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OCR for page 159
15
DEFORESTATION AND ITS ROLE IN POSSIBLE
CHANGES IN THE BRAZILIAN AMAZON
Eneas Salati, Reynaldo Luiz Victoria,
Luiz Antonio Martinelli, and Jeffrey Edward Richey
Global deforestation, and in particular deforestation of the humid
tropics, has become a controversial issue both scientifically and polit-
ically. The polemical aspects of the question are due primarily to the
lack of detailed information on the changes that have occurred and on the
processes that would permit the establishment of a sustainable use of the
renewable natural resources. One of the most important global aspects of
deforestation is the transfer of carbon stored in the forest biomass to
the atmosphere (Woodwell et al., 1978; Houghton et al., 1985~. In 1980
it was estimated that 25 percent of the global atmospheric carbon dioxide
(CO2) emissions was derived from the transformation of forests into
annual cropland or grassland in the tropics (Houghton et al., 1987~.
Extinction of flora and fauna may be expected whenever the diversity of
a natural forest ecosystem is reduced by the substitution of any other
single species or less diverse ecosystem (Prance, 1986~. Depending on
the extent of the cleared area, deforestation can affect the climate at
micro- and meso-scales, with local and regional and possibly global
consequences (Salati and Marques, 1984; Henderson-Sellers, 1987~.
Deforestation and its consequences in the Amazon basin are discussed
in the present paper. The Amazon, the richest and most diverse ecosystem
on the planet, is presently undergoing rapid transformations due to the
expansion of new settlements undertaking diverse activities.
CAUSES FOR DEFORESTATION
In the beginning of the colonization of Brazil by Europeans in 1530,
and in the centuries thereafter, deforestation in Amazonia was the con-
sequence of very few and small-scale human activities. Slash-and-burn
agriculture and the commercial harvesting of timber resulted in the
opening of settlements, some of which turned into important cities in the
beginning of this century, including Manaus and Belem. Such activities
were almost always developed along the Solimoes (as the Amazon is called
above its confluence with the Rio Negro) and Amazon Rivers and along the
more important tributaries. The rivers were then the natural transport
system in the region.
The trend of deforestation changed during the 1960s, with the onset
of new human activities induced by the opening of highways that promoted
159
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160
easy and quick access to "terra-firma" areas. The most important of
those highways were the Belem-Brasilia, the Transamazonica, the Cuiaba-
Porto Velho (BR 364) in Rondonia, and the Porto Velho-Manaus-Boa Vista,
and more recently (in the 1980s) the railway between Sac Lutz and
Carajas. With the expanded transportation system combined with govern-
ment incentives for development of the region, the population increase
was rapt d, reaching over 15 million people in the last 2 decades (Sudam,
1987~. The main economic activities associated with the occupation
process are the following:
o Extensive cattle ranching.
o Timber extraction.
O Perennial crops like cocoa, rubber, and homogeneous forests for
pulp and paper.
0 Annual crops like sugar cane, soybeans, corn, and rice.
O Charcoal production for the cast iron industry.
O Construction of several major dams for hydroelectric power
stations.
o Gold exploration and mining.
O Oil exploration.
For example, extensive cattle ranching has been the major cause of de-
forestation and has led to many unsuccessful projects both ecologically
and economically (Fearnside' 1988~. Four industries in the Carajas area
are already operating and producing 240,000 tons of cast iron per year,
consuming 192,000 tons of charcoal per year. It is estimated that in the
next decade production will jump to 280,000 tons per year, consuming
230,000 tons of charcoal per year. With the country's land-tenure
criterion, deforested land is a synonym for developed land and real-
estate speculation, and even the boldness of the new settler. These
processes are all linked to social and economic factors that generate or
stimulate migrations, as well as to external factors like the external
debt pressure pushing the government to stimulate export policies.
Several of these activities, which lead to deforestation without the
introduction of sustainable agriculture or any other real benefit for the
population, may be corrected in the near future with the implementation
of the program NOSSA NATUREZA (April 1989~. This program would regulate
the application of fiscal incentives to the development of the Amazon;
hopefully, this program will be realized.
THE EXTENT OF DEFORESTATION
One of the most controversial issues recently in the literature, and
in the past few months in the Brazilian and international press, has been
the extent to which the Amazon region is being deforested. The increas-
tng international concern, as well as the increasing scientific aware-
ness of the role of the tropical forest in future environmental global
changes, is the major driving force behind these discussions.
It is now well known that tropical forests are being deforested at
increasing rates, but the critical question of knowing with a better
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161
accuracy the actual values of such rates is as yet unanswered. Estimates
range from predictions that very little primary forest will remain, with
the exception of western Amazonia and central Africa, by the turn of the
century, to the other extreme that proposes deforestation rates of only
0.6 percent per year (Myers, 1988a). Estimates of deforestation in the
Brazilian Amazon range from 5 percent in a recent study by the Instituto
Nacional de Pesquisas Espaciais (INPE, 1989) to the 12 percent stated by
Mahar (1988), with a more conservative figure of 8 percent given by
Fearnside (1989~. One of the most striking reports comes from Setzer and
Pereira (1989), which shows that over 80,000 km2 Of Amazonian forests
were burned in 1987 alone. Comparing this figure with that given by
Myers (1988b) of 200,000 km2 Of annual global destruction leaves Brazil
as the leading country of tropical deforestation.
When dealing with such controversial numbers, it is important to
understand that most of the problems arise from the methodologies now in
use to estimate deforestation. Even the use of satellite imagery is
liable to errors in interpretation of the data. It is recognized that
the National Oceanic and Atmospheric Administration's advanced very high
resolution radiometer images with their low resolution (1 km) will have
an entire pixel (100 ha) saturated even if only a few hectares are act-
ually burning. Landsat images, although much better as far as resolu-
tion is concerned (30 to 100 m), present problems in discriminating
primary forest from regrowth and in mapping the borders between forest
and savannas. Cloud cover is also a major problem with Landsat images.
An assessment using available techniques with greater availability than
Landsat images for critical regions like Rondonia and Acre at cheaper
prices is urgently needed in order to better evaluate the problem.
Nevertheless, what really counts is knowledge of the rates at which
deforestation is occurring, rather than the percentage of deforested
areas in the Amazon, whether it be 5 percent or 12 percent. For example,
curves fitting the numbers given by Mahar (1988) for several Brazilian
states in the Amazania (Table 15.1) show exponential growth in all cases
(Figure 15.1~. Critical areas like Rondonia do show an alarming rate,
but it is also important to note that areas considered to be noncritical,
like Roraima and Amapa, are also showing exponential growth. Assuming
the above to be realistic and that the pattern will continue, curve
extrapolations show that by the year 2000 most of the Amazonian states
will have had their territory completely cleared.
DEFORESTATION AND ITS POSSIBLE PHYSICAL AND BIOLOGICAL CONSEQUENCES
Biodiversity
As stated by Myers (1988a), deforestation "will mean the virtual
elimination of what is frequently termed the richest and most complex
expression of nature that has ever appeared on the face of the planet.
Or, to put it another way, the culmination of almost 4 thousand million
years of evolution will have been all but eliminated in less than a
century."' This statement, besides being alarming, points to the fact
that diversity is the basis for the functioning of the tropical forest
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162
TABLE 15.1 Exponential Regression Equations for the Deforestation in
Several Amazonian States
State
Total
Deforested
Area Area 1988 Equationa
(km2 ~ (km2 ~
Acre 152,589 19,500 1,053 X 100.0928x
Amapa 140,276 572 117 X 100.0465x
Amazonas 1,567,125 10S, 790 413 X 100.168x
Goias 285,793 33,120 4,022 X 100.0688x
Maranho 257,451 50,670 2,758 X 100.0921x
Mato Grosso 881,001 208,000 1,047 X 100.0969x
Para 1,248,042 120,000 8,930 X 100.0838x
Rondonia 243,044 58,000 1,137 X 10125x
Roraima 230,104 3,270 41 X 1oO.136x
Total S,00S,42S S98, 922 27~600 X 100.098x
NOTE: Data were extracted from Mahar (1988) and cover a range of
measurements taken between 1975 and 1988.
aThe equations are given in the form y = a X 10bX where x is an integer
starting from 1975.
ecosystem. The higher the number of species present in one environment,
the higher are the probabilities of adaptation to changes and adversities
of the environment.
For the Amazon region, tree diversity has been documented in the
literature. Prance et al. (1976) found 505 species higher than 2.S m in
0.2 ha in a "terra firme" forest near Manaus. Schubart (1982) referred
to between 300 to 500 species with breast height diameter (BHO) greater
than 5 cm in 1 ha. Martinelli et al. (1988), working in a ''terra firmet'
forest in Rondania, found about 210 species with BHD greater than 10 cm
in 1 ha and estimated a biomass of approximately 400 tons/ha. The lat-
ter authors also pointed out the difficulties of estimating biomass for
tropical forests. Very little information is available on the chemical
composition of the biomass in tropical forests, and this information is
urgently needed if the natural biogeochemical cycles are to be under-
stood.
This enormous diversity should serve as the basis for not consider-
ing tropical forests as mere sources of wasteful exploitation; much more
attention should be paid to what this environment represents to our
planet and to the necessity to preserve it. Apart from soil protection
and balance of the hydrological cycle, forests are not only sources of
timber and fuel wood, but they also can provide many other products like
resins, essential and edible oils, fruits and nuts, natural fibers, and
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163
4
3
2
1
o
60
o
o
O
_'
A:
LL
in
o
lL
C)
Roraima
t
-
t
Rondonia
40
20 -
120 -
80
40
Para'
)1
600
400
2nn
Total Legal Amazon t
1970 1 975
1980 1985 1990
YEAR
FIGURE 15.1 Deforestation trends in selects
(Data extracted from Mahar, 1988.)
d areas of the Amazon region.
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164
_
/ ATMOSPHERE OF OTHER /
REGIONS
Fo = 3-5
j .
7.2 AMAZON BASIN 13.8
RECYCLE
~ P
~ ~ R = 5.5 - / 1 / .
_ ~ RIVER FLOW ~ ATLANTIC OCEAN /
FIGURE 15.2 A schematic model of the water cycle in the Amazon basin.
E is evaporation; P is precipitation.
pharmaceuticals. Many of the drugs that are routinely bought at drug
stores--analgesics, tranquilizers, diuretics, and so forth--are derived
from alkaloids and other biochemicals found in tropical forest plants.
Two drugs derived from the rosy periwinkle, a native of Madagascar's
forests, are being largely and successfully used against HodgRin's
disease, leukemia, and other blood cancers. The perennial species of
wild corn that is found in a montane forest in Mexico (Iltis et al.,
1979) and is resistant to several viruses and mycoplasms might be the
basis of new commercial cultivars and therefore could expand corn culti-
vation areas, representing multibillion-dollar savings for mankind. This
was probably the last habitat of the species; it would have been lost
forever with uncontrolled deforestation. That has been the fate of
several endogenous species in places like Rondonia, one of the richest
areas in the world in terms of flora and fauna (Brown, Jr., 1987), where
a substantial part of the region has already been completely cleared.
Hydrological Cycle and Climate
Figure 15.2 schematically shows the water balance for the Amazon
basin, including an area of approximately 6 million km2 from the river
mouth at Marajo Island to the headwaters at "Cordilheira dos Andes.' The
data shown in Figure 15.2, although carrying uncertainties and errors due
to the lack of a measuring network with a good spatial distribution over
the basin, were obtained through successive approaches using different
methods and techniques (Salati, 1986~. The most important fact, however,
is to note that the water vapor flux originating in the Atlantic Ocean is
not of sufficient magnitude to explain the rainfall and the vapor outflux
in the basin. As a direct consequence, it is necessary to assume the
recirculation of evapotranspired water in the basin. This conclusion is
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165
strongly supported by the spatial distribution of the 180 and D isotopes
in the region (Salati et al., 1979~. Other conclusions are that the
present atmospheric steady state equilibrium in the region is dependent
on the vegetation cover, i.e., the forest. Further, the Amazon basin is
a source of water vapor to other regions, especially to the Brazilian
central plateau, and eventually to the ''Pantanal" (a large area of swamp
and seasonally flooded land in central-western Brazil).
Bearing such evidence in mind, it is clear that a major alteration in
vegetation cover of the region would lead to changes in the climate at
the micro- and meso-levels. Changes would be felt particularly through
variations in the albedo, in the rainwater residence time, and in an
increase in runoff and a decrease in evapotranspiration (Salati et al.,
1979~. Increases in maximum temperatures and daily thermal amplitudes,
due to a decrease in precipitation, would also be expected. Such alter-
ations would be felt not only in the Amazon region itself but also in
other nearby regions, especially the Brazilian central plateau. Simula-
tion models, although showing several uncertainties, also point to such a
scenario (Henderson-Sellers, 1987~.
Transport of Sediments
Soil erosion is one of the most commonly cited consequences of de-
forestation, particularly in tropical areas where precipitation is high.
Besides being directly responsible for a reduction in soil fertility,
erosion also plays a major role in the decrease of the lifespan of
hydroelectrical power dams. For example, although it was difficult to
predict at the time, the sedimentological studies done for the con-
struction of the Samuel power dam in Rondonia did not take into account
the possible changes in land use and their consequences for the sediment
load of the Rio Jamari. Studies that are currently being carried out
using the 210Pb technique to calculate the sedimentation rate in a lake
near the dam are showing increases in the rates that might be closely
correlated with deforestation and/or tin mining activities in the basin
(B. R. Forsberg, personal communication). These data are, however, very
preliminary and urgently need further confirmation.
Although consequences as just exemplified could actually be foresee-
able, their prediction is impaired by lack of data. There are very few
studies of land erosion and river sediment loads in tropical areas. The
little existing data do show, however, that erosion losses can be 100
times greater in soils changed to agricultural use when compared to
similar soil covered with forest (Salati and Vase, 19849. This lack of
data is in reality a result of the difficulties in applying conventional
methods of erosion measurement to tropical areas. Alternatively, the
sediment flux per unit area of a river basin, the so-called denudation
rate, can be used to estimate erosion losses. There are, however, doubts
about the accuracy of such methods. Some authors argue that several
depositional areas may exist in a baste, which would lead to long lag
times in the response from the river to changes in land use (Trimble,
1975; Meade, 1989~. Graham, Jr. (1986), for instance, working in the Rio
Jamari, estimated erosion losses by using both the classical Universal
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166
Soil Loss Equation (USLE) and measurements of the sediment load in the
river from 1978 to 1983. Both methods showed an increase in erosion,
latter, however, giving smaller numbers than the first. The ratio be-
tween estimates calculated by the denudation rate and the ones calcu-
lated through the USLE was on average 0.06 and was highly variable,
ranging from 0.01 to 0.12. Although differences observed between the
methods were great, it is important to note that both presented similar
trends and provide a basis for long-term estimates.
Since 1982, as a result of a joint cooperation program between the
Instituto Nacional de Pesquisas na Amazonia (INPA), the Centro de Energia
Nuclear na Agricultura (CENA), the Escola Superior de Agricultura Luiz de
Queiroz (ESALQj, and the University of Washington, sediment concentra-
tions and fluxes have been systematically measured in the Amazon/Sol~moes
main channel and several of the major tributaries, including the Rio
Madeira and some of its tributaries. Table 15.2 summarizes the avail-
able data. Details about sample collection, analysis, and other spe-
cific information may be found in Meade et al. (1985), Meade (1985),
Richey et al. (1986), Mertes (1985), and Martinelli et al. (1989~.
These data are, however, preliminary for use in deforestation mon-
itoring; greater knowledge of their spatial and temporal variability is
needed. The results do show the general expected trend for denudation
rates in the basin. Rivers with headwaters in the Andean and sub-Andean
regions have the highest values, and tributaries originating in the
Brazilian Plateau show the lowest values. It should be noted, however,
that Rondonia rivers carry very little sediment and could therefore be
useful if used as monitors of the rapid deforestation that is occurring
in their basins.
Carbon Dioxide Emissions
Changing the forest cover to other land use systems transfers sub-
stantial quantities of carbon stored in the biomass to the atmosphere,
potentially increasing the greenhouse effect (Houghton et al., 1987~.
Since 1988, when the massive forest burnings in Rondonia generated
enormous pressure by the international media, many scientists started
worrying about obtaining better estimates of the contribution of forest
burnings to CO2 emissions to the atmosphere.
Here we calculate Amazonia's potential contribution to atmospheric
CO2. We made several simplifying assumptions: (1) biomass will always
be completely burned, (2) successional ecosystems will always have a
small biomass when compared to the original forest (this is true taking
into consideration that it takes about 100 years to completely regenerate
a forest to its original status in the region), and (3) soil organic
matter will not increase significantly with time after burning. Vari-
ability in the calculations arises from the uncertainty in biomass esti-
mation for the Amazon forest. We used the values found by Martinelli et
al. (1988) of 360 + 60 tons/ha of above-ground biomass plus 40 tons/ha of
litter and fallen trunks for the environmental protection area of the
Samuel power dam in Rondonia. Total biomass available for burning could
therefore vary between 280 and 400 tons/ha, which would give from 140 to
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167
TABLE 15.2 Summary of Available Data on Water Discharge, Sediment Flux,
and Denudation Rate of the Amazon and Madeira River Basins Between 1982
and 1986
Total Suspended
River Basin Discharge Sediment Denudation Rate
(103 m3/s) (106 tons/year) (tons/km2 per yr)
Amazon
Vargem Grande 47.9 647 571
Obidos 159.0 1156 250
Tributaries
Iga 7.4 19 127
Jutai 1.4 2 23
Jurua 3.0 26 116
Japura 13.9 23 79
Purus 10.8 29 78
Negro 30.8 6 8
Madeira
Main channel
Tributaries
Pimenta Bueno
Jiparana
29.2 488 357
0.245 0.17
0.875 0.75
Jaru 0.081 0.03
14
23
6
200 tons of carbon per hectare if it is assumed that biomass contains 50
percent carbon. The final numbers used in our calculations are the total
deforested area and the annual rate of deforestation. These numbers are
highly controversial, as already stated, and the total deforested area
ranges from the very optimistic estimate of 250,000 km2 (5 percent of the
Legal Amazon--INPE, 1989) to the other extreme of 600,000 km2 (12 percent
of the Legal Amazon--Mahar, 1988~. As far as annual deforestation rates
are concerned, the numbers given for 1988 range from 17,000 km2/yr (INPE,
1989) to 80,000 km2/yr (Setzer and Pereira, 1989~.
Taking the above cited numbers and assumptions into account, we es-
timated that the Amazon region has already contributed emissions ranging
from 3.5 X 1015 g carbon to 12 X 1015 g carbon to the atmosphere (Table
1S.3~. That is on the order of 2 to 7 percent of the total atmospheric
CO2 emitted due to deforestation and burning until 1980 (Woodwell, 1987~.
Table 15.3 also shows that annual emissions, considering the 1988 rates,
ranged from 0.24 X 1015 to 1.6 X 1015 g carbon per year, which is between
4 to 25 percent of the global CO2 emissions, estimated to be 7 X 1015 g
carbon per year (Woodwell, 1987~. Even if, to be on the conservative
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168
TABLE 15.3 Estimated CO2 Emission due to Burning in the Amazon
Estimate of Carbon
Biomass Availablea
(tons/ha = 108 g/km2)
Lower (140)
Upper (200)
Range of CO2 Emissions (X 1015 g carbon)
Cumulative Total Total in 1988C
3.5 to 8.4 0.24 to 1.1
5.0 to 12.0 0.34 to 1.6
NOTE: Estimate based on the assumption that 100 percent of the burned,-
biomass is transformed into CO2.
aBased on data from Martinelli et al. (1988~.
bThe total range of emissions is calculated as the product of the lower
and upper estimates of the carbon biomass available and the lower
(250,000 km2--INPE, 1989) and upper (600,000 km2--Mahar, 1988) estimates
of the total area deforested.
CThe range of emissions for 1988 is calculated as the product of the
lower and upper estimates of the carbon biomass available and the lower
(17,000 km2--INPE, 1989) and upper (80,000 km2--Setzer and Pereira, 1989)
estimates of the area deforested in 1988.
side, we assumed that only 50 percent of the biomass is burned during
forest fires, the numbers would still be significant, ranging from 2.0 to
12 percent of global emissions. Although these data may not be precise,
they are useful as a warning for the potential dangers that uncontrolled
deforestation in the Amazonia poses to our environment.
CONCLUS IONS AND RECOMMENDATIONS
Present knowledge reveals the key role of the forest in maintaining
the dynamic equilibrium of the Amazonian ecosystem. In summary, the
forest controls water dynamics in the basin, the energy balance, the
sediment yield, the nutrient balance, the diversity of species, the
quality of surface water, the soil quality, and the carbon stock in the
biosphere.
The above conclusions were drawn from an analysis of many papers
published about the Amazonia in the last few years. Although the in-
formation available is relevant and permitted those conclusions, many
doubts still persist, because with rare exceptions the information is not
continuous in time. Spatial distribution of the available information is
also poor. It is therefore still difficult to visualize the entire
Amazonian ecosystem as a whole. The lack of knowledge of the basic
functioning mechanisms of the Amazonian ecosystem and of the most
suitable methods for sustainable development of the region are the main
reasons for the failure of many of the agricultural and cattle ranching
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169
projects. In addition, institutional problems are serious. The lack of
research funds is impairing the continuity of many research programs and
also the implementation of technical recommendations and enforcement of
legal exigencies. We therefore recommend the following:
o An increase in the number of biological conservation areas in
regions representative of different ecosystems, in order to preserve
endogenous species from extinction.
o An expansion of international support to research groups and in-
stitutions dedicated to the study of the basic functioning mechanisms of
the ecosystem, especially those with programs already under way for a
considerable time.
o The design of integrated interdisciplinary regional programs to
study the factors affecting the steady state equilibrium of the entire
ecosystem.
o The design of programs to reclaim already degraded areas, partic-
ularly through reforestation.
0 The implementation of anthropology research programs designed to
acquire better knowledge of the forest management practices of native
peoples. We should not forget that they have been living in the forest
and from the forest for thousands of years.
o The implementation of programs for the protection of the native
Indian communities and their culture and traditions.
o The stimulation of extractive activities for natural products,
apart from logging, that have already proved to be economically profit-
able and that cause no harm to forest integrity.
ACKNOWLEDGMENTS
The authors wish to acknowledge the financial support to Eneas Salati
by the Smithsonian Institution during the preparation of this paper.
This paper is contribution No. 35 from the National Science Foundation
CAMREX project and contribution No. 6 of the International Atomic Energy
Agency Amazonia I project IAEA-BRA/0/010.
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Representative terms from entire chapter:
amazon basin
