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

requirements of one species are in opposition to those of another species of conservation con- cern. Therefore, these measures can be considered low risk. These are options which provide benefits regardless of the uncertainties in the climate change projections [83]. The sizeable impacts on biodiversity of the Tana River Basin, even in a situation when the Paris Agreement global temperature targets are met, shown here demonstrate the urgency of the problem and show that is paramount that the GoK start considering climate change in the policies now rather than planning to do so in the future. Existing policies and plans should be re-evaluated with the effects of climate change borne in mind. Implications for restoration Protecting biodiversity has the potential to contribute to other environmental goals, including ecosystem restoration targets. In order to account for climate change projections, restoration efforts should focus on areas of projected refugia which have already been converted to other land uses. These areas are projected to remain climatically suitable for most of the species pres- ent in the area prior to conversion to agriculture, some of which may persist within the agricul- tural landscape. Therefore, the benefits of these refugia may not be entirely lost, which may facilitate ecological restoration or the implementation of sustainable practises to better protect biodiversity. Particular attention should be paid to areas that border current protected areas, as restoring these lands may increase habitat connectivity and facilitate dispersal, and pro-

jected refugia, where species will be more likely to persist in a changing climate. Many of these areas are in the highlands in the northwest of the basin. Restoring these slopes ties in with the GoK’s targets of protecting the Water Towers [84, 85]. Kenya’s Bonn Challenge commitments include a total restoration target of 4,210,000 hectares, including all degraded forests and river- ine vegetation. This strategy includes growing over 7 billion trees by 2030 [84]. There is also significant restoration potential within the PAs of the Tana River Basin. Restoring degraded land to ensure biodiversity protection could also lead to synergistic benefits, such as increasing the supply of ecosystem services, such as pollination services and carbon storage and sequestration. Restoration will lead to trade-offs between agricultural development and biodiversity pro- tection or forest regeneration. Around 80% of Kenya is arid or semi-arid land (ASAL), so there is a limited amount of land available for natural habitats and agriculture. The restoration of land which is currently used for agriculture can lead to increased pressure in other areas. Therefore, restoration should be carefully planned at the basin or country scale in order to minimise negative effects across the whole area. Abandoned agricultural land should be a pri- ority for restoration. Within the Tana River Basin, several large-scale agricultural schemes have become abandoned due to low yields and climate variability. This land could be restored without significantly altering the economy of the basin.

However, as the area projected to contain refugia decreases with greater levels of warming, so does the restoration potential. Areas not considered to be refugia, by definition, are expected to become climatically unsuitable for at least 25% of current species. Therefore, many of the species present in the area prior to conversion to agriculture may be unable to tolerate the new climatic conditions if higher levels of warming are realised. The projected reduction in plant species richness may undermine efforts towards achieving these restoration targets. The Kenya Forestry Research Institute [86] compiled a list of suitable tree species for afforesta- tion or reforestation projects. However, many of these species have been projected to see a reduction in climate suitability with higher temperatures [60]. Some species identified as less sensitive to climate changes are the neem tree (Azadirachta indica), sycamore fig (Ficus syco- morus) and wild date palm (Phoenix reclinata). Future research into additional tree species PLOS ONE Risks to Kenya’s biodiversity from climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0254879 July 21, 2021 17 / 25