Showing papers by "Andreas Hemp published in 2006"

Continuum or zonation? Altitudinal gradients in the forest vegetation of Mt. Kilimanjaro

Abstract: Based on the analysis of 600 vegetation plots using the method of Braun-Blanquet (1964) the composition of the whole vascular forest plant flora with about 1220 species was studied in the forests of Mt. Kilimanjaro. The altitudinal distribution of all strata (trees, shrubs, epiphytes, lianas and herbs) along a transect of 2400 m is discussed with respect to altitudinal zonation and ecological factors. With uni-dimensionally constraint clustering significant discontinuities were revealed that occurred simultaneously in the different strata. Thus even in structurally highly complex, multilayered tropical montane forests distinct community units exist that can be surveyed and classified by the Braun-Blanquet approach. This observed zonation was significantly correlated with altitude, temperature and soil acidity (pH); rainfall was of importance in particular for the zonation of epiphytes. Other key factors were humidity (influenced by stable cloud condensation belts) and minimum temperature (in particular the occurrence of frost at 2700 m altitude upslope). The contrary results of other transect studies in East Africa in respect to continuity of change in floristic composition appear to be caused by different sampling methods and intensities or mixing of data from areas with different climate conditions, whereas species richness did not influence the clarity of floristic discontinuities on Kilimanjaro and other parts of East Africa.

Vegetation of Kilimanjaro: hidden endemics and missing bamboo

Abstract: Kilimanjaro has a large variety of forest types over an altitudinal range of 3000 m containing over 1200 vascular plant species. Montane Ocotea forests occur on the wet southern slope. Cassipourea and Juniperus forests grow on the dry northern slope. Subalpine Erica forests at 4100 m represent the highest elevation cloud forests in Africa. In contrast to this enormous biodiversity, the degree of endemism is low. However, forest relicts in the deepest valleys of the cultivated lower areas suggest that a rich forest flora inhabited Mt Kilimanjaro in the past, with restricted-range species otherwise only known from the Eastern Arc mountains. The low degree of endemism on Kilimanjaro may result from destruction of lower altitude forest rather than the relatively young age of the mountain. Another feature of the forests of Kilimanjaro is the absence of a bamboo zone, which occurs on all other tall mountains in East Africa with a similarly high rainfall. Sinarundinaria alpina stands are favoured by elephants and buffaloes. On Kilimanjaro these megaherbivores occur on the northern slopes, where it is too dry for a large bamboo zone to develop. They are excluded from the wet southern slope forests by topography and humans, who have cultivated the foothills for at least 2000 years. This interplay of biotic and abiotic factors could explain not only the lack of a bamboo zone on Kilimanjaro but also offers possible explanations for the patterns of diversity and endemism. Kilimanjaro's forests can therefore serve as a striking example of the large and long-lasting influence of both animals and humans on the African landscape. Resume Le Kilimandjaro possede, sur un gradient d'altitude de 3000 metres, une grande variete de types forestiers qui comprennent plus de 1200 especes de plantes vasculaires. Les forets de montagne aOcotea se trouvent sur le flanc sud, humide. Les forets aCassipourea et aJuniperus poussent sur le versant nord, plus sec. Les forets subalpines aErica situees a 4100 m representent les plus hautes forets nepheliphiles d'Afrique. Face a cette formidable biodiversite, le degre d'endemisme est faible. Cependant, des reliquats de forets dans les plus profondes vallees des zones cultivees en basse altitude suggerent qu'il y avait une riche flore forestiere sur le Kilimandjaro dans des temps anciens, avec des especes a la distribution restreinte que l'on ne connait que sur les monts Eastern Arc. Le faible taux d'endemisme du Kilimandjaro pourrait etre la consequence de la destruction de la foret de basse altitude plutot que de l’âge relativement jeune de la montagne. Une caracteristique des forets du Kilimandjaro est l'absence de zone de bambous, que l'on retrouve sur toutes les autres hautes montagnes d'Afrique de l'Est qui ont des fortes chutes de pluie comparables. Les tiges d'Sinarundinaria alpina sont appreciees par les elephants et les buffles. Sur le Kilimandjaro, on trouve ces gros herbivores sur les flancs nord, trop secs pour qu'une grande zone de bambous puisse se developper. Ils sont exclus des forets humides des flancs sud par la topographie et par les hommes qui cultivent le pied de la montagne depuis plus de 2000 ans. Ce melange de facteurs biotiques et abiotiques pourrait expliquer non seulement l'absence d'une zone de bambous sur le Kilimandjaro, mais aussi, de plusieurs facons, les schemas de la diversite et de l'endemisme. Les forets du Kilimandjaro peuvent servir d'exemple parfait de l'influence enorme et durable qu'ont eue les animaux et les hommes sur le paysage africain.

The banana forests of Kilimanjaro : biodiversity and conservation of the Chagga Homegardens

Abstract: Natural flora, vegetation, diversity and structure of 62 traditional coffee-banana plantations on Kilimanjaro were investigated and compared with the other vegetation formations on this volcano on basis of over 1400 plots following the method of Braun-Blanquet. The vegetation of the so-called Chagga homegardens belongs floristically to the formation of ruderal vegetation forming two main communities that are determined by altitude. These coffee-banana plantations maintain a high biodiversity with about 520 vascular plant species including over 400 non-cultivated plants. Most species (194) occurring in the Chagga homegardens are forest species, followed by 128 ruderal species, including 41 neophytes. Typical of the agroforestry system of the Chagga homegardens is their multilayered vegetation structure similar to a tropical montane forest with trees, shrubs, lianas, epiphytes and herbs. Beside relicts of the former forest cover, which lost most of their former habitats, there are on the other hand (apophytic) forest species, which were directly or indirectly favoured by the land use of the Chagga people. High demand of wood, the introduction of coffee varieties that are sun-tolerant and low coffee prizes on the world marked endanger this effective and sustainable system.