A peat fire in the Okavango Delta, Botswana, and its importance as an ecosystem process

Abstract

Summary The progressive abandonment and desiccation of the lower Nqoga River system and its associated vegetation‐covered peat deposits, has resulted in the development of subsurface peat fires. These appear to have been burning within the study area for decades and consist of a mosaic of burning fronts, the first of which burns to a depth of up to 15 cm. This relatively shallow fire destroys the bases of stems and plant rhizomes, thereby preventing re‐establishment of the former plant community by vegetative growth. Deeper fires are initiated where cracks develop in the peat during drying and desiccation. The depths to which these burn are limited by peat moisture content or by the presence of an incombustible inorganic substrate. The initial collapse is some 30–40 vol. %. Further compaction is brought about by rainfall and animal trampling which may cause volume reductions of as much as 98%. The short‐term consequences of subsurface peat fires include the release of plant nutrients, enhancement of soil texture and soil water retention properties, and temporary transformation of the area into a terrestrial habitat. However, physiographic changes induced by the peat fire result in its eventual reflooding. It is proposed that the time delay between burning and reflooding, and the rate and depth of reflooding, determine the nature of the habitats which form after re‐inundation. These processes are important in maintaining the overall structure and functioning of the Okavango Delta ecosystem. Résumé L'abandon progressif et le dessèchement de la basse Nqoga et des dépôts de tourbe qui y sont associés ont abouti au développement de feux de tourbe sous la surface. II semble que ceux‐ci brûlaient depuis des décennies à l'endroit des recherches et qu'ils se composent d'une mosaique de petits feux dont le premier brûle jusqu'à une profondeur de 15 cm. Ce feu assez superficiel détruit les bases des tiges et les rhizomes des plantes, empêchant de ce fait le rétablissement de la plante originelle par simple croissance végétative. Des feux plus profonds surviennent lorsque des fissures se développent dans la tourbe en voie de dessication. La profondeur à laquelle ils brûlent est limitée par l'humidité de la tourbe ou par la présence d'un substrat inorganique incombustible. l'effondrement initial correspond à quelque 30 à 40% en volume. Les chutes de pluies et le pietinement des animaux peuvent tasser encore plus et causer des réductions de volume atteignant 98%. Les conséquences à court terme des feux de tourbe souterrains comprennent la libération de nutriments végétaux, une amélioration de la texture du sol et de ses propriétés de rétention d'eau, et la transformation temporaire de la région en un habitat terrestre. Cependant les modifications physiographiques induites par les feux de tourbe résultent ultérieurement en de nouvelles inodations. On pense que le délai entre le feu et l'inondation ainsi que l'importance et la prondeur de Pinondation déterminent la nature des habitats qui se forment après inondation. Ces process...

In the line of fire: the peatlands of Southeast Asia

“…the Moscow region of Russia [18,19], Canada and Alaska [20][21][22][23], Africa, e.g. the Okavango Delta [23], South America, in Peru [24] and Brazil [25] and Southeast Asia, particularly Indonesia [26][27][28][29].…”

Water depth and biotic insulation: Major determinants of back-swamp plant community composition

“…While the bulk of the flow is diverted, the old channel system, including the back-swamp areas, becomes increasingly dry and susceptible to burning. Slow burning peat fires result in the collapse of the peat deposits, thus lowering the land surface and initiating reflooding (Ellery et al 1989) and the plant succession described above. Resource accumulation in the Okavango Delta does not necessarily lead to long-term stability but instead sets off a diffuse set of interactions which later feed back to disrupt the insulation.…”

Mapping the annual area burned in the wetlands of the Okavango panhandle using a hierarchical classification approach

“…Like the surrounding savannah, the panhandle has a predominantly sandy base, with soils and peat forming only where perennial water moves very slowly, allowing the accumulation of decomposing organic matter. Most of the sediment washing into the Okavango is fine bed-load sand (Ellery et al 1989). The dry, cool winters run from June to August.…”

“…In the Okavango Delta, research on the effects of fire has been limited to peat fires (Ellery et al 1989, Gumbricht et al 2002. This is partly because by burning the soil, peat fires bring about more permanent changes to the land and substrate than do surface fires.…”