Eastern Arc Mountains
The Eastern Arc Mountains are a chain of mountains in Kenya and Tanzania. The range runs from northeast to southwest, with the Taita Hills in Kenya and the other ranges in Tanzania. To the southwest, the Makambako Gap separates them from the Kipengere Range, and to the northeast Mount Kilimanjaro marks their boundary. The chain forms a crescent and is considered a tentative World Heritage Site.
These mountains are the oldest in East Africa. They formed at least 100 million years ago along a fault east of the East African Rift. About 30 million years ago, the area was covered by rainforest. Around 10 million years ago, a cooler, drier climate turned the lowland forests into savanna, leaving the mountains as “islands” where tropical forests continued to thrive. This isolation caused many unique species to evolve.
The Eastern Arc is one of the world’s top biodiversity hotspots. About 75 vertebrate species are endemic to the range, along with thousands of invertebrates. Roughly 15 plant genera are endemic, including Streptocarpus sect. Saintpaulia, the African violet. Some endemics are very new, while others are remnants of populations that were once more widespread. The Uluguru Mountains and the eastern Usambara Mountains have the greatest biodiversity, with many endemics found on a single range. Four endemic birds resemble Asian species, suggesting a historic connection. The Udzungwa forest partridge is a relict species found only on the Rubeho and Udzungwa Mountains, with closest relatives among Asia’s hill partridges.
This page was last edited on 3 February 2026, at 17:33 (CET).