Abstract and Figures

As the terrestrial human footprint continues to expand, the amount of native forest that is free from significant damaging human activities is in precipitous decline. There is emerging evidence that the remaining intact forest supports an exceptional confluence of globally significant environmental values relative to degraded forests, including imperilled biodiversity, carbon sequestration and storage, water provision, indigenous culture and the maintenance of human health. Here we argue that maintaining and, where possible, restoring the integrity of dwindling intact forests is an urgent priority for current global efforts to halt the ongoing biodiversity crisis, slow rapid climate change and achieve sustainability goals. Retaining the integrity of intact forest ecosystems should be a central component of proactive global and national environmental strategies, alongside current efforts aimed at halting deforestation and promoting reforestation.
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https://doi.org/10.1038/s41559-018-0490-x
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1School of Earth and Environmental Sciences, The University of Queensland, St. Lucia, Brisbane, Queensland, Australia. 2Wildlife Conservation Society,
Global Conservation Program, Bronx, New York, NY, USA. 3Natural Resources & Environmental Studies Institute, University of Northern British Columbia,
Prince George, British Columbia, Canada. 4Canadian Forest Service, Sault Ste, Marie, Ontario, Canada. 5Wildlife Conservation Society Canada, Toronto,
Ontario, Canada. 6The Grantham Institute - Climate Change and the Environment and Department of Infectious Disease Epidemiology, Imperial College
London, London, UK. 7University of Maryland, College Park, MD, USA. 8Division of Ornithology, American Museum of Natural History, New York, NY, USA.
9Centre for Tropical Environmental and Sustainability Science (TESS) and College of Science and Engineering, James Cook University, Cairns, Queensland,
Australia. 10Woods Hole Research Center, Falmouth, MA, USA. 11Swedish University of Agricultural Sciences, Umeå, Sweden. 12Forest Trends Association,
Washington DC, USA. 13Global Programme on Nature for Development, United Nations Development Programme, New York, NY, USA. 14Fenner School of
Environment and Society, The Australian National University, Canberra, Australian Capital Territory, Australia. 15These authors contributed equally: James
E. M. Watson and Tom Evans. *e-mail: jwatson@wcs.org
Although Earth has lost at least 35% of its pre-agricultural for-
est cover over the past three centuries1, forests are still widely
distributed, covering a total of 40 million km2 (~25%) of
Earth’s terrestrial surface2. Of the remaining forests, as much as 82%
is now degraded to some extent as a result of direct human actions
such as industrial logging, urbanization, agriculture and infrastruc-
ture3,4. This figure is probably an underestimate of the true level
of anthropogenic impact as it does not incorporate other, more
cryptic forms of degradation, such as over-hunting5. As the human
footprint continues to expand4, remaining forest free of significant
anthropogenic degradation is in rapid decline (Fig. 1).
Over the past decade, there has been increasing international
concern around the loss of forest and the impact this has on climate
change, the loss of biodiversity and the provision of ecosystem ser-
vices1. The 2015 Paris Agreement, together with earlier agreements
under the United Nations Framework Convention on Climate
Change (UNFCCC), acknowledges the importance of forests for
limiting a future temperature increase to well below 2 °C above pre-
industrial levels6. The United Nations’ Sustainable Development
Goals (adopted in 2016) have the ambitious aim of fully halting
deforestation by 20207. However, while these targets are clearly war-
ranted, they fall short of specifically prioritizing the crucial quali-
ties of a forest that contribute most to achieving each convention’s
specific goals1. For example, indicators tracking progress towards
the 2015 New York Declaration on Forests — among the most sig-
nificant global forest conservation targets to date — focus on forest
extent and make almost no acknowledgement of forest condition8.
In this Perspective, we argue that to achieve the goals of global
international environmental accords it is insufficient to treat all for-
ests as equal regardless of their condition. Instead, forest that is free
of significant anthropogenic degradation (which we term ‘intact
forest’) should be identified and accorded special consideration in
policymaking, planning and implementation. Anthropogenic deg-
radation here includes all human actions that are known to cause
physical changes in a forest that lead to declines in ecological func-
tion9,10. Well-studied examples include forest fragmentation, stand-
level damage due to logging, over-harvesting of particular species
(such as over-hunting) and changes in fire or flooding regimes.
We first summarize published evidence that intact forests sup-
port an exceptional confluence of globally significant environmen-
tal values relative to forests that have experienced those damaging
human actions. We show that intact forests are indispensable not
only for addressing rapid anthropogenic climate change, but also for
confronting the planet’s biodiversity crisis, providing critical ecosys-
tem services and supporting the maintenance of human health. We
then show that the relative value of intact forests is likely to become
magnified as already-degraded forests experience further intensi-
fied pressures (including anthropogenic climate change). While it is
beyond the scope of this paper to set thresholds for acceptable for-
est fragment size and configuration, logging intensity or any other
measure of damage, we provide evidence that human activity that
exceeds the natural range of variation in a forested system reduces
key ecological functions, and the greater the level of alteration, the
greater the reduction in function. Here we outline the significant,
The exceptional value of intact forest ecosystems
James E. M. Watson 1,2,15*, Tom Evans2,15, Oscar Venter3, Brooke Williams1,2, Ayesha Tulloch 1,2,
Claire Stewart1, Ian Thompson4, Justina C. Ray5, Kris Murray6, Alvaro Salazar1, Clive McAlpine1,
Peter Potapov7, Joe Walston2, John G Robinson2, Michael Painter2, David Wilkie2,
Christopher Filardi8, William F. Laurance9, Richard A. Houghton 10, Sean Maxwell1,
Hedley Grantham1,2, Cristián Samper2, Stephanie Wang2, Lars Laestadius11, Rebecca K. Runting1,
Gustavo A. Silva-Chávez12, Jamison Ervin13 and David Lindenmayer 14
As the terrestrial human footprint continues to expand, the amount of native forest that is free from significant damaging
human activities is in precipitous decline. There is emerging evidence that the remaining intact forest supports an exceptional
confluence of globally significant environmental values relative to degraded forests, including imperilled biodiversity, carbon
sequestration and storage, water provision, indigenous culture and the maintenance of human health. Here we argue that main-
taining and, where possible, restoring the integrity of dwindling intact forests is an urgent priority for current global efforts to
halt the ongoing biodiversity crisis, slow rapid climate change and achieve sustainability goals. Retaining the integrity of intact
forest ecosystems should be a central component of proactive global and national environmental strategies, alongside current
efforts aimed at halting deforestation and promoting reforestation.
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and probably intensifying, threats to intact forests and argue that
action is required to halt and reverse their loss. Such action requires
explicit consideration on global, national and sub-national scales,
and we conclude by identifying specific policy mechanisms where
intact forests should be addressed.
Our call for an increased emphasis on intact forests does not
imply that other forms of forest are unimportant. Given the scale
of the environmental challenges facing humanity, there is also an
undoubted need to cease deforestation and degradation at forest
frontiers11, and to promote large-scale reforestation12. We believe
that coherent environmental policy should give due weight to
intact forests, clearance frontiers and restoration opportunities,
because all three have crucial and complementary roles to play.
The primary reasons why we focus on intact forests are twofold.
First, they are overlooked in international policy. Second, intact
forest protection can typically secure very high environmental
values with often relatively low implementation and opportunity
costs13, which serves to reinforce the need for their direct inclusion
in global environmental accords.
Evidence for the exceptional values of intact forest
ecosystems
There has been rapid growth in our understanding of the link between
anthropogenic pressures on forest and impacts on ecosystem ser-
vice values across a range of forest types (Box 1). Anthropogenic
pressures, especially at industrial intensities and large spatial scales,
have been shown to alter forest characteristics, including physical
structure, species composition, diversity, abundance and functional
organization compared with their natural state, and as a result, to
reduce a wide range of environmental values1417. These pressures
also interact with natural disturbance regimes such as fire and pests
to perturb forests beyond their capacity to regenerate18. The follow-
ing sections show how the loss of forest intactness leads to declines
or changes in these key environmental values: global and regional
scale climate regulation; local climate and watershed regulation;
biodiversity conservation; indigenous cultures; and human health.
Climate mitigation. Climate change is causing pervasive and
potentially irreversible impacts on ecosystems and people19. Of the
anthropogenic contribution to atmospheric CO2 since 1870, 26%
is due to emissions from deforestation and forest degradation20. It
is now accepted that actions that avoid emissions from the land
sector, especially forests, and maximize removals of greenhouse
gases are critical if the goals of the UNFCCC Paris Agreement are
to be achieved12,21.
Degradation typically causes fewer emissions per hectare than
deforestation, but is much more widespread3,4,9. In the tropics,
where most net forest emissions occur, degradation may account
for 10–40% of total emissions of aboveground carbon22. Industrial-
scale logging (that is, large-scale market-orientated logging using
heavy machinery, with offtakes that exceed natural rates of tree
mortality) directly reduces carbon stocks through a combination of
tree removal, collateral damage to non-target trees, decomposition
of logging waste and wood fibre products23, and the depletion of
soil and peatland carbon stocks24,25. Industrial logging creates for-
ested systems dominated by regenerating stands of younger, smaller
trees, and although some regrowth does occur during each logging
cycle, the cyclical peaks in biomass typically do not return to pre-
logging levels, and the time-averaged carbon stocks can be expected
to decline progressively over subsequent cutting cycles in many
cases26. Reported carbon losses through industrial logging vary
widely across forest types and due to the different types of logging
undertaken (Fig. 2).
As forest patches are fragmented by agriculture and infrastruc-
ture, the area exposed to edge effects increases disproportionately;
already 70% of the world’s forests lie within 1 km of a forest edge
and this proportion is rising27. Globally, locations up to 500 m
from a forest edge average 25% less biomass carbon than locations
Degree of human footprintGlobal forest cover
a
c
b
High NoneLowForest Intact forest
Tundra
Tropical and subtropical moist broadleaf forests
Tropical and subtropical grasslands, savannas and shrublands
Tropical and subtropical dry broadleaf forests
Tropical and subtropical coniferous forests
Temperate grasslands, savannas and shrublands
Temperate coniferous forests
Temperate broadleaf and mixed forests
Montane grasslands and shrublands
Mediterranean forests, woodlands and scrub
Flooded grasslands and savannas
Boreal forests/taiga
0 10 15 200 1015
Million km
2
Million km
2
20
Fig. 1 | The global extent of intact forest. ac, There are many ways to map intact forest: the first example is mapped as defined by Intact Forest
Landscape methodology3 (a), the second example by the global Human Footprint methodology138 (b) and, for both measures, by biome (c). The definition
of overall forest estate was based on ref. 136, with forests defined as > 75% tree coverage.
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remote from forest edges, and even locations up to 5 km from an
edge can have > 10% less biomass carbon28. These edge effects are
mediated by a wide range of ecological changes, including increased
windthrow and evaporation, and increased access for people, fire
and invasive species27. Another form of degradation is loss of fauna
through over-hunting, which can significantly disturb vegetation
composition and the long-term carbon storage potential of tropical
forests by depriving key, high-carbon tree species of their seed dis-
persal agents, and through other ecological disruptions29,30 (see Box
2). Such effects can extend over vast areas (for example, at least 36%
of the Amazon31) because over-hunting is pervasive where human
access is facilitated by new infrastructure, and can also occur even
in very remote areas32,33.
Degradation reduces the capacity of forests to function as major
net carbon sinks, actively sequestering carbon into soils and living
biomass34,35. The global residual terrestrial sink, much of which is
considered to take place in intact forests, removes an extraordinary
25% (2.4 Pg C yr1) of anthropogenic emissions from all sources,
and hence greatly slows the pace of climate change36,37. This aspect
of global carbon dynamics is often under-emphasized in climate
policy because it is seen as part of the background of natural fluxes.
However, the large-scale degradation of intact forests would result
in a major anthropogenic reduction in this critical ecosystem ser-
vice38. The intact forest sink is distinct from the sink resulting from
reforestation and forest recovery following cessation of degradation.
Both are large and both are likely to be indispensable in efforts to
meet global climate targets36,39.
Regulating local climate regimes and providing watershed ser-
vices. There is increasing evidence that forests are a key factor
in the regulation of local and regional climate regimes through
the exchange of radiation, moisture and wind energy between the
Box 1 | Evidence of the exceptional values intact forest ecosystems have when compared with degraded ecosystems
Climate change mitigation
More above- and belowground carbon stored. Intact forests
store more carbon than logged, degraded or planted forests
in ecologically comparable locations. Industrial logging and
conversion of forest to cropland causes heavy erosion and
contributes to the loss of belowground carbon21,22,144 (see Fig. 2 and
Supplementary Table 1).
More faunal complexity, which helps carbon storage and
sequestration. Defaunation can signicantly erode the long-term
carbon storage potential of forests by depriving key, high-carbon
tree species of seed-dispersal agents, and through other ecological
disruptions such as reduced vegetation diversity and composition
or increased herbivory by non-hunted species (see Box 2)29,31.
Major carbon sequestration. Intact forests continue to function
as major net carbon sinks, actively sequestering carbon into soils
and living biomass12,34,37.
Regulating local and regional weather regimes
Eects on weather. Local and regional weather patterns are
partly a function of the amount of intact forest cover and its
condition40,42,167.
Generation of rain and reduced risk of drought. When intact forests
are cleared or degraded, there is a reduction in cloud cover and rainfall.
Degradation and loss of intact forest can increase the number of dry
and hot days, decrease daily rainfall intensity and wet day rainfall, and
increase drought duration during El Niño years41,168,169.
Ensuring hydrological services are maintained
Eects on water runo availability. Intact forests have a positive
eect on the redistribution of runo, stabilize water table levels and
retain soil moisture by altering soil permeability. ese processes
interact with physiography to regulate the ow distribution of
energy and materials across the land surface and help stabilize
slopes, prevent water and wind erosion, and regulate the transport
of nutrients and sediments48,50.
Buer human settlements against negative eects of extreme
climatic events. Non-degraded forests diminish the impact of
heavy rain events by decreasing runo and reducing the negative
consequences of climate extremes50,170.
Conserving biodiversity
Consistently higher numbers of forest-dependent species. More
forest-dependent species are found in intact ecosystems than
degraded ones. In some regions, the loss of large tracts of forest has
meant wide-ranging forest-dependent species have either retreated
to the last remaining intact forest systems or gone extinct14,68,171.
More eectively sustain important large-scale ecological
processes. Key functions supported by intact forests include
natural disturbance regimes that sustain habitat resources,
constitute selective forces to which species are adapted, or
otherwise inuence community composition17,172,173.
Intact forests have higher functional diversity. Degrading
activities such as selective logging lead to trait shis in communities
that can aect ecosystem functioning, in addition to taxonomic
diversity5,33,173 (see also Box 2).
Higher intra-species genetic diversity. e larger populations of
forest-dependent species that inhabit intact forests provide greater
options for local adaptation and phenotypic plasticity, which will
facilitate species’ potential for evolutionary and plastic responses
to the rapidly changing environmental conditions69,126,128.
Higher ability for species to undertake dispersal or retreat to
refugia. e connectivity provided by large, contiguous areas
spanning environmental gradients, such as latitude, altitude,
rainfall or temperature, maximize the potential for key processes
such as gene ow and genetic adaptation to play out, while also
allowing species to track shiing climates131,152.
Refuge for forest species from increased re frequencies in
degraded landscapes under changing climates. Intact forests
act as re refuges in landscapes where non-intact forests burn too
frequently to support persistence of plant and animal communities
dependent on long time intervals between burning100,124.
Increased likelihood of providing key pollination and dispersal
processes. Direct logging and secondary eects of degradation
such as loss of vertebrate seed dispersers or pollinators leads
to reduced ecosystem functions, such as seed dispersal and
pollination services, for example, reduced fruit set due to reduced
pollinations in fragmented forests31,174.
Indigenous cultures
Increased basis for the material and spiritual aspects of
traditional indigenous cultures to function. Long-established
cultural norms intricately linked to the ecology of intact areas and
vulnerable to damaging change80,91,92.
Human health benets
Reduced health impacts of wildres. Fires attributed to forest
degradation activities such as burning for land clearing result in
premature deaths due to generation of haze. Lower burning rates
in intact forests mean that health eects of wildres are lower than
in degraded landscapes with larger, more frequent res99.
Reduced infectious disease risks. e emergence of novel
diseases from forests and the increase of endemic disease impacts
in forested landscapes are thought to be related to encroachment
and degradation arising from increasing human presence in these
habitats96,97,175.
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land and atmosphere. Local and regional weather patterns are
therefore a function of not just the amount of forest cover but also
its state and condition40.
Intact tropical forests are critical for rain generation because
air that passes over these forests produces at least twice as much
rain as air that passes over degraded or non-forest areas41. When
intact forests are degraded, there is a resulting reduction in con-
vective cloud cover and rainfall42. The influence of intact forests
on precipitation, temperature and surface hydrology is particu-
larly relevant in reducing the risks of drought imposed by cli-
mate extremes42. In Australia, the degradation and loss of intact
forest can increase the number of dry and hot days, decrease
daily rainfall intensity, and increase drought duration during El
Niño years43. The last pattern also has been shown in Amazonia,
where deforestation and forest degradation produce warmer and
drier conditions that favour more frequent and intense droughts
than in the past44. Importantly, the local climate benefits of
tropical and sub-tropical forests occur primarily during the dry
season and in regions with low rainfall, and during heat
waves where the temperature is buffered by the cooling effects
of evapotranspiration45.
Intact forests also have a direct influence on water availability
through the redistribution of runoff, water table levels and soil
moisture by altering soil permeability46. These processes interact
with physiography to regulate the flow distribution of energy and
materials across the land surface and help stabilize slopes, prevent
water and wind erosion, and regulate the transport of nutrients
and sediments46. Several studies have shown that when forests are
degraded, the soil infiltration rates and water infiltration capacity
are decreased because of changes in soil structure and aggregation
by organic matter and plant litter production47. For example, intact
mountain ash (Eucalyptus regnans) forested ecosystems of south-
ern Australia have been shown to produce > 12 Ml ha1 yr1 more
water than equivalent forested ecosystems that have been degraded
through logging48. In many cases, intact forests also buffer the nega-
tive effects of heavy rainfall events by reducing peak discharge and
regulating runoff, and by diminishing the negative consequences of
climate extremes49,50.
Conservation of biodiversity. The global biodiversity crisis is
heavily driven by anthropogenic threats to forests51, as forested
ecosystems support the majority of global terrestrial biodiversity52.
Biodiversity has intrinsic value and there is also increasing evidence
that diverse, intact species assemblages underpin ecosystem func-
tions such as tree productivity, nutrient cycling, seed dispersal,
pollination, water uptake and pest resistance that are critical for
human well-being53.
Intact forests have particular value for the conservation of bio-
diversity54. Beyond outright forest clearance (which is the great-
est threat facing biodiversity51), forest degradation from logging is
the most pervasive threat facing species inhabiting intact forests3.
Many species are sensitive to logging, and studies across many taxo-
nomic groups have shown impacts increasing with the intensity of
logging and with the number of times a forest has been logged17,55.
Fragmentation of intact forest blocks (and associated edge effects)
is also a severe threat to forest-dependent species, especially those
requiring large areas to maintain viable populations (for example,
wide-ranging predators and tree species that occur naturally at very
low densities)27,56. In temperate, boreal and tropical forest regions,
the loss of large contiguous tracts of forest has meant wide-ranging
forest-dependent species have either retreated to the last remaining
intact forest systems or are extinct5760. Furthermore, there is evi-
dence that — even for some forest species that may persist for a time
in degraded fragments — intact forests are necessary to ensure their
persistence over the long term18,61,62.
Defaunation resulting from commercial and subsistence hunting
is a critical threat for large-bodied forest vertebrates, especially in
the tropics5,63. Many large carnivores and ungulates that play impor-
tant roles as ecosystem engineers (for example, Sumatran serow
(Capricornis sumatraensis), gaur (Bos gaurus) and forest elephant
(Loxodonta cyclotis)) are now found only as remnant populations
in the remaining intact tropical forests33,64. The synergistic interac-
tion of stand damage, fragmentation and hunting is an increasingly
significant challenge for biodiversity conservation65,66 as it is well
known that forest fragmentation increases access for hunters67, and
logging damage has more severe impacts when combined with frag-
mentation17. Forest biodiversity is best conserved by minimizing the
6. Papua New Guinea. A
decline of 31% was measured
in a medium-crowned
rainforest within four years of
logging
181,182
1. Canada. A decline of
12% was modelled over
250 years within a
boreal forest
176
15. United States.
A decline of 50% was
modelled over 57 years
in a temperate
coniferous forest
23,191
1. Canada. A decline of
10–51% was modelled
over 250 years within
coastal forest ecosystems
in British Columbia
176
1. Canada. A decline of
7–25% was modelled
over 250 years within
forest ecosystems in the
interior of British Columbia
176
7. Australia. A 55%
decline was measured in a
montane ash forest
repeatedly logged since
before the 1930s
23
8
. Australia. A 50%
decline over 100 years
was modelled in a
Tasmanian wet eucalypt
forest
23,183,184
11. Brazil. A decline of
24% was measured in
Paragominas. Time
since last disturbance
was two years
187
13. Brazil. A decline of
35–57% was measured in
Santarem. Time since last
disturbance unknown
189
14. French Guiana.
A decline of more than
50% was measured in
a lowland tropical rainforest
immediately post-logging
190
12. Brazil. A decline of
37% was measured within
various areas of the
Amazon. Disturbance
ages varied
182,188
2. Malaysia. A decline
of 53% was measured
at a maximum of 19
years since disturbance
in a dipterocarp forest
117
4. Indonesia. A decline
of 15% was measured
after various years of
disturbance in a lowland
tropical forest
178,179
5. Papua New Guinea. A
decline of 24–37% was
measured over various
lowland tropical forest
within a year after logging
180
3. Philippines. A decline of
50% was measured in a
dipterocarp forest. Measurements
were taken in a using a
chronosequence of 1–21 years
177
9. Republic of Congo.
A decline of 3% was
measured after one
year since logging
within a rainforest
182,185
10. Gabon. A decline
of 6% was measured
after logging within a
dense humid evergreen
rainforest
182,186
Fig. 2 | Forest degradation and carbon loss. Examples of published case studies that have examined the effects of forest degradation on carbon loss23,117,1 76191.
Supplementary Table 1 provides in-depth summaries of each of the 15 case studies.
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encroachment of productive activities that promote forest loss and
fragmentation because the initial intrusion leads to rapid degrada-
tion of intact forests, via not only the direct effects of habitat loss,
but also the coinciding effects of wildfires, overhunting, selective
logging and biological invasions, alongside other stressors65,68. For
example, a recent global analysis of nearly 20,000 vertebrate spe-
cies showed that even minimal initial deforestation within an intact
landscape had severe consequences for vertebrate biodiversity in a
given region, emphasizing the special value of intact forests in mini-
mizing extinction risk68. Moreover, those forest ecosystems that are
more affected by humans support less genetic diversity than those
systems that are still intact, which has potentially significant ramifi-
cations for evolutionary change69.
Indigenous peoples. At least 250 million people70 live in forests, and
for many of them, their cultural identities are deeply rooted in the
plant and animal species found there71. Archaeological and ethno-
graphical evidence indicate that forests have been inhabited by peo-
ple for millennia: in Latin America, records go back 13,000 years72;
in Asia, some 40,000 years73; and in Central Africa, more than
250,000 years74. Forest-dwelling indigenous peoples have tended to
do so at very low population densities distributed in dispersed set-
tlements75. Today, tropical forest societies that depend almost exclu-
sively on the direct use of natural resources to meet their basic needs
seldom exceed population densities of 1–2 people km2 (ref. 76), and
tend to change location from time to time to ensure that their taking
of food and other products will not permanently deplete an area of
key resources. Through their selection and management of useful
plants and animals, these communities have significant and long-
lasting impacts on the structure and composition of the forests in
which they live77,78.
Industrial-scale degradation of intact forest erodes the mate-
rial basis for the livelihoods of indigenous forest peoples, depleting
wildlife and other resources79. It also renders traditional resource
management strategies ineffective, and undermines the value of tra-
ditional knowledge and authority80. Fragmentation and degradation
of the forest makes a traditional life style no longer tenable, push-
ing indigenous peoples off their land81, and driving people to adopt
Box 2 | The eect of defaunation on carbon storage and sequestration in intact forests
Even where forests have not been cleared, many are not func-
tioning as they once were166. Species such as the Asian and South
American tapirs (Tapirus spp.), forest elephant (L. cyclotis) and the
great apes have disappeared across much of their ranges. Habitat
degradation and fragmentation are major causes of this defauna-
tion, as many large-bodied species depend on great expanses of
high-quality forest to sustain viable populations5,192. Increased hu-
man accessibility to forests is another, with unsustainable hunting
now aecting greater areas of tropical forest than the combined
extent of deforestation, selective logging and wildres193. Wildlife
species are not equally aected by hunting, with stronger impacts
of hunting pressure on larger-bodied primates and ungulates
compared with smaller-bodied vertebrates such as birds and ro-
dents31,75,194.
Defaunation signicantly erodes key ecosystem services and
functions through direct and indirect cascading eects on species
diversity and trophic webs195197. ere is evidence for negative
eects on pollination, seed dispersal, pest control, nutrient cycling,
decomposition, water quality and soil erosion192,198. Studies
across the African and Atlantic tropical forests indicate that the
disappearance of large frugivores and subsequent loss of seed
dispersal reduces recruitment and natural regeneration of large-
seeded hardwood plant species, which are key contributors to
carbon storage199201. By simulating the local extinction of trees that
depend on large frugivores in 31 Atlantic forest communities, one
study29 found that defaunation has the potential to signicantly
erode carbon storage even when only a small proportion of large-
seeded trees are extirpated. is is because of strong functional
relationships between seed diameter, wood density and tree height,
which are traits related to carbon storage202. Similar results have
been shown for the Amazon31 and other parts of the tropics203.
ere is also likely to be another link between defaunation and
lowered carbon storage in tropical forests; lower herbivory rates
in defaunated forests allow fast-growing herbivore-sensitive plants
to outcompete slower-growing animal-dispersed trees that have
better defence mechanisms against hunted frugivores31,204,205. In
defaunated forests, carbon storage is potentially reduced when
these fast-growing carbon-poor plants replace an equal basal area
of carbon-rich animal-dispersed trees206 — a process that may be
irreversible once the seed stock is lost.
Degree of defaunation
Schematic representation of the transition (from left to right) of a non-hunted, faunally intact tropical forest to an overhunted, defaunated forest.
Shown is the degree to which large arboreal or terrestrial forest frugivores such as elephants and apes decline in abundance and, with these declines,
the associated replacement of large-fruited high-biomass trees by smaller-fruited and wind-dispersed trees that have lower biomass and carbon
storage. Credit: Blake Alexander Simmons.
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production systems that are incompatible with the maintenance
of intact forests8285. As traditional forest peoples become increas-
ingly sedentary and connected to urban markets, gender roles,
diets and cultural values also change8688. These changes in the life
styles of indigenous and traditional peoples create greater depen-
dence on urban markets for provisioning, which can lead to effects
that erode their cultural identities89. Indeed, for many indigenous
forest peoples their cultural sense of self is inextricably linked to
intact forests80.
Forcible alienation from their territories has even more severe
impacts, with the forest homes of many indigenous and traditional
peoples being taken from them, often by force, by more powerful
state, corporate and private actors, whose interests often involve for-
est conversion for cattle pasture, agricultural fields, oil-palm planta-
tions90 and mining concessions9193. This can have serious impacts
on the health of these peoples as they are often exposed to new
disease vectors and hostile settlers and ranchers. As many indig-
enous and traditional peoples are motivated to conserve their for-
ests (because they are the foundation of their economic and cultural
well-being), there is now mounting evidence (which we discuss
below) that strengthening the land tenure of indigenous peoples is a
powerful way to protect intact forests94,95.
Human health. Forested ecosystems are major sources of many
medicinal compounds that supply millions of people with medi-
cines worldwide96,97. Degradation and outright forest loss com-
promise the supply of these benefits as medically relevant species
decline or are lost98. Degradation can also cause substantial nega-
tive health impacts. For example, during the 2015 human-caused
forest fires in Indonesia, the haze generated after 261,000 ha of
degraded forest and peatland was burned caused more than 100,000
premature deaths across Indonesia, Malaysia and Singapore99.
Fragmented forests experience more numerous and intense edge-
related wildfires in comparison with intact forests100, which severely
exacerbates the extent of health impacts of both intentional and
unintentional burning.
Forest degradation may also lead to infectious disease impacts.
Against a backdrop of declining overall burden of infectious dis-
eases on a global scale101, an increasing rate of novel disease emer-
gence and an increase in the incidence of some endemic diseases in
forested landscapes have been, at least in part, attributed to increas-
ing human presence in, and degradation of, these habitats102,103. For
example, deforestation and resultant environmental changes are
considered key drivers of zoonotic malaria in Malaysian Borneo104.
Although wildlife and arthropod vector species within forests are
natural sources of potential human infections105, increasing human
presence and anthropogenic land-use changes often promote oppor-
tunities for disease transmission, as human-reservoir/vector contact
rates increase or as impacts on host or vector distributions or com-
munity composition perturb natural disease dynamics106. Numerous
infectious diseases associated with forests, including Ebola virus103,
dengue fever107, Zika virus108, several hantaviruses109, yellow fever110
and malaria111, are undergoing changes in risk to humans due to
deforestation, forest degradation and human encroachment.
The increasing significance of intact forests
The differences in important environmental and social values of
intact forests relative to degraded forests are likely to become mag-
nified in the future due to two negative processes in degraded areas:
progressive anthropogenic damage and reduced resilience to envi-
ronmental change.
Vulnerability of degraded forests to further degradation. Once
initiated, forest degradation often intensifies over time112. This is
mediated by: (1) increased levels of human accessibility; (2) suc-
cessive cycles of logging of often progressively lower value trees113;
(3) increased hunting pressure5; (4) forest clearance and fragmenta-
tion due to colonization by farmers and loggers facilitated by new
roads114; and (5) the entry of new extractive development projects
such as mining55. For example, in the Brazilian Amazon, 16% of
logged areas are cleared for agriculture in the first year following
logging, with further losses of more than 5% per year for the next
four years115. This cycle is exacerbated if conversion becomes more
politically acceptable once a forest has been labelled ‘degraded’116.
Once identified as ‘lower value’ for conservation, degraded forests
can mistakenly be considered to have ‘no value’ by some stakehold-
ers, despite extensive evidence to the contrary17,117.
Degraded forests also have increased risk of, and susceptibility
to, natural disturbances such as fire, as forests are drier along their
edges118. There is clear evidence that forests that are logged are at
high risk of burning at uncharacteristically high severity119, with
an elevated fire proneness lasting for decades120. Degraded forests
are also at higher risk from invasion by exotic invasive species18
when compared with non-degraded forests. With fire frequency in
many forest areas predicted to increase under climate change sce-
narios121123, intact forests might become refuges from fire in many
landscapes where degraded forests burn too frequently to support
the persistence of plant and animal communities dependent on old
forests. This cascade of damage, referred to as a ‘landscape trap124,
is becoming more common and many forests are now subject to
repeated disturbances that lock them in early successional states.
Loss of resilience following forest degradation. In addition to
present direct anthropogenic threats, forested ecosystems also have
to adapt to large-scale environmental changes, including changes
in climate19, which interact with the myriad of current threats that
they already face125. Intact forest ecosystems have greater capability
to overcome these regional and global stressors than degraded ones,
as they have inherent properties that enable them to maximize their
adaptive capacity126. For example, intact forested ecosystems often
house important populations of forest-dependent species and high
intraspecific genetic diversity, which both provide options for the
local adaptation and phenotypic plasticity127 that facilitates species
ability to survive changing environmental conditions128. Large, con-
nected and functionally intact forest ecosystems also enable species
to undertake adaptive responses such as dispersal or retreating to
refugia129, which will be critical as the climate changes and species
react130. Moreover, the connectivity provided by large, contiguous
areas spanning multiple environmental gradients, such as altitude,
latitude, rainfall or temperature, will maximize the potential for
key processes such as gene flow and genetic adaptation to play out
naturally, while also allowing species to track shifting climates in
space131,132. Intact forests have been shown to be more resilient in
response to short-term climatic anomalies (for example, droughts
and wildfires during drought) than degraded forests133.
Intact forest ecosystems sustain large-scale ecological processes,
such as natural disturbance regimes, which maintain disturbance-
adapted species that influence native community composition18,127.
For example, the biodiversity of boreal and temperate forests
includes evolutionary lineages that are uniquely adapted to survive
major seasonal temperature changes and landscape-level distur-
bances over time, such as large fires and insect infestations134.
The future of intact forests
The capacity to map human pressures on the environment on
global scales is rapidly improving135 and published results so far
show that not only has loss of global forest cover accelerated since
the 1990s8,136,137 but also that there are higher levels of degradation
within the shrinking forest estate. The recently updated global
Human Footprint138, a composite index of eight human pressures
that is believed to be a good proxy for overall intactness, found that
in 2009, 18% of forests had no detectable human pressure, a 35%
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decline since 1993 (Fig. 1b). According to a related but distinct met-
ric, Intact Forest Landscapes covered 24% of the world’s forests in
2013, a decline of 7.2% since 20003. Recent mapping of roadless for-
est139 and hinterland forest140 shows similar declines using alterna-
tive data sources.
These assessments underestimate the total loss of intactness as
they do not fully take into account other forms of forest degrada-
tion, including invasive species, some forms of logging, over-hunt-
ing, and altered fire and flood regimes, nor do they address the
impacts of climate change. For example, vast areas of Central Africa
that are mapped as ‘intact’ by both satellite imagery and the Human
Footprint have lost their forest elephant (L. cyclotis) populations in
the past 20 years due to poaching. This causes dramatic long-term
ecological changes, given the role of this species as an ‘ecosystem
engineer’ though seed dispersal, trampling and herbivory33.
These figures suggest that even if existing global targets to halt
deforestation are achieved, much of what is saved will be no lon-
ger intact. Outright deforestation is currently concentrated in the
tropics and sub-tropics136, but the loss of intactness is a pervasive
global forest phenomenon3. It seems likely that this rapid decline
in forest intactness will accelerate in line with the underlying driv-
ers of change (including human economic demands, which are
growing rapidly as a result of rising population and even more
quickly rising per-capita consumption141). One stark forecast is
that 25 million km of new roads will be built globally by 2050142,
threatening many intact areas.
Focal mechanisms for action on intact forests. It is clear that many
intact forests are under severe and rising pressure, and there is an
urgent need for greater conservation efforts3. Below, we offer some
potential avenues for enhanced action, while acknowledging that
the scale of the challenge is very significant, and will achieve long-
term success only if nations turn away from ‘business as usual’ activ-
ities that extract natural resources without appropriately valuing the
cost of lost natural capital. An essential first step towards greater
success is achieving widespread recognition that rapid loss of for-
est intactness represents a major threat to sustainable development
and human well-being. Policymakers need to understand the chal-
lenge that the loss of forest intactness represents for achieving stra-
tegic goals outlined in key multilateral environmental agreements,
including the Convention of Biological Diversity, the UNFCCC and
the UN Sustainable Development Goals139,143, and this recognition
needs to be translated into meaningful changes on the ground.
A fundamental constraint to progress is the fact that interna-
tional definitions of forests have not differentiated among types of
forest and, in most policy settings, they treat all forests, regardless
of their condition, as equivalent1,144. As such, international policy
processes seldom acknowledge the special qualities and benefits
that flow from intact ecosystems as compared with those that are
degraded. The consequence is that few policy processes (or partici-
pating nations) clearly articulate conservation goals for intactness,
forest quality or integrity143. There is an emerging, critical role for
the science community to develop policy-relevant metrics of for-
est intactness that account for the different forms and levels of for-
est degradation, and assess how they impact on different globally
important social and environmental values. The lack of recognition
of the varying qualities and condition among forest types has impli-
cations for targeting by international funding programmes such as
the Global Environment Facility, Green Climate Fund and Critical
Ecosystems Partnership Fund, which are distributing billions of
dollars annually to help developing countries achieve the goals of
multilateral environmental agreements. All three of these mecha-
nisms could adjust their criteria for funding so as to explicitly rec-
ognize the value of investments that protect intact forests.
A number of emerging policy opportunities for the global com-
munity to recognize the special values that intact forests preserve,
when compared with degraded ones, are within the UNFCCC.
Because the scientific community has not worked out a practi-
cable definition for emissions from land use, land use-change and
forestry (LULUCF) that would separate direct human-induced
effects from indirect human-induced and natural effects, parties
to the UNFCCC in reporting on LULUCF in their greenhouse gas
inventories may choose to apply the managed land proxy145. Under
the managed land proxy, land where human practices have been
applied is considered ‘managed’ and included in reporting under
the UNFCCC. However, by definition, many intact forest land-
scapes are located on ‘unmanaged lands’ and therefore their contri-
bution to meeting mitigation goals is not quantified or understood.
Increased attention to unmanaged lands, and to transitions between
the managed and unmanaged lands categories, through key venues
such as the Intergovernmental Panel on Climate Change Special
Reports and the Global Stocktake and Facilitative Dialogue will not
just improve understanding of the climate mitigation role of intact
forests but also support nations in articulating interventions, targets
and funding needs for protecting these forests in formulating and
implementing their nationally determined contributions.
Further policy enhancements could be identified in existing
frameworks and programmes for financing for tropical intact for-
est conservation, such as the UNFCCC REDD+ process (reducing
emissions from deforestation and forest degradation and the role of
conservation, sustainable management of forests and enhancement
of forest carbon stocks in developing countries), the Green Climate
Fund and the Forest Carbon Partnership Facility. To date, these pro-
cesses have been focused on rewarding countries and jurisdictions
with performance-based payments for reducing near-term threats
of deforestation and (to a much lesser extent) degradation, based
on a historical emissions baseline. Given this goal of achieving
near-term climate mitigation results (that is, typically within five
to ten years), programme rules often directly limit the eligibility or
amount of support for conservation of intact forests that have, by
definition, low historical emissions from deforestation and degra-
dation, and that may be under threat over one or more decades.
For example, so-called ‘high forest, low deforestation’ nations have
relied on projections that implicitly or explicitly assume higher rates
of emissions in the future. A more straightforward approach would
focus on existing stocks and reservoirs of forest carbon, which could
be elaborated within the ‘+ ’ in REDD+ (the role of conservation,
sustainable management of forests and enhancement of forest car-
bon stocks in developing countries). Such an approach may require
new incentives that differ from and are complementary to existing
results-based payment approaches; instead, they would reward the
long-term maintenance of existing carbon stocks and the other ‘+
activities, and bypass rules stipulating that this financing must
target areas with high historical (‘baseline’) levels of emissions146.
Additional climate-related policy approaches are also clearly needed
for temperate and boreal intact forests, especially those in devel-
oped countries that would not expect to receive finance support
under the Paris Agreement and related UNFCCC mechanisms.
There are current efforts underway to generate new 2030 global
biodiversity targets, and operationalizing a clear, mandated target on
preserving ecosystem intactness is critical to this143. The first steps
are underway, with the International Union for the Conservation
of Nature recently adopting a new key biodiversity area criterion
(criterion C) covering those sites that contribute significantly to
the global persistence of biodiversity because they are exceptional
examples of ecological integrity and naturalness147. If the key biodi-
versity area standard becomes formally recognized within the 2030
strategic plan for biodiversity, this would be a very positive step in
proactively conserving intact forests.
Change in policy at the global level should be reflected in the
design and implementation of effective national and sub-national
policies, and forest management plans that recognize the value of
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PersPective Nature ecology & evolutioN
intact forests to the host nation and specify policies for their pro-
tection and restoration. National and sub-national policies can be
supported by longer-term planning that is incentivized by climate
funding streams (for example, conditional targets in nationally
determined contributions, the Green Climate Fund) that recog-
nize the mitigation contribution of intact forest landscapes. These
policies will vary based on the specific context of different nations,
but there is a clear need to focus on halting degrading activities,
including limiting road expansion142, reducing negative impacts of
hunting through legal controls coupled with sustainable resource
use strategies5, preventing large-scale developments such as mining,
forestry and agriculture in intact forests51, and investing in restora-
tion activities. One obvious intervention that nations can prioritize
is the creation of large protected areas, including transboundary
areas. When well designed, financed and enforced, protected areas
have been shown to be effective in slowing the impacts of industrial
logging3, land clearance148 and over-hunting33,148.
A range of other designations exists beyond protected areas
that can prevent the loss of intactness or promote its restoration.
There is evidence that the designation of ‘roadless areas’ in the
USA, for example, has led to an effective expansion in the degree
of ecoregional representation under protection and increases in the
number of areas big enough to provide refugia for species needing
large tracts relatively undisturbed by people149. There is a need for
mechanisms relating to the private sector that prioritize the protec-
tion and restoration of intact forest, including specific investment
and performance standards for lenders and investors (for example,
the World Bank, International Finance Corporation and regional
development banks) and increasing the effectiveness of existing for-
est and extractive industry certification standards. Recent initiatives
to make supply chains deforestation-free need to be strengthened,
and to include measures to protect intact forests. While there are
some signs of success (for example, the Brazil Soy Moratorium150),
implementation is lagging well behind pledges and it is too early to
demonstrate lasting impacts151.
One emerging strategy that can be effective in slowing the
degradation of intact forests is enabling indigenous communi-
ties to establish title and management over their traditional lands.
Although comprehensive global analyses are lacking, some regional
data reveal the remarkable contribution of stewardship by forest
peoples to sustaining high-integrity forest systems, often in the
face of substantial pressures to liquidate forest timber or mineral
resources. For instance, the creation and management of indig-
enous territories has reduced (although, as with protected areas, not
halted) deforestation across the Amazon Basin152154. It is believed
over half of the Amazon Basin’s 7 million km2 are under some form
of protection, and nearly 1.8 million km2 are indigenous lands155. In
the boreal north of Canada, First Nations peoples have been able to
sign formal agreements with the government and the private sector
to ensure that national economic development policies and prac-
tices respect their rights and commit to conserving their lands and
waters. For example, the Final Recommended Peel Regional Land
Use Plan, co-developed by the government of Yukon and four First
Nation governments, has an explicit goal of “managing develop-
ment at a pace and scale that maintains ecological integrity”, and has
placed 81% of the 67,000 km2 area under protection156. These exam-
ples are drawn mostly from regions where indigenous peoples live
at very low densities and have made cultural choices not to exploit
the territories they own for timber or minerals; where population
densities are higher, or where communities make different cultural
choices, levels of forest degradation associated with subsistence and
income-generating activities will also tend to be proportionately
higher, as with non-indigenous communities.
Funding for protection and restoration of intact forests could also
be used to establish payments for ecosystem services. The approach
has many challenges, but there are some encouraging examples
where these types of activities are being undertaken. For example,
in Brazil, the Amazon Regional Protected Areas programme, partly
funded by international performance-based payments under a pro-
totype REDD+ framework, supports the creation and management
of protected areas and sustainable natural resource use157. This is
being accomplished in collaboration with local peoples with the
overarching aim to maintain forest carbon stocks and protect large-
scale ecological processes158.
There is also a need for increased efforts to restore the intact-
ness of degraded systems. This should not be seen as a substitute for
conserving fully intact systems in their current state, as forest deg-
radation can often only be partially reversed over reasonable tim-
escales112, and it is generally more cost-effective to conserve at-risk
intact forests than to protect or restore fragmented and degraded
ones. If the goal of restoration is to achieve sustainably managed
production forests, this may serve to alleviate pressure on intact for-
ests, while also providing some biodiversity and ecosystem service
benefits159. Further intensifying production systems in previously
degraded land may allow even more intact forests to be spared.
Such a ‘land sparing’ approach has been shown to achieve biodi-
versity benefits in agricultural landscapes relative to ‘land sharing’
(integrating biodiversity and production objectives on the same
land)160, and emerging evidence suggests the same is true in timber
production landscapes161. In both cases, it is imperative that strong
regulation and governance systems are in place to ensure intact
forests are actually spared in practice; otherwise, the higher eco-
nomic returns that come from intensifying production may create
incentives for further forest degradation162. Nonetheless, in already-
degraded systems, partial restoration will clearly bring significant
environmental benefits in many cases112. Important efforts are being
undertaken worldwide, for example through UN-REDD and the
Bonn Challenge, ranging from enabling natural regeneration, active
replanting of native forests, removal of invasive exotic species163, fire
management164, reconnecting landscapes through the establishment
of corridors165, and ‘rewilding’ initiatives to re-establish top preda-
tors and large-scale ecosystem processes in regenerating forests166.
Conclusion
There are still significant tracts of forest that are free from the dam-
aging impacts of large-scale human activities. These intact forests
typically provide more environmental and social values than forests
that have been degraded by human activities. Despite these values,
it is possible to envisage, within the current century, a world with
few or no significant remaining intact forests. Humanity may be left
with only degraded, damaged forests, in need of costly and some-
times unfeasible restoration, open to a cascade of further threats
and lacking the resilience needed to weather the stresses of climate
change. The practical tools required to address this challenge are
generally well understood and include well-located and managed
protected areas, indigenous territories that exemplify sound stew-
ardship, regulatory controls and responsible behaviour by logging,
mining, and agricultural companies and consumers, and targeted
restoration. Currently these tools are insufficiently applied, and
inadequately supported by governance, policy and financial arrange-
ments designed to incentivize conservation. Losing the remaining
intact forests would exacerbate climate change effects through huge
carbon emissions and the decline of a crucial, under-appreciated
carbon sink. It would also result in the extinction of many species,
harm communities worldwide by disrupting regional weather and
hydrology, and devastate the cultures of many indigenous commu-
nities. Increased awareness of the scale and urgency of this problem
is a necessary pre-condition for more effective conservation efforts
across a wide range of spatial scales.
Received: 14 July 2017; Accepted: 30 January 2018;
Published: xx xx xxxx
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Acknowledgements
We thank the John D. and Catherine T. MacArthur Foundation for funding this research,
and C. Holtz, A. Rosenthal, B. Mackey, D. DellaSalla, C. Kormos, J. Funk, J. Feidler,
S. Lewis, B. Mercer, S. Rumsey, P. Dargusch and E. Sanderson for conversations around
different ideas that have been presented within this manuscript. A special thank you to
B. Simmons for creating the figure in Box 2.
Author contributions
J.E.M.W. and T.E. conceived the study. The remaining authors provided ideas and
critical feedback.
Competing interests
The authors declare no competing interests.
Additional information
Supplementary information is available for this paper at https://doi.org/10.1038/
s41559-018-0490-x.
Reprints and permissions information is available at www.nature.com/reprints.
Correspondence and requests for materials should be addressed to J.E.M.W.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
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