| Abstract |
The miombo woodland is an extensive tropical seasonal woodland and dry forest formation in extent of 2.7 million km². The woodland contributes highly to maintenance and improvement of people’s livelihood security and stable growth of national economies. The woodland faces a wide range of disturbances including fire that affect vegetation structure.
An investigation into the impact of fire on the natural regeneration of six tree species was conducted along a rainfall gradient. Baikiaea plurijuga, Burkea africana, Guibourtia coleosperma, Pterocarpus angolensis, Schinziophyton rautanenii and Terminalia sericea were selected on basis of being an important timber and/or utilitarian species, and the assumed abundance. The objectives of the study were to examine floristic composition, density and composition of natural regeneration; stand structure and vegetation cover within recently burnt (RB) and recently unburnt (RU) sections of the forest. The study was conducted at Kanovlei, Caprivi, Sesheke and Kabompo State Forests, along a rainfall gradient from Namibia to Zambia. A systematic random sampling, using a 3-plot cluster, was replicated nine times. A 2 x 4 factorial treatment structure was used (two fire treatment and four rainfall classes) on the research design.
Sixty-eight vascular plant species were encountered in 25 families and 54 genera, dominated by Caesalpinioideae (15.7 %), Papilionoideae (12.9 %) and Combretaceae (11.4 %). Species richness was high and increased with MAP along the rainfall gradient. High species richness translated into high species diversity among the fire treatments and ranged from 1.5 to 2.8 Shannon diversity index units. The selected tree species contributed to stand parameters as important timber species with importance value indices from 4.5 % to 44.8 % across the study sites. Woody species showed high regeneration density across fire treatments and ranged between 3 039 and 18 274 individuals per hectare with tree species contributing up to 55 %. Fire treatment (p<0.0001) and fire frequency (p=0.027) had a statistically significant relationship with regeneration density. All selected tree species were recruiting, evidenced by the > 1 recruitment ratios and negative regression slopes for size class distributions, however the latter also revealed that the populations of some of species are unstable and declining. Basal area was small and not significantly different among fire treatments at all sites except at Sesheke were recently burnt sites had significantly higher basal area. Furthermore, the basal area of the Sesheke (8.2 ± 0.2 m² haˉ¹) which was significantly greater than Kanovlei (1.2 ± 0.2 m² haˉ¹), Caprivi (1.7 ± 0.2 m² haˉ¹) and Kabompo (3.2 ± 0.2 m² haˉ¹) suggested that anthropogenic influences (forest harvesting and disturbance) are having an effect on the stand structure. Canopy cover varied from 20 % to 75 % in the forests showing an increase in forest cover from drier to wetter sites.
The study proved fire treatment did not significantly affect or alter floristic composition of woody vegetation in the short-term. It also showed good recruitment for the selected tree species (as coppice or seedling) but lacking rejuvenation of the population structure. Fire treatment on vegetation cover is potentially useful and could be advantageous to regeneration of tree species for a few years. Hence, the study calls for a long-term investigation of natural regeneration of tree species taking into account the factors that could not be considered in this study. |
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