectiveness of doing this, especially over larger spatial and temporal scales, relevant to operational contexts. We evaluated the cost-effectiveness of South Africa’s national invasive alien plant control programme, Working for Water, in reducing invasive alien plant cover in the Krom and Kouga river catchments over 7 years. We assessed change in invasive alien plant cover by comparing post-treat- ment cover with the first recorded pre-treatment cover across all 740 of the two project’s treatment sites (ranging from 0.03 to 227.6 ha in size). We also used regression analysis to estimate the effect of predic- tor variables on the cost-effectiveness of invasive alien plant clearing. We found – by dividing the total costs by the change in invasive alien plant cover – that it cost 2.4 times more (1.5 times for the Krom, and 8.6 times for the Kouga project) to clear invaded land than the highest equivalent estimate made elsewhere. At current rates of clearing, it would take 54 and 695 years to clear the catchments, in the Krom and Kouga, respectively, assuming no further spread. If spread is considered, current control efforts are inadequate, and invasions are likely to continue to spread in the catchments. Pre-treatment invasive alien plant cover and treatment costs per hectare had the greatest positive and negative influence, respectively on cost-effectiveness. Our assessment suggests that invasive alien plant control projects urgently need to monitor their cost-effectiveness so that management practices can be adapted to use scarce conservation funds more effectively. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Invasive alien plants pose a significant threat to the biodiversity and functioning of the world’s ecosystems (Mack et al., 2000; Pimentel et al., 2005); consequently, billions of dollars have been spent controlling them (Pyšek and Richardson, 2011). The most cost-effective approach is prevention, followed by early detection and eradication (Hulme, 2006). When the invasive population is established, biological control can be highly effective for some species and contexts (van Driesche et al., 2010; de Lange and van Wilgen, 2010); however, in most cases, costly mechanical clearing treatments are also required (Pyšek and Richardson, 2011). Few studies have measured the cost-effectiveness of clearing invasive alien plants over time (Kettenring and Adams, 2011). Fur- thermore, most studies make measurements over small temporal and spatial scales making it difficult to extrapolate findings that are relevant to operational contexts (Kettenring and Adams, 2011). Having no reliable measurement of cost-effectiveness hampers the optimal allocation of scarce conservation funds (Mur- doch et al., 2007; McCarthy et al., 2010). It also makes it difficult to learn from successes and failures, and to adapt accordingly to achieve desired outcomes (Sutherland et al., 2004; Grantham et al., 2011). Large numbers of alien plant species, including many trees and shrubs (Henderson, 2001), have invaded South African ecosys- tems (Henderson, 2007; Kotze et al., 2010). Some of these plants reduce scarce water supplies and negatively affect biodiversity and the functioning of riparian zones (Le Maitre et al., 2000; van Wilgen et al., 2008). Growing awareness of the problem re- sulted in the formation of the government-funded invasive alien plant control programme ‘Working for Water’ (WfW) in 1995. It is arguably the largest conservation project in Africa (van Wilgen, 2009) and the world’s most ambitious invasive alien plant control programme (Koenig, 2009). Unlike other national control pro- grammes that focus on prevention and early detection, WfW spends most of its funds on labour-intensive clearing because, as a public works project, it is expected to create employment in South Africa’s impoverished rural areas (van Wilgen et al., 1998; Koenig, 2009). 0006-3207/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biocon.2012.06.006 ⇑ Corresponding author. Tel.: +27 21 461 1068. E-mail address: mattmccza@gmail.com (M.M. McConnachie). Biological Conservation 155 (2012) 128–135 Contents lists available at SciVerse ScienceDirect Biological Conservation journal homepage: www.elsevier.com/locate/biocon