Browsing Okavango Research Institute (ORI) by Author "Heinl, M."
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Ramberg, L.; Lindholm, M.; Hessen, D.O.; Murray-Hudson, M.; Bonyongo, C.; Heinl, M.; Masamba, W.; Vanderpost, C.; Wolski, P. (Springer, http://www.springer.com, July 19, 2010)[more][less]
Abstract: The frequency of fires in the Okavango Delta seasonal floodplains peaked at an intermediate frequency of flooding. Floodplains are commonly burnt every 3–5 years. This study showed fundamental changes in ecosystem properties due to burning. A burnt seasonal floodplain in the aquatic phase had oxygen levels well above saturation, 100–200%, while the levels in the un-burnt control site were below saturation and, at night, could decline to 10–40% saturation. The total phosphorous and total nitrogen concentrations were similar on both floodplains but considerably enriched relative to inflowing water, due to nutrient release from the flooded soil-sediment and animal droppings. Zooplankton biomass was very high in both systems although the abundance of fish fry was ten times higher on the un-burnt floodplain. In a low flood year the un-burnt floodplain water had high nutrient levels, primary production, methane emission, and subsequent uptake of methane in biota, as well as a high zooplankton biomass. The very high flood the following year showed the opposite with much lower production at all levels owing primarily to greater dilution of nutrients. The abundance of fish, however, was much higher during the high flood year. Macrophytes and litter provide direct shelter for fish fry but also promote low oxygen levels when decaying. Large flooded areas result in high fish production by removing obstacles related to congestion. This interplay between hydroperiod and fire may be crucial for the maintenance of high biological productivity both in the aquatic and terrestrial phases in a very nutrient poor wetland landscape. Understanding these interactions is crucial for optimal management. URI: http://hdl.handle.net/10311/838 Files in this item: 1
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Heinl, M.; Frost, P.; Vanderpost, C.; Sliva, J. (Elsevier; http://www.elsevier.com/wps/find/journaldescription.cws_home/622855/description#description, May 8, 2006)[more][less]
Abstract: Satellite imagery derived fire history data for the southern Okavango Delta, Botswana from 1989 to 2003 were used to analyse the temporal and spatial distribution of fires and to assess changes in fire activity. Maximum fire activity was encountered for 1997 with 24.1% of the study area burned. The annual extent of the burned area fluctuated considerably, but there appeared to be a regular oscillation apparently induced by floodplain fires. The main fire activity on drylands is in September at the end of the dry season, while most floodplains burn earlier in the year. Both burning of floodplains and drylands appear to peak prior to floods and rainfall-events, respectively. Areas with highest fire frequency were outlined and spatial analyses showed that fires on the drylands are largely due to burning of adjacent floodplains. The floodplains were therefore identified as the centres of fire activity, being the regions with the highest fire frequency and serving as source of fires spreading into drylands. Floodplains showed higher fire frequencies compared to drylands, but no increase in fire activity was detected over the study period for both floodplains and drylands. Description: The study was part of the project 'Fire regime and vegetation response in the Okavango Delta, Botswana' funded by the Volkswagen Foundation, Germany and carried out by the Chair of Vegetation Ecology, Technische Universitaet Muenchen, Germany in collaboration with the Harry Oppenheimer Okavango Research Center (HOORC, University of Botswana) and University of Pretoria, South Africa. Financial support was also given by Conservation International Botswana and the German Academic Exchange Service (DAAD). URI: http://hdl.handle.net/10311/151 Files in this item: 2
heinl_j_arid_env.pdf (392.9Kb)license.txt (1.998Kb) -
Heinl, M.; Neuenschwander, A.; Sliva, J.; Vanderpost, C. (Springer: http://www.springerlink.com, NaN, 2006)[more][less]
Abstract: A series of 98 satellite images was analysed to reconstruct the fire and flood history of a floodplain system in southern Africa(Okavango Delta, Botswana). The data was used to investigate interactions between fire and flooding, and to determine the relevance of rainfall and flood-events for fire occurrences on floodplains and on drylands. The aims of the study are (1) to analyse and compare the fire frequency on floodplains and on adjacent drylands, (2) to investigate the influence of rainfall and flooding on the fire occurrence and (3) to determine correlations between fire frequency and flood frequency. The analyses show higher fire frequencies on floodplains than on drylands because of higher biomass production and fuel loads. The fire occurrence on drylands shows a correlation with annual rainfall events, while the fire frequency on floodplains is in principle determined by the flood frequency. Between floodplain types, clear differences in the susceptibility to fire where shown by analysing flood frequency vs. fire frequency. Here, the highest potential to burn was found for floodplains that get flooded about every second year. By calculating mean fire return intervals, the potential to burn could be specified for the different floodplain types. URI: http://hdl.handle.net/10311/792 Files in this item: 1
Heinl_Michael_LE_2006.pdf (1.827Mb)
Now showing items 1-3 of 3