Triennial Burning Research Articles

Effect of burning and mowing on grass and forb diversity in a long-term grassland experiment

Disturbance may be an important determinant of plant community composition and diversity owing to its effects on competitive interactions, resources, dominance and vigour. The effect of type, timing and frequency of disturbance on grass and forb species richness was examined using data from a long-term (> 50 yr) grassland burning and mowing experiment in KwaZulu-Natal, South Africa.Grass species richness declined considerably (> 50%) in the absence of disturbance, whereas forb species richness was unaffected. Annual burning in sites not mown in summer tended to increase grass species richness relative to triennial burning (22% increase) with the reverse being true in sites mown twice in summer (37% decline). Forb species richness declined by 25% in sites mown twice in summer relative to sites mown in early summer only. Disturbance was necessary to achieve maximum grass species richness presumably by removing litter and increasing the availability of light. The interaction of time of mowing in summer (early versus late) and time of burning during the dormant period (spring versus winter) had the most dramatic effect on species richness. Time of burning had no effect on richness in sites mown in early summer, but winter burning resulted in a dramatic decline (27–42%) in richness in sites mown in late summer. This effect may be related to possible greater soil desiccation with this combination of disturbances.Nomenclature: Arnold & De Wet (1993).Abbreviation: AGP = Above-ground phytomass production.

The effect of different fire treatments on the population structure and density of the Marula, Sclerocarya birrea (A. Rich.) subsp. caffra (Sond.) kokwaro (Kokwaro & Gillet 1980) in the Kruger National Park

To determine the influence of frequency and season of burn on the growth structure and density of Sclerocarya birrea, six replicated fire treatments of the experimental burning plot trial were surveyed in the Sclerocarya birrea / Acacia nigrescens savanna of the central Kruger National Park. Studies were also conducted in an exclosure to determine the success of recruitment of Sclerocarya birrea individuals across a range of fire intensities in the absence of herbivory. The results indicated that the lower canopy structure (individuals <2m) was greatly affected by fire, whereas density was unaffected. The lower canopy generally responded to the interaction between frequency and season, and not to the main effects of season or frequency. August triennial burns had the greatest impact on the total seedling structure, with higher fire intensities resulting in the development of a multi-stemmed morphology.

The influence of fire on populations of small mammals of the Kruger National Park

A total of 16 000 trap-nights was employed over eleven months to examine the influence of burning on small mammal populations in two major veld-types of the Kruger National Park. Four burning treatments (control, annual August burning, triennial August and April burning) were examined in detail and the following parameters determined: small mammal species composition, population density, biomass and species diversity. The control treatment had a high, stable small mammal density, biomass and diversity; the annual burning treatment had a low diversity and was dominated by Tatera leucogaster. The triennial burning treatments showed a cycle of species composition from domination by T. leucogaster following burning, through domination by other rodent species to domination by Crocidura hirta at the end of the cycle. The distributions and movements of the small mammals can be explained in terms of cover and litter preferences.