SHORT-TERM EFFECTS OF EARLY-SEASON FIRE ON HERBACEOUS COMPOSITION, DRY MATTER PRODUCTION AND SOIL FERTILITY IN GUINEA SAVANNA, NIGERIA

The ecological impact of fire regimes on plant diversity and soil fertility has become a subject of intense discussion, especially in savannas where recurring incidences are common. This study assessed the short-term effects of early-season fire on herbaceous composition, dry matter yield and soil fertility in the Guinea savanna belt of Nigeria. Data on ground cover, dry matter yield (DMY) in plants and concentrations of C, N, P, K, Ca and Mg in soil were collected from 10 delineated subplots in the burned and unburned zones of four sites after annual wildfire had occurred. Ground cover was significantly higher in the burned zones, increasing progressively from January to April (dry season). Eleven herbaceous species in addition to 2 tree seedlings occurred and represented families of Asteraceae, Cyperaceae, Fabaceae and Poaceae. Digitaria nuda, Brachiaria lata, Daniellia oliveri and Aeschynomene indica were limited to the burnt zones while Cyperus tuberosus, Mariscus alternifolius and Rottboellia cochinchinensis were restricted to the unburned zones. DMY ranged from 0.32 g m(-2) (Desmodium tortuosum) to 52.96 g m(-2) (Megathyrsus maximus). Average biomass in the burned and unburned sites was 35.86 g m(-2) and 28.42 g m(-2), respectively. Soil C, N and P concentrations decreased (positive deterioration index - DI), while those of K, Ca and Mg improved (negative DI) in the burned sites. Burning altered the growth (ground cover) and composition of plant species in the short term, and could significantly influence soil nutrient dynamics in the long term, especially with recurring fire events.