The Impact of Fire on the Soil Seed Bank and Regeneration of Harenna Forest, Southeastern Ethiopia

Abstract

The composition and density of soil seed banks was studied at Harenna Forest after a major fire in the year 2000. Soil samples were collected from burned and unburned portions of the forest using quadrants 15 × 15 cm and 9 cm deep, laid along line transects. Forest recovery was also monitored on burned sites using permanent plots of 0.1 ha. One hundred fifty-five seedlings germinated from the soil samples, of which 140 and 15 were from the unburned and burned sites, respectively. The proportion of woody species found on the unburned site was 47%, while on the burned site only one woody species was recorded. Overall mean densities were 621 ± 15 and 66 ± 2 seeds per m2 on the unburned and burned sites, respectively. The greatest diversity was found in the upper soil layer, followed by the middle, litter, and lower soil layers collected from the unburned site. Eighteen months after the fire, the burned site was covered with 32 species of dense vegetation, which attained a height of 3.5 m. Our results revealed that although the fire exhausted the soil seed bank, the vegetation could regenerate quickly with pioneer species, which differed in composition from the neighboring unburned stand. This implies that most species in Harenna Forest are sensitive to fire and could be eliminated easily from the area unless they are properly protected. Therefore, an appropriate management plan should be developed and implemented for the remaining forest, including protection from fire.