Vegetation changes after single fire-events in the Okavango Delta wetland, Botswana

Abstract

A comparative study on burned and unburned areas has been conducted for the south-eastern floodplains of the Okavango Delta wetland, Botswana to assess differences in vegetation composition and structure after single fire-events. Main findings on plant traits and species occurrences supported the theory of only slight vegetation changes after fire in fire-prone environments. No specific plant trait was found to be favoured by the fire-event and only Urochloa mosambicensis showed a highly significant correlation to burning. Main changes were observed in vegetation structure, e.g. height and cover of the herb layer or biomass production. Interestingly, no main trends regarding how vegetation structure is generally affected by fire-events were derivable. Detailed analyses of five derived habitat types clearly showed different and contradictory responses to burning. This variability of vegetation response to fire-events, dependent on the habitat, was explained along a productivity gradient from active floodplains to dry Mopane woodlands. While floodplains showed an obvious decrease of standing biomass after the fire-event, an increase of biomass was observed for the Mopane woodlands. The nutrient pulses often described after fire-events, therefore seem to improve nutrient conditions best in poorer habitats, while for more productive sites, the enhanced nutrient availability after burning seem to be minor. Nomenclature: Arnold and De Wet (1993).