Highland forest

The tiny highland forest remnant in City Park offers a glimpse into the composition of the natural vegetation that, until just one hundred years ago, still covered much of the highland areas of Nairobi area. In this sense, the Park’s now isolated patch of forest may be thought of as a living museum.

This fragment is of a dry highland forest: the kind of forest that historically in Kenya thrived in exactly the altitude range – of between 1,600 and 1,800 m (5,250–5,900 ft) above sea level.

Several of its plants (presumably common once) are today either Rare or globally Threatened.

Dominant among the larger trees, here as in other remnants of Nairobi’s dry upland forest, is Croton megalocarpus, known locally as Mukinduri. Often over 25 m tall, these are graceful, upper-storey trees, with flattish, spreading crowns and layered silvery leaves.

Another large tree that is characteristic of this forest type, and of which there are some fine, aged specimens in City Park, is Diospyros abyssinica, the ‘Giant Diospyros’ (Muiruthi in Kikuyu), whose compact, mushroom-shaped crown, borne aloft on a dark, slender trunk, may tower 20 m or higher above the forest floor.

Conspicuously typical when it is flowering is Calodendrum capense, the ‘Cape Chestnut’, a striking forest tree rising 20 m with a shapely, spreading crown – to say nothing of its exquisite pale pink flowers.

Then there is Brachylaena huillensis, the ‘Silver Oak’ (Muhuhuin Kiswahili), a very slow-growing tree with a pale-barked, often dividing trunk, whose steeply rising branches clad in greyish foliage culminate in a narrow, irregular crown, up to 18m off the ground. The species is IUCN-listed as Near Threatened, on account of over-exploitation by wood carvers.

An impressive forest tree that flourishes in City Park, which boasts some of the tallest specimens in Kenya, is Markhamia lutea (Muu in Kikuyu), whose showy clusters of bright yellow, trumpet-shaped flowers give way to very long, thin, twisted pods, which trail like brown streamers from the trees after splitting open to release their seeds.

Another striking forest tree, often with a knobbly trunk, is Craibia brownii (Mukubu), whose beautiful sprays of fragrant,pink- or mauve-tinged creamy white flowers are always a particular delight.

One of the tallest trees on view is ‘Pillarwood’, Cassipourea malosana (Muthaithi), whose smooth greyish trunks rise pillar-like for 18m, or more, before branching.  One such tree, near the Bowling Green in City Park, is in the process of being throttled by an especially ambitious ‘Strangler Fig’, Ficus thonningii.

Also represented, not surprisingly, is the ‘East African Greenheart’, Warburgia ugandensis (Muthiga). It is for this medicinal tree, whose leaves have a hot and peppery taste, that the adjacent suburb of Muthaiga – where the species was abundant once – is named.

Other prominent trees are Elaeodendron buchananii (Mutanga), which – as the food plant for the larvae of the Ermine Moth, (Yponomeuta sp.) – is at times festooned with the protective webs woven by the caterpillars, and Drypetes gerrardii (Munyenye), an evergreen with drooping foliage that may be up to 15 m tall, and whose tiny berries, orange-red when ripe, are especially attractive to foraging monkeys, and fruit-eating birds.

Rawsonia lucida (Mutendera), a small tree growing to about 12 m with mottled grey bark scaling to reveal orangered under-bark, is also well represented.

City Park boasts some fine examples too of that widely occurring species, the ‘Cape Ash’, Ekebergia capensis (called Mununga in Kikuyu), and of Schrebera alata (Mutoma),known as the ‘Wing-leaved Wooden Pear’ on account of its small, pear-shaped ‘wooden’ fruit capsules, which stay on the trees long after splitting open to shed their delicate, gossamerwinged seeds.

The tropical African genus of ‘Wild Medlars’, Vangueria, has no fewer than four representatives in City Park, including V.madagascariensis, V. infausta, and V. volkensii. All bear round, edible fruits, which – because the eating of their flesh is said to cause constipation – are sometimes referred to as ‘Bum Stitches’.

Two of the defining tree species of dry highland forests elsewhere in Kenya, Olea europaea ssp. africana (the ‘African Olive’, Mutamaiyu in Kikuyu) and Chrysophyllum viridifolium (Murundu), are comparatively sparse in City Park, where in the absence of mature trees only saplings are present.

Smaller trees typical of dry forests around Nairobi that abound in the Park include Vepris (or Teclea of two species, T. simplicifolia and T. trichocarpa, both known as Munderendu), which are much-branched evergreens with dense foliage; three Strychnos species, including S.henningsii and S. usambarensis (known locally as Muteta and Mutikani), both with stiff leaves, smooth and glossy on top, in opposite pairs on the twigs, and small creamy- or greenishwhite flowers, forming round fleshy fruits; Acokanthera (‘Arrow Poison Trees’) of two species, A. schimperi and A. oppositifolia, both referred to as Muricu in Kikuyu, and Rothmannia urcelliformis (Mukombokombo), an evergreen with low, sweeping branches and distinctive funnel-shaped, creamy-white flowers dusted with maroon and yellow flecks, bearing hard, ridged, dark-green oval fruits that turnblack on the tree.

One tree genus well represented in City Park is Ficus, the Figs, of which there are five native species on view (and two exotics as well, which have been planted on the lawns as ornamentals).  Ficus thonningii, the ‘Strangler Fig’ (Mugumo in Kikuyu), is especially prevalent. The fruits of these towering trees, and of the Park’s other African ‘Wild Figs’ (F. sur, F. natalensis, F. lutea, and F. diversifolia), are feasted on by monkeys and other resident mammals, along with numerous birds, including those noisy gatecrashers, the Silvery-cheeked Hornbills.

There are some fine examples in the Park of other, more widely occurring tree species, such as Albizia gummifera (Mukurue in Kikuyu),a tall, elegant deciduous tree with a smooth grey trunk and a shapely crown of feathery,paired leaflets.

From the same family (Mimosaceae), the genus Acacia is represented by six species, including A. nilotica, the‘Scented-pod Acacia’ (Mgunga in Kiswahili) and the familiar A. xanthophloea, or ‘Fever Tree’.

There is, near the Plant Nursery, a thriving‘Sausage Tree’, Kigelia africana (Muratina in Kikuyu), unmistakable when fruiting, while that widely planted African ornamental, the ‘Nandi Flame’, Spathodea campanulata, native to forests west of the Rift Valley, assumes pride of place down by the river.

The abundance in City Park of Dracaena steudneri (Muthari in Kikuyu), a distinctive, palm-like species with prominent, clustered leaf rosettes and – atop long spikes – sharp-scented creamy-green flowers that open out at night, is partly a reflection of deliberate planting, and partly due to the retention of specimens found growing in the original forest.

Where forests are encroached upon, or opened up, it is the undergrowth species that are most at risk, for such plants depend for their survival on the sheltering cover and shade provided by the larger upper- and middle-storey trees.

Two small highland forest undershrubs, Croton alienus (Muthenia) and Canthium keniensis (‘Wild Coffee’, or Mubiru-wathi), both endemic to the Nairobi area, and both eliminated from most of their former haunts, live on in City Park, along with the rare Psychotria kirkii, a dryland shrub with dull reddish branches that also occurs in the distant Kibwezi Forest.

Lianas of more than 75 species have been recorded in less disturbed forest areas of City Park, and today these climbers, rising spectacularly in some cases – notably those of Combretum paniculatum, Hippocratea africana, and Landolphia buchananii – are among the Park’s principal attractions.

Orchids of six species are known from the Park, including one – Habenaria bonateoides – that was discovered here, and which (to date) has yet to be found anywhere else. Another of the orchids, Microcoelia moreauae, which after the rains produces hanging racemes of delicate white flowers, is typical of relict dry highland forests around Nairobi.

On the ground, meanwhile, in wetter areas of the Park, the lowly Balsam, Impatiens sodenii,endemic to Kenya and Tanzania, bears demure clusters of white flowers, often lightly tinged with pink.

Beside the pathway skirting the Kei-apple Maze, stand a few Euphorbia cussonioides trees, believed to be some of the last remaining individuals of this species left on Earth (Three or four can still be seen near the top of the Chania Falls in Thika). The City Park individuals of this species may have been planted here in the 1950s by the Park’s long-serving gardener in-residence Peter Greensmith.

One Response to “Highland forest”

  1. Samuel19/05/2016 at 9:47 pm #

    Very educational. I grow flowers and tree seedlings from home so this article has helped me identify some species in my nursery. Thanks

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