Early Secondary Succession on Abandoned Shifting Cultivator's Plots in the Miombo of South Central Africa

Abstract

In the burned miombo of northern Zambia, succession was followed on plots cleared and burned during the practice of shifting cultivation. Twelve formerly cultivated gardens were surveyed in various stages of regrowth (1, 2, 4, 6, 13, and 25 yr after burning). The early vegetation was woody, mainly caused by stumps and root stocks remaining at the site from the preexisting cover. Species diversity was lowest after four years, primarily because the distribution of individuals among species was highly uneven in the middle of the succession. Early and late stages of succession were found be more similar than intermediate stages. An apparant dynamism of the ecological processes was observed; the turnover between different succession stages varied significantly. Three phases could be distinguished: 0-1 yr, 2-6 yr, and 6-25 yr. The canopy of woody species developed in the late stage did not include the dominant miombo species. The diminution of Brachystegia and Julbernardia spp. and the presence of species characteristic of Combretum savanna strongly question the interpretation that succession is occuring towards miombo woodland. THE CONCEPT OF SECONDARY SUCCESSION in southern Africa has recently been contested by Walker (1981), but few studies provide data test the concept of early directed succession. Often the interest is focused more on later stages in the changing of vegetation communities (Trapnell & Langdale-Brown 1962), frequently with emphasis on special ecological groups (Lawton 1964, 1978; Brenan, 1978). Especially, the miombo, the most widespread type of vegetation in southern Africa, is well described Jeffers & Boaler 1966; Malaisse et al. 1972; Freson 1973; Malaisse 1974, 1978; Ernst 1975; Celander 1981; Lawton 1982). Other works from southern Africa are purely grassland studies (Brockington 1960, Vesey-Fitzgerald 1963). Only Adams and Baker (1962) and Strang (1974) described the effects of local cultivation practices on the vegetation. The studies, however, chiefly covered effects recorded several years after the cutting of the forest. Early plant succession after shifting cultivation has been studied in other continents (Richardson 1963, Walker 1966, Harris 1971, Kunstadter et al. 1978, Scott 1978). However, from Africa most works deal with vegetation change (Pielou 1952, Clayton 1958, White 1965, Boaler 1966), soils (Trapnell et al. 1976), or the effects of burning (Trapnell 1959, West 1965, Philips 1974, Trapnell et al. 1976). Trapnell's studies from Zambia are in this respect current, but deal more with changes in woodland composition under varying degrees of fire-protection. Here, too, the effect of fire is studied, though slightly differently. Burning is part of the local agricultural system of the Bemba tribe of northern Zambia. The system, chitemene (Chibemba: to cut), is described by Rich' Received 25 June 1984, revision accepted 24 January 1985. ards (1939), Trapnell (1953), Allan (1967), and Stromgaard (1984b, c, 1985a). It is an infield outfield farming system, i.e., a farming system utilizing its area at two different levels of intensity, an intensively farmed infield and an outfield exploited at low intensity (Stromgaard 1985b). The branches lopped from a larger surrounding area, the outfield, are concentrated on the future field, the infield. The stacked branches are burned just before the beginning of the rain, and seeds are then sown in the ash patch. The large trees are not felled, only branches are lopped; thus, the trees will reach reproductive age faster. The chitemene shifting cultivation system requires vegetative matter for nutrients, and the system also influences the structure and composition of the vegetation. In the study area, two vegetation types are dominant: miombo woodland and Combretum savannah. A dynamic interaction is hypothesized when the recovery of miombo is delayed after cultivation and the fallow becomes dominated by species characteristic of Combretum savannah. In order test this hypothesis, early secondary succession was followed on abandoned shifting cultivator's plots of varying age.