The study sites are located within the Eastern Arc ecoregion, which extends in elevational patches along a chain of isolated mountain ranges, from the Taita Hills, close to the Kenyan border with Tanzania, down through eastern Tanzania to the gap between the Udzungwa Mountains and Mt. Rungwe (Makambako Gap)
The forests and grasslands of the ecoregion might have persisted in this location up to 30 million years, and hence been formerly connected to a forest belt that stretched across the tropical region of Africa. They likely survived the driest and coldest periods of the Ice Ages, as the Indian Ocean did not cool appreciably and rainfall patterns may not have been greatly disrupted.
The Eastern Arc is comprised of heavily metamorphosed Pre-Cambrian basement rocks. The main blocks are uplifted along ancient faults, with uplift events occurring periodically, probably at least since the Miocene (about 30 million years ago). However, the faults, and therefore perhaps also the mountains, appear to be considerably older than this.
The eastern slopes of the mountains are covered by a dense rain forest, which represents the richest bioma in terms of biodiversity and presence of endemism within the ecoregion. Open vegetation bog and grassland habitats can be found in the higher areas of the Ulugurus, whereas grasslands and stands of bamboo can be found in the Udzungwas.
It has been estimated that there are over 2000 plant species in 800 genera in these montane and surrounding forests. At least 800 of these species are believed endemic to this ecoregion. On a broader scale, the montane forests of Tanzania contain 7% of the endemic plant species of Africa on only 0.05% of the total area.