Yushania alpina

Cultivation Details

A plant of high elevations in the tropics, where it can be found at elevations from 2,000 - 4,000 metres. It is found in areas with cool growing conditions, with average annual temperatures in the range of 14 - 17°c; with an average monthly maximum temperatures are 13 - 32°c; and average monthly minimum temperatures that range from -4°c to 11°c, implying that some populations tolerate frost. Rainfall is seasonal, with 3 - 6 dry months (where the mean rainfall is less than 50mm) in eastern Africa, but only 2 dry months in Cameroon. Annual rainfall totals vary from 800mm in Tanzania to 2,000mm in Ethiopia and 3,000mm in Cameroon^[1]. The climate requirements of the plant over-ride its soil type requirements, it being found growing on impoverished ferralsols, moderately fertile cambisols, and richer andosols and nitisols. Well-drained humus-rich soil on gentle slopes and in ravines, with space for vigorous rhizome development, allows luxuriant growth, whilst on shallow soils and rocky ground individuals are stunted^[1]. Afromontane bamboo forest has been described as a climax formation, but burnt forest tree stumps within Sinarundinaria alpina stands have been interpreted as evidence of a fire-induced community. Another view treats the species as a light-demanding pioneer forming populations maintained by large herbivore activity^[1]. Although nursery seedlings have been raised in Kenya, there is no published description of the germination and initial growth of African alpine bamboo. Small plants, consisting entirely of new shoots, form loose, but discrete, clumps. With time, stems at the centre die and disappear, while new stems are added at the periphery. Repeated exposure to fire causes mortality of young peripheral rhizomes and concentration of new shoots close to older ones, maintaining relatively compact clumps^[1]. Rhizome networks producing new stems annually may survive for at least 40 years, but individual stems survive only 8 - 14 years^[1]. New stem production is a seasonal process, allowing cohorts of stems in different age classes to be recognized^[1]. A year of vigorous stem production may be followed by a 2 - 3 year period of low stem production. Unusual droughts also reduce production in the subsequent growing season^[1]. The annual growth cycle involves the development of new stems at rhizome apices where growth is activated when the rainy season starts. New stems reach full height in 2 - 4 months and form branches in the following year. By the fourth year of growth the stems are glabrous and sufficiently rigid for use as poles^[1]. Estimates of the interval between flowering events vary from 15 years (Mount Elgon, Kenya) to 40 years (Aberdares Range, Kenya). Flowering may be synchronous in patches several hectares in extent within a population^[1]. It is generally assumed that plants die after flowering, although development of new shoots from parts of the rhizome network surviving after flowering has been noted in Kenya^[1]. Natural stands of African alpine bamboo can be clear-felled but recovery is slow, development of full-sized stems taking 9 - 10 years^[1]. Stems must be full-sized and at least 3 years old before they can be exploited for structural use, and numbers must accumulate to levels making harvesting worthwhile, so felling cycles of 14 - 21 years have been recommended. This cycle can be reduced to 5 - 6 years on good sites if modest yields are acceptable and 50% of the mature stems are retained^[1]. Harvesting of stems under 2 years old suitable for weaving, and harvesting of edible shoots as vegetable are rainy season activities^[1]. The dry weight of a standing crop of stems of well-stocked stands in Masha, Ethiopia has been estimated at 51 tonnes per hectare, and in Kenya at 97 tonnes. With a 5-year cutting cycle exploiting only mature stems, representing 20% of the number of stems present, a potential yield of 10 tonnes per hectare per year has been estimated for Ethiopia. Better management might raise this to 15 tonnes per year^[1].