Arsi Mountains

A(i)Site contains one or more globally threatened species, C(iii)Site contains nationally threatened or restricted habitat or vegetation types, AND/OR habitats that have severely declined in extent nationally

The Arsi Mountains qualify as an IPA under criteria A and C. The presence of thirteen threatened endemic species that trigger criterion A(i). Additionally, criterion C(iii) is triggered by the presence of a severely declined vegetation type within the IPA, Afroalpine vegetation, for which the Arsi Mountains is one of the most intact remaining examples.

The Arsi Mountains IPA is located in the highlands of the central rift valley of Ethiopia, in the Arsi and West Arsi Zones of the Oromia Regional State in the Arsi floristic region. It is located ca. 200 km southeast of Addis Ababa and 15 km from the town of Asella. This site contains the second largest expanse of Afroalpine vegetation in Ethiopia. The IPA consists of three disjunct polygons of remnant alpine vegetation, the largest being the Chilalo-Galama Mountain Range, then Kecha (also referred to as Kaka) to the southwest, and Enkolo (also referred to as Encuolo, Hunkolo) to the southeast. The IPA reaches its peak at Mount Bada (4173 m), followed by Mount Chilalo (4081 m), Kecha (4073 m) and Enkolo (3803 m).The northern slopes of the Galama Range drain towards the Awash River, while the southern slopes are the source of the headwater streams of the Wabi Shebelle River. Additionally, some of the major Rift Valley lakes such as Lake Ziway are fed by tributaries from the Arsi Mountains.
The boundary of this IPA largely overlaps with the Arsi Mountains National Park, however modifications to exclude encroachment of agriculture and mixed forestry plantations have been made. The other disjunct patch of the Arsi Mountains NP, Dera Dilfaqar, has not included in this IPA as it is a different vegetation community and there are no records of priority plant species to support its assessment.

The Arsi Mountains IPA falls within the Eastern Afromontane biodiversity hotspot. This IPA is one of the most intact remaining intact examples of alpine vegetation, 97% of which has been lost in Ethiopia (UNESCO, 2020). Afroalpine flora harbors unique taxonomic and genetic diversity that is particularly fragile (Brochmann et al., 2022) and this site is globally important for 27 endemic and 13 threatened (1 CR, 5 EN, 7 VU) plant taxa. A study of the botany of the Arsi Mountains also recorded the presence of two further threatened endemic grasses, Festuca gilbertiana (EN) and Festuca macrophylla (VU) (Girma et al., 2018); however, as these records could not be verified by herbarium specimens they have not been included in this assessment.
Of particular note, this site is critical habitat for the charismatic Afroalpine species Lobelia rhynchopetalum (CR) as one of the four remaining locations for this species. Under future climate scenarios, a range reduction of 87% in the Bale-Arsi region is predicted by 2080 for this species, therefore all remaining Afroalpine habitat is vital for its persistence (Chala et al., 2016). Additionally this IPA is important habitat for several endangered terrestrial orchids. This site is one of two known locations for Disperis meirax (EN) which has not been collected in over 50 years, as well as one of 4 locations for Habenaria decumbens (EN) which has not been recorded at the site in over 100 years. Targeted surveys are urgently needed to confirm the continued presence and current status of these orchid species.
Of the three polygons that constitute this IPA, the Chilalo/Galama Mountains are the most extensively studied botanically. This IPA has a floristic affinity to the nearby Bale Mountains IPA, sharing critical habitat for six endemic threatened species, two of which are only shared between the two sites, namely Callitriche favargera (VU) and Poa hedbergii (EN).

The Arsi Mountains IPA is characterized by Afroalpine vegetation (Friis et al., 2010). The slopes surrounding these peaks have been highly modified, with most of the Ericaceous scrub and Dry Afromontane Forest vegetation that once connected the three polygons of this site now only extant in isolated patches within the IPA.
The Afroalpine communities at the site have scattered shrubs such as Helichrysum and Alchemilla, as well as tussock grass species, with stands of the charismatic endemic giant lobelia, Lobelia rhynchopetalum (Girma et al., 2018). There are some small, fragmented patches of Dry evergreen Afromontane vegetation (DAF) occupying lower-elevation areas of the IPA (2,500–3,000 m). DAF is dominated by tree species such as Afrocarpus gracilior, Juniperus procera, and Hagenia abyssinica (Girma et al., 2018). Ericaceous Belt shrubland (EB) is also scattered in the subalpine zone (3,000–3,500 m) and is dominated by Erica arborea and Erica trimera.
The geology of the Arsi Mountains is volcanic in origin, and there is some evidence of past glaciation at the site (Ulmer, 2004). Mt Chilamo, Mt Kecha and Mt Enkolo are volcanic calderas. The soil type varies throughout the site, from pellic vertisols in lower elevations to eutric nitosols on the mountain summits (Girma et al., 2018).
The area is characterized by a humid montane climate with a bimodal rainfall pattern. The mean annual rainfall ranges from 778–1,090 mm (ENMA, 2015).

The Ethiopian highlands have a long history of human settlement and interaction, and this site continues to be subject to intense anthropogenic pressures. Despite formal protection as a National Park, activities such as clearing, grazing and wood collection have altered vegetation composition and structure in the Arsi Mountains. Satellite imagery suggests that since the designation of the Arsi Mountains National Park (NP) in 2011, the park boundary has gradually been encroached upon and converted to agricultural land (Google Earth, 2024). Agricultural lands surround the IPA, with remnant natural habitat occurring mostly on steep slopes and alpine zones above ca. 3,000 m where cultivation is less feasible. These areas of remnant vegetation are further threatened by intense grazing pressure (Girma et al. 2018). A study at the site revealed that stocking rates exceed the sustainable carrying capacity recommended for highland areas and are currently at 4x the recommended density (Abdulahi, 2023). Overstocking has had a demonstrable impact on vegetation at the site, with rare species absent from overgrazed plots (Girma et al., 2018). Ericaceous belt shrubland and Dry Afromontane Forest (DAF) vegetation is further threatened by logging for fuelwood and fires set for fresh pasture (Girma et al. 2018). The rate of tree removal exceeds the rate of regeneration in the DAF present at this IPA. Dominant tree species at the lower elevations have been found to be overharvested (Girma et al., 2018). While some mixed plantations of Eucalyptus spp. occur in the vicinity, presenting alternative means of obtaining wood resources, these plantations have encroached on remnant forest. Based on the current trends of anthropogenic pressures in the study area, species diversity and abundance is predicted to diminish over time (Girma et al., 2018; Mekasha et al., 2023). Urgent conservation measures including control of tree harvesting and livestock encroachment should be prioritized in Arsi Mountains National Park.
Climate change poses a serious future threat to this IPA. Alpine areas are among the environments most likely to be impacted by climate change as mountaintop specialist species are already at the edge of their climactic envelope. The predicted response of tropical highland grassland species within the Arsi Mountains in Ethiopia has been modeled under future climate scenarios (Mekasha et al., 2013). For 67 species of grasses and legumes, it was determined that the projected warming significantly reduced altitudinal ranges and habitat areas for all the species studied (Mekasha et al., 2013). An additional 42 species (representing 63% of the data set) are predicted to lose their entire current range and habitat area, hence these species are predicted to face local extinctions (Mekasha et al., 2013). As climate warms, it is predicted that Alpine areas will become more suitable for cultivation and more susceptible to fire, further compounding threats to this IPA. Careful in-situ management and monitoring of threatened species is critical.

The Ecosystem Services of the Arsi Mountains have not been well documented however, as the second largest alpine area in Ethiopia, it is a critical water source, and surely provides diverse ecosystem services such as provisioning of resources (food, freshwater, wood, medicine) and ecosystem regulation (flood mitigation, water purification) (Girma et al., 2018). Rainfall at the Arsi Mountains sustains numerous rivers, streams and lakes including some of Ethiopia’s most important water resources. Tributaries from the IPA feed Lake Ziway, the largest of the Rift Valley lakes. The northern slopes of the site drain towards the Awash River, while the southern slopes are drained by headwater streams of the Wabi Shebelle River, the longest river in Ethiopia. The hydrographic catchment area of the Wabi-Shebelle basin is shared by Ethiopia, Somalia, and Kenya and 90% of the flow for this vitally important resource comes from run-off in the southeastern highlands of Ethiopia including Arsi (Kebbede, 2016).
The cultural value and tourism potential of the site have not been well documented, however there is some infrastructure for such activity, with extensive walking trails present around the Mt Chilalo crater.

Gabriella Hoban, Royal Botanic Gardens, Kew

Iain Darbyshire, Royal Botanic Gardens, Kew

Sebsebe Demissew, Addis Ababa University

Ermias Lulekal, Addis Ababa University

Sileshi Nemomissa, Addis Ababa University