Stated preference and cost-based approaches to estimate the benefits of controlling invasive alien plant species in the Hhohho region of Swaziland

Abstract

This study uses stated preference and cost-based approaches to estimate the benefits to cattle farmers of controlling invasive alien plant species (IAPS) on communal grazing lands in the Hhohho region of Swaziland, where about 80% of the grazing land is invaded. This invasion has lead to some government ranches having to close down and the death of over 7,000 heads of cattle due to starvation-related ailments, thus causing huge welfare losses. In response, the study assessed cattle farmers’ levels of knowledge of IAPS and their associated impacts, used a probit model to identify factors affecting cattle farmers’ willingness to pay (WTP) for their control, estimated cattle farmers’ mean WTP for reducing IAPS infestation from current levels by 50% and 100% respectively, and elicited cattle farmers’ preferences for institutional arrangements to control and manage IAPS. Using a sample size of 192 farmers, the study established that over 85% of the cattle farmers had a high level of knowledge of the dominant IAPS affecting their grazing lands. Over 90% of the farmers were familiar with the negative effects of IAPS (e.g. reducing agriculture land, contributing to economic loss and great threat to biodiversity). Over 60% of the farmers were at least familiar with the positive effects of IAPS (e.g. providing food, firewood and preventing soil erosion). Levels of knowledge of IAPS were significantly influenced by age (ᵡ2 = 3.43, p=0.000). The mean WTP for complete removal of IAPS was found to be significantly influenced by level of bid offered (Z= -3.371, p=0.000), number of dependents (Z= -2.23, p=0.026), levels of income (Z= 2.19, p=0.029), and number of cattle owned (Z= -.3.12, p=0.020). A mean WTP of E60.50 per head of cattle (95, 54.51 – 72.64) was established for 100% removal of IAPS and a mean WTP of E35.89 per head of cattle (95, 31.53 – 49.95) for 50% removal. Mean WTP for 100% removal was significantly higher than that of 50% removal (t= -10.23, p=0.000) satisfying the scope test for stated preference responses. An estimated mean WTP of E52.23 per animal was obtained using the mitigation cost approach, which is consistent with theoretical expectations considering that the later gives a lower bound to the true Hicksian welfare measure. Finally, the study revealed a preference for community members to control and manage the spread of IAPS over private contractors or NGOs. In conclusion, this study demonstrates that making investments in the control of IAPS today would potentially save society huge future welfare losses.