Changes in miombo woodland structure under different land tenure and use systems in central Zambia

Aim: Population pressure and communal land ownership are often perceived as serious threats to forest conservation in savanna woodlands of central and southern Africa. I aimed at testing the hypothesis that the rate of miombo woodland recovery after clearing and re-growth structure are determined by land tenure and use. Location: Miombo woodland under customary, leasehold, forest reserve and national park on ten permanent and temporary sites was studied in central Zambia. Two sites were in mature woodland and eight sites were in re-growth miombo ranging in age from 1 to 30 years. Methods: I enumerated and measured girth at breast height (1.3 m above ground) of trees/stems in sixty-four 20 × 10 m plots in 1982, 1986 and 2000 at six sites and annually from 1990 to 2001 at four sites to determine stem density and status (live, dead or cut) and wood biomass. A total of 239 trees were cut, wood biomass measured and the data used to develop equations for estimating wood biomass on study plots. Distance between each study site and the nearest human settlement was estimated during each sampling period using aerial photographs, topographical maps and the global positioning system. Results: Land tenure was responsible for significant differences in stem density, wood biomass and rate of biomass accumulation in re-growth following clearing of mature miombo woodland. Although stem density was highest on customary land, wood biomass and accumulation rate were lowest. The highest biomass was on plots in forest reserves, with intermediate values for leasehold and national park. Fire was responsible for tree mortality at all the study sites and its impact was highest at a site in a national park. Sites close to human settlements had the highest density of cut stems but this activity did not significantly reduce wood biomass. Rate of woodland recovery was higher on sites cleared in the 1970s than on sites cleared in the 1990s, irrespective of age of re-growth. The development of the first, second and third re-growths following successive woodland clearing in 1972, 1981 and 1990, respectively, was not significantly different, except for stem density which was highest in the second re-growth. Analysis of interactions between five land tenure and use factors (independent variables) and re-growth structure revealed that 52% (P = 0.0000) of the variation in stem density was because of re-growth age and decade in which the woodland was cleared while distance to human settlements and age of re-growth explained 42% (P = 0.0000) of the variation in wood biomass. Individually, distance to human settlements explained 25% (P = 0.0000) of the variation in wood biomass accumulation rate. Conclusion: The results supported the hypothesis that rate of miombo woodland recovery and structure were influenced by land tenure and use. However, analysis of interactions between factors revealed that use related factors (i.e. decade in which woodland was cleared and distance to human settlements) and re-growth related factors (age and type of re-growth) were more important than land tenure per se in explaining variation in miombo recovery. The conclusion from these results is that regulation of land use is more important than change in land tenure to the proper management of miombo woodland.