Effect of restricting fire on trees and grass cover on savanna in the Red Volta West Forest Reserve, northeast Ghana
Most African savanna is subject to annual fire, which burn off the dry grass and restricts regeneration of woody plants. Experiments to investigate the effects of savanna fires have been carried but few have been long-term. The experiment summarised here, situated in the Red Volta West Forest Reserve, north-east Ghana, was started in 1949 to look at the effects of burn or no burn management regimes on trees, ans subsequently also investigated grass response up to the mid-1970s. The reserve is the main source of thatch grass for nearby villages.
Experimental plots: The experiment was set up in 1949. Three adjacent plots (visually homogenous habitat each 4.05 ha), were defined by fire breaks about 8 m wide. Trees were counted and then plots were clear-felled and the following treatments were applied, commencing in the dry season of 1949-50:
1) annually burnt late in the dry season (April);
2) annually burnt early in the dry season (November);
3) no burning (control).
Plant monitoring: Periodic monitoring of trees and herbaceous vegetation (cover, diversity and biomass) were undertaken up to 1977.
Soil: Four randomly located soil pits (0.2 x 0.2 x 0.2 m) were dug per plot, and soil samples analysed for organic matter, total nitrogen, available phosphorus and exchangeable potassium. Four additional samples were taken per plot to estimate bulk density.
Trees: In 1976-77 there were 202 trees/ha (> 30 cm girth) on the unburned plot, 42/ha on the early burn plot and 23/ha on the late burn plot. Corresponding figures for basal area were 3.43, 0.51, 0.24 m²/ha.
Grasses: Grass cover in the burnt plots remained constant at about 13% since 1960, whereas that in the unburned plot declined and was around 6% by 1976. Grass productivity (dry biomass) at the end of the growing season in 1976 was 182 g/m² on the unburned plot, and 260 g/m² and 144 g/m² on the early and late burn plots respectively.
Plant diversity: In 1977, there were 73 species of vascular plants in the unburned plot, 53 in the early burn and 44 in the late burn plots.
Soil: Only slight differences in soils were observed but the unburned plot had significantly more organic matter and total nitrogen.
Conclusions: Protection from burning enhanced floristic diversity and tree cover. Early burning favoured desirable thatch species (Andropogon ascinodis, Loudetia flavida, Monocymbium ceresiiforme and Schizachyrium schweinfurthii). Early burning and no burn treatments were better than late burning for enhancing production of more palatable forage species such as Andropogon gayanus.