Addressing risks to biodiversity arising from a changing climate: The need for ecosystem restoration in the Tana River Basin, Kenya

the area of activities proposed in the National Spatial Plan) could protect areas projected to contain refugia with the highest warming levels in the north of the basin. Another geographical region that may experience trade-offs is the Tana Delta. In the Delta, the Lower Tana Delta Conservation Trust, Witu Forest Reserve and the Hanshak-Nyongoro Community Conservancy are important PAs that are also projected to be refugia for a range of species under high levels of warming. The Basra Reed Warbler (Acrocephalus griseldis), for example, overwinters in the Tana River Delta and so is also threatened by the large-scale agri- culture projects planned for the area [76]. Without PAs in this delta region being suitable for the species, the reed warbler may not be able to overwinter in the basin. It is helped a little if dispersal is feasible but limiting warming (mitigation) would be particularly beneficial for this species. This area is already highlighted as a hotspot of human-wildlife conflict [77]. Develop- ment plans and refugia for biodiversity in the delta region are likely to exacerbate this conflict in the future. The policymakers aim to establish more community conservancies around the Tana Delta development to protect wildlife, but many wildlife routes in this area are currently considered as blocked [77], suggesting that species will find it difficult to disperse and adapt to the changing climate and land uses. The changing climate may undermine the development activities, making some land use

changes unsustainable and inappropriate. The GoK has identified climate change as a signifi- cant challenge to attaining the Vision 2030. However, to date, there is little direct consideration of climate change in existing sectoral development plans. Adaptation options Based on these results, various recommendations for adaptation can be determined. First, improving the connectivity of the PAs would be extremely important to facilitate species’ movement. Maintaining or improving corridors is generally considered to be a better adapta- tion choice than other options, such as assisted colonisation (also known as managed reloca- tion). Wildlife corridors are seen as lower risk and reduce the possibility of invasive species problems [78]. Facilitating dispersal may involve restoring or protecting the habitats between existing PAs; therefore encouraging species to move into areas that become climatically suit- able. However, if corridors are not sufficient or if the rate of warming is too fast for species to keep up, assisted colonisation may become necessary to preserve some species. Harmful development and land uses on the edge of reserves could disturb the wildlife. This could prove a particular problem for the small PAs, such as the forest reserves. Extremely small PAs are unlikely to maintain sufficient genetic diversity to fully protect the species within them. Small PAs within larger unprotected ecosystems are some of the most vulnerable [79]. As land use changes occur, and the reserves become increasingly isolated through a loss of

landscape connectivity, the species present may suffer. Enlarging some of the smallest PAs may help conserve biodiversity. In addition, creating buffer zones of partially restricted land around the PAs may prevent the encroachment of harmful land uses which may affect the con- servation inside the parks [80]. However, the effectiveness of this method has been questioned. The concept is used in South Africa to protect land around the edge of PAs where the biodiver- sity, hydrology or aesthetics of the park could be affected by development activities [81]. Furthermore, the biodiversity of the Tana River Basin would benefit from the better regula- tion of the PAs both now and in the future. There are still problems of deforestation and live- stock within the PAs [36, 82], and, as shown in the results, cropland is present in all PAs to some extent. In practice, biodiversity conservation and adaptation are likely to involve a range of these measures, which are known as integrated conservation strategies. Biodiversity adapta- tion measures are generally compatible with other adaptation strategies, except where the PLOS ONE Risks to Kenya’s biodiversity from climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0254879 July 21, 2021 16 / 25