The Afromontane Bamboo, Yushania alpina, on Kilimanjaro

Abstract

The rarity of Afromontane bamboo, Yushania alpina (K.Schum.) W.C.Lin (syn. Arundinaria alpina K.Schum), on Kilimanjaro, is one of the great biogeographical mysteries of the East African mountains. The cause of this scarcity has never been satisfactorily resolved and although in this article I confIrm its existence on the mountain, I can only offer suggestions for its restricted occurrence there. The unfamiliar name is the result of the taxonomic revision of old, catch-all bamboo genera; Arundinaria was one such. Although this species has been referred to recently as Sinarundinaria alpina (K.Schum.) Chao & Renv. (e.g. Lovett, 1994), Chris Stapleton at Kew informs me that the best name, as generic concepts at present permit, is Yushania alpina. It seems, however, that this is still unsatisfactory, and a further change is mooted. Bambusologists avoid the diffIculty by simply calling it alpinal Afromontane bamboo Yushania alpina is a conspicuous element in the vegetation of most East African mountains from Ethiopia to the Southern Highlands of Tanzania and Malawi, also occurring on the Bamenda Mountains of Cameroon. Y. alpina characteristically occurs between 2,400-3,000 m, with isolated occurrences in favoured places between 1,630 m and 3,200 m (Clayton, 1970; White, 1983), favouring volcanic soils with rainfall in excess of 1,250 mmlyr·I (Lind & Morrison, 1974; White, 1983), although on Mt Kenya Bussmann (1994) found that 800-1,000 mmlyr·I was suffIcient. Temperature has also been found to be limiting, with bamboo and bamboo-Podocmpus forest on the eastern slopes of the Aberdares confmed to areas with a mean annual temperature of 11.6-15.9°C (Schmitt, 1991); on Mt Kenya pure bamboo stands occur in the temperature range 1O-12°C, with mixed forest in the range 12-14°C (Winiger, 1979, in Schmitt, 1991). This agrees with observations from Fries & Fries (1948) onwards that bamboo does not occur in valleys where cold katabatic winds flow or cold air accumulates. Where conditions are favourable it can cover large areas (e.g. 65,000 ha on the Aberdares, 51,000 ha on the Mau, 39,000 ha on Mt Kenya (Clayton in FTEA, 1970». On other mountains, e.g. Ruwenzori and Mt Elgon, it is most abundant on the