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ACKNOWL EDGME NTS
The authors thank A. Rhimes and K. McKinnon for
suggestions on the use of quantile regression with count
data. We thank two reviewers who provid ed constructive
and helpful comments. M.K.T. and C.L. were partially
supported by a Columbia University Research Initiatives
for Science and Engineering (RISE) award; Office of Naval
Research awards N00014-12-1-0911 and N00014-16-1-2073;
NOAA’s Climate Program Office’s Modeling, Analysis,
Predictions, and Projections program award
NA14OAR4310185; and the Willis Research Network.
J.E.C. was partially supported by U.S. National Science
Foundation grant DMS-1225529 and thanks P. K. Rogerson
for assistance during this work. The views expressed
herein are those of the authors and do not necessarily
reflect the views of any of the sponsoring agen cies. The
study was led by M.K.T.; calculations were carried out and
the manuscript was drafted by M.K.T. C.L. prepared the
environmental data. All authors were involved with designing
the research, analyzing the results, and revising and
editing the manuscript. All the authors d eclare no competing
interests. Correspondence and material reques ts should
be addressed to M.K.T. U.S. tornado report data come
from NOAA’s Storm Prediction Center www.spc.noaa.gov/wcm.
North American Regional Reanalysis data are provided by the
NOAA/Office of Oceanic and Atmospheric Research/Earth System
Research Laboratory Physical Sciences Division, Boulder, Colorado,
USA, from their website at www.esrl.noaa.gov/psd and the Data
Support Section of the Computational and Information Systems
Laboratory at the National Center for Atmospheric Research (NCAR).
NCAR is supported by grants from the National Science Foundation.
SUPPLEMENTARY MATERIALS
www.sciencemag.org/content/354/6318/1419/suppl/DC1
Materials and Methods
Figs. S1 to S5
Tables S1 and S2
References (22–29)
4 August 2016; accepted 17 November 2016
Published online 1 December 2016
10.1126/science.aah7393
CONSERVATION
A global map of roadless areas and
their conservation status
Pierre L. Ibisch,
1,2
*Monika T. Hoffmann,
1
Stefan Kreft,
1,2
Guy Pe’er,
2,3,4
Vassiliki Kati,
2,5
Lisa Biber-Freudenberger,
1,6
Dominick A. DellaSala,
7,8
Mariana M. Vale,
9,10
Peter R. Hobson,
1,2,11
Nuria Selva
12
*
Roads fragment landscapes and trigger human colonization and degradation of ecosystems,
to the detriment of biodiversity and ecosystem functions. The planet’s remaining large and
ecologically important tracts of roadless areas sustain key refugia for biodiversity and provide
globally relevant ecosystem services. Applying a 1-kilometer buffer to all roads, we present a
global map of roadless areas and an assessment of their status, quality, and extent of
coverage by protected areas. About 80% of Earth’s terrestrial surface remains roadless, but
this area is fragmented into ~600,000 patches, more than half of which are <1 square
kilometer and only 7% of which are larger than 100 square kilometers. Global protection of
ecologically valuable roadless areas is inadequate. International recognition and protection of
roadless areas is urgently needed to halt their continued loss.
The impact of roads on the surrounding land-
scape extends far beyond the roads them-
selves. Direct and indirect environmental
impacts include deforestation and fragmen-
tation, chemical pollution, noise disturbance,
increased wildlife mortality due to car collisions,
changes in population gene flow, and facilitation
of biological invasions (1–4). In addition, roads
facilitate “contagious development,”in that they
provide access to previously remote areas, thus
opening them up for more roads, land-use changes,
associated resource extraction, and human-caused
disturbances of biodiversity (3,4). With the length
of roads projected to increase by >60% globally
from 2010 to 2050 (5), there is an urgent need
for the development of a comprehensive global
strategy for road development if continued bio-
diversitylossistobeabated(6). To help mitigate
the detrimental effects of roads, their construc-
tion should be concentrated as much as poss ible in
areas of relatively low “environmental values”(7).
Likewise, prioritizing the protection of remaining
roadless areas that are regarded as important for
biodiversity and ecosystem functionality requires
an assessment of their extent, distribution, and
ecological quality.
Such global assessments have been constrained
by deficient spatial data on global road networks.
Importantly, recent publicly available and rapidly
improving data sets have been generated by
crowd-sourcing and citizen science. We demon-
strate their potential through OpenStreetMap, a
project with an open-access, grassroots approach
to mapping and updating free global geographic
data,withafocusonroads.Theavailableglobal
road data sets, OpenStreetMap and gROADS,
vary in length, location, and type of roads; the
former is the data set with the largest length of
roads (36 million km in 2013) that is not restricted
to specific road types (table S1). OpenStreetMap is
more complete than gROADS, which has been
used for other global assessments (7), but in cer-
tain regions, it contains fewer roads than sub-
global or local road data sets [see the example of
Center for International Forestry Research data
for Sabah, Malaysia (8);tableS1].Giventhepace
of road construction and data limitations, our
results overestimate the actual extent of global
roadless areas.
The spatial extent of road impacts is specific
to the impact in question and to each particular
road and its traffic volume, as well as to taxa,
habitat, landscape, and terrain features. Moreover,
for a given road impact, its area of ecological in-
fluence is asymmetrical along the road and can
vary among seasons, between night and day, accord-
ing to weather conditions, and over longer time
periods. We conducted a comprehensive literature
review of 282 publications dealing with “road-effects
zones”or including the distance to roads as a
covariate, of which 58 assessed the spatial influ-
ence of the road (table S2). All investigated road
impacts were documented within a distance of
SCIENCE sciencemag.org 16 DECEMBER 2016 •VOL 354 ISSUE 6318 1423
1
Centre for Econics and Ecosystem Management, Eberswalde
University for Sustainable Development, Alfred-Moeller-
Straße 1, 16225 Eberswalde, Germany.
2
Society for
Conservation Biology–Europe Section, 1133 15th Street
Northwest, Suite 300, Washington, DC 20005, USA.
3
Department of Conservation Biology, UFZ–Centre for
Environmental Research, Permoserstraße 15, 04318 Leipzig,
Germany.
4
German Centre for Integrative Biodiversity
Research (iDiv) Halle-Jena-Leipzig, Deutscher Platz 5e,
04103 Leipzig, Germany.
5
Department of Environmental and
Natural Resources Management, University of Patras, Seferi
2, 30100 Agrinio, Greece.
6
Department of Ecology and
Natural Resources Management, Center for Development
Research, University of Bonn, Walter-Flex-Straße 3, 53113
Bonn, Germany.
7
Geos Institute, 84 4th Street, Ashland, OR
97520, USA.
8
Society for Conservation Biology–North America
Section, 1133 15th Street Northwest, Suite 300, Washington,
DC 20005, USA.
9
Department of Ecology, Federal University of
Rio de Janeiro, Av. Brg. Trompowski s /n, 21044-020 Rio de
Janeiro, Brazil.
10
Society for Conservation Biology–Latin
America and Caribbean Section, 1133 15th Street Northwest,
Suite 300, Washington, DC 20005, USA.
11
Writtle College,
Lordship Road, Writtle, Chelmsford, Essex CM1 3RR, 01245
42420, UK.
12
Institute of Nature Conservation, Polish Academy
of Sciences, Mickiewicza 33, 31-120 Kraków, Poland.
*Corresponding author. Email: pierre.ibisch@hnee.de (P.L.I.);
nuriselva@gmail.com (N.S.)
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1424 16 DECEMBER 2016 •VOL 354 ISSUE 6318 sciencemag.org SCIENCE
Fig. 1. The global distribution of roadless areas, based on a 1-km buffer around all roads. The distribution is depicted according to (A) size classes, (B)the
ecological value index of roadless areas (EVIRA; based on patch size, connectivity, and ecosystem functionality), and (C) representation in protected areas (8).
RESEARCH |REPORTS
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1kmfromtheroad,39%reachedoutto2km
from the road, and only 14% extended out to 5 km
from the road (fig. S1). Because the 1-km buffer
along each side of the road represents the zone
with the highest level and variety of road impacts,
we defined roadless areas as those land units
that are at least 1 km away from all roads and,
therefore, less influenced by road effects. We com-
pared results from using this criterion with the
outcomes from using an alternative 5-km buffer
(see fig. S2 and table S3). We excluded all large
water bodies, as well as Greenland and Antarctica,
which are mostly covered by ice, from the analyses.
Roadless areas with a 1-km buffer to the nearest
road cover about 80% of Earth’s terrestrial surface
(~105 million km
2
). However, these roadless areas
are dissected into almost 600,000 patches. More
than half of the patches are <1 km
2
;80%are
<5 km
2
;andonly7%are>100km
2
(table S4 and
fig. S3). If the buffer is extended to 5 km, there is
a substantial reduction in roadless areas to about
57% of the world’s terrestrial surface (~75 million
km
2
), dissected into 50,000 patches (fig. S2 and
table S3). The occurrence, distribution, and size
of roadless areas differ considerably among con-
tinents (Fig. 1A and fig. S4). For instance, the mean
sizeofroadlesspatches(1-kmbuffer)is48km
2
in
Europe, compared with >500 km
2
in Africa. Be-
cause of comparatively large gaps in available spa-
tial data on roads in many segments of the tropics,
thenumberandsizeofroadlessareasareover-
estimated and should be treated with caution (e.g.,
Borneo; table S1).
All identified roadless areas were assessed for
a set of ecological properties that were selected to
reflect their relative importance to biodiversity,
ecological functions, and ecosystem resilience:
patch size, connectivity, and ecosystem function-
ality (9) (table S5). We normalized these three
indicators to between 0 and 100 to calculate an
additive and unitless index of the ecological val-
ue of each roadless area identified (termed the
ecological value index of roadless areas, or EVIRA)
[Fig. 1B and fig. S5; the specific rationale and
technicalities of the chosen indicators are described
in table S5 (8)]. The EVIRA values range from 0 to
80. A sensitivity analysis shows that ecosystem
functionality and patch size are the best single
indicators for the final index values (table S6 and
figs. S6 to S8). Areas with relatively high index
values tend to have a l ower coe fficient of varia-
tion (fig. S9).
We used the International Union for Conser-
vation of Nature (IUCN) and UN Environment
Programme–World Conservation Monitoring Centre
data set of global protected areas to determine
the extent of roadless areas that are protected (8)
(Fig. 1C). The roadless areas distribution across
human-dominated landscapes was determined
following the classification of so-called anthromes,
definedasbiomesshapedbyhumanlanduseand
infrastructure (10)(Fig.2andtableS7).
When examining the density of roads within
different biomes, large discrepancies in distribu-
tion are apparent. The tundra and rock and ice-
covered biomes are nearly entirely roadless, whereas
temperate broadleaf and mixed forests have the
lowest share of roadless areas (41%; figs. S9 and
S10). Boreal forests of North America and Eurasia
still retain large tracts of roadless areas (figs. S10
and S11). In the tropics, large roadless landscapes
(>1000 km
2
)remaininAfrica,SouthAmerica,
and Southeast Asia, with the Amazon having the
single largest roadless segment. In relation to the
anthromes (10),about two-thirds of the world’s
roadless areas can be described as remote and un-
modified landscapes [26% uninhabited or sparsely
inhabited treeless and barren lands; 21% natural
and remote seminatural woodlands, with 17% wild
woodlands therein (8); Fig. 2 and table S7]. The
remaining one-third consists of rangelands, indicat-
ing that roadless areas can also occur in anthro-
pogenically modified landscapes.
SCIENCE sciencemag.org 16 DECEMBER 2016 •VOL 354 ISSUE 6318 1425
0
2
4
6
8
10
12
14
16
18
20
Share of roadless areas (%)
Urban
Mixed settlements
Rice villages
Irrigated villages
Rainfed villages
Pastoral villages
Residential irrigated croplands
Residential rainfed croplands
Populated croplands
Remote croplands
Residential rangelands
Populated rangelands
Remote rangelands
Residential woodlands
Populated woodlands
Remote woodlands
Inhabited treeless and barren lands
Wild woodlands
Wild treeless and barren lands
Anthromes
Dense settlements
Villages
Croplands
Rangelands
Seminatural lands
Wildlands
Fig. 2. Extent of roadless areas (1-km buffer) across anthromes. The majority of the world’sroadless
areas are in remote and unmodified landscapes, but they also occur in anthropogenically modified
landscapes. The so-called anthromes were mapped according to (10).
EVIRA Classes
Coverage by strict protected areas [%]
0−13 14−28 29−33 34−37 38−42 43−47 48−53 54−58 59−64 65−80
0 20 40 60 80 100
North America
South America
Asia
Africa
Europe
Australia
Oceania
Global
Fig. 3. Coverage of roadless areas by strictly protected areas (IUCN categories I and II) compared
with global and continental EVIRA values. If priority were given to protecting roadless areas with high
ecological functionality, we should see a positive correlation, with higher coverage associated with higher
EVIRA values.
RESEARCH |REPORTS
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About one-third of the world’sroadlessareashave
low EVIRA values. Patches with relatively low EVIRA
values (ranging from 0 to 37; namely, <50% of the
maximum value) account for 35% of the overall
roadless area distribution, because most are small,
fragmented, isolated, or otherwise heavily disturbed
by humans. Some large tracts of roadless areas,
suchasaridlandsinnorthernAfricaorcentral
Asia, occur in areas of sparse vegetation and low
biodiversity and, thus, have low index values for
ecosystem functionality (9)(Fig.1B).HighEVIRA
values occur both in tropical and boreal forests.
The relative conservation value of roadless areas
is context-dependent. Comparatively small or
moderately disturbed roadless areas have higher
conservation importance in heavily roaded envi-
ronments, such as most of Europe, the conter-
minous United States, and southern Canada.
Although the world’s protected areas cover
14.2% of the terrestrial surface, only 9.3% of the
overall expanse of roadless areas is within pro-
tected areas (all IUCN categories; Fig. 1C and
table S8). There is no major difference in the
coverage of roadless areas by strictly protected areas
(IUCN categories I and II) versus the coverage of
the overall landscape by strictly protected areas
(3.8% roadless versus 4.2% overall). Only in North
America, Australia, and Oceania are more than
6% of roadless areas under strict protection (table
S8). If conservation efforts were to prioritize func-
tional, ecologically important roadless areas, we
would find a positive relation between strict pro-
tection coverage and EVIRA values of roadless
areas. However, with the exception of Australia,
this is not the case (Fig. 3 and table S9). Asia and
Africa have particularly low protection coverage
for roadless areas with high EVIRA values. For
instance, we found gaps in the Asian tropical
southeast, as well as in boreal biomes.
The recent Global Biodiversity Outlook (11)gives
a bleak account of the progress made toward
reaching the United Nations’biodiversity agenda
as specified in the 20 Aichi Targets of the Con-
vention on Biological Diversity (12).Governments
have failed on several accounts to keep their use of
natural resources well within safe ecological limits
(target 4); to halt or at least halve the rate of
habitat loss and substantially reduce the degrada-
tion and fragmentation of natural habitats (target
5); and to appropriately protect areas of particular
importance for biodiversity and ecosystem ser-
vices (target 11). To achieve global biodiversity
targets, policies must explicitly acknowledge the
factors underlying prior failures (13). Despite in-
creasing scientific evidence for the negative im-
pacts of roads on ecosystems, the current global
conservation policy framework has largely ignored
road impacts and road expansion. Furthermore,
key policies on road infrastructure and develop-
ment, such as the Cohesion Policy of the European
Union, fail to take into account biodiversity.
In the much wider context of the United Na-
tions’Sustainable Development Goals, conflict-
ing interests can be seen between goals intended
to safeguard biodiversity and those promoting
economic development (14). We analyzed how
roadless areas relate to the global conservation
and sustainability agendas. As a transparent syn-
thesis, we calculated simple scores of conflicts
versus synergies of Sustainable Development
Goals and Aichi Targets with the conservation
of roadless areas (tables S10 and S11). Roads are
explicitly mentioned in the Sustainable Develop-
ment Goals only for their contribution to economic
growth (goal 8), promoting further expansion
into remote rural areas, and consideration is
given neither to the environmental nor the social
costs of road development. The resulting scores
reflect substantial imminent conflicts (Fig. 4 and
table S10); only in five Sustainable Development
Goals do synergies with conservation of roadless
1426 16 DECEMBER 2016 •VOL 354 ISSUE 6318 sciencemag.org SCIENCE
Fig. 4. Synergies and
conflicts between
conservation of road-
less areas and the
United Nations’Sus-
tainable Development
Goals. Scores <–0.5
(blue bars) indicate that
conflicts with the goal
prevail; scores between
–0.5and0.5(yellow)
indicate a mixture of
synergies and conflicts
with the goal; and
scores >0.5 (green)
indicate prevailing syn-
ergies with the goal [for
details, see table S11
(8)]. The scores reflect
substantial imminent
conflicts between vari-
ous Sustainable Devel-
opment Goals and
conservation of road-
less areas (table S11).
RESEARCH |REPORTS
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areas prevail, and four Sustainable Develop-
ment Goals are predominantly in conflict with
conservation of roadless areas. Maybe even more
surprisingly, several of the Aichi Targets are am-
bivalent with respect to conserving roadless areas,
rather than being in synergy entirely [six conflicting
versus 11 synergistic targets (8); table S11].
There is an urgent need for a global strategy
for the effective conservation, restoration, and
monitoring of roadless areas and the ecosystems
that they encompass. Governments should be en-
couraged to incorporate the protection of exten-
sive roadless areas into relevant policies and other
legal mechanisms, reexamine where road devel-
opment conflicts with the protection of roadless
areas, and avoid unnecessary and ecologically
disastrous roads entirely. In addition, governments
should consider road closure where doing so can
promote the restoration of wildlife habitats and
ecosystem functionality (4). Our global map of
roadless areas represents a first step in this di-
rection. During planning and evaluation of road
projects, financial institutions, transport agencies,
environmental nongovernmental organizations,
andtheengagedpublicshouldconsidertheiden-
tified roadless areas.
The conservation of roadless areas can be a key
element in accomplishing the United Nations’
Sustainable Development Goals. The extent and
protection status of valuable roadless areas can
serve as effective indicators to address several Sus-
tainable Development Goals, particularly goal 15
(“Protect, restore and promote sustainable use of
terrestrial ecosystems, sustainably manage forests,
combat desertification, and halt and reverse land
degradation and halt biodiversity loss”)andgoal
9(“Build resilient infrastructure, promote inclu-
sive and sustainable industrialization and foster
innovation”). Enshrined in the protection of road-
less areas should be the objective to seek and
develop alternative socioeconomic models that
do not rely so heavily on road infrastructure.
Similarly, governments should consider how
roadless areas can support the Aichi Targets (see
tables S10 and S11). For instance, the target of
expanding protected areas to cover 17% of the
world’s terrestrial surface could include a repre-
sentative proportion of roadless areas.
Although we acknowledge that access to trans-
portation is a fundamental element of human
well-being, impacts of road infrastructure require
a fully integrated environmental and social cost-
benefits approach (15). Still, under current condi-
tions and policies, limiting road expansion into
roadless areas may prove to be the most cost-
effective and straightforward way of achieving
strategically important global biodiversity and
sustainability goals.
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ACKNOW LEDGM ENTS
The data set is available through www.roadless.online and Dryad at
http://dx.doi.org/10.5061/dryad.q4975. The study was funded
by the Centre for Econics and Ecosystem Management at
Eberswalde University for Sustainable Development, Germany;
the Academy of Sciences and Literature, Mainz, Germany
(“Biodiversity in Change,”Nees Institute, Bonn University); and the
Institute of Nature Conservation, Polish Academy of Sciences.
Special thanks go to W. Barthlott for continued inspiration and
support. The authors declare that they have no competing
interests. P.L.I. acknowledges the research professorships
“Biodiversity and natural resource management under global
change”(2009–2015) and “Ecosystem-based sustainable
development”(2015 onward) awarded by Eberswalde University
for Sustainable Development. G.P. acknowledges funding from the
European Union Framework Programme 7 project EU BON (ref.
308454). N.S. acknowledges funding from the National Science
Center (DEC-2013/08/M/NZ9/00469) and the National Centre for
Research and Development in Poland (Norway grants, POLNOR/
198352/85/2013). P.L.I., N.S., and V.K. conceived the study. M.T.H.
collected and analyzed all data, with assistance from P.L.I.,
L.B.-F., and G.P. P.L.I. wrote a first draft of the text and moderated
its critical revision with important contributions by M.T.H., S.K.,
N.S., and D.A.D. All authors contributed to the interpretation of the
data and critical revision of further versions. N.S., M.T.H., M.M.V.,
V.K., S.K., L.B.-F., and P.L.I. elaborated the supplementary
materials. We appreciate the extraordinary contribution of
D. Biber, who adapted Insensa-GIS to our needs. We acknowledge
J. Sauermann’s contributions to data processing. J.-P. Mund
suggested exploring the OpenStreetMap data set. This study is
part of the Roadless Areas Initiative of the Society for Conservation
Biology, led by the Policy Committee of the Europe Section.
SUPPLEMENTARY MATERIALS
www.sciencemag.org/content/354/6318/1423/suppl/DC1
Materials and Methods
Figs. S1 to S11
Tables S1 to S11
Data Sources
References (16–180)
18 March 2016; accepted 16 November 2016
10.1126/science.aaf7166
PL A NT PATH OLO GY
Regulation of sugar transporter
activity for antibacterial defense
in Arabidopsis
Kohji Yamada,
1,2
*Yusuke Saijo,
3,4
Hirofumi Nakagami,
5
†Yoshitaka Takano
1
*
Microbial pathogens strategically acquire metabolites from their hosts during
infection. Here we show that the host can intervene to prevent such metabolite loss
to pathogens. Phosphorylation-dependent regulation of sugar transport protein 13
(STP13) is required for antibacterial defense in the plant Arabidopsis thaliana.
STP13 physically associates with the flagellin receptor flagellin-sensitive 2 (FLS2)
and its co-receptor BRASSINOSTEROID INSENSITIVE 1–associated receptor kinase
1 (BAK1). BAK1 phosphorylates STP13 at threonine 485, which enhances its
monosaccharide uptake activity to compete with bacteria for extracellular sugars.
Limiting the availability of extracellular sugar deprives bacteria of an energy source
and restricts virulence factor delivery. Our results reveal that control of sugar
uptake, managed by regulation of a host sugar transporter, is a defense strategy
deployed against microbial infection. Competition for sugar thus shapes host-pathogen
interactions.
Plants assimilate carbon into sugar by pho-
tosynthesis, and a broad spectrum of plant-
interacting microbes exploit these host sugars
(1,2). In Arabidopsis, pathogeni c bacterial
infection causes the leakage of sugars to
the extracellular spaces (the apoplast) (3), a major
site of colonization by plant-infecting bacteria.
Although leakage may be a consequence of mem-
brane disintegration during pathogen infection,
some bacterial pathogens promote sugar efflux
to the apoplast by manipulating host plant sugar
transporters (4,5). Interference with sugar ab-
sorption by bacterial and fungal pathogens re-
duces their virulence, highlighting a general
SCIENCE sciencemag.org 16 DECEMBER 2016 •VOL 354 ISSUE 6318 1427
RESEARCH |REPORTS
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(6318), 1423-1427. [doi: 10.1126/science.aaf7166]354Science
2016)
Mariana M. Vale, Peter R. Hobson and Nuria Selva (December 15,
Vassiliki Kati, Lisa Biber-Freudenberger, Dominick A. DellaSala,
Pierre L. Ibisch, Monika T. Hoffmann, Stefan Kreft, Guy Pe'er,
A global map of roadless areas and their conservation status
Editor's Summary
, this issue p. 1423Science
degradation of the world's remaining wildernesses.
Furthermore, environmental protection of roadless areas is insufficient, which could lead to further .
2
it is fragmented by them, with only 7% of land patches created by roads being greater than 100 km
cataloged the world's roads. Though most of the world is not covered by roads,et al.species loss. Ibisch
and trade. However, roads also damage wild areas and rapidly contribute to habitat degradation and
Roads have done much to help humanity spread across the planet and maintain global movement
Too many roads
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