REVIEW: ECOLOGY
Economic Reasons for Conserving
Wild Nature
Andrew Balmford,
1
* Aaron Bruner,
2
Philip Cooper,
3
Robert Costanza,
4
† Stephen Farber,
5
Rhys E. Green,
1,6
Martin Jenkins,
7
Paul Jefferiss,
6
Valma Jessamy,
3
Joah Madden,
1
Kat Munro,
1
Norman Myers,
8
Shahid Naeem,
9
Jouni Paavola,
3
Matthew Rayment,
6
Sergio Rosendo,
3
Joan Roughgarden,
10
Kate Trumper,
1
R. Kerry Turner
3
On the eve of the World Summit on Sustainable Development, it is timely to assess
progress over the 10 years since its predecessor in Rio de Janeiro. Loss and degradation
of remaining natural habitats has continued largely unabated. However, evidence has
been accumulating that such systems generate marked economic benefits, which the
available data suggest exceed those obtained from continued habitat conversion. We
estimate that the overall benefit:cost ratio of an effective global program for the
conservation of remaining wild nature is at least 100 :1.
H
umans benefit from wild nature (1)in
very many ways: aesthetically and cul-
turally; via the provision of ecological
services such as climate regulation, soil forma-
tion, and nutrient cycling; and from the direct
harvest of wild species for food, fuel, fibers,
and pharmaceuticals (2). In the face of increas-
ing human pressures on the environment, these
benefits should act as powerful incentives to
conserve nature, yet evaluating them has
proved difficult because they are mostly not
captured by conventional, market-based eco-
nomic activity and analysis.
In 1997, Costanza et al. published a synthe-
sis (3) of more than 100 attempts to value
ecosystem goods and services using a range of
techniques including hedonic pricing, contin-
gent valuation, and replacement cost methods
(4). Using case studies to derive average values
per hectare for each of 17 services across 16
biomes and then extrapolating to the globe by
multiplying by each biome’s area, the Costanza
team estimated the aggregated annual value of
nature’s services (updated to 2000 US$) to lie
in the range of $18 trillion to $61 trillion (10
12
),
around a rough average of
$38 trillion. These
figures are of similar size to global gross na-
tional product (GNP), but have been criticized
by some in the economic community (5–9).
One problem is that such macroeconomic
extrapolations are inconsistent with microeco-
nomic theory: extrapolation from the margin to
a global total should incorporate knowledge
about the shape of the demand curve (3, 5–8). In
practice, it is very likely that per-unit demand
for nonsubstitutable services escalates rapidly as
supply diminishes, so that simple grossing-up of
marginal values (as is also done in calculating
GNP from prices) will probably underestimate
true total values. On the other hand, high local
values of services such as tourism may not be
maintained if extrapolated worldwide. In addi-
tion, while some policy decisions are made us-
ing macroeconomic indicators, many others are
made at the margin, and so are more appropri-
ately informed by marginal rather than total
valuations (9).
Another problem with the original estimate
is that landscapes can yield substantial (albeit
rather different) flows of goods and services
after, as well as before, conversion by humans
(which is of course why people convert them).
A clearer picture of the value of retaining habitat
in relatively undisturbed condition might there-
fore be obtained by estimating not the gross
values of the benefits provided by natural bi-
omes, but rather the difference in benefit flows
between relatively intact and converted versions
of those biomes.
Net Marginal Benefits
To address these concerns, we reviewed
more than 300 case studies, searching for
matched estimates of the marginal values of
goods and services delivered by a biome
when relatively intact, and when converted
to typical forms of human use. To ensure
we did not neglect private benefits of con-
version, studies were only included if they
covered the most important marketed
goods, as well as one or more nonmarketed
services delivering local social or global
benefits. We cross-validated figures for in-
dividual goods and services with other es-
timates from similar places. Finally, we
checked that the comparisons across differ-
ent states of a biome used the same valua-
tion techniques for particular goods and
services. Our survey uncovered only five
examples that met all these criteria. Here,
we summarize their findings, with all fig-
ures expressed as net present values (NPVs,
in 2000 US$ ha
1
), and using the discount
rates considered by the authors [see Fig. 1
and supplemental online material (10) for
further details].
Two studies quantified net marginal ben-
efits of different human uses of tropical forest
areas. Kumari compared the values obtained
from timber plus a suite of nontimber forest
products (NTFPs), as well as the values of
water supply and regulation, recreation, and
the maintenance of carbon stocks and endan-
gered species, for forests under a range of
management regimes in Selangor, Malaysia
(11). Compared with two methods of re-
duced-impact logging, high-intensity, unsus-
tainable logging was associated with greater
private benefits through timber harvesting (at
least at high discount rates and over one
harvesting cycle), but reduced social and
global benefits (through loss of NTFPs, flood
protection, carbon stocks, and endangered
species). Summed together, the total econom-
ic value (TEV) of forest was some 14%
greater when placed under more sustainable
management (at
$13,000 compared with
$11,200 ha
1
).
A study from Mount Cameroon, Cam-
eroon, comparing low-impact logging with
more extreme land-use change again found
that private benefits favor conversion, this
time to small-scale agriculture (12). Howev-
er, a second alternative to retaining the forest,
conversion to oil palm and rubber planta-
tions, in fact yielded negative private benefits
once the effect of market distortions was
1
Conservation Biology Group, Department of Zoology,
University of Cambridge, Cambridge CB2 3EJ, UK.
2
Cen-
ter for Applied Biodiversity Science at Conservation In-
ternational, 1919 M Street, NW, Suite 600, Washington,
DC 20036, USA.
3
Centre for Social and Economic Re-
search on the Global Environment (CSERGE), School of
Environmental Sciences, University of East Anglia, Nor-
wich NR4 7TJ, UK.
4
Center for Environmental Science,
Biology Department and Institute for Ecological Eco-
nomics, University of Maryland, Box 38, Solomons, MD
20688, USA.
5
Graduate School of Public and Internation-
al Affairs, University of Pittsburgh, Pittsburgh, PA 15260,
USA.
6
The Royal Society for the Protection of Birds, The
Lodge, Sandy, Bedfordshire SG19 2DL, UK.
7
UN Environ-
ment Programme–World Conservation Monitoring Cen-
tre (UNEP-WCMC), 219 Huntingdon Road, Cambridge
CB3 ODL, UK.
8
Green College, Woodstock Road, Oxford
OX2 6HG, UK; and Upper Meadow, Old Road, Heading-
ton, Oxford OX3 8SZ, UK.
9
Department of Zoology,
University of Washington, 24 Kincaid Hall, Box 351800,
Seattle, WA 98195–1800, USA.
10
Department of Biolog-
ical Sciences, Stanford University, Stanford, CA 94305,
USA.
*To whom correspondence should be addressed.E-
mail: a.balmford@zoo.cam.ac.uk
†Address after Sept.2002: Gund Institute of Ecolog-
ical Economics, The University of Vermont, Burling-
ton, VT 05405, USA.
S CIENCE’ S C OMPASS
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REVIEW
9 AUGUST 2002 VOL 297 SCIENCE www.sciencemag.org950

removed. Social benefits from NTFPs, sedi-
mentation control, and flood prevention
were highest under sustainable forestry, as
were global benefits from carbon storage
and a range of option, bequest, and exis-
tence values. Overall, the TEV of sustain-
able forestry was 18% greater than that of
small-scale farming (
$2570 compared
with $2110 ha
1
), whereas plantations had
a negative TEV.
Three other biomes yielded single studies
meeting our criteria. Analysis of a mangrove
system in Thailand revealed that conversion
for aquaculture made
sense in terms of
short-term private
benefits, but not once
external costs were
factored in (13). The
global benefits of
carbon sequestration
were considered to be
similar in intact and
degraded systems.
However, the sub-
stantial social bene-
fits associated with
the original man-
grove cover—from
timber, charcoal,
NTFPs, offshore
fisheries, and storm
protection—fell to
almost zero follow-
ing conversion. Sum-
ming all measured
goods and services,
the TEV of intact
mangroves exceeded
that of shrimp farm-
ing by around 70%
(
$60,400 com-
pared with $16,700
ha
1
).
van Vuuren and
Roy (14 ) reported that
draining freshwater
marshes in one of
Canada’s most pro-
ductive agricultural
areas yielded net pri-
vate benefits (in large part because of substan-
tial drainage subsidies). However, social bene-
fits of retaining wetlands, arising from sustain-
able hunting, angling, and trapping, greatly ex-
ceeded agricultural gains. Consequently, for all
three marsh types considered, TEVs were high-
er when the wetlands remained intact, exceed-
ing figures for conversion by a mean of around
60% (
$8800 compared with $3700 ha
1
).
Finally, a synthesis of economic studies
examining Philippine reef exploitation dem-
onstrated that despite high initial benefits,
destructive techniques such as blast fishing
had a far lower NPV of private benefits than
did sustainable fishing (15). The social ben-
efits of sustainable exploitation, arising from
coastal protection and tourism, were also lost
upon dynamiting reefs. As a consequence,
the TEV of retaining an essentially intact
reef was almost 75% higher than that of
destructive fishing (at
$3300 compared
with $870 ha
1
).
One clear message from our survey is
the paucity of empirical data on the central
question of the changes in delivery of
goods and services arising from the conver-
sion of natural habitats for human use. For
10 of the largely natural biomes (including
rangelands, temperate forests, rivers and
lakes, and most marine systems) in
Costanza et al. (3), we found no studies that
met all of our criteria. For the four biomes
which were analyzed, only a handful of
well-established ecosystem services were
considered, and some particularly valuable
services, such as nutrient cycling, waste
treatment, and the provision of cultural val-
ues, were not examined at all.
Despite the limited data, our review also
suggests a second broad finding: in every
case examined, the loss of nonmarketed ser-
vices outweighs the marketed marginal ben-
efits of conversion, often by a considerable
amount. Across the four biomes studied,
mean losses in TEV due to conversion run
at roughly one-half of the TEV of relatively
intact systems (mean  54.9%; SE 
13.4%; n  4). This is certainly not to say
that conversion has never been economical-
ly beneficial; in most instances, past clear-
ance of forests and wetlands for prime
agricultural land and other forms of devel-
opment probably benefited society as a
whole. But unless the present case studies
or the range of ser-
vices and biomes
examined in the lit-
erature are extreme-
ly unrepresentative
(and we know of no
reason why this
should be the case),
our synthesis indi-
cates that at present,
conversion of re-
maining habitat for
agriculture, aquac-
ulture, or forestry
often does not make
sense from the per-
spective of global
sustainability.
Continuing Losses
These results there-
fore provide a clear
and compelling eco-
nomic case, alongside
sociocultural and
moral arguments (16–
18), for us to strength-
en attempts to con-
serve what remains of
natural ecosystems.
Yet, when we sum-
marized available es-
timates of recent
trends in the global
status of natural habi-
tats and free-ranging
vertebrate popula-
tions, we found that
although key data are again disturbingly scarce,
they show that rates of conversion are high
across most biomes (10).
We included in our survey any estimate of
global trend in habitat cover based on a series
which began in 1970 or later and included a
period of at least 5 years after the 1992
United Nations Conference on Environment
and Development in Rio de Janeiro. We sup-
plemented this with biome-specific indices
based on time-series data on populations of
wild vertebrates, derived from the World
Wildlife Fund (WWF) 2000 Living Planet
Index (LPI) and UN Food and Agricultural
Fig. 1. The marginal benefits of retaining and converting natural habitats, expressed as NPV (in
2000 US$ ha
1
) calculated using the discount rates () and time horizons presented.Values of
measured goods and services delivered when habitats are relatively intact and when converted
are plotted as green and black columns, respectively.[From (11–15); see (10) for further
details.]
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