Regeneration of fire degraded peatswamp forest in Berbak National ...

Regeneration of fire degraded peatswamp forest in Berbak National Park and implementation in replanting programmes
5.1.3. Radar
The set of radar images available (17 in total) ranges from 1992 to 1998 and gives, similar to the
Landsat images, a clear view on pre-fire disturbances. In addition it provides insight in flooding
duration. Disturbances are evident north-west of the core zone, where logging trails can be clearly
discerned (1998 images). Other impacts are visible in the east of the core zone (figure 5.1). The square
clear-felled site, visible on the 1997 Landsat image, is already present in the 1992 radar image,
indicating that this disturbance already occurred several years earlier than formerly was presumed. It
was not visible on the 1992 Landsat image as it was just out of reach of the satellite’s sensor. Several
kilometres to the north the image reveals a second similar sized and clear felled rectangle. This site is
also visible on the 1997 Landsat image, but is much less clear than the other square, probably because
regrowth of vegetation obscured the extent of disturbance.
The pre-1998 images show that flooding in the core zone (indicated by light grey tones) increased over
the years. On the oldest images flooding is mainly present in the direct vicinity of rivers. Later images
indicate that flooding extends over a much larger area exactly covering the site that burnt in 1997. Of
course the extend of flooding may change from year to year but it is probable that this pattern is
caused by a structural change in hydrology, presumably induced by human influences (e.g. logging,
drainage). The area seems to face relatively deep flooding in the wet season and relatively strong
desiccation in the dry season, and consequently may have become more susceptible to fires.
The 1998 images were used to make an assessment of flooding duration. By comparison of the four
images available for that year (figure 5.4a,b,c and d), a distinction could be made between six classes
of sites ranging from areas that face very long flooding (black colour for rivers and lakes, white colour
for floodplains) to locations that face very short (several weeks or months) flooding (dark grey on
radar). In this way, each site could be assigned to a certain flooding class. However, the exact duration
of flooding for each class is impossible to determine and to do this a larger database of radar images
would have been necessary. Measurements in the field that were originally meant for determining
flooding duration (current water level, level of maximum flooding, water level retreat) were combined
with observations on the extent of decomposition of logs 10 , and used to test the reliability of the classes
discerned, derived from the radar images.
10 Logs that remain submerged, were observed to have a low rate of decomposition. Areas that face short flooding
contain strongly decomposed logs, although the exact rate is also dependant on the type of wood.
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