Tanzania Forest Conservation Group - Naming the Arc

Dr Jon Lovett
University of York

Orginally printed in The Arc Journal, Issue No. 7 May 1998

This article first appeared in the Arc Journal in 1994 (issue No. 2). We felt it timely to reprint the article as there has been such a surge of interest over the past year in the Eastern Arc and we are sure some of you are wondering as to how the name came about?!! –Ed

If you look on a map of East Africa you won't find the Eastern Arc. But it is a place that is listed as a global environmental hot spot by international conservation organizations and environmental foundations. You will also find the name in many scientific papers about forests of East Africa and in the official Tanzania Forest Action Plan term – and it of course inspired the name of this newsletter.

The name originated as a handy way to describe an area of forest that contained many rare plants and animals. Biologists have known about the extraordinary species richness of the mountains of eastern Tanzania and southeastern Kenya for a long time. The Usambara Mountains in northeastern Tanzania were one of the first areas to be studied seriously, starting about 100 years ago. Gradually other areas such as the Uluguru Mountains were visited by scientist and also to be biologically very important. It wasn't until late 1970's when Alan Rogers and co-workers started research in the Udzungwa Mountains, was it realized that many of the species thought to be found only in the Usambara Mountains were also present in southern Tanzania.

In 1983, with Roger Polhill of the Royal Botanical Gardens at Kew, London, I made a rough estimate of the number and distribution of Tanzanian forest species occurring in the mountains. The results were surprising. There turned out to be about 2,000 species in approximately 800 genera. Some 25% were found only in Tanzania, and over 30% were found only in Tanzania and southeastern Kenya. The majority of the species of restricted distribution occurred in the mountain forests in the east. In comparison to the rest of tropical African flora, the Tanzanian forests contained 33% of the tropical Africa genera and 7% of the species in 0.075% of the area.

From the analysis it was clear that the rare forest plants were found only on the crystalline peaks are the Taita Hills of Kenya, and, in Tanzania, the Pare, Usambara, Nguru, Ukaguru, Rubeho, Udzungwa, and Mahenge Mountains. Most of these mountains rise to 2000 metres and have a high rainfall, being the first high ground encountered by rain-bearing winds blowing in off the Indian Ocean.

Geologists think these mountains are tens of millions of years old. The forests on them are probably of a similar age. Many of them are isolated from each other, islands of forest surrounded by a sea of dry Savannah.

The plants in the Arc Forest show that at one time they were connected to the much larger forests of west and central Africa; millions of years ago, before the uplift of the central African plateau fragmented the great pan-African rainforests that stretched from east to west across the continent. These are the forests that were left behind, kept alive by the Indian Ocean Monsoon, surviving as the world's climate went through ice ages and drought. That is, until people arrived on the scene.

It is generally thought that we evolved first in eastern Africa and tamed fire more than one million years ago. At present we know little of our ancestors, but there is no reason to doubt that they had a well-developed culture. Certainly the forests bear witness to the ebb and flow civilization, as in some areas they now growing on sites of earlier settlements. But it is not until the last 100 years that there has been a sustained assault on millions of years of accumulated biodiversity. Extraction of valuable timber, establishment of commercial tea and coffee plantations, and clearance for small-scale agriculture has all taken their toll on the forest.

As we pieced together the patterns in the distribution of rare plants, it became clear that the distinct forested crystalline mountains needed a name that could be used to focus conservation efforts on the whole range and not just on one or two better known areas. In 1983, Roger Polhill, John Hall and myself were sitting together on the porch of John's house at Sokoine University of Agriculture at the foot of Uluguru Mountains. We were discussing the new discoveries on the Udzungwa Mountains. The name we thought of was the Eastern Arc simply because the ranges are set in a half-moon 'arc' shape in eastern Kenya and Tanzania.

The term first appeared in print in an article I wrote for Swara magazine, which was published in 1985. The article contained a map, which showed the Udzungwa Mountain as the southern boundary for the Eastern Arc. At that time I had not worked farther south than Mufindi, and I was worried I might be missing some important forests on crystalline rocks further south in the Livingstone Mountains above Lake Nyasa. So at the 1984 AETFAT congress in St. Louis, Missouri, I presented a paper that included the crystalline Livingstone Mountains in the definition of the Eastern Arc.

It was a mistake. In 1985 and 1986, with the butterfly aficionado Colin Congdon, I visited the Livingstone and Kipengere mountains for the first time. Standing on the edge of the huge escarpment above the northern end of lake Nyasa it was clear that much of the rain which maintained the forests there came not from the Indian Ocean, but from great thunder storms arising by convection from the lake. The forests had some interesting plants, to be sure, but there was none of the characteristic Eastern Arc specials. This realization taught me the danger about making pronouncements about areas that I had not been to in the field: if you want to know what is going on you have actually be there and feel the rain in your face.

That experience led to a tighter definition of the Eastern Arc, this time with a geological and climatological caveat, which I presented at the AETFAT congress in Hamburg. I then defined the Eastern Arc as the crystalline mountains in south east Kenya and eastern Tanzania under the direct climatic influence of the Indian Ocean. The forests around Lake Nyasa were different.

Having worked out a climatological and geological definition for the Eastern Arc which coincided with the known distribution of rare plants, the next step was to test it by visiting areas within the Eastern Arc parameters that were not well known botanically to see if the right plants were there. This was the acid test. Having bungled once, was I going to bungle again? The two big unknowns were the Rubeho and northern Nguru Mountains.

The nomadic, indefatigable Norwegian entomologist Jan Kielland (Deceased) had blazed to both ranges and had found interesting butterflies. Were the right plants there as well? My first visit to Rubeho was in 1988 with Colin Congdon, a safari to the isolated Mangalisa plateau just south of the Rubeho range. I have enjoyed many safaris with Colin, but the journey to the plateau was one of the more hair raising. The only evidence that a vehicle had passed that way before was the remains of the vital parts of a LandRover's steering rods at the base of what appeared to me to be a near vertical wall of boulders that constituted the road.

In the first forest we visited there was a Zimmermannia tree, an Arc classic. I went to bed that night a happy man. Mangalisa, and therefore Rubeho, fit the model.

The following year my next safari to Rubeho was to the main range itself, at a place called Ukwiva, with Richard Minja, an old friend in the Forestry Division. Richard particularly wanted to visit this area for at that time Rubeho was a part of his beat as Assistant Catchment Forest Officer in Morogoro, but he lacked the means to get there. At 78,000 hectares it is one of the largest forest reserves in the country, but like Mangalisa it is remote: few visitors come here. As we drove into Ukwiva at dusk the villagers crowded around the car, assuming that the reason we should make the journey was to return a resident to their last resting place as is the tradition in Tanzania. We were glad to say this was not the case, and were looked after with great hospitality by the village chairman. For the next three days we walked as far as we could in the forest. Nothing, no Eastern Arc plants. A complete bust. I began to think that again I was wrong, that the model didn't fit. Then on the third day Richard pointed out all the pot shards on the forest floor. I had been too busy, looking up into the trees to notice them, and like many biologists I harboured a notion of primeval ancient forest growing in the tropics, forgetting that there is an incredibly long human history in eastern Africa.

Since then botanists, notably Tamas Pocs, have visited many other areas, including the little-known Northern Nguru mountains. In all the different places, Eastern Arc plants have turned up just where we would expect them to be. The pattern not only fits plant distributions. Birds and snakes also so the same species richness and rarity in the Eastern Arc and the model is now becoming generally accepted.

This is important as it enables us to predict areas where there might be rare species in advance of doing detailed scientific surveys and inventories. Conservation and management plans can then take into account the possibility that a particular forest might contain many plants and animals that occur only there and no where else in the world.

If the forests are disturbed, it is the rare species that are lost first, and as we know only too well: extinction is forever.