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

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)

The Southern Africa Fire Network (SAFNet) Regional Burned-area Product-validation Protocol

The development of appropriate validation techniques is critical to assess uncertainties associated with satellite-data-based products, to identify needed product improvements and to allow products to be used appropriately. At regional to global scales, there are several outstanding issues in the development of robust validation methodologies, including the need to increase the quality and economy of product validation by developing and promoting international validation standards and protocols. This paper describes a protocol developed to validate a regional southern Africa burned-area product derived from Moderate Resolution Imaging Spectroradiometer (MODIS) 500m time series data. The protocol is based upon interpretations by members of the Southern Africa Fire Network (SAFNet) of multitemporal Landsat Enhanced Thematic Mapper plus (ETM + ) data to derive maps of the location and approximate date of burning. The validation data are derived using Landsat ETM+ scenes distributed to encompass representative regional variation in the conditions for which the MODIS burned-area product was generated and to capture the more important factors that influence product performance. The protocol was developed by consensus to ensure inter-comparison of the independent data derived by the different SAFNet members and to allow these data to be scaled up to provide regional validation of the MODIS burned-area product. Biomass burning in southern Africa, the ETM+ sampling rationale, the interpretation and mapping approach, SAFNet member fire activities, and illustrative 2001 results and difficulties encountered with the protocol are described