A review
essay
as a
requirement for the Advanced Readings Module
MA
Environmental Management
May 1999
Since the early days of mankind, fires have been used as a management tool in using natural resources. It is therefore closely linked to many other ecosystems. Fire is one of the natural disturbance that initiates cycles of vegetation succession. However, large fires can do more damage than good, both to human beings and the natural environment. Natural fires are common in many parts of the world and are an integral part of many terrestrial ecosystems. Along with the advancement in science we learn more about how large fires devastate the environment and better management is needed to control it. On occasions, efforts to arrest such fires can do little but hope that weather changes, this shows as evidence how vulnerable many areas of the world are to this disturbance. A few fires can ruin years of effort in fire prevention and fire fighting and several large fires can change the landscape for many years. In the period of 1993-1994, several large fire episodes took place in California, southeastern Australia and Spain. In 1997, extended drought in Indonesia incited many fires in the peat swamp forest that caused major disruptions in the region. Smoke plumes from the fires polluted the air and caused health problems and disturbances to air and sea traffic.
Every year, vegetated areas
around the world caught fire; for instance the boreal forests of Canada,
wildfires burn in America, Australia and also in the tropical forests of
Southeast Asia. Some of this is caused naturally but most damage is usually
caused by humans. For instance no more than 2 per cent of the fires that occur
in the Mediterranean region are of natural origin (Trabaud et al. 1993
cited in Blondel and Aronson 1995). While in the sparsely populated areas of
the boreal forests, fires are mostly caused by lightning. Deforestation for
logging or agriculture are the major cause of fires in tropical forest fires.
In this century, the return rate of fire has increased dramatically. In the
past decade, about 0.56 x 106 ha of woodland and shrubland have
burned every year in the Mediterranean region (ECE/FAO 1990 cited in Blondel
and Aronson 1995).
Bush fires are endemic to the
Australian continent and much of the native flora and fauna has evolved
symbiotically with these events and has the capability to reestablish over time
(Pyne 1992 cited in Adams 1995). Australia is a large, flat and dry continent
covering an area about 7.7 million km2, half of which is tropical
and half of which is temperate. Virtually the whold continent is fire prone
(Gill et al. 1981 cited in Gill and Moore 1998). In the north, fires are
most common from April to November (the dry season) while in the south the main
fire season is from November to March. In coastal and subcoastal of New South
Wales, fires occur mainly in spring (September to November) and summer
(December to February) but sometimes also in March (early autumn).
In the beginning of 1994, these
bush fires impacted urban areas. The wildfires happen just in the suburbs of
Sydney, in southeastern Australia. The fire was fought by roughly 10,000
firefighters from all over the Australian continent. It was exacerbated by
several factors: hot weather, low humidity, strong and gusty winds, dense
overlapping vegetation canopies and accumulated vegetation litter. The
resulting damage was extensive: several lives lost; hundreds injured; almost
200 properties destroyed; parks and reserves transformed into semblances of
moonscapes; 500,000 hectares of bushland devastated (Adams 1995).
Prosser and Williams (1998)
compared plots of burnt and unburnt sites after the 1994 fires near Sydney.
They found out that fire alters runoff and erosion processes in native Eucalyptus
forests. Moderately intense fires, such as the 1994 Sydney fires, can produce
substantial erosion if rainfall events of 1-year recurrence interval, and
possibly as high as 10-year recurrence interval, follow in the year after the
fire. Such events are of probability and did not occur after the 1994 Sydney
fires. So, whilst there were legitimate concerns over acceletared erosion these were not realised.
In the northern hemisphere,
boreal forests cover 10% of the land surface. There are wide ranges of
temperature and precipitation (Eastwood et al. 1998). Van Wagner (1988
cited in Weber and Stocks 1998) estimates the average annual area burned during
the period between 1949 and 1971 at 1.3 million ha/yr with variations between
14 per cent to 412 per cent about the mean.
Extreme fires are common, with
recent examples of large areas burned covering 7.4 million ha in 1989, 6.4
million ha in 1994, and 7.3 million ha during the 1995 fire season (CIFFC 1995
cited in Weber and Stocks 1998). Cheng et al. (1998) studied a large
forest fire that occurred about 300 km to the northeast of the Edmonton area in
Canada, early summer 1995. They found that significantly higher NO2
and O3 concentrations in rural areas were observed when air came
from the direction of the forest fire area.
Lightning is a significant cause
of fires in the boreal forest accounting for about 90% of the area
burned (Hardy and Franks 1963, Requa 1964, Barney 1969, 1971, Stocks 1974,
Johnson and Rowe 1975, Stocks and Street 1983 cited in Johnson 1992).
Lightning-caused fires decline northward generally as the frequency of
thunderstorm days declines (Johnson 1992).
In many parts of the boreal
zone, fire drives vegetation succession, landscape dynamics and carbon cycling.
Golbal climate change may affect the frequency and size of wildfires and alter
the rate of carbon release into the atmosphere (Eastwood et al. 1998).
For example in northwestern Ontario, Canada, the frequency and intensity of
large-scale watershed disturbances is increasing (Paterson et al. 1998).
Timber harvesting and wildfires have been shown to alter water quality in
stream ecosystems. Unfortunately, scientific studies of these impacts on lakes
are considerably rarer (Paterson et al. 1998).
It would seem that boreal forest
fires take place over both a large landscape scale and long time span.
Ecologists have found these spatial and temporal scales difficult to study
rigorously. Knowledge on population effects and fire behaviour to date is not
very sophisticated (Johnson 1992). At best, they can state that on average,
boreal wildfires are large, infrequent, of high intensity and consume large
amounts of the forest floor duff (Johnson 1992).
Boreal forest fire behaviour
results primarily from: vegetation which produces a large amount of relatively
fine fuels (£ 2 cm in diameter) which
decays slowly; and fire seasons which, over the life span of a tree (an average
of about 50-150 years), can be expected to have at least one synoptic weather
pattern which severely dries the ground fine and duff fuels, has lightning
which ignites the fuel and high winds which cause high rate of fire spread and
intensity (Johnson 1992).
When fires occur, the
populations are reduced and then have the possibility of rapid increases,
usually by recruitment or regeneration. Thus, fire behaviour and population
recruitment may control population abundance and distributions. In arguing that
by stopping fires a shade tolerant, self-reproducing tree composition would
eventually result, means disregarding the life histories of most boreal trees.
This also means that it would require a major change in climate and in
vegetation architechture (Johnson 1992).
Other parts of north America
also experience forest fires such as in Florida where in 1998 fires set ablaze
by abnormally hot and dry weather. The fires forced more than 112,000 people
from their homes (Mazza 1998). Not long before the incident happened, forests
in Mexico burned, sending smoke as far as the US state of North Dakota (Mazza
1998).
Over a period fo less than 10
days in autumn 1993, the southern California landscape exploded in massive
wildfires that burned more than 80,000 ha (Keeley 1995). Wildfires play an
important ecological and evolutionary role in many California ecosystems and
potentially affect biodiversity. Plant species are not equally adapted to all
fire frequencies and there is evidence that entire ecosystems may be replaced
by altering the burning regime (Keeley 1995).
Andrea et al. (1990 cited
in Arino and Melinotte 1998) estimate that the biomass burn every year for
Africa totals 390 Mt for forest and 2430 Mt for savannah. Hao and Liu (1994
cited in Arino and Melinotte 1998) estimate that 2500 Mt of biomass are burned
every year over Africa. This means that around half of the world biomass
burnings occurs in Africa.
On the African continental
scale, fire events are correlated to bioclimatic and phytogeographic regions,
as well as to human practice and meteorological conditions (Malingreau 1990
cited in Arino and Melinotte 1998). It is worth noting that the peak in fire
activity occurs in the afternoon. This peak activity is related to daily human
activity as well as to the fire physics: during the day the vegetation dries
out, favouring flaming (Arino and Melinotte 1998).
In 1987, in the Brazilian
Amazon, 350,000 independent fires, possibly corresponding to 200,000 km2
of area burned various types of vegetation (Setzer and Pereira 1991). These burnings
let out emissions comparable to those of a large volcano, it is highly
significant in regard to tropospheric chemistry on a world scale, air-pollution
problems at the synoptic scale, as well as carbon dioxide, hydrological and
radiation budget changes. With current growth in deforestation rates the
burning phenomena and interactions with the atmosphere will increase, making
control a major concern for the world community (Setzer and Pereira 1991).
As a comparison, Sahai et al.
(1997) did a study on the effects of Mt. Pinatubo’s eruptions in 1991 on
stratospheric O3 and SO2 over Brasil. Total ozone
observations at Cuiaba, Brasil, showed a significant (11%) decrease in
stratospheric ozone levels during the winter months of 1992.
A common practice associated
with forest clearings and land management in the Amazon is the burning of the
existing vegetation cover. Although there is a large number of biomass burnings
every year and adverse effects to the environment are known to result, no
efforts have been made to measure the magnitude of these burnings (Setzer and
Pereira 1991).
Similar land clearing practices
was done in Southeast Asia. As in many countries worldwide, a ‘burning season’
occurs every year in Indonesia, primarily to prepare agricultural land for
plantation before the rains, but also as a ‘slash and burn’ practice at the
forest edge in order to extend the area available for agriculture (Wooster et
al. 1998). In 1997 however, the rains arrived late and the drought
conditions allowed the burning activity to become more intense than in
non-drought years (Wooster et al. 1998). The 1997 fires produced dense
layers of smoke that reportedly blanketed the Indonesian islands of Borneo and
Sumatra, as well as large sections of Malaysia, Singapore, Brunei and the
Philippines and Thailand. The scale of the fires, and the associated haze, was
such that the activity was widely reported around the world (Wooster et al.
1998).
Haze from tropical burning is
known to contain, amongst other constituents, large concentrations of carbon
monoxide, carbon dioxide, nitrogen monoxide and ozone (Wooster et al.
1998). Though smoke from fires initially rises to a few kilometers altitude,
convective activity ultimately mixes material from the haze layers down into
the boundary layer, forming a ground level smog (Andreae et al. 1988
cited in Wooster et al. 1998).
Biomass smoke plumes from forest
fires in North America produced observed surface temperatures 1o to
6oC cooler than forecast (Marshall et al. 1996). Penner et
al. (1991, 1992) found that the radiative effects of smoke plumes can
approach that of a doubling of CO2 (though of opposite sign)
(Marshall et al. 1996). This suggests that prolonged biomass burnings
events (such as for tropical deforestations) may locally mask the effects on
regions or seasons that have relatively little natural cloud cover, i.e., the
dry season (Marshall et al. 1996).
Nichol (1997) statistically
evaluated the impact of the smoke haze event in Southeast Asia in 1994 for its
impact on regional and global climate. It was found that several local
parameters are closely related to air quality on a daily basis. Nichol (1997)
also estimated that a total of 164 million tons carbon were released during the
1994 smoke haze event (of which 77 million tons was due to peat burning).
The changes in tropospheric
column O3 during the course of the 1997-1998 El Niño appear to be
caused by a combination of large-scale circulation processes associated with
the shift in the tropical convection pattern and surface/boundary layer
processes associated with forest fires in the Indonesian region (Chandra et
al. 1998).
Relative to 1996, the El Niño in
1997 produced a significant increase in tropospheric column ozone (TCO) by
10-20 Dobson units (DU) in the Indonesian region at the time when there was
large-scale burning from uncontrolled fires in the tropical rainforests of
Sumatra and Borneo (Chandra et al. 1998). Chandra et al. (1998)
suggests that a significant increase in TCO and decrease in tropospheric water
vapour in this region are associated with supressed convection and downward
motion.
The deforestation in tropical
lands have both local and global consequences. Locally, climates may become
more extreme, soils may suffer physical and chemical deterioration, and hydrological
balances may be perturbed (Whitmore and Sayer 1992). Massive deforestation,
altering albedo and regional atmospheric water balance, could affect weather
patterns, and there is particular concern at the possible contribution to
atmospheric warming of the addition of carbon dioxide into the atmosphere from
the burning or decomposition of the biomass (Whitmore and Sayer 1992). Perhaps
the single greatest cause for concern over the loss of tropical forests is that
there is a considerable body of evidence to suggest that it is leading to
unprecedented loss of the biological diversity that these forests contain
(Myers 1983, Raven 1987 cited in Whitmore and Sayer 1992).
Monitoring changes in fire
frequency are vital for forest management and predicting climate change
impacts. The continuity of remotely sensed data, combined with the extent of
the boreal ecosystem make Earth observation an important tool for fire
monitoring (Eastwood et al. 1998).
A comprehensive experiment to
study biomass burning and their climatic effects as field project in Brazilian
Amazon, the Smoke, Clouds and Radiation – Brazil (SCAR-B), detected fires in
Brazil which are responsible for 60-85% of the burned biomass (Kaufman et
al. 1998).
Forest fires in large sparsely
populated areas in the boreal forest zone are difficult to detect by ground
based means. Satellites can be a viable source of information to augment
air-borne recoinnasance. The Advanced Very High Resolution Radiometer (AVHRR)
sensor aboard the National Oceanographic and Atmospheric Administration (NOAA)
satellites has been used to detect and map fires in the past mainly in the
tropics and mainly for environmental monitoring purposes (Rauste et al.
1997).
In Finland, a fire management
model use satellite imagery that are then transferred to the forest fire
detection system. The present receiving system at Finnish Meteorological
Institute (FMI) obtains data 4-8 orbits a day. The orbit configuration of the
NOAA satellites (usually one morning satellite and one afternoon satellite)
gives 2-4 scenes – some of them separated by about 100 minutes when the same
satellite from consecutive orbits – in the morning (approximately 3-10 local
time) and 2-4 scenes in the afternoon (approximately 13-20 local time). Between
these time frames there is a gap in the availability of data. The length of
this gap varies (between 4 and 6 hours) within the orbit repeat period. There
is another gap around midnight but this is a less severe problem for forest
fire detection since most fires tend to get started in daytime (Rauste et
al. 1997).
During the fire hazardous
seasons of 1995-1996, Minko et al. (1998) tried to determine the
efficiency in the use of NOAA/AVHRR data to detect forest fires on East
Siberia’s territory. They developed an algorithm to detect forest fires, which
shows a reasonably good performance on Siberia’s territory.
An effort to build energy maps
can be very useful to prevent and fight forest fires effectively. An example of
such efforts was done in Spain. Nunez Regueira et al. (1999) used
thermochemical parameters – calorific values and flammability, elementary
chemical composition and heavy metal contents which make up the woodland map of
the northern coast of Galicia, Spain.
Satellite-based detection of
forest fires supplements the existing fire detection methods, especially in
sparsely inhabited forest areas, but it cannot completely replace air
surveillance of forest fires (Rauste et al. 1997). Many research is
being done in perfecting the fire detecting model. Marshall et al.
(1996) made a series of general circulation model (GCM) simulations with the
National Center fro Atmospheric Research (NCAR) Community Climate Model,
version 2 (CCM2) in order to examine on the direct and indirect short-wave
effects of the smoke clouds as well as the transport of these smoke plumes
outside of the source region and its effct on the regional climate.
Finally a decision support
system for detecting and fighting forest fires should be put in place for fire
prone areas. Designing such system means combining tasks such as automated data
processing, efficient access to relevant data, and integrate the appropriate
information so that effective and efficient decision can be done. Wybo (1998)
proposed a design of such system, called FMIS – the Fire Management Information
System – which demonstrated to be a reliable detection system based on smoke
detection.
Conclusion
Fire is one of the natural disturbance that initiates cycles of vegetation succession. A lot of time efforts to arrest large fires can do little but hope that weather changes, this shows as evidence how vulnerable many areas of the world are to this disturbance. The resulting damage can be devastating such as the 1994 Sydney fires where several lives was lost, scores injured and not to mention the extensive effect to the environment. Biomass burnings have both local and global consequences. Monitoring changes in fire frequency are vital for forest management and predicting climate change impacts.
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