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

Land degradation increases the vulnerability of biodiversity. 36% of the Tana River Basin has already been converted to agriculture, so some ecosystem restoration may be necessary to best protect species in a changing climate. The United Nations declared 2021–2030 as the UN Decade on Ecosystem Restoration, which aims to restore degraded land to help tackle the climate crisis and protect natural resources. This restoration goes beyond benefits to biodiversity, as it also increases societal benefits derived from ecosystem services especially carbon removal. This study uses the outputs of species distribution models to assess the impacts of projected climate change on the biodiversity (mammals, birds, reptiles, amphibians and plants) of Ken- ya’s Tana River Basin. It will determine the presence of climate refugia and the extent to which they are threatened by agriculture and development activities, and identify areas where biodi- versity would benefit most from focused restoration efforts in the context of a changing cli- mate. This study is the first to use the recent Government of Kenya development plans and compare them to projected changes in species distributions in Kenya. By identifying climate refugia and using their locations to show the trade-offs between proposed development and biodiversity conservation, the results of this research will be useful to those seeking to protect the biodiversity of Kenya in a changing climate. Materials and methods Study area The Tana River Basin (Fig 1) is located in South-eastern Kenya and covers around 95,000km2;

20% of the country’s total land area. At approximately 1000 km from source to mouth, the Tana River is the longest river in the country, originating from the southern slopes of Mount Kenya and flowing into the Indian Ocean through the Tana Delta. The land type varies greatly within the basin, with the highest elevations classified as humid; central and coastal areas as semi-arid; and the remainder as arid. The majority of the population of the Tana River Basin lives in rural areas. Populations in Kenya are concentrated around the wetter areas and high potential agricultural areas [42]. Population growth rates in the Tana Basin are relatively low compared with other catchments in the country [43]. However, even this population increase is likely to put increased pressure on limited water and land resources [35]. The population growth is particularly significant in the upper basin, where higher numbers of people are leading to land shortages and increased land degradation. Peoples’ livelihoods within the basin comprise a wide range of activities, including fishing, agriculture and pastoralism, as well as work related to conservation and employment within urban areas [43]. The basin contains 43 protected areas (PAs) either in whole or in part (Fig 1). Forest reserves of less than 20km2 and private ranches were not included in this research due to the spatial scale of the data used (20km2). S1 Table shows the full list of PAs considered here and their designation and size in km2 [44]. In the upper reaches of the Tana River, the slopes of

Mount Kenya and the Aberdare range are protected as a National Park or as forest reserve. The north of the basin also includes PAs adjacent to the main Tana River, such as Meru and Kora National Parks (northeast). Much of the floodplain adjacent to the lower reaches of the river around the Tana Delta region is protected as community nature reserves and also con- tains the Tana River Primate Reserve. The Tsavo East National Park and South Kitui National Reserve are located in the southwest of the basin, furthest away from the Tana River itself. Many species, such the African lion and buffalo, are already largely confined to PAs so they provide important habitats for the region’s biodiversity. Endemic Bird Areas are located in the mountains in the Upper Tana and at the coast around the Tana Delta. The basin is home to PLOS ONE Risks to Kenya’s biodiversity from climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0254879 July 21, 2021 3 / 25