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

Potential areas for restoration The land projected to contain refugia for plants but converted to agriculture would be areas to prioritise for restoration, contributing to Kenya’s post-2020 biodiversity and restoration tar- gets. Fig 4 showed the projected refugia with 2˚C and 4.5˚C for at least one taxonomic group that have been converted to agriculture, compared to other categories of refugia within the basin. By contrast, Fig 5 shows projected refugia for plants with all levels of warming that have been lost to agriculture. Agricultural lands that were projected to be refugia for plants with 1.5˚C global mean temperature rise are spread throughout the basin, covering 23% of the total area. If warming is limited to this level, a greater proportion of agricultural land within the basin could be restored to benefit biodiversity, act as carbon sinks, and provide additional eco- system services. Significantly less agricultural land was projected to have the potential to act as refugia for plants with 2˚C warming (8.7% of the basin) or greater, so the refugial area available for restoration is reduced. Refugia for plants are concentrated in the high elevations in the north and delta region in the south, as well as along the main Tana River in the east. With higher levels of warming, the agricultural land which could be restored is confined to the upland areas in the north of the basin. Much of this land borders PAs, including the Mount Kenya and Aberdare National Parks. Very little agricultural land in the basin was projected to

be refugia with 4.5˚C warming, covering only 0.7% of the total area of the basin. This land would be the most beneficial to restore as it is likely to protect biodiversity even if warming is not limited to levels agreed in the Paris Agreement or through INDCs. Importance of facilitating movement Ensuring species are able to move freely across the Tana River Basin–to shift with their pre- ferred climate envelope–is likely to help preserve biodiversity in a changing climate. The differ- ences in species richness for mammals and birds when dispersal is included compared to when species are unable to shift their ranges outside of their current climate envelope are greatest in the northeast of the basin (S9–S12 Figs). The differences between the two scenarios are more pronounced when temperatures reach 4.5˚C above pre-industrial levels (S2 and S4 Figs), showing the importance of allowing species to adapt in scenarios with high global temperatures. The importance of facilitating movement in terms of avoided loss of species richness is shown in Fig 6 for birds and mammals. Although these PAs may not be refugia for the existing taxa, they are still important for protecting biodiversity, especially that which is moving in response to a changing climate Allowing species to adapt to the changing conditions by Table 1. Projected refugia at risk from National Spatial Plan activities. With 2˚C warming With 4.5˚C warming NSP Activity Area (sq km) % of refugia % of basin Area (sq km) % of refugia % of basin Proposed irrigation 6,981 9 7 4,274 21 5

Proposed economic growth areas 3,148 4 3 2,791 14 3 High agricultural potential land 1,193 2 1 126 1 0 Medium agricultural potential land 3,434 4 4 1,634 8 2 All activities a 10,586 14 11 6,281 31 7 The area of projected refugia for at least one taxonomic group within the Tana River Basin with 2˚C warming and 4.5˚C warming that is at risk from activities proposed within the National Spatial Plan (NSP) [53]. This table refers to areas that have not already been converted to agriculture. Some NSP activities overlap with one another. a This includes all proposed agricultural, irrigation and economic expansion areas. Some of which overlap with one another spatially. https://doi.org/10.1371/journal.pone.0254879.t001 PLOS ONE Risks to Kenya’s biodiversity from climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0254879 July 21, 2021 10 / 25