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The global tree restoration potential


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The potential for global forest cover The restoration of forested land at a global scale could help capture atmospheric carbon and mitigate climate change. Bastin et al. used direct measurements of forest cover to generate a model of forest restoration potential across the globe (see the Perspective by Chazdon and Brancalion). Their spatially explicit maps show how much additional tree cover could exist outside of existing forests and agricultural and urban land. Ecosystems could support an additional 0.9 billion hectares of continuous forest. This would represent a greater than 25% increase in forested area, including more than 200 gigatonnes of additional carbon at maturity.Such a change has the potential to store an equivalent of 25% of the current atmospheric carbon pool. Science , this issue p. 76 ; see also p. 24
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The global tree restoration potential
Jean-Francois Bastin
*, Yelena Finegold
, Claude Garcia
, Danilo Mollicone
Marcelo Rezende
, Devin Routh
, Constantin M. Zohner
, Thomas W. Crowther
The restoration of trees remains among the most effective strategies for climate change
mitigation. We mapped the global potential tree coverage to show that 4.4 billion hectares
of canopy cover could exist under the current climate. Excluding existing trees and
agricultural and urban areas, we found that there is room for an extra 0.9 billion hectares
of canopy cover, which could store 205 gigatonnes of carbon in areas that would naturally
support woodlands and forests. This highlights global tree restoration as our most effective
climate change solution to date. However, climate change will alter this potential tree
coverage. We estimate that if we cannot deviate from the current trajectory, the global
potential canopy cover may shrink by ~223 million hectares by 2050, with the vast majority
of losses occurring in the tropics. Our results highlight the opportunity of climate change
mitigation through global tree restoration but also the urgent need for action.
Photosynthetic carbon capture by trees is
likely tobe among our most effective strat-
egies to limit the rise of CO
tions across the globe (13). Consequently,
a number of international initiatives [such
as the Bonn Challenge, the related AFR100, and
the New York Declaration on Forests (4,5)] have
established ambitious targets to promote forest
conservation, afforestation, and restoration at a
global scale. The latest special report (1) by the
Intergovernmental Panel on Climate Change
(IPCC) suggests that an increase of 1 billion ha
of forest will be necessary to limit global warm-
ing to 1.5°C by 2050. However, it remains unclear
whether these restoration goals are achievable
might be possible under current or future cli-
mate conditions or where these trees could exist.
Previous efforts to estimate global tree cover
potential have scaled existing vegetation esti-
mates to the biome or ecoregion levels to provide
coarse approximations of global forest degra-
dation (6,7). However, quantitatively evaluating
which environments could support trees requires
that we build models using direct measurements
of tree cover (independent of satellite-derived
models) from protected areas, where vegetation
cover has been relatively unaffected by human
activity. With enough observations that span
the entire range of environmental conditions,
from the lowest to the highest possible tree cover,
we can interpolate these natural tree coveres-
timates across the globe to generate a predictive
understanding of the potential tree cover in the
absence of human activity.
To explore the determinants of potential tree
cover, we used 78,774 direct photo-interpretation
measurements (data file S1) (8)oftreecover
across all protected regions of the world (fig. S1)
(9,10). Using global environmental layers (table
S1) (11), we examined how climate, edaphic, and
topographic variables drive the variation in nat-
ural tree cover across the globe. The focus on
protected areas is intended to approximate nat-
ural tree cover. Of course, these regions are not
entirely free of human activity (11), presenting
slightly lower tree cover than expected in some
regions or higher tree cover than expected in
other regions because of low fire frequency, but
these ecosystems represent areas with minimal
human influence on the overall tree cover. We
then used a random forest machine-learning ap-
proach (12) to examine the dominant environ-
mental drivers of tree cover and generated a
predictive model (Fig. 1) that enables us to inter-
polate potential tree cover across terrestrial eco-
systems. The resulting mapEarthstreecarrying
capacitydefines the tree cover per pixel that
could potentially exist under any set of environ-
mental conditions, with minimal human activity
(Fig. 2A). This work is directly underpinned by
our systematic dataset of direct tree cover mea-
surements (entirely independent of climate and
modeled remote sensing estimates) (13)acrossthe
globe (fig. S1) (10).
Across the worlds protected areas (fig. S2),
tree cover ranged between peaks of 0% in dry
desert and 100% in dense equatorial forest, with
fewer values falling between these two extremes
(figs. S2 and S3). We paired these tree cover mea-
data (table S1) (11). Our resulting random forest
model had high predictive power [coefficient of
determination (R
) = 0.86; intercept = 2.05%
tree cover; slope = 1.06] (Fig. 1); rigorous k-fold
cross-validation (fig. S4A) (11) revealed that our
model could explain ~71% of the variation in tree
cover without bias (R
= 0.71; intercept = 0.34%
tree cover; slope = 0.99) (fig. S3, B and C). Our
k-fold cross-validation approach also allows us
to generate a spatially explicit understanding
of model uncertainty (figs. S5 and S6) (11). Across
all pixels, the mean standard deviation around
the modeled estimate is ~9% in tree cover (28%
ofthemeantreecover)(figs.S5andS6)(11). As
such, these models accurately reflected the dis-
tribution of tree cover across the full range of
protected areas. We then interpolated this ran-
dom forest model across all terrestrial ecosystems
using all 10 soil and climate variables to project
potential tree cover across the globe under exist-
ing environmental conditions.
The resulting map reveals Earths tree carry-
ing capacity at a spatial resolution of 30 arc sec
(Fig. 2A). The model accurately predicts the pres-
ence of forest in all existing forested land on the
planet (fig. S7A) but also reveals the extent of tree
cover that could naturally exist in regions beyond
existing forested lands. The most recent Food and
Agriculture Organization of the United Nations
(FAO) definition of forestcorresponds to a land
of at least 0.5 ha covered by at least 10% tree
Bastin et al., Science 365,7679 (2019) 5 July 2019 1of4
Crowther Lab, Department of Environmental Systems
Science, Institute of Integrative Biology, ETH-Zürich, Zürich,
Food and Agriculture Organization of the
United Nations, Rome, Italy.
Department of Environmental
Systems Science, Institute of Integrative Biology, ETH-Zürich,
Zürich, Switzerland.
Centre de Coopération Internationale
en la Recherche Agronomique pour le Développement
(CIRAD), UR Forest and Societies, Montpellier, France.
*Corresponding author. Email:
Fig. 1. Predicted vs. observed tree cover. (Aand B) The predicted tree cover (xaxes) compared
with the observed tree cover (yaxes). (A) Results as a density plot, with the 1:1 line in dotted
black and the regression line in continuous black (intercept = 2% forest cover; slope = 1.06;
= 0.86), which shows that the model is un-biased. (B) Results as boxplots, to illustrate the quality
of the prediction in all tree cover classes.
on July 7, 2019 from
cover and without agricultural activity or human
settlements (14). Using this definition, our map
reveals that about two-thirds of terrestrial land,
8.7 billion ha, could support forest (table S2).
That value is 3.2 billion ha more than the current
forested area (fig. S7A) (11,15). We estimate that
1.4 billion ha of this potential forest land is lo-
cated in croplands (>99%) and urban areas (<1%),
as delineated by the European Space Agencys
global land cover model (fig. S7B and table S2)
(16), and 1.5 billion ha with croplands as de-
lineated by Fritz et al. (fig. S7C and table S2) (17).
Therefore, ~1.7 billion to 1.8 billion ha of po-
tential forest land (defined as > 10% tr ee co ver)
exists in areas that were previously degraded,
dominated by sparse vegetation, grasslands, and
degraded bare soils.
To avoid the pitfalls of categorical forest defi-
nitions, we also evaluated the tree canopy cover
in a truly continuous scale (fig. S8). We refer to
canopy coveras the area of the land that is
covered by tree crown vertically projected to the
ground (for example, 50% of tree cover over 1 ha
corresponds to 0.5 ha of canopy cover) (fig. S8).
By accounting for all levels of tree cover (from
0 to 100%), this approach balances the relative
contribution of different forest types (such as
woodlands, open forest, and dense forest) and of
wooded lands outside forests (such as savannas)
across the globe.
In total, 4.4 billion ha of canopy cover can be
supported on land under existing climate con-
ditions (pixel uncertainty = 28%; global uncer-
tainty <1%) (table S2) (11). This value is 1.6 billion
ha more than the 2.8 billion ha existing on land
today (10,15). Of course, much of the land that
could potentially support trees across the globe is
currently used for human development and agri-
culture, which are necessary for supporting an
ever-growing human population. On the basis
of both the European Space Agencysgloballand
cover model (16) and on Fritz and colleagues
cropland layer (17), we estimate that 0.9 billion
hectares are found outside cropland and urban
regions (Fig. 2, B and C, and table S2) (11) and
may represent regions for potential restoration.
More than 50% of the tree restoration potential
can be found in only six countries (in million
hectares: Russia, +151; United States, +103; Canada,
+78.4; Australia, +58; Brazil, +49.7; and China,
+40.2) (data file S2), stressing the important re-
sponsibility of some of the worldsleadingeco-
nomies. By comparing our country-level results
to the commitments of 48 countries in the Bonn
Challenge (4), we can provide a scientific eval-
uation of the country-level restoration targets.
Approximately 10% of countries have committed
to restoring an area of land that considerably ex-
ceeds the total area that is available for restora-
tion (data file S2). By contrast, over 43% of the
countries have committed to restore an area that
is less than 50% of the area available for resto-
ration. These results reinforce the need for better
country-level forest accounting, which is critical
for developing effective management and resto-
ration strategies. Of course, it remains unclear
what proportion of this land is public or privately
owned, and so we cannot identify how much
land is truly available for restoration. However,
at a global scale, our model suggests that the
global forest restoration target proposed by the
IPCC (1) of 1 billion ha (defined as >10% tree
cover) is undoubtedly achievable under the cur-
rent climate. By scaling these forest area calcu-
lations by biome-level mean estimates of carbon
storage (18,19), we estimate that vegetation in
the potential restoration areas could store an
Bastin et al., Science 365,7679 (2019) 5 July 2019 2of4
Fig. 2. The current global tree restoration potential. (A) The global potential tree cover
representing an area of 4.4 billion ha of canopy cover distributed across the world. (Band C) The
global potential tree cover available for restoration. Shown is the global potential tree cover (A), from
which we subtracted existing tree cover (15) and removed agricultural and urban areas according to
(B) Globcover (16) and (C) Fritz et al.(17). This global tree restoration potential [(B) and (C)]
represents an area of 0.9 billion ha of canopy cover (table S2).
on July 7, 2019 from
additional 205 gigatonnes of carbon (GtC) if they
were restored to the status of existing forests
(table S2).
Our model accurately depicts the regions
environmental conditions. However, changing
climate conditions may alter the area of land
that could support forest growth over the rest
of the century, a point that needs to be consid-
ered when developing long-term restoration
projects. We tested this possibility by rerunning
our potential tree cover model under future cli-
mate conditions, projected under three Earth
System Models (10) and two Representative Con-
centration Pathways (RCP) scenarios (RCP 4.5
and 8.5) (1). Under both scenarios, the global
tree carrying capacity is lower than the present
day potential because of reductions in the po-
tential area of tropics. This is in stark contrast
to most current model predictions, which ex-
pect global tree cover to increase under climate
change (20). Although warming is likely to in-
crease tree cover in cold regions with low tree
cover (for example, in northern boreal regions
such as Siberia) or with existing open forests
(such as in tropical drylands) (Fig. 3), our model
highlights the high probability of consistent de-
clines of tropical rainforests with high tree cover.
Because the average tree cover in the expand-
ing boreal region (30 to 40%) is lower than that
in declining tropical regions (90 to 100%), our
global evaluation suggests that the potential glob-
al canopy cover will decrease under future cli-
mate scenarios, even if there is a larger total forest
area with >10% tree cover. Therefore, despite
potential increases in canopy cover in boreal
(~130 Mha), desertic (~30 Mha), montane
(~30 Mha), and temperate (~30 Mha) regions, the
potential loss of forest habitat in tropical regions
(~450 Mha) leads to a global loss of 223 Mha
of potential canopy cover by 2050, correspond-
ing to 46 GtC (Fig. 3B and table S3). Such risks
of loss do not account for future changes in
land use, such as pasture and cattle raising (7),
which might also contribute to the urgency of
the situation.
These models of future changes in tree cover
potential reveal insights into how the structure
of vegetation might change over time. Of course,
these models are characterized by high un-
certainty because, unlike the present-day in-
terpolations, we rely on extrapolation of our
machine-learning models outside of the existing
range of global climate conditions. These extrap-
olations cannot be considered to be future pro-
jections of potential forest extent because they do
not incorporate any of the ecological, hydrolog-
ical, and biogeochemical feedbacks that would
be associated with changes in forest cover. For
example, it is possible that elevated CO
trations under future climate scenarios might
enhance the growth of those existing trees, al-
though recent evidence suggests that increased
growth rate does not necessarily translate to in-
crease of carbon storage (21). However, our ap-
proach has a strong predictive power to describe
the potential tree cover in the absence of humans
under any given set of future climate scenarios.
The global photointerpretation dataset offers
the capacity to characterize the potential tree
cover under any given set of environmental con-
ditions. The resulting openly accessible map can
serve as a benchmark map to assess restoration
opportunities (such as tree planting and natural
assisted regeneration) around the globe, with a
tree cover of reference that respects the natu-
ral ecosystem type (for example, from wooded
savannah to dense forest). However, restoration
initiatives must not lead to the loss of existing
natural ecosystems, such as native grasslands,
that can support huge amounts of natural bio-
diversity and carbon. Using existing global land-
cover layers (1517), our maps reveal that there
is likely to be space for at least an additional
0.9 billion ha of canopy cover. If these restored
woodlands and forests were allowed to mature
to a similar state of existing ecosystems in pro-
tected areas, they could store 205 GtC. Of course,
the carbon capture associated with global res-
toration could not be instantaneous because it
would take several decades for forests to reach
maturity. Nevertheless, under the assumption
that most of this additional carbon was sourced
from the atmosphere, reaching this maximum
restoration potential would reduce a consid-
erable proportion of the global anthropogenic
carbon burden (~300 GtC) to date (1). This places
ecosystem restoration as the most effective solu-
tion at our disposal to mitigate climate change.
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Bastin et al., Science 365,7679 (2019) 5 July 2019 3of4
Fig. 3. Risk assessment of future changes in potential tree cover. (A) Illustration of expected losses in potential tree cover by 2050, under the
business as usualclimate change scenario (RCP 8.5), from the average of three Earth system models commonly used in ecology (cesm1cam5,
cesm1bgc, and mohchadgem2es). (B) Quantitative numbers of potential gain and loss are illustrated by bins of along a latitudinal gradient.
on July 7, 2019 from
15. M. C. Hansen et al., Science 342, 850853 (2013).
16. O. Arino et al., Global Land Cover Map for 2009 (GlobCover
2009) (European Space Agency, Université catholique de
Louvain, PANGAEA, 2012).
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We warmly thank all the members of the Crowther lab team,
not listed as coauthors of the study, for their incredible support.
We also are very grateful to the Google Earth Outreach team for
allowing us the storage expansion for ou r laboratory. Fu ndin g:
This work was supported by grants to T.W.C. from DOB Ecology,
Plant-for-the-Planet, and the German Federal Ministry for Economic
Cooperation and Development. The data collection was partially
supported by the International Climate Initiative of the Federal
Ministry for the Environment, Nature Conservation, Building and
Nuclear Safety of Germany. Author contributions: J.-F.B. conceived
the study. J.-F.B. and D.R. performed the analyses. J.-F.B., Y.F.,
C.G., D.M., M.R., D.R., C.M.Z., and T.W.C. wrote the manuscript.
Competing interests: The authors declare that there are no
competing interests. Data and materials availability: All data are
available in the manuscript or the supplementary materials. The
global tree cover potential map, corresponding to Fig. 2A, isaccessible
online for visualization at https://bastinjf_climate.users.earthengine.
app/view/potential-tree-cover, the Earth engine script to produce the
map is accessible online at
ee5cf5186b5ad0f659cc7a43054f072c, and all related layers are
accessible online at or upon request to the
corresponding author.
Materials and Methods
Figs. S1 to S12
Tables S1 to S3
References (2229)
Data Files S1 and S2
21 February 2019; accepted 21 May 2019
Bastin et al., Science 365,7679 (2019) 5 July 2019 4of4
on July 7, 2019 from
The global tree restoration potential
Zohner and Thomas W. Crowther
Jean-Francois Bastin, Yelena Finegold, Claude Garcia, Danilo Mollicone, Marcelo Rezende, Devin Routh, Constantin M.
DOI: 10.1126/science.aax0848
(6448), 76-79.365Science
, this issue p. 76; see also p. 24Science
cut the atmospheric carbon pool by about 25%.
than 500 billion trees and more than 200 gigatonnes of additional carbon at maturity. Such a change has the potential to
billion hectares of continuous forest. This would represent a greater than 25% increase in forested area, including more
cover could exist outside of existing forests and agricultural and urban land. Ecosystems could support an additional 0.9
the globe (see the Perspective by Chazdon and Brancalion). Their spatially explicit maps show how much additional tree
used direct measurements of forest cover to generate a model of forest restoration potential acrosset al.change. Bastin
The restoration of forested land at a global scale could help capture atmospheric carbon and mitigate climate
The potential for global forest cover
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... Different zoning schemes showing areas of greater importance for the implementation of restoration activities have been produced worldwide based on different objectives such as biodiversity [16,17], protected areas [18], social aspects [19], tree cover [20], and landcover change [21], as well as integrating the above with cost-benefit analysis [22], and future scenarios up to 2050 [23]. Regardless of the underlying objective, all results aim to generate benefits in mitigating climate change and improving biodiversity and human well-being. ...
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Plant-based animal product alternatives are increasingly promoted to achieve more sustainable diets. Here, we use a global economic land use model to assess the food system-wide impacts of a global dietary shift towards these alternatives. We find a substantial reduction in the global environmental impacts by 2050 if globally 50% of the main animal products (pork, chicken, beef and milk) are substituted—net reduction of forest and natural land is almost fully halted and agriculture and land use GHG emissions decline by 31% in 2050 compared to 2020. If spared agricultural land within forest ecosystems is restored to forest, climate benefits could double, reaching 92% of the previously estimated land sector mitigation potential. Furthermore, the restored area could contribute to 13-25% of the estimated global land restoration needs under target 2 from the Kunming Montreal Global Biodiversity Framework by 2030, and future declines in ecosystem integrity by 2050 would be more than halved. The distribution of these impacts varies across regions—the main impacts on agricultural input use are in China and on environmental outcomes in Sub-Saharan Africa and South America. While beef replacement provides the largest impacts, substituting multiple products is synergistic.
... Forests are large and persistent sinks for atmospheric carbon dioxide (CO 2 ; Pan et al., 2011) and large-scale afforestation and reforestation have been suggested as methods for mitigating climate change through carbon sequestration (Law et al., 2018;Nave et al., 2018;Bastin et al., 2019;Pugh et al., 2019;Domke et al., 2020). However, intensification of forestry (Kastner et al., 2021), including removal of organic residues for bioenergy (Daiogloua et al., 2019), has led to concern about sustainability of base-cation supply (Achat et al., 2018;Akselsson et al., 2019), and better understanding of the ecological and biogeochemical consequences of different management practices is needed (Palmer, 2021). ...
Tree growth in boreal forests is driven by ectomycorrhizal fungal mobilisation of organic nitrogen and mineral nutrients in soils with discrete organic and mineral horizons. However, there are no studies of how ectomycorrhizal mineral weathering and organic nitrogen mobilisation processes are integrated across the soil profile. We studied effects of organic matter (OM) availability on ectomycorrhizal functioning by altering the proportions of natural organic and mineral soil in reconstructed podzol profiles containing Pinus sylvestris plants, using 13 CO2 pulse labelling, patterns of naturally occurring stable isotopes (26 Mg and 15 N) and high-throughput DNA sequencing of fungal amplicons. Reduction in OM resulted in nitrogen limitation of plant growth and decreased allocation of photosynthetically derived carbon and mycelial growth in mineral horizons. Fractionation patterns of 26 Mg indicated that magnesium mobilisation and uptake occurred primarily in the deeper mineral horizon and was driven by carbon allocation to ectomycorrhizal mycelium. In this horizon, relative abundance of ectomycorrhizal fungi, carbon allocation and base cation mobilisation all increased with increased OM availability. Allocation of carbon through ectomycorrhizal fungi integrates organic nitrogen mobilisation and mineral weathering across soil horizons, improving the efficiency of plant nutrient acquisition. Our findings have fundamental implications for sustainable forest management and belowground carbon sequestration.
... Degraded landscapes with the potential for forest restoration cover approximately 1.7-1.8 billion hectares of land worldwide, and increasing forest soil C pools on these landscapes represents an opportunity for global C sequestration (Bastin et al., 2019). The regreening of mining and smelting degraded landscapes is of particular interest as soils on these landscapes are generally low in C and their potential for C accumulation is high (Ussiri and Lal, 2005). ...
Increasing forest cover by regreening mining and smelting degraded landscapes provides an opportunity for global carbon (C) sequestration, however, the reported effects of regreening on soil C processes are mixed. One of the world's largest regreening programs is in the City of Greater Sudbury, Canada and has been ongoing since 1978. Prior to regreening, soils in the City of Greater Sudbury area were highly eroded, acidic, rich in metals, and poor in nutrients. This study used a chronosequence approach to investigate how forest soil C pools and fluxes have changed with stand age in highly "eroded" sites with minimal soil cover (n = 6) and "stable" sites covered by soil (n = 6). Encouragingly, the relationship between stand age and soil C processes (litterfall, litter decomposition, soil respiration, fine root growth) at both stable and eroded sites were comparable to observations reported for jack pine (Pinus banksiana Lamb.) and red pine (Pinus resinosa Ait.) plantations that have not been subject to over a century of industrial impacts. There was a strong "home-field advantage" for local decomposers, where litter decomposition rates were higher using a site-specific pine litter compared with a common pine litter. Higher soil respiration at eroded sites was linked to higher soil temperature, likely because of a more open tree canopy. Forest floor C pools increased with stand age while mineral soil C and aggregate C concentrations decreased with stand age. This loss of soil C is small relative to the substantial increases in aboveground tree and forest floor C pools, leading to a sizeable increase in total ecosystem C pools following regreening.
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Land use, land use change, and forestry (LULUCF) are critical in climate change mitigation. Producing or collecting activity data for LULUCF is essential in developing national greenhouse gas inventories, national communications, biennial update reports, and nationally determined contributions to meet international commitments under climate change. Collect Earth is a free, publicly accessible software for monitoring dynamics between all land use classes: forestlands, croplands, grasslands, wetlands, settlements, and other lands. Collect Earth supports countries in monitoring the trends in land use and land cover over time by applying a sample-based approach and generating reliable, high-quality, consistent, accurate, transparent, robust, comparable, and complete activity data through augmented visual interpretation for climate change reporting. This article reports forest extent estimates in Azerbaijan, analyzing 7782 0.5-ha sampling units through an augmented visual interpretation of very high spatial and temporal resolution images on the Google Earth platform. The results revealed that in 2016, tree cover existed in 31.9% of total land, equal to 2,751,167 ha and 1,301,188 ha or 15.1% of the total land, with a 5.4% sampling error covered by forests. The estimate is 15 to 25% higher than the previous estimates, equal to 169,418 to 260,888 ha of forest that was never reported in previous studies.
Woody plant encroachment (WPE) is a global trend that occurs in many biomes, including savannas, and accelerates with fire suppression. Since WPE can result in increased storage of soil organic carbon (SOC), fire management, which may include fire suppression, can improve ecosystem carbon (C) sequestration in savannas. At our study site in Kruger National Park, South Africa, we used a long‐term (~70 year) fire experiment to study the drivers and consequences of changes in woody cover (trees and shrubs) on SOC sequestration. We surveyed four fire manipulation treatments, replicated at eight locations within the park: annual high‐intensity burns, triennial high (dry season) and low‐intensity (wet season) burns, and fire exclusion, to capture the range of fire management scenarios under consideration. The changes in woody cover were calculated over a period similar to the experiment's duration (~80 years) using aerial photographs (1944–2018). Soils were analysed to 30 cm depth for SOC and δ ¹³ C, under and away from the tree canopy to isolate local‐ and landscape‐level effects of WPE on SOC. The largest increases in woody cover occurred with fire exclusion. We found that plots with higher increases in woody cover also had higher SOC. However, trees were not the only contributor to SOC gains, sustained high inputs of C 4 ‐derived C (grasses), even under canopies in fire suppression plots, contributed significantly to SOC. We observed little difference in SOC sequestration between cooler triennial (wet season) burns and fire suppression. Synthesis . Grass input to soil organic carbon (SOC) remained high across the full range of woody cover created by varying burning regimes. The total SOC stocks stored from tree input only matched grass‐derived SOC stocks after almost 70 years of fire exclusion. Our results point to C 4 grasses as a resilient contributor to SOC under altered fire regimes and further challenge the assumption that increasing tree cover, either through afforestation schemes or fire suppression, will result in large gains in C sequestration in savanna soils, even after 70 years.
Trees are an integral part in European landscapes, but only forest resources are systematically assessed by national inventories. The contribution of urban and agricultural trees to national-level carbon stocks remains largely unknown. Here we produced canopy cover, height and above-ground biomass maps from 3-meter resolution nanosatellite imagery across Europe. Our biomass estimates have a systematic bias of 7.6% (overestimation; R = 0.98) compared to national inventories of 30 countries, and our dataset is sufficiently highly resolved spatially to support the inclusion of tree biomass outside forests, which we quantify to 0.8 petagrams. Although this represents only 2% of the total tree biomass, large variations between countries are found (10% for UK) and trees in urban areas contribute substantially to national carbon stocks (8% for the Netherlands). The agreement with national inventory data, the scalability, and spatial details across landscapes, including trees outside forests, make our approach attractive for operational implementation to support national carbon stock inventory schemes.
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Confronting biome-scale threats in the 21st century will require new and adaptive approaches for conservation. The overarching theme of this dissertation is co-produced science for the conservation of grasslands threatened by woody encroachment. Each chapter reflects a research question co-developed by scientists and managers to better understand and manage the threat of woody encroachment. First, I examine the dimensions of grassland risk through a series of field studies. Risk is the outcome of a grassland’s sensitivity and exposure to encroaching woody plants. Sensitivity reflects the rate and ease of grassland transition to a woodland, while, exposure is driven by propagule sources and their dispersal. My findings demonstrate the importance of exposure in driving patterns of encroachment and provide a basis for managing the spatial dimensions of exposure. Second, I assess the potential impacts of plant invasions in grasslands using a participatory ecosystem service assessment. Findings illustrate the potential for severe impacts associated with woodland transitions driven by a native-invasive tree compared to non-native invasive weeds. Third, I assess the sustainability of grassland conservation approaches, including the lifespan of restoration treatments. Overall, I find unsustainable trends of grassland loss to encroachment across a network of priority conservation areas. Conservation efforts tended to be outpaced by encroachment of intact grasslands and re-encroachment of sites undergoing restoration, which rapidly transition back to a woodland without follow-up management. Large-scale fire management provided the only example of counteracting regional trends of encroachment and serves as a model for improving conservation efforts in other grasslands threatened by encroachment. However, the viability of this approach will likely depend upon broader acceptance of the role of prescribed fire in grasslands. To this end, I developed fire management scenarios to contrast air-quality outcomes of large-scale fire management versus those of fire exclusion. The scenarios illustrate the inevitable nature of fire in flammable ecosystems and provide a basis for communicating the role of prescribed fire in avoiding long-term consequences associated with wildfire.
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Boreal forests sequester and store vast carbon (C) pools that may be subject to significant feedback effects induced by climatic warming. The boreal landscape consists of a mosaic of forests and peatlands with wide variation in total C stocks, making it important to understand the factors controlling C pool sizes in different ecosystems. We therefore quantified the total C stocks in the organic layer, mineral soil, and tree biomass in 430 plots across a 68 km ² boreal catchment. The organic layer held the largest C pool, accounting for 39% of the total C storage; tree and mineral C pools accounted for 38% and 23%, respectively. The size of the soil C pool was positively related to modelled soil moisture conditions, especially in the organic soil layer (R ² = 0.50). Conversely, the tree C pool exhibited a unimodal relationship: storage was highest under intermediate wetness conditions. The magnitude and variation in the total soil C stocks observed in this work were comparable to those found at the national level in Sweden, suggesting that C accumulation in boreal landscapes is more sensitive to local variation resulting primarily from differences in soil moisture conditions than to regional differences in climate, nitrogen deposition, and parent material.
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It is generally accepted that animal heartbeat and lifespan are often inversely correlated, however, the relationship between productivity and longevity has not yet been described for trees growing under industrial and pre-industrial climates. Using 1768 annually resolved and absolutely dated ring width measurement series from living and dead conifers that grew in undisturbed, high-elevation sites in the Spanish Pyrenees and the Russian Altai over the past 2000 years, we test the hypothesis of grow fast-die young. We find maximum tree ages are significantly correlated with slow juvenile growth rates. We conclude, the interdependence between higher stem productivity, faster tree turnover, and shorter carbon residence time, reduces the capacity of forest ecosystems to store carbon under a climate warming-induced stimulation of tree growth at policy-relevant timescales.
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Land change is a cause and consequence of global environmental change1,2. Changes in land use and land cover considerably alter the Earth's energy balance and biogeochemical cycles, which contributes to climate change and-in turn-affects land surface properties and the provision of ecosystem services1-4. However, quantification of global land change is lacking. Here we analyse 35 years' worth of satellite data and provide a comprehensive record of global land-change dynamics during the period 1982-2016. We show that-contrary to the prevailing view that forest area has declined globally5-tree cover has increased by 2.24 million km2 (+7.1% relative to the 1982 level). This overall net gain is the result of a net loss in the tropics being outweighed by a net gain in the extratropics. Global bare ground cover has decreased by 1.16 million km2 (-3.1%), most notably in agricultural regions in Asia. Of all land changes, 60% are associated with direct human activities and 40% with indirect drivers such as climate change. Land-use change exhibits regional dominance, including tropical deforestation and agricultural expansion, temperate reforestation or afforestation, cropland intensification and urbanization. Consistently across all climate domains, montane systems have gained tree cover and many arid and semi-arid ecosystems have lost vegetation cover. The mapped land changes and the driver attributions reflect a human-dominated Earth system. The dataset we developed may be used to improve the modelling of land-use changes, biogeochemical cycles and vegetation-climate interactions to advance our understanding of global environmental change1-4,6.
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In an era of massive biodiversity loss, the greatest conservation success story has been the growth of protected land globally. Protected areas are the primary defense against biodiversity loss, but extensive human activity within their boundaries can undermine this. Using the most comprehensive global map of human pressure, we show that 6 million square kilometers (32.8%) of protected land is under intense human pressure. For protected areas designated before the Convention on Biological Diversity was ratified in 1992, 55% have since experienced human pressure increases. These increases were lowest in large, strict protected areas, showing that they are potentially effective, at least in some nations. Transparent reporting on human pressure within protected areas is now critical, as are global targets aimed at efforts required to halt biodiversity loss.
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Carbon stocks in vegetation have a key role in the climate system. However, the magnitude, patterns and uncertainties of carbon stocks and the effect of land use on the stocks remain poorly quantified. Here we show, using state-of-the-art datasets, that vegetation currently stores around 450 petagrams of carbon. In the hypothetical absence of land use, potential vegetation would store around 916 petagrams of carbon, under current climate conditions. This difference highlights the massive effect of land use on biomass stocks. Deforestation and other land-cover changes are responsible for 53-58% of the difference between current and potential biomass stocks. Land management effects (the biomass stock changes induced by land use within the same land cover) contribute 42-47%, but have been underestimated in the literature. Therefore, avoiding deforestation is necessary but not sufficient for mitigation of climate change. Our results imply that trade-offs exist between conserving carbon stocks on managed land and raising the contribution of biomass to raw material and energy supply for the mitigation of climate change. Efforts to raise biomass stocks are currently verifiable only in temperate forests, where their potential is limited. By contrast, large uncertainties hinder verification in the tropical forest, where the largest potential is located, pointing to challenges for the upcoming stocktaking exercises under the Paris agreement.
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Significance Most nations recently agreed to hold global average temperature rise to well below 2 °C. We examine how much climate mitigation nature can contribute to this goal with a comprehensive analysis of “natural climate solutions” (NCS): 20 conservation, restoration, and/or improved land management actions that increase carbon storage and/or avoid greenhouse gas emissions across global forests, wetlands, grasslands, and agricultural lands. We show that NCS can provide over one-third of the cost-effective climate mitigation needed between now and 2030 to stabilize warming to below 2 °C. Alongside aggressive fossil fuel emissions reductions, NCS offer a powerful set of options for nations to deliver on the Paris Climate Agreement while improving soil productivity, cleaning our air and water, and maintaining biodiversity.
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We created a new dataset of spatially interpolated monthly climate data for global land areas at a very high spatial resolution (approximately 1 km 2). We included monthly temperature (minimum, maximum and average), precipitation, solar radiation, vapour pressure and wind speed, aggregated across a target temporal range of 1970–2000, using data from between 9000 and 60 000 weather stations. Weather station data were interpolated using thin-plate splines with covariates including elevation, distance to the coast and three satellite-derived covariates: maximum and minimum land surface temperature as well as cloud cover, obtained with the MODIS satellite platform. Interpolation was done for 23 regions of varying size depending on station density. Satellite data improved prediction accuracy for temperature variables 5–15% (0.07–0.17 ∘ C), particularly for areas with a low station density, although prediction error remained high in such regions for all climate variables. Contributions of satellite covariates were mostly negligible for the other variables, although their importance varied by region. In contrast to the common approach to use a single model formulation for the entire world, we constructed the final product by selecting the best performing model for each region and variable. Global cross-validation correlations were ≥ 0.99 for temperature and humidity, 0.86 for precipitation and 0.76 for wind speed. The fact that most of our climate surface estimates were only marginally improved by use of satellite covariates highlights the importance having a dense, high-quality network of climate station data.
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Mapping the world's dry forests The extent of forest area in dryland habitats, which occupy more than 40% of Earth's land surface, is uncertain compared with that in other biomes. Bastin et al. provide a global estimate of forest extent in drylands, calculated from high-resolution satellite images covering more than 200,000 plots. Forests in drylands are much more extensive than previously reported and cover a total area similar to that of tropical rainforests or boreal forests. This increases estimates of global forest cover by at least 9%, a finding that will be important in estimating the terrestrial carbon sink. Science , this issue p. 635
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This paper describes the technical development and accuracy assessment of the most recent and improved version of the SoilGrids system at 250m resolution (June 2016 update). SoilGrids provides global predictions for standard numeric soil properties (organic carbon, bulk density, Cation Exchange Capacity (CEC), pH, soil texture fractions and coarse fragments) at seven standard depths (0, 5, 15, 30, 60, 100 and 200 cm), in addition to predictions of depth to bedrock and distribution of soil classes based on the World Reference Base (WRB) and USDA classification systems (ca. 280 raster layers in total).
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The GlobCover initiative of ESA developed and demonstrated a service for the generation of global land cover maps, based on Envisat MERIS Fine Resolution (300 m) mode data. ESA and Université catholique de Louvain demonstrated the possibility to use the GlobCover system operationally by delivering GlobCover 2009, the 2009 global land cover map, within a year of the last satellite acquisition. For maximum user benefit the thematic legend of GlobCover is compatible with the UN Land Cover Classification System (LCCS). The system is based on an automatic pre-processing and classification chain. Finally, the global land cover map was validated by an international group of land cover experts and the validation reports are also available to the user community.
Plans to triple the area of plantations will not meet 1.5 °C climate goals. New natural forests can, argue Simon L. Lewis, Charlotte E. Wheeler and colleagues.