Okavango Delta Management Plan - Ramsar Convention on Wetlands

natural factors. There are two major types of natural fires, namely surface fires which are
caused by lightening and peat fires which are caused by combustion of peat.
Frequency of burning
The floodplains in the Seasonal Swamps in the <strong>Okavango</strong> <strong>Delta</strong> are more frequently burnt
than the dryland areas because of greater grass fuel loads due to their higher production
potential and lower grazing pressure caused by the occurrence of less palatable grasses.
The mean fire return period for these floodplains during the 14 year period between 1989 -
2003 was 6.6 years and for the drylands 22.2 years. The highest fire frequency occurred in
the floodplains that are inundated approximately every second year resulting in a mean fire
return period of 5 years. Generally the dryland areas rarely burn however the frequency of
burning varied greatly in the different habitat types in the drylands with some areas being
burnt more frequently than biennially particularly with fires spreading into the drylands
from adjacent more frequently burnt floodplains (Heinl 2005)
Type and intensity of fires
Little information is available in the scientific literature on the types and intensities of fires
occurring in the <strong>Okavango</strong> <strong>Delta</strong> <strong>Ramsar</strong> Site. There is some information of ground fires
burning accumulations of organic peat material (peat fires) in areas where the channels
have dried out as part of the normal dynamic variations in the water flow through the fan of
the <strong>Delta</strong> (ODMP Fire <strong>Management</strong> Strategy 2006). A general description of the formation
and accumulation of organic peat material in wetlands like the <strong>Okavango</strong> <strong>Delta</strong> is provided
by Roggeri (1995).
The plant photosynthesis processes consume CO2 which is partly transformed into organic
carbon and accumulated in plant tissue. Under certain conditions (increased acidity, lack
of oxygen, lack of nutrients or low temperatures) the organic matter is only partially
decomposed and accumulates in the soil. The peat formed in this way forms a reservoir of
organic carbon. Once stored in this form, carbon can only be returned to the atmosphere
by oxidation or by combustion of the peat. Swamps, and in particular peat swamps, thus
trap large amounts of carbon.
Therefore burning of peat soils lead to the destruction of natural carbon reservoirs that could
have moderated the increase in atmospheric CO2 contributing to the greenhouse effect and
global warming. This, if confirmed could give a special significance to this function performed
by some wetlands.
It is estimated that the blockage of the Thaoge River has gradually occurred since the
1870’s and the drying of the peat deposits flanking the channel has resulted in the
occurrence of peat fires, which have destroyed the original plant communities and peat
deposits (Ellery et al 1989). This has resulted in the release of nutrients into the soil which
improves forage quality. In addition more recently there has been the cultivation of crops
such as tropical fruit and sugar cane in this area because of the elevated soil fertility
associated with the former burning of the peat deposits in this area
Thus a conflicting set of circumstances exists regarding the occurrence of peat fires in the
<strong>Ramsar</strong> Site. On the one hand these fires are releasing CO2 into the atmosphere thereby
contributing to the greenhouse effect and global warming. On the other hand the peat fires
have and are raising the nutrient levels of highly infertile soils resulting in the production of
grass forage with significantly improved quality for grazing animals. Therefore these fires
are playing a significant role in the normal nutrient cycle occurring in the <strong>Okavango</strong> <strong>Delta</strong>
ecosystem (ODMP Fire <strong>Management</strong> Strategy 2006). It should also be considered that these
fires are probably not a recent occurrence but have been occurring since time immemorial
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