3.6 Method used to analyse fire regime
According to Multilingual Glossary of Dendrochronology, fire
regime means the combination of fire frequency, intensity, size and seasonality
that determine the role of fire in a given ecosystem. When a bush fire passes,
the trees of this specified site are injured forming the fire scares that are
often observed on cross wood section. In the present study, these fire scares
were used to assess the fire interval, its frequency and intensity for
comparing both studied sites.
Fire interval means the number of years between two consecutive
fi res scars in a specific cross-wood section.
Fire frequency differs from fire interval in the sense that it
means the number of fires per year in a given area. To determine this, we
examine d fire season by their intra annual position in the fire scars using
high accuracy. The scars observed in ring boundary were formed during dry
season and those that were observed in ring growth zone occurred during the
growth season (rain period).
To assess the intensity of each fire, all the stem discs were
examined. For individual tree, a fire is qualified as low intensity when the
scar was observed only in sample cut ted at 10 cm from ground. When the same
fire was identified from both samples of height (10 cm and 1.3 m) for a same
tree, it was considered as a high intensity fire. However, we carefully
completed this analysis with the number of tree that recorded the fire and
sometimes we analyzed the season of fire that allowed confirming the
observations. We must precise that most discs samples were cutted from two
levels in Comoé National Park that is not the case in Upper Aguima
Catchment where the most stem discs were only collected at 10 cm from
ground.
3.7 Nature of data
Quantitative and qualitative data were obtained from the stem
discs analysis. The qualitative
data were obtained through macroscopically
and micr oscopic appreciation of the wood
colour, the analysis of rings structure, the distribution of
vessels and parenchyma that helped to describe the wood anatomy of the species.
The position (year) of the identified fire scares on cross wood was also a
qualitative data that allowed the determination of the years of bush fire from
sampled trees.
The quantitative data were the number of tree rings per stem
discs, their widths, the number of scarred trees per species and the number of
rings scarred on each stem disc. To do this, it was necessary to prepare the
stem discs by their processing.
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