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

dispersal could protect a greater proportion of birds and mammals in all PAs. When species are able to move freely to track their preferred climatic conditions, Rahole National Reserve and Kora National Park become extremely important for both birds and mammals with the higher levels of warming. The same is shown for North Kitui and Bisanadi National Reserves for mammals. An increase in bird and mammal species richness compared to current mod- elled levels is projected for these PAs. Discussion Implications of climate change for species richness The five taxa examined here have been shown to be at risk from climate change, with higher temperatures leading to greater impacts. Large proportions of the current species richness could be lost from the basin with higher levels of warming. There are clear benefits of mitiga- tion (i.e. the reduction of GHG emissions) to preserving the biodiversity of the Tana River Basin. The dangers of higher warming to biodiversity in terms of climatic range loss have pre- viously been discussed [12, 47, 51]. Limiting global temperature rise to 2˚C could avoid around 60% of global climatic range loss compared to higher (3.6–4˚C) warming [13]. A trait-based assessment of birds, amphibians and corals found that large proportions were highly vulnera- ble to 2˚C of warming [12]. All PAs analysed here have been shown to benefit from mitigation. However, as sizeable losses are still projected when warming is constrained to 2˚C above pre- industrial levels, it is clear that adaptation is also important, as well as the achievement of the

true goal of the Paris Agreement to limit global warming to ‘well below 2˚C’ and to ‘pursue efforts’ to limit warming to 1.5˚C. The benefits of limiting warming to as close to this 1.5˚C level as possible for the biodiver- sity of the basin are clear. There is a substantial difference between the proportion of the basin that is projected to contain refugia for plants between 1.5 and 2˚C warming. The benefits of allowing species to track their preferred climate space are clearly shown in the results for mammals and birds. This was also noted in a global analysis [51], which consid- ered the effects of different levels of warming and dispersal scenarios on WWF priority places [41]. The rate of climate warming will also have implications for biodiversity. If temperature thresholds are crossed early, few species will have the time to disperse and adapt. Birds and mammals tend to see the greatest population declines in areas that experienced the most rapid warming, with the relationship stronger for birds [56]. However, it is important to remember that more data typically exists for these taxa than others, such as reptiles and amphibians. If natural dispersal does not occur at a sufficient rate, wildlife corridors may not be effective in preserving the species [57]. In addition, decision-makers will have less time to facilitate move- ment, for example by expanding PAs or developing corridors [47]. A slower rate of warming allows greater time for such conservation action, as well as for the natural processes of dispersal

and even (for some species) evolutionary change [58]. This further demonstrates the impor- tance of mitigation for preserving biodiversity, since mitigation ‘buys time’ for adaptation. Projected climate refugia Refugia are projected within the Tana River Basin, demonstrating the importance of protecting the area. Even with high levels of warming (4.5˚C), projected refugia are still identified within the mountains in the north of the basin, as well as in the Tana Delta region in the southeast. For amphibians, there is a shift in the location of refugia in the north of the basin with different levels of warming. It is likely that this is due to changes to rainfall projections between the sce- narios. Within the Wallace Initiative, RCP 2.6 in the 2080s is a proxy for a 2˚C world and RCP PLOS ONE Risks to Kenya’s biodiversity from climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0254879 July 21, 2021 13 / 25