ArticlePDF Available

The global tree restoration potential

July 2019
Science 365(6448):76-79

DOI:10.1126/science.aax0848

Authors:

Claude A. Garcia

Bern University of Applied Sciences

Danilo Mollicone

Food and Agriculture Organization of the United Nations

Show all 8 authorsHide

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

Predicted vs. observed tree cover. (A and B) The predicted tree cover (x axes) compared with the observed tree cover (y axes). (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; R 2 = 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.

…

Figures - uploaded by Claude A. Garcia

Content may be subject to copyright.

Content uploaded by Claude A. Garcia

Content may be subject to copyright.

RESTORATION ECOLOGY

The global tree restoration potential

Jean-Francois Bastin

*, Yelena Finegold

, Claude Garcia

3,4

, 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

concentra-

tions across the globe (1–3). 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

becausewedonotknowhowmuchtreecover

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 cover”es-

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 map—Earth’streecarrying

capacity—defines 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 world’s 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-

surementswith10globallayersofsoilandclimate

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 Earth’s 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 “forest”corresponds to a land

of at least 0.5 ha covered by at least 10% tree

RESEARCH

Bastin et al., Science 365,76–79 (2019) 5 July 2019 1of4

Crowther Lab, Department of Environmental Systems

Science, Institute of Integrative Biology, ETH-Zürich, Zürich,

Switzerland.

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: bastin.jf@gmail.com

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 http://science.sciencemag.org/Downloaded 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 Agency’s

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 cover”as 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 Agency’sgloballand

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 world’sleadingeco-

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 365,76–79 (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).

RESEARCH |REPORT

on July 7, 2019 http://science.sciencemag.org/Downloaded 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

wheretreegrowthispossibleunderexisting

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

concen-

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 (15–17), 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.

REFERENCES AND NOTES

1. Intergovernmental Panel on Climate Change (IPCC), An IPCC

Special Report on the Impacts of Global Warming of 1.5 °C

Above Pre-Industrial Levels and Related Global Greenhouse

Gas Emission Pathways (IPCC, 2018).

2. B. W. Griscom et al., Proc. Natl. Acad. Sci. U.S.A. 114,

11645–11650 (2017).

3. S. L. Lewis, C. E. Wheeler, E. T. A. Mitchard, A. Koch, Nature

568,25–28 (2019).

4. United Nations Environment Programme (UNEP), The Bonn

Challenge (2011).

5. UN Climate Summit, New York Declaration on Forests

(2014).

6. P. Potapov, L. Laestadius, S. Minnemeyer, Global Map of

Potential Forest Cover (World Resources Institute, 2011).

7. K.-H. Erb et al., Nature 553,73–76 (2018).

8. A. Bey et al., Remote Sens. 8, 807 (2016).

9. United Nations Educational, Scientific and Cultural

Organization (UNESCO), The World Database on Protected

Areas (UNESCO, 2011).

10. Materials and methods are available as supplementary

materials.

11. K. R. Jones et al., Science 360, 788–791 (2018).

12. L. Breiman, Mach. Learn. 45,5–32 (2001).

13. J.-F. Bastin et al., Science 356, 635–638 (2017).

14. Food and Agriculture Organization (FAO), Global Forest

Resources Assessment 2020: Terms and Definitions

(FAO, 2018).

Bastin et al., Science 365,76–79 (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 usual”climate 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 5° along a latitudinal gradient.

RESEARCH |REPORT

on July 7, 2019 http://science.sciencemag.org/Downloaded from

15. M. C. Hansen et al., Science 342, 850–853 (2013).

16. O. Arino et al., Global Land Cover Map for 2009 (GlobCover

2009) (European Space Agency, Université catholique de

Louvain, PANGAEA, 2012).

17. S. Fritz et al., Glob. Chang. Biol. 21, 1980–1992 (2015).

18. Y. Pan et al., Science 333, 988–993 (2011).

19. J. Grace, J. Jose, P. Meir, H. S. Miranda, R. A. Montes,

J. Biogeogr. 33, 387–400 (2006).

20. X.-P. Song et al., Nature 560, 639–643 (2018).

21. U. Büntgen et al., Nat. Commun. 10, 2171 (2019).

ACKNOWL EDGMENTS

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 https://code.earthengine.google.com/

ee5cf5186b5ad0f659cc7a43054f072c, and all related layers are

accessible online at www.crowtherlab.com or upon request to the

corresponding author.

SUPPLEMENTARY MATERIALS

science.sciencemag.org/content/365/6448/76/suppl/DC1

Materials and Methods

Figs. S1 to S12

Tables S1 to S3

References (22–29)

Data Files S1 and S2

21 February 2019; accepted 21 May 2019

10.1126/science.aax0848

Bastin et al., Science 365,76–79 (2019) 5 July 2019 4of4

RESEARCH |REPORT

on July 7, 2019 http://science.sciencemag.org/Downloaded 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

ARTICLE TOOLS http://science.sciencemag.org/content/365/6448/76

MATERIALS

SUPPLEMENTARY http://science.sciencemag.org/content/suppl/2019/07/02/365.6448.76.DC1

CONTENT

RELATED http://science.sciencemag.org/content/sci/365/6448/24.full

REFERENCES http://science.sciencemag.org/content/365/6448/76#BIBL

This article cites 26 articles, 9 of which you can access for free

PERMISSIONS http://www.sciencemag.org/help/reprints-and-permissions

Terms of ServiceUse of this article is subject to the

is a registered trademark of AAAS.Science

licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. The title

(print ISSN 0036-8075; online ISSN 1095-9203) is published by the American Association for the Advancement ofScience

on July 7, 2019 http://science.sciencemag.org/Downloaded from

Harmonization Approach to Spatial and Social Techniques to Define Landscape Restoration Areas in a Colombian Andes Complex Landscape

Article

Full-text available

Sep 2023

Landscape restoration activities must be conducted through a transdisciplinary process, integrating social, economic, environmental, and governance aspects. Combining visions from the natural and social sciences is a challenge in highly complex territories, where unique ecosystem characteristics, economic processes, stakeholders of diverse nature, and different normativity converge. The harmonization of multiple techniques, such as multicriteria spatial analysis, expert knowledge elicitation, and social mapping, allows for an approach to defining landscape restoration areas in complex regions. This paper employs multiple techniques to define ecosystem restoration areas in a complex Colombian Andes landscape, integrating ecological and social components for sustainable development. We observed that areas of high and very high feasibility for ecological restoration, encompassing 179.5 hectares (4.84% of the study area), are predominantly located near primary forests. Although some areas have a low feasibility for conservation processes, they should not be disregarded as they still require protection. Landowners prioritize watershed and soil restoration as the most important landscape restoration activity due to their interest in improving water-related ecosystem services. This proposal enables the identification of areas with a higher restoration potential at the property level, facilitating prioritization and investment allocation for future implementation.

Mapping Above-Ground Carbon Stocks at the Landscape Scale to Support a Carbon Compensation Mechanism: The Chocó Andino Case Study

Article

Full-text available

Sep 2023

(1) Background: Tropical Mountain forests (TMF) constitute a threatened major carbon sink due to deforestation. Carbon compensation projects could significantly aid in preserving these ecosystems. Consequently, we need a better understanding of the above-ground carbon (AGC) spatial distribution in TMFs to provide project developers with accurate estimations of their mitigation potential; (2) Methods: integrating field measurements and remote sensing data into a random forest (RF) modelling framework, we present the first high-resolution estimates of AGC density (Mg C ha−1) over the western Ecuadorian Andes to inform an ongoing carbon compensation mechanism; (3) Results: In 2021, the total landscape carbon storage was 13.65 Tg in 194,795 ha. We found a broad regional partitioning of AGC density mediated primarily by elevation. We report RF-estimated AGC density errors of 15% (RMSE = 23.8 Mg C ha−1) on any 10 m pixel along 3000 m of elevation gradient covering a wide range of ecological conditions; (4) Conclusions: Our approach showed that AGC high-resolution maps displaying carbon stocks on a per-pixel level with high accuracy (85%) could be obtained with a minimum of 14 ground-truth plots enriched with AGC density data from published regional studies. Likewise, our maps increased precision and reduced uncertainty concerning current methodologies used by international standards in the Voluntary Carbon Market.

Feeding climate and biodiversity goals with novel plant-based meat and milk alternatives

Article

Full-text available

Sep 2023

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.

Ectomycorrhizal fungi integrate nitrogen mobilisation and mineral weathering in boreal forest soil

Article

Sep 2023
NEW PHYTOL

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.

Soil carbon pools and fluxes following the regreening of a mining and smelting degraded landscape

Article

Sep 2023

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.

Open Foris Collect Earth: a remote sensing sampling survey of Azerbaijan to support climate change reporting in the land use, land use change, and forestry

Article

Full-text available

Sep 2023
ENVIRON MONIT ASSESS

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.

Soil organic carbon is buffered by grass inputs regardless of woody cover or fire frequency in an African savanna

Article

Sep 2023

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.

The overlooked contribution of trees outside forests to tree cover and woody biomass across Europe

Article

Sep 2023

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.

A BIOME IN TRANSITION: CO-PRODUCED SCIENCE FOR GRASSLAND CONSERVATION

Thesis

Full-text available

Dec 2022

Dillon Fogarty

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.

Soil moisture controls the partitioning of carbon stocks across a managed boreal forest landscape

Article

Full-text available

Sep 2023

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.

Limited capacity of tree growth to mitigate the global greenhouse effect under predicted warming

Article

Full-text available

May 2019

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.

Global land change from 1982 to 2016

Article

Full-text available

Aug 2018
NATURE

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.

One-third of global protected land is under intense human pressure

Article

Full-text available

May 2018

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.

Unexpectedly large impact of forest management and grazing on global vegetation biomass

Article

Full-text available

Jan 2018
NATURE

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.

Natural climate solutions

Article

Full-text available

Oct 2017

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.

WorldClim 2: New 1-km spatial resolution climate surfaces for global land areas

Article

Full-text available

May 2017

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.

The extent of forest in dryland biomes

Article

Full-text available

May 2017

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

SoilGrids250m: Global gridded soil information based on machine learning

Article

Full-text available

Feb 2017
PLOS ONE

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).

Global Land Cover Map for 2009 (GlobCover 2009)

Data

Full-text available

Jan 2012

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.

Restoring natural forests is the best way to remove atmospheric carbon

Article

Apr 2019

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.

The global tree restoration potential

Abstract and Figures

Recommendations

Prioritizing biodiversity and carbon

Response to Comment on “The global tree restoration potential”

Forest restoration: Transformative trees—Response

Response to Comments on “The global tree restoration potential”

Response to Comment on "The extent of forest in dryland biomes"