Excessive logging can make forest fires even more devastating, according
to a paper published in this week’s Nature magazine. Using data from
ESA’s ERS-2 satellite, a team of scientists from Germany and Indonesia
has concluded that the extensive forest fires in Indonesia in 1997-98
damaged recently-logged land much more seriously than virgin forest or
land that had been untouched for many years.

“The fires severely damaged the remaining forest, and significantly
increased the risk of recurrent fire disasters by leaving huge amounts
of dead flammable wood,” says Dr Florian Siegert, of Remote Sensing
Solutions GmbH.

The team used satellite photographs and imagery from the ERS-2 synthetic
aperture radar (SAR), combined with ground and aerial surveys, to
investigate the effects of the forest fires in the East Kalimantan
region of the island of Borneo. The 97-98 fires were the result of
drought caused by El Nino turning the forests into a dry and flammable
tinderbox, needing only a spark to explode into an inferno. The fires
were widespread and fierce. “A total of up to 5.2 million hectares was
burned”, explains Dr Siegert, ” just under half of which was forest.”

The fires were monitored using the AVHRR radiometers — which can
detect ‘hot spots’ with a resolution of about 1 km — aboard two US
National Oceanic and Atmospheric Administration satellites. Hot spot
detection showed that the fires began in the Mahakam river basin. The
resolution of the radiometer is not high enough to measure the extent
of the fires, though, and assess damage, so the team turned to ERS-2
and its SAR. “Optical satellite systems were severely limited by smoke
and haze during the fires, and by the cloud and rain that followed the
drought,” comments Dr Siegert. “The SAR can penetrate clouds and haze.”

The team used a technique called difference detection’ — essentially
comparing details of ‘before’ and ‘after’ images looking for changes
in the radar signature of the forest below. “Fires destroy plants and
foliage, reduce moisture content and open the forest canopy,” says
Dr Siegert, “which significantly changes the way the forest appears
to radar.”

“Our analysis showed that in the fire area, 24% of the forest had up
to half the trees killed, 42% was severely damaged, with up to 80% of
the vegetation killed, and the remaining 36% showed total destruction,
with vegetation burned off completely and almost all trees dead,” says
Dr Siegert. The team then compared their fire map with a land-use map,
derived from Landsat TM imagery!.

Only 5.7% of undisturbed forest was affected by fire, compared to 59%
of logged forest, and the damage was more severe: 48% of logged forest
had total damage, compared to 4% of the undisturbed forest. The
results clearly show that recently logged forests were hit harder by
fire than undisturbed or partly recovered forest.

The team found that selective logging directly contributed to the
unprecedented extent of the 1998 fires. Many areas burned in the
1982-83 fires did not recover into fire-resistant tropical rain-forest,
and burned once again. Similarly, the fire hazard has greatly increased
for areas burned in 1998.

“Unless land-use policies are changed to control logging and to
introduce reduced-impact logging techniques, recurrent fires will
lead to a complete loss of Borneo’s lowland rainforests,” concludes
Dr Siegert.

Related news

* Fighting forest fires from space


Related links

* ESA/NASDA cooperation on forest fires



[Image 1:
Using data from ESA’s ERS-2 satellite, a team of scientists from
Germany and Indonesia has concluded that forest fires in 1997-98
forest fires in Indonsesia damaged recently-logged land much more
seriously than virgin forest. Photo: F. Siebert

[Image 2:
Scene of total devastation after the forest fires of 1997-98 in East
Kilamantan, Borneo. Up to 5.2 million hectares were burnt. Using data
from ESA’s ERS-2 satellites a team of scientists from Germany and
Indonesia has concluded that excessive loggin can make forest fires
even more devastating. Photo: F. Siegert

[Image 3:
ERS-2 SAR data was used to investigate the effects of forest fires
in the East Kilmantan region of Borneo, in 1997/98. Optical satellite
systems were severely limited by smoke and haze — no obstacles for
SAR. Burnt areas are visible in different shades of yellow to orange
which can be related to different damage levels of the vegetation.
Unburned vegetation appears in blue. Photo: ESA

[Image 4:
Burnt peat swamp forest (to the right) and unburnt forest (to the
left). This type of fire damage is important because huge amounts of
dead biomass were left over by the fire. This means a very high fire
risk. The fire burnt the peat layer and root system of the trees, but
not the trunks. Photo: F. Siegert