Vegetation of the Rwenzori
The montane forest begins at about 1,800 metres. From this level upwards it is convenient to consider separately the several floral zones, which succeed one another as altitude is gained, indicating some of the commoner and more conspicuous species. The vegetation zones cannot be described simply in terms of altitude as the vegetation varies considerably with other environmental factors such as the soil and the type of site. The change from one zone to the next is by no means always abrupt.
Afro Montane forest 1,800 to 2,500 metres
With few exceptions trees are of moderate size and the forest canopy tends to be broken. Among the more prominent trees are the Red Stinkwood (pygeum africanum), which is present throughout the forest; the ‘podo’ or yellow wood tree, podocarpus milanjianus; symphonia globulifera with waxy red flowers; two pieces of Dombeya and Vernonia adolfi-friderici. There is also a wide variety of smaller understorey trees such as Grumilea megistocticta, a wild relative of the gardenia. Thickets are extensive and dictate the character of the forest at least as much as the taller trees. The wild banana, Ensete edulis, and the tree ferns, Cyathea deckenii are prominent. Among numerous herbaceous plants are a fine begonia, begonia mayari-johannis, and several balasms, impatiens. Trees are festooned with creeps and tree orchids are not uncommon.
Bamboo-Mimulopsis Zone 2,500 to 3,000 metres
On moderate slopes with good soil the mountain bamboo, Arundinaria alpina, form pure, dense stands, the ground being covered by a thick litter of bamboo leaves. On steep and rocky slopes the bamboo is replaced by tangled undergrowth dominated by an Acanthus-type shrub, Mimulopsis ellioti. A giant lobelia, lobelia gibberoa, grows in wet and swampy places. Giant heathers, philippia johnstonii and Erica kingaensis grow on narrow ridges but do not reach their maximum size. Helichrysum everlastings begin to appear in this zone. The bamboo flowers at intervals of about thirty years.
Trees, many of which also occur in the forest below, grow among the bamboos and the undergrowth: podocarpus milanjianus; Dombeya sp; Afrocrania volkensii; Maesa lanceolata; Dracaena aframontana; and Hagenia abyssinica, a spreading tree with yellow flowers. Shrubs and herbaceous plants are plentiful and include the Ruwenzori blackberry, Rubus dogetti; tree ferns, Cyathea deckenii; an Arumlily, Arisoema ruwenzoricus, and an Amaryllid, Choananthus cyrtanthiflorus. The tree orchid, Canarian eminii with striped orange and crimson flowers, grows in the forks of many of the larger trees.
Heather-Rapanea zone 3,000 to 4,000 metres
Three distinct types of vegetation are to be found in the zone.
The true Heather Forest occurs only where the soil is poor: on ridge tops, rocky or moderately boggy ground. The stems of the trees and the ground are enveloped in thick Sphagnum moss: branches are draped in Usnea beard lichens. The coral pink ground orchid, Disa stairsii, and a red and mauve balsam, impatiens runsorrensis, are almost the only herbaceous plants. The tree heathers philippia trimera and Erica kingaensis, which occasionally produces pink flowers, are abundant. On Mount Elgon, a heath-like composite, Stoebe kilimamdscharica, is almost as plentiful as the true heathers with which it grows; it occurs also at the upper levels of the drier Karamoja Mountains.
The valley bottoms are filled with huge bogs, which are almost completely occupied, by various forms of sedge of which Carex runsorrensis, growing in tussocks, is the most important. Between the tussocks the ground is covred with Sphagnum moss and the fine lobelia becquaertii occurs.
On well drained slopes there is a mixed type of woodland dominated by Rapanea rhododendroides, a small shrubby tree with rhododendron-like leaves, and two arboreal St John’s Worts, Hypericum lanceolatum and Hypericum keniense with yellow flowers; hypericum becquaertiee, with orange flowers, also occurs at the top of this zone. The first of the tree groundsels, senecio longeligulatus, and the tallest of the lobelias, lobelia stuhlmanni, and a few Hagebia abyssinica trees are found in this woofland. Much of the undergrowth consists of the everlasting Helichrysum guilelmi with white and pink flowers. The Ruwenzori blackberry, Arisoema lilies, wild celery, a yellow Alyssum, wild violets and the common chickweed are all plentiful. Open ground a golden sedum sprawls across the rocks. The Hagenia tree are very much more abundant in other mountain areas where, in places, they form the dominant species.
Alpine zone 4,000 to 4,500 metres
This part of the Ruwenzori, is dominated by the giant groundsel, Senecio adnivalis, which replaces senecio longeligulatus at about 12, 500 feet and grows in great abundance on all deep and well-watered soils; the torch lobelia, lobelia wollastonii; and a thick tangled growth of the everlasting Helichrysum stuhlumani. The bogs and lake verges are occupied by Carex tussocks and some rushes.
The St John’s Wort, Hypericum becquaeritii, is prominent; several plants from the zone below, including the tree heathers, persist into the lower levels of this zone but in much reduced profusion. On rough stony ground little grows except moss and a few short grasses.
Drier slopes and open meadows are often carpeted with a silvery-leafed, woody-stemmed Alchemilla. Above 4,300 metres the vegetation begins to thin out until nothing grows except moss, a blackish coloured lichen and a few everlasting, which (at this altitude) are small plants, covered with white woolly hairs, growing to a height of twelve inches or less. For example Weismans Peak 4,620m which is dome shaped and flatish is carpeted with green, rusty yellow and brown mosses.