Individual study: The effect of savanna burning on tree regeneration in the Olokemeji Forest Reserve, Nigeria
Hopkins B. (1965) Observations on savanna burning in the Olokemeji Forest Reserve, Nigeria. Journal of Applied Ecology, 2, 367-381
Fire is often used in management of savanna grasslands. The nature and effects of savanna burning on herbs and trees in a Nigerian forest reserve was investigated. Almost all savanna is burnt annually in this region. Of particular interest was the effect of different burn times on the herb layer, and on tree regeneration.
Study area: Most observations were made on a previously established research plot of derived savanna woodland in the Olokemeji Forest Reserve, or near to this on similar plots. Fire temperatures measurements were made on 'early burnt' and 'late burnt' plots of an experiment, about 3 km away.
Fire temperatures: Fire temperatures were recorded by thermo-sensitive paints ('Tempilaq'), whose colour or form changes at a specific temperature. Five paints were chosen to cover a range of temperatures (66-1,000º F). Five aluminium strips (6 cm long), with a hole near one end, were joined together by a wire to form a ‘star’. Paint was applied to the upper surfaces, one for each paint. Generally, 10 stars were placed in a series from ground level to 6 m height.
On the 'early burnt' plot and 'late burnt' plot, five observations were made on the days when deliberately burnt: 30 December and 15 March during the 1960-61 dry season; and 30 December and 9 March during the 1963-64 dry season. On the 'research' plot eight vertical series of varying height were used: they were arranged so as to cover the various physiognomic variations of the vegetation in the plot. The 'research' plot was allowed to be burnt by chance (as usual) and observations were made during the 1960-61 dry season, when it was burnt on about 7 February.
Vegetation: Tree cover (height and basal area classes) and mortality was assessed after burns. Dry weight samples of the herb layer before and after burning was used to calculate percent lost upon burning.
Burn temperatures: At ground level, temperatures were generally over 540° C and decreased with height. The rate of fall was rapid with early burning (ambient temperature maintained at about 3 m); later burning produced temperatures over 100° C through a height of 6 or 7 m.
Effect on herbs and trees: Herb distribution after burning was in a banded pattern perhaps reflecting fluctuating wind during the fire. Early in the dry season 25%, averaging 84% from January onwards.
Late burning for five consecutive years reduced the tree population by 32%. Most losses were of smaller height and basal area classes so that, even though the total loss of basal area was only l0%, regeneration was virtually prevented. Some species were more fire-tolerant than others.