Islands in a Savanna Sea - the Eastern Arc Mountains

Islands in a Savanna Sea - the Eastern Arc Mountains

The Eastern Arc is a chain of rugged mountain blocks which rise from the flat topography of the East African coastal plain. Stretching from the Taita Hills, in southern Kenya, down through eastern Tanzania from the Usambaras to the Udzungwas and Mount Rungwe, the mountains form a crescent shaped ‘arc'. Geographically isolated for millions of years, the mountains formed through a process of uplifting and faulting at least 30 million years ago, but they are almost certainly considerably older than this. In comparison to Kilimanjaro and East Africa's other volcanic peaks (which are thought be around one million years of age) the Eastern Arc mountains are truly ancient. Most of the mountain blocks rise to about 2 200 metres, with plateaus on the crests of the Uluguru and Udzungwa supporting unique forest-grassland mosaics.

Over the millennia, in synchrony with global ice-ages, Africa has undergone repeated wet and dry epochs which have periodically caused the expansion and retraction of rain forests. Throughout this time, the high rainfall climate of the Eastern Arc Mountains has remained constant so that many forest-dependent species have persisted and slowly evolved into new forms as they have become isolated. Today, the forested mountains can be considered 'islands', surrounded not by water, but a 'sea' of dry woodland savanna.

The high conservation significance of the Eastern Arc Mountains is due to the remarkable biodiversity including numerous endemic species. Such is the uniqueness of the mountains, that they have been collectively classified as one of planet Earth's 24 most important biodiversity 'hotspots'. Of the more than 2000 plant species, some 800 exist nowhere else; among these are the various African Violets (Saintpaulia) - beloved as pot plants around the world, as well as towering trees such as Ocotea usambarensis and Allanblackia stuhlmannii. Endemism is similarly high in other groups, particularly birds and amphibians.

The Uluguru Bushshrike is confined to the forests of the Uluguru, while the
Udzungwa Partridge is similarly restricted to that mountain. The Usambara Eagle-Owl, Banded Sunbird and Mrs Moreau's Warbler occur in various places throughout the range, while several 'near endemics' such as Long-billed Tailorbird are shared with other remote localities in south-eastern Africa. Among the diverse amphibian fauna are 25 strict endemics, including five tree-frogs and five toads. A remarkable ten species of chameleon are endemic to the Eastern Arc. Not surprisingly, endemism among invertebrates is particularly high, with up to 80% of the insects on any particular mountain block being unique. Because of the relatively small size of the forests, no larger mammals are endemic but one galago and five species of musk-shrew are found nowhere else. In addition to this extraordinary wealth of endemism are some fascinating evolutionary links, which pose interesting questions. Many forest species have close affinities with the Congo Basin or the Albertine Rift, while being absent from the rest of Tanzania.

Numerous mosses and liverworts from the Usambaras are also found on Madagascar, while being absent from the nearby but much younger Kilimanjaro. Perhaps most intriguingly, the Long-billed Tailorbird and Udzungwa Partridge appear to have their closest relatives on the distant Indian subcontinent.

There is growing concern for the long-term conservation of the Eastern Arc Mountains, with international organisations working alongside African authorities to protect the remaining forests from expanding human populations which rely on the natural resources for medicine, fuel and fresh water. The role of the forested mountains as water catchments is indeed critical, with the four million inhabitants of Dar es Salaam completely dependant on the Uluguru Mountains for their fresh water. In early 2004, the integrity of the East Usambaras was threatened by a miscalculated and illegal 'gold rush' which attracted thousands of hopeful migrants who began digging and panning, while damaging or depleting forest resources, before government action was taken. The presence of endemic and range-restricted birds is a major
attraction for global birdwatchers who are visiting the mountains in increasing numbers.

The creation of community-based ecotourism facilities and the promotion of iconic endemic birds such as the Uluguru Bushshrike, offers the chance to attract sustainable sources of revenue for local people.

Posted: Other by CC Africa, Date: 21 November 2006