Seite - 368 - in Biodiversity and Health in the Face of Climate Change

368 lion hectares (more than 8% of the land area) with significant ecological and economic costs. With high evapotranspiration rates, invasive alien trees are an immense burden to already water-scarce regions and reduce the amount of water available to reservoirs, industry and downstream agriculture. Large-scale pro- grammes to remove these species are being undertaken in many of South Africa’s watersheds, providing benefits to biodiversity, water supplies and employment opportunities for poor and disenfranchised communities under the Working for Water Programme (World Bank 2010). The multiple roles of protected areas will become more valuable as climatic events become more severe, helping to reduce the impact of natural hazards and disasters and buffering vulnerable communities against all but the most severe flood and tidal events, landslides and storms (Stolton et  al. 2008). Intact mangroves pro- vide protection and reduce the damage caused by tsunamis and hurricanes, while also harbouring vital fish nurseries. In Sri Lanka, the Muthurajawella marsh near Colombo affords flood protection valued at over US$5 million/year (Costanza et  al. 2008). In some cases, investments in protecting and restoring natural habitats may be more cost-effective for reducing disaster risk than investing in hard infrastructure alone. In Vietnam, where local communities have been planting and protecting man- grove forests as a buffer against storms, an initial investment of $1.1  million has saved an estimated $7.3  million a year in sea dyke maintenance and significantly reduced the loss of life and property from Typhoon Wukong in 2000  in comparison with other areas (IFRC 2002). Although the value of ecosystem services in terms of water regulation and supply of clean water alone has been estimated at US$2.3 trillion globally (Costanza et  al. 1997), very little of this potential value is spent on ensuring that these ecosystem functions are sustained. Many protected area systems are inadequately funded (Watson et  al. 2014). One promising trend is the implementation of payment for ecosystem services (PES) schemes to compensate protected areas, upstream com- munities, indigenous peoples and private landowners for maintaining forests and other water-regulating habitats, such as those being piloted in Colombia, Ecuador, Mexico and Nicaragua (WCPA 2012). 16.2.2 Local and  Global Medicines Natural ecosystems are an important source of local, traditional and global medi- cines. Indeed, more species of medicinal plants are harvested than of any other natu- ral product, and many rural and urban communities, especially in the developing world, rely on medicinal plants for primary health-care (Stolton and Dudley 2010). The economic value of medicinal plants and their extracts and drug derivatives has been estimated in billions of dollars (Ahn 2017). Today many of these plants are conserved only in protected areas; indeed, some protected areas have been specifi- cally established to protect plants used in traditional medicines. A good example is K. MacKinnon et al.