Forum

A Global Mitigation Hierarchy for

Nature Conservation
WILLIAM N. S. ARLIDGE, JOSEPH W. BULL, PRUE F. E. ADDISON, MICHAEL J. BURGASS, DIMAS GIANUCA,
TAYLOR M. GORHAM, CÉLINE JACOB, NICOLE SHUMWAY, SAMUEL P. SINCLAIR, JAMES E. M. WATSON,
CHRIS WILCOX, AND E. J. MILNER-GULLAND

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Efforts to conserve biodiversity comprise a patchwork of international goals, national-level plans, and local interventions that, overall, are
failing. We discuss the potential utility of applying the mitigation hierarchy, widely used during economic development activities, to all negative
human impacts on biodiversity. Evaluating all biodiversity losses and gains through the mitigation hierarchy could help prioritize consideration
of conservation goals and drive the empirical evaluation of conservation investments through the explicit consideration of counterfactual
trends and ecosystem dynamics across scales. We explore the challenges in using this framework to achieve global conservation goals, including
operationalization and monitoring and compliance, and we discuss solutions and research priorities. The mitigation hierarchy’s conceptual
power and ability to clarify thinking could provide the step change needed to integrate the multiple elements of conservation goals and
interventions in order to achieve successful biodiversity outcomes.

Keywords: adequacy, biodiversity, development, no net loss, sustainability

H umans’ growing demand for resources is resulting 

in the rapid erosion of natural habitats (Watson et al.
2016b). This is leading to an irreplaceable loss of biodi-
and important sites for biodiversity remaining unprotected
(Butchart et al. 2015, Dinerstein et al. 2017).
Biodiversity loss, much like climate change, is an environ-
versity (Hoffmann et  al. 2010) that can compromise the mental crisis that requires a coordinated international effort
healthy functioning of ecosystems (Hooper et al. 2012). The if it is to be managed effectively. The 2015 Paris climate
primary causes of biodiversity loss include overexploita- agreement specifies a clear goal to limit global warming by 2
tion of species, habitat modification, invasive alien species degrees Celsius above preindustrial levels (UNFCCC 2015),
and disease, pollution, and climate change (Maxwell et  al. and the recent publication of a roadmap for rapid decarbon-
2016). However, although we have an increasing under- ization offers guidance on actions required at the national
standing of the causes of biodiversity loss, the main drivers level to effectively limit carbon emissions in order to meet
can be obscured, in part, because existing frameworks for the goal (Rockström et  al. 2017). A call has recently been
conservation planning, implementation, and evaluation do made for a similar roadmap for global biodiversity conserva-
not consider conservation efforts to tackle drivers of biodi- tion to guide the necessary steps to achieve goals and targets
versity loss as a cohesive whole. The current patchwork of for stopping the biodiversity crisis (Watson and Venter
international goals and targets (e.g., the UN Convention on 2017). This requires an integrated global framework, capable
Biological Diversity [CBD] Aichi Targets, and Sustainable of being implemented at national and project levels, which
Development Goals), national plans, and local interven- would enable the quantification and subsequent reduction of
tions can result in the gaps and weaknesses of conservation humanity’s impact on biodiversity. To date, no one has tried
efforts being difficult to identify or articulate (Rands et  al. to conceptualize all human biodiversity impacts and conser-
2010). For example, the global terrestrial protected area vation efforts within such a framework. The benefits of such
(PA) network now covers 14.8% of all terrestrial surfaces an approach would be to unite all aspects of conservation
and 5.1% of the global ocean (UNEP–WCMC and IUCN under a standardized paradigm with a broad biodiversity
2016), but many of these PAs occur in residual areas, avoid- conservation goal, supporting multiscale, evidence-based
ing locations with high value for natural-resource extraction decision-making. Exploring the potential benefits of such a
(Devillers et  al. 2014, Venter et  al. 2017). The results are a framework is particularly timely given that the CBD’s bio-
significant shortfall in protection of nature across ecoregions diversity strategy will be renegotiated in 2020 (CBD 2010).

BioScience 68: 336–347. © The Author(s) 2018. Published by Oxford University Press on behalf of the American Institute of Biological Sciences. This is an
Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/
by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For
commercial re-use, please contact journals.permissions@oup.com
doi:10.1093/biosci/biy029 Advance Access publication 18 April 2018

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through national planning processes and

negotiations between government agen-
cies, conservation actors, and develop-
ers, with elements of the process often
formalized within an Environmental
and Social Impact Assessment (ESIA).
The mitigation hierarchy comprises four
broad actions step that are designed to be
implemented sequentially: (1) avoid, (2)
minimize, (3) remediate, and (4) offset
(figure 1). The first step involves avoiding
impacts on biodiversity, such as screening
potential risks prior to project design and

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selecting an alternate development site
(Phalan et  al. 2017). The second step of
the hierarchy requires that before and dur-
ing development, impacts are minimized,
such as by using more environmentally
friendly construction methods. The third
step requires that biodiversity loss is then
remediated within the footprint of the
development, which could entail actions
such as reseeding affected land or devel-
oping a breeding program for affected
species during and after project comple-
tion. The fourth and final step requires
that any residual impacts not captured by
the first three steps of the hierarchy are
offset elsewhere, such as through wet-
land restoration or the removal of inva-
sives from ecologically important areas
(Gardner et  al. 2013). The four steps of
the mitigation hierarchy represent broad
categories of biodiversity impact reduc-
tion and compensation, meaning that
most conservation actions can be catego-
rized within these steps (table 1).
As it stands, the mitigation hierarchy
Figure 1. An example of the mitigation hierarchy applied to the oil palm
offers transparency between stakehold-
industry in order to achieve no net loss of biodiversity for the negative impact
ers, with flexibility to address a variety of
on biodiversity (deforesting rainforest) as a result of planting oil palm
anthropogenic impacts on biodiversity,
monocultures, in this case African oil palm (Elaeis guineensis). The images
across different sectors and scales. Many
marked with an (a) represent the types of negative impacts from planting oil
regulatory and financial instruments are
palm monocultures, and the corresponding images marked (b) represent ways to
now in place that aim to balance bio-
address these impacts by undertaking the four steps of the mitigation hierarchy.
diversity conservation with (sustainable)
Steps 1 to 3 occur at the site of negative impact on biodiversity, whereas step 4
economic development by requiring the
occurs away from the impact site, addressing residual adverse impacts.
application of the mitigation hierarchy. For
example, 69 countries have NNL policies
Industrial sectors such as mining, energy, and manufac- in place or under development (Maron et al. 2016). However,
turing are increasingly using a framework known as the taken overall, these commitments operate in a system that has
mitigation hierarchy to guide their activities toward limiting allowed significant loss of biodiversity, even when develop-
negative impacts on biodiversity (BBOP 2012, IFC 2012). A ment was legally compliant (BBOP 2012, Watson et al. 2016b).
goal either of no net loss (NNL) or net gain of biodiversity The mitigation hierarchy is not widely applied to the
is typically set (also referred to as net neutral and net posi- most prevalent impacts on biodiversity that result from
tive goals, respectively), relative to a predetermined baseline the direct removal of biological materials in sectors such
(BBOP 2012, Maron et al. 2018). The process is implemented as agriculture, fisheries, forestry, and wildlife trade (Rainey

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Table 1. Examples of biodiversity conservation tools and actions categorized into each of the four steps of the mitigation
hierarchy.
Mitigation-hierarchy step Examples of existing conservation tools and approaches
Protected areas†; Alliance for Zero Extinction sites; Key Biodiversity Areas; no development in
Vulnerable Marine Ecosystems (FAO vulnerable ecosystems) or critical habitat (International Finance
Avoid Corporation PS6+); no damage to any listed threatened species or ecosystems (IUCN Red List of
threatened species and ecosystems; national conservation list species); no damage to intact habitat,
UNESCO World Heritage Sites, or Wilderness Areas.
Sustainable use; agrienvironment schemes; shift from passive nonselective gear to actively targeted
gear in fisheries; multiuse protected areas; payment for ecosystem services; demand reduction;
Minimize certification and ecolabeling; economic incentives (market prices, taxes, subsidies, and other signals);
green infrastructure; corporate environmental strategies and operations; maintenance of ecosystem
resilience.
Remediate Rewilding†; restoration†; natural flooding of wetlands†; artificial habitat creation†; deextinction.
Degraded ecosystem restoration away from impact site†; averted risk; reseeding or respawning†;

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Offset
captive breeding; invasive removal; species creation.
†Conservation tool or action that can shift between steps of the mitigation hierarchy depending on (a) whether the biodiversity baseline is set at
a present-day or historic point in time and (b) what national and regional legislation is in place to enforce the action taken.

et al. 2015, Maxwell et al. 2016). Various frameworks exist are to become better balanced. Here, we first describe the
to manage the impacts that result from extracting biological critical elements of the mitigation-hierarchy approach and
resources and promote sustainable use (e.g., forest certifica- then outline a conceptual application of the framework to
tion schemes, Lattimore et al. 2013; ecosystem-based fisher- integrate human biodiversity impacts with nature conserva-
ies management, Pitcher et  al. 2009; and agrienvironment tion efforts as a novel first step toward achieving a more stra-
schemes, Pretty 2008). However, these frameworks often tegic approach to achieving global biodiversity conservation
fail to account for all the negative biodiversity impacts goals. We then clarify how achieving a conservation goal
caused by extracting target resources. For example, in through the mitigation hierarchy might be structured at the
forestry, road building to access previously inaccessible planetary scale by outlining four key factors for application.
trees opens up remote wilderness areas to the secondary
pressures of hunting, human colonization, invasive species, Critical elements of the mitigation hierarchy
and fire (Bennett 2004). Major certification schemes such approach
as the Forest Stewardship Council have also been criticized Developers adhering to the mitigation hierarchy are first
for failing to explicitly account for incidental biodiversity required to set a biodiversity goal (BBOP 2012). This
impacts, such as bushmeat harvesting (FSC 2015). Applying typically takes the form of NNL or net gain of biodiversity,
a standardized framework such as the mitigation hierarchy although a goal such as improving trends in biodiversity
to all human impact would allow for seemingly disparate could also be used (e.g., as in national species recovery
impacts on biodiversity to be categorized and accounted plans). Next, quantitative targets and associated biodiversity
for between sectors, scales, and nations. For example, the metrics or indicators must be defined in order to measure
direct and immediate biodiversity impacts of clearing achievement of the goal (BBOP 2012, Butchart et al. 2015).
species-rich forest for an oil palm plantation, the longer- Undertaking this process means that assumptions surround-
term and potentially more diffuse indirect biodiversity ing what achieving the biodiversity goal would look like and
impacts that result from new forestry infrastructure (e.g., the calculations required to verify it are made explicit.
illegal hunting and informal clearance for settlement), and The consideration of counterfactual scenarios (i.e., what
the transboundary effects of air pollution from clearance would have happened in the absence of a development and
fires could be accounted for within the same framework, its associated mitigation measure[s]) is key to evaluating
whereas apparently disparate mitigation efforts could be whether the biodiversity goal has been met (table 2; Bull
linked (figure 1). et  al. 2014, Maron et  al. 2016). The practice of empirically
The lack of coherence between sectors of conservation evaluating whether a specific intervention works better than
associated with sustainable use (e.g., certification), mini- alternate interventions or no action at all remains woefully
mizing the impact of development (e.g., NNL), and direct lacking in conservation science (Ferraro and Pattanayak
protection (e.g., protected areas) is currently limiting the 2006), and a major benefit of the mitigation hierarchy is
opportunities for strategic achievement of biodiversity con- that it requires this critical thinking. This process requires
servation at a global scale. A far more structured approach to the involvement of all stakeholders: regulators, industry, and
planning, implementing, and evaluating actions to achieve conservationists. The wider use of the mitigation hierarchy
global conservation goals is needed if natural-resource would therefore precipitate a shift toward the routine empir-
extraction, industrial development, and nature conservation ical evaluation of biodiversity conservation investments.

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Table 2. Approaches to addressing the theoretical and practical challenges of applying the mitigation hierarchy, with
particular focus on the offsetting step, based on practical experience to date (as articulated in, e.g., Bull et al. 2013,
BBOP 2012).
Challenge Description Current project-level best practice Conceptual examples of global-level best
recommendations practice
Additionality Whether an intervention Only biodiversity benefits that are Nations required to account for offset-funded
has an effect, when the additional to a baseline scenario biodiversity protection (alongside associated
intervention is compared to count as valid offsets. biodiversity losses that triggered offset) separately
a baseline from biodiversity protection going toward existing
global conservation commitments (e.g., CBD Aichi
target 11; Maron et al. 2015b).
Compliance and Noncompliance with Ensure relevant authorities follow up No net loss impact to biodiversity targets are made
monitoring mitigation hierarchy; with monitoring to ensure compliance. legally binding where possible (e.g., for all UN
insufficient compensation fisheries through UNCLOS, requiring stipulation of
resulting in lack of defined baselines, indicators, and best-practices
incentive; legislative implementation); global-level monitoring and

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changes during evaluation program created; requirements for
development national-level reporting to international body (e.g.,
CBD).
Biodiversity Unitary measures of Use multiple or compound indicators; Use established mechanisms to develop and
indicators biodiversity lost, gained, or incorporate measure of ecological test indicators (e.g., the Biodiversity Indicators
exchanged function as well as biodiversity. Partnership, which evaluates the CBD Aichi targets
and biodiversity SDGs): www.bipindicators.net.
Equivalency Demonstrating equivalence Encourage “in-kind” or like-for- An international governing body, such as the
between biodiversity losses like trades, and prevent “out-of- United Nations, stipulates that biodiversity offsets
and gains kind” trading unless “trading up” are restricted to “in-kind” trades implementable
from losses that have little or no within a predetermined radius of the impact site,
conservation value; ensure that based on ecologically meaningful scales for the
there are requirements for spatial biodiversity concerned.
constraints within which biodiversity
offsets will and will not be considered.
Least cost Guiding actions Ensure offset cost is set at a Evidence that alternate scenarios representing
economically by costs so sufficient level to incentivize actions higher up the mitigation hierarchy have
that efficiency dictates that adherence to avoidance and been investigated, and their ruling out is justified
each hierarchical step be minimization steps higher up in the prior to any offsets commencing. Require this to
undertaken to the point at mitigation hierarchy. be recorded in Environmental and Social Impact
which marginal costs are Assessments and submitted by all signatory
equalized nations to the international governing body. Free
public access to reports is granted.
Longevity The length that an offset Offsets should last the length of Nations are required to adopt the stipulated time
scheme should endure the negative impacts at a minimum; period for agreed-on global biodiversity goals and
offsets should be adaptively managed to enforce regulation that ensures the longevity of
in the light of ongoing external biodiversity offsets. Failure to successfully manage
change. offsets for their necessary lifetime would result in
censure.
Multipliers A factor that increases Calculation of multiplier is based Legal requirements are put in place to ensure
the amount of biodiversity on various factors (e.g., discount that appropriate biodiversity offset calculators are
gains required by an offset rate for future biodiversity gains used for all offset projects, ensuring a minimum
and uncertainty in definition and biodiversity offset multiplier accounts for the time
measurement of biodiversity). discounting, additionality, and permanence of the
project (e.g., Laitila et al. 2014).
Reversibility Defining a development’s Ensure all biodiversity losses are Nations’ goals for preventing species extinction
reversibility reversible; otherwise, categorize the and ecosystem collapse would be required to
affected biodiversity as a no go. map onto international goals, with international
reporting requirements concerning compliance and
monitoring.
Substitutability The degree to which Base the value of biodiversity types Clarify and justify when one ecosystem, species,
the “value” of a certain on national legislation and societal or population is seen as equivalent to another and
biodiversity type influences value. therefore tradable.
demand for one or more
other biodiversity types
Thresholds Areas or components of Define explicit thresholds for Internationally recognized no-go zones for
biodiversity that should biodiversity losses and gains that biodiversity offsets such as the Protected Area
not be compensated for cannot be offset. network, Key Biodiversity Areas, crisis ecoregions,
because they are too and the Wildlife Conservation Society’s Last of the
important Wild places; consideration is also given to aspects
of human development, which should not be traded
off because of their contribution to the future of
humanity, such as adequate safe water for all.
Time lag Deciding whether to allow Incorporate a preoffset step in the A preimpact conservation gain requirement could
a temporal gap between form of mitigation banking. be built into international funding for economic
development and offset development.
gains

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Arguably the most important step of the mitigation hier- compliance and monitoring to evaluate the true effective-
archy is its first step, impact avoidance. This requires devel- ness (Lindenmayer et al. 2017). As we illustrate here, many
opers to predict and prevent negative impacts on biodiversity of the issues with offsets result from poor operationalization,
prior to any development actions taking place (BBOP 2012). monitoring, and compliance rather than being inherent to
The conservation benefits of avoiding impacts are likely to the concept itself (Quétier et al. 2014).
outweigh taking more uncertain remediation and offsetting
measures once damage has occurred (Watson et  al. 2016b, Expanding the mitigation hierarchy to encompass all
Lindenmayer et  al. 2017). Actions that drive adherence to human impact on biodiversity
the first step of the mitigation hierarchy include following The direct extraction of biological resources is the dominant
environmental regulations designed to protect biodiversity driver of current species loss (Maxwell et al. 2016), but the
(e.g., through national planning processes and negotiations practical application of the mitigation hierarchy to the bio-
between stakeholders), giving clear guidance on critical logical resource use sectors has received little attention (but
biodiversity areas (e.g., Key Biodiversity Areas), and mak- see Aiama et  al. 2015). In fisheries management, all four

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ing political decisions to set aside areas of high societal steps of the mitigation hierarchy are discussed (Wilcox and
value (e.g., World Heritage Sites). Failure to comply with Donlan 2009, Gjertsen et al. 2014), but they have yet to be
the avoidance step of the mitigation hierarchy may eventu- formalized into a conservation framework to manage fishing
ate from a lack of political or regulatory enforcement; poor impacts. Using a mitigation hierarchy, NNL of biodiversity
process; or lack of capacity and technical knowledge of (or a similar goal such as population recovery) could be
regulators, developers, and consultants (Phalan et al. 2017). extended to managing the incidental impacts on biodiver-
The minimization step is central to current project-level sity caused by extracting target resources (e.g., fisheries
conservation activities, including sustainable use, agrienvi- bycatch management; table 3; Milner-Gulland et  al. 2018).
ronment schemes, alternative livelihoods, and payments for A NNL goal could then be incorporated into international
ecosystem services. At the national level, many states have natural-resource management agreements such as the UN
adapted ESIA legislation and guidance, which feeds down Convention on the Law of the Sea (UNCLOS) conservation
into the incorporation of biodiversity concerns into eco- and sustainable use of marine biological diversity instru-
nomic activities at the project level (Bull et al. 2017), whereas ment (United Nations 2015a).
rewilding, restoration projects, and the natural flooding Particularly crucial to an extension of the mitigation hier-
of wetlands align with remediation measures for affected archy to global conservation is consideration of the scale at
biodiversity. Remediation equally applies to reestablishing which goals and targets are evaluated (table 3). Although
depleted resource stocks (table 1). achieving NNL of biodiversity is often a goal for individual
Many of the key issues regarding quantifying and com- projects, some have suggested that net human impact on bio-
pensating biodiversity, which emerge when the mitigation diversity should be evaluated at landscape or national scales
hierarchy is applied, have parallels with the wider challenge of considering the aggregate impact of individual developments
defining and measuring sustainability (e.g., Heal’s 2012 review and their associated mitigation programs (Kiesecker et  al.
on managing natural capital and the interactions between 2010, Bull et al. 2014). Bull and Maron (2016) also considered
human economic activity and the environment). The most the conceptual global application of the NNL principle to
controversial element of the mitigation hierarchy is its last changes in species richness worldwide. A strategic approach
step, offsetting, because it is here that these challenges come to NNL could evaluate biodiversity gain and loss at eco-
into sharp relief; they can be sidestepped to some extent in logically and institutionally meaningful scales (ranging from
the first three steps of the hierarchy. Offsetting happens when local to global), enabling conservation efforts of different
significant residual impacts from a development remain after types and at a range of scales to be integrated and categorized
application of the first three levels of the mitigation hierar- within the hierarchy’s four steps: avoid, minimize, remediate,
chy (BBOP 2012). It is controversial because it requires the and offset. A multiscale approach to NNL, not just a project-
acceptance of a development that harms biodiversity on the level one, would mean that wider goals are not contradicted
assumption that this harm can be accurately quantified and by piecemeal approaches to NNL at the project level (Maron
balanced by benefits elsewhere (Maron et al. 2016). et al. 2018). Table 3 shows how the application of the mitiga-
The theoretical and practical challenges of achieving tion hierarchy would change depending on the scale under
NNL of biodiversity from development are increasingly well consideration. By considering local, regional, and national
described and are widely reported (table 2). For example, a actions under the same framework, we could begin to piece
nest box program in Australia intended to offset the clearing together a global picture of action toward an overarching net
of hollow-bearing trees did not achieve the intended bio- goal, offering a coherent framing for conservation efforts.
diversity outcomes for three threatened vertebrates reliant
on the trees because of (a) a failure to consider equivalency Key factors for successful application of the global
(the nest boxes failed to provide habitat for the target spe- mitigation hierarchy
cies), (b) incorrect use of multipliers (the 1:1 offset ratio did In the next section, in order to conceptualize what biodi-
not account for the risk of offset failure), and (c) a lack of versity attributes could and could not be included in each

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step of the global mitigation hierarchy, we discuss four key to drive action in the minimize part of the hierarchy could
factors for application. specify that by 2020, all fish stocks are managed accord-
ing to the FAO Code of Conduct for Responsible Fisheries
Goals, targets and indicators. At each scale of application (FAO 1995) and all forests according to the Resolution on
(global, regional, and local), there would be a need to Sustainable Forest Management (United Nations 2008).
set NNL goals (or similar goals that account for losses In this way, a global mitigation-hierarchy framework
and gains) that focus on particular facets of biodiversity could help achieve a desired future state of biodiversity by
(figure 2). These could include the elements of biodiversity setting multiple goals and targets at meaningful scales, mea-
embodied in the essential biological variables (Pereira et al. sured through relevant biodiversity indicators. We present
2013, Gonçalves et  al. 2015), which are recommended to one example of goal and target setting in figure 2.
guide the setting of biodiversity goals and indicators in
policymaking (Pereira et al. 2013). Ideally, these goals would Frames of reference and counterfactuals. Assessing achieve-
be set to reflect existing aspirations for sustainable develop- ment of NNL requires specification of a frame of reference

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ment (e.g., the sustainable development goals, SDGs; United containing a biodiversity baseline or counterfactual scenario
Nations 2015b), international conservation (e.g., the CBD (table 2; Bull et al. 2015, Maron et al. 2018). This could take
Aichi targets; United Nations 1992), and national legislation the form of a static baseline (i.e., biodiversity levels at a fixed
relating to environmental protection. point in time), such as the current state of biodiversity (i.e.,
To successfully achieve biodiversity goals, there is a need 2017 levels) as is expressed using the chosen indicator set.
to set targets that specify a quantitative amount of change Alternatively, a historic level of biodiversity could be set as
required for success. SMART (specific, measurable, ambi- a static baseline, such as species status in the year 1990 (to
tious, realistic, and time-bound) targets are preferred; a be compatible with the baselines used in the UN Framework
hypothetical example of a SMART target would be that all Convention on Climate Change). Or a counterfactual sce-
UN countries’ fishing fleets will achieve a NNL impact on nario could be chosen, such as the expected state of nature
biodiversity by 2050, set against the frame of reference of in the absence of any further development or conservation
the Food and Agriculture Organization’s (FAO’s) 1955 global interventions (figure 2).
fish stock assessments and benthic biodiversity assess- A frame of reference is key to incorporating biological
ments from the International Union for Conservation of resource extraction into the framework. For example, incor-
Nature (IUCN; table 2). Currently, many targets suffer from porating a NNL of biodiversity goal into the management
ambiguity, complexity, and redundancy; lessons need to be of a natural resource, such as fish stocks, does not require
learned from failings with the CBD Aichi targets, more than compensation for losses related to this harvest if the baseline
two-thirds of which were found to lack a quantifiable com- is current biodiversity status and the stock in question is
ponent (Butchart et al. 2016). sustainably harvested and nondeclining. By contrast, taking
Next, relevant biodiversity indicators can be developed a preexploitation baseline, or evaluating against a reduced
to measure the desired change in biodiversity in order to human impact counterfactual, could require compensation
achieve specific goals and targets at varying scales (e.g., for lost biodiversity even if harvesting is sustainable. It is also
those developed by the Biodiversity Indicators Partnership; important to note that harvesting can be sustainable under a
table 2; Butchart et  al. 2007). These need to be context target-species-focused goal and still have adverse effects on
dependent, with best practices suggesting that they should nontarget biodiversity, which would need to be compensated
(a) be sensitive to and respond predictably to human impact, under another part of the overall framework (e.g., to address
(b) be feasible to monitor, (c) be informative at different spa- the negative impact of leatherback turtle bycatch from long-
tial and temporal resolutions, and (d) be practical in terms line fishing; table 3).
of monitoring costs and data availability (Jones et al. 2011, When setting a frame of reference, there is also an essential
Gonçalves et al. 2015). There are added levels of complexity need to clearly specify which elements of biodiversity are or
surrounding indicator development that are not outlined are not appropriate to address at lower stages of the mitiga-
here; for a more detailed explanation, see Jones and col- tion hierarchy (e.g., through offsetting). Some elements may
leagues (2011). be deemed too valuable to incur any human impact, and
The clear articulation of desirable biodiversity outcomes therefore, impact must be avoided (table 2; Bull et al. 2013).
then drives relevant conservation actions through different There are many situations in which offsets are unaccept-
levels of the mitigation hierarchy. For example, an ecosystem- able, regardless of whether large multipliers are applied (e.g.,
focused target to drive action in the avoid part of the mitiga- more than 10 units of habitat supplied elsewhere for every 1
tion hierarchy might be the following: By 2020, 25% of areas unit destroyed; Moilanen et al. 2009). Irreplaceability is one
currently in a predominately natural state in each of Earth’s criterion for whether biodiversity damage should be allowed
825 terrestrial ecoregions (Olson et al. 2001) and 232 marine and then offset. This may relate to a critically endangered or
ecoregions (Spalding et al. 2007) will have full no-take pro- endemic species, a keystone species, an iconic area of wilder-
tected area status and nondeclining biodiversity value rela- ness, or biodiversity characterized by long restoration times,
tive to a 2017 baseline (figure 2). A species-focused target such as deep-sea coral systems, hydrothermal vents, and

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Basic framework for setting a global net neutral target Example

The Sustainable Development Goals vision or the IUCN

Set a global vision statement for biodiversity conservation vision for RIO+20 of “A just world that values and conserves
nature for a sustainable future”.
Vision and
goals
Set relevant Sustainable Development Goals or Convention on
Incorporate existing global biodiversity conservation goals
Biological Diversity Aichi Targets

Develop a global net goal for reducing negative biodiversity

All UN countries will achieve a net neutral impact on both
impact that is set with a frame of reference by a relevant
terrestrial and marine biodiversity by 2100
global authority Global net
impact
targets

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Require UN or similar global authority to set a series of NNL (or From 2017 onward, all species listed on the IUCN Red List of
similar) goals that focus on specific elements of biodiversity (e.g. Threatened Species remain at their current status or improve in
drawing on Essential Biological Variables) enforced using all of Earth’s 825 terrestrial ecoregions and 232 marine
legislation such as UNCLOS ecoregions

Set a biodiversity baseline against which to measure progress Baseline set at 2017 biodiversity levels, with action to be
and timeframe for action is set implemented by 2020
Frame of
reference
Set a counterfactual scenario: an Set a static baseline: a Red List status of species in the
expected biodiversity trajectory absence of further Current Red List status of
known level of biodiversity
that would have occurred if Or at a fixed point in time development and any proposed
Or species
there had been no action conservation intervention

Choose specific indicators to measure the change in the Indicators An index is required to measure species extinction and
element of biodiversity of interest decline e.g. Red List status

By 2020 make all Alliance for Zero Extinction sites no-go for all
Avoid
economic development activities

By 2020 ensure that all species listed on Threatened Red List

Minimise categories are either exempt from exploitation or sustainably
At the global level, set targets that are SMART at each stage of the harvested to enable them to maintain or improve their Red List status
hierarchy, which would combine to achieve the global no net loss of
biodiversity goal. Change is monitored with selected indicators and
assessed against the targets, leading to re-evaluation By 2020 restore priority habitat for Critically Endangered Species
Remediate such that habitat is adequate to allow all Critically Endangered
species to recover to Least Concern

Any continued decline in a Red List species' status beyond 2017

Offset levels in one part of their range will be balanced by
improvements in another part of their range until the global
target is achieved

Avoid

Minimise

Repeat the SMART targets setting process at meaningful National and landscape level SMART targets that map onto the
scales (i.e. national and landscape) global targets for species relevant to the country concerned
Remediate

Offset

Figure 2. The key steps required to implement a global no net loss of biodiversity target through the mitigation hierarchy,
with associated goals and targets. The left column shows the basic framework for setting a global no net loss target. The
right column gives a specific example focusing on the International Union for Conservation of Nature’s Red List. This
example shows one particular set of approaches among many that would be needed to achieve global no net loss human
impact on biodiversity.

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Table 3. Applying the mitigation hierarchy to the examples of housing development and commercial fisheries bycatch,
to demonstrate its applicability at multiple scales and for different sectors.
Mitigation Harmful event: Housing development leading to loss of Harmful event: Pacific leatherback sea turtles bycaught in
hierarchy biodiversity and habitat commercial fisheries
step
Local National (state Global (human Local (one turtle National (local Global (species
(one house built) housing plan urbanization killed by one extinctions sent to
implemented) footprint vessel) or population extinction)
increasing) reduction in a
nation’s Exclusive
Economic Zones)
Avoid Restriction Strategic plan International Enforcement of Nationally legislated Multinational
of building identifies areas protected-area small scale time or caps on turtle no-take fishing
permissions to set aside for commitments area closures takes for countries zones tracking
given areas only housing and operating fisheries in leatherback turtle
areas for areas frequented by migration

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conservation turtles
Minimize Drainage areas, Regulatory International Gear modification Fleetwide gear Demand
fence to prevent requirements for lenders require all resulting in changes (e.g., reduction through
overflow of house building new housing to be increased implementing circle international
extracted dirt ecologically friendly likelihood of turtle hooks, branch lines education
survival long enough to allow campaigns
turtles breathing at targeting
the surface, effort consumers of
restrictions) Pacific-sourced
tuna and swordfish
Remediate Restoration of Land area International fund Better turtle- Increased marine Protection and
land along digger restoration plans for urban greening handling and gear- protected area reallocation of
tracks at the state scale projects removal practices monitoring and nests to increase
resulting in higher enforcement hatching success
survival rates resulting in fewer at known Pacific
for postcapture illegal fishing events, leatherback turtle
release allowing turtle nesting sites
population to recover throughout range
Offset Protect an area of State supports International fund Protection of Protection of Protection of
existing wetland protection of for restoration nesting turtles and nesting turtles and Atlantic leatherback
or create a new similar natural of habitat types their eggs at local their eggs at nesting sea turtles in an
wetland nearby areas in other preferentially nesting beaches beaches within effort to ensure
parts of the affected by and restoration of another area of the they don’t meet the
country urbanization degraded nesting country same fate
sites

old-growth forest. For example, a recent study demonstrated places (Maron et  al. 2015b). A global mitigation hierarchy
that if delays between a development and the compensation with a clear set of goals and targets would enable integration
of the resultant biodiversity losses through restoration are 55 of the different commitments and legislative requirements
or more years, then an offset is unlikely to be successful at already in place, facilitating explicit consideration of how
achieving a NNL effect on biodiversity (Gibbons et al. 2016). commitments at different scales complement or conflict
Improving international recommendations for no-go areas with each other. Transparent consideration of baselines and
to protect biodiversity (e.g., that all categories of protected of where each biodiversity conservation action sits within
areas and World Heritage Sites be considered no-go areas the levels of the hierarchy would reduce the risk of indirect
for large-scale development; IUCN 2016), backed up by leakage of environmentally damaging activity to other areas
national legislation, could help address this issue for a global following locally avoided losses (Moilanen and Laitila 2016).
mitigation hierarchy and provide a strong and agreed basis It would also mitigate against perverse outcomes such as
for the avoid step of the hierarchy (Phalan et al 2017). governments using industry money generated by offsets to
The lack of counterfactuals remains a widespread problem achieve existing national biodiversity commitments (Maron
in practice, both for the mitigation hierarchy as currently et al. 2015b; see “additionality” in table 2).
applied to development (e.g., Maron et al. 2015a) and in the
wider conservation and environmental policy literature (e.g., Ensuring equity and subsidiarity.  An important consideration for
Ferraro 2009). It is only just starting to be applied to mea- a global biodiversity conservation framework is the equitable
suring the impact of traditional conservation interventions distribution of costs and benefits between stakeholders (Ives
(e.g., Hoffmann et  al. 2015). Failure to properly consider and Bekessy 2015, Bull et al. 2017). For example, the manage-
counterfactual scenarios promotes the idea that loss in one ment of any global biodiversity conservation goal through
place can be offset by “protection” in another, even if that the mitigation hierarchy could follow a similar framework to
protection involves no more than relabeling already-secure the United Nations’ management of carbon emissions, with

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Forum

nation states setting their own national goals and targets that (Watson et al. 2016b), as are the benefits of avoiding destruc-
then sum to achieve overarching planetary goals. Managing tion of small but important areas of biodiversity value within
the framework in such a way could allow for equity between modified settings, such as sites containing populations of
nations, recognizing that industrialized countries reached very vulnerable species (e.g., Alliance for Zero Extinction
their present wealth through exploiting natural resources sites; Ricketts et al. 2005). However, the opportunity costs of
and reducing biodiversity. Mediated through the United degrading many of these areas are not currently well articu-
Nations Framework Convention on Climate Change, mech- lated; adopting the mitigation-hierarchy framework would
anisms exist that allow for the transfer of funds and capacity catalyze consideration of these costs, because it requires the
from richer to poorer countries to enable the latter to meet comparison of relative biodiversity gains achievable at each
their obligations (i.e., the Central African Forest Initiative; step of the hierarchy and the associated uncertainties.
Müller 2016), as well as a staged process for poorer countries For example, the incidental environmental impacts of
to reduce emissions in line with their capacity to do so. A deep-sea fishing gear making contact with continental
similar framework for differential development, such that slopes and offshore seamounts are rarely accounted for in

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the burden of reducing impacts on biodiversity was equita- fisheries policy (Clark et  al. 2016). Making a requirement
bly distributed, could support achievement of a global NNL of NNL for biodiversity targets legally binding (e.g., for all
of biodiversity goal. Such an adjustment could also consider United Nations fisheries through UNCLOS) would drive
the international market drivers of biodiversity loss, such the stipulation of defined baselines, indicators, and best-
as China’s demand for soy (mainly as cattle feed) driving practices implementation concerning deep-sea fishing using
biodiversity loss in Brazil’s Cerrado, a biodiversity hotspot of National Biodiversity Strategies and Action Plans (NBSAPs),
conservation priority (Strassburg et al. 2017). formalized through ESIA processes. This would drive stron-
This raises the issue of the equivalency of biodiversity ger avoidance and minimization actions for deep-sea fishing
in space and time, between biodiversity types, and by type nations because of the high level of uncertainty surrounding
of conservation action (equivalency of offsets; table 2). We whether it is possible to generate biodiversity gains for ben-
are not advocating the creation of a global market allowing thic deep-sea organisms, such as corals, using remediation
the trading of biodiversity offsets toward NNL over large and offset measures, such as construction of artificial reefs.
scales; instead, the mitigation hierarchy must be applied What kinds of conservation action fall within a given
at biologically meaningful scales to avoid “out-of-kind” stage of the mitigation hierarchy depends crucially on the
actions that allow one part of the planet to be damaged baseline, goal, and target chosen (table 1). Taking a 2017
in return for enhancement of others (table 2; BBOP 2012, static baseline, for example, avoidance would comprise
Bull et al. 2013). Although organizations such as the United efforts to ensure that existing but currently unprotected
Nations can endorse best practices at the international areas of biodiversity value are preserved at the current status
level, individual nations would need to implement the legal rather than being developed (e.g., to meet an area-based
framework that would ultimately drive adherence. This is target; this could be done through new PAs); minimization
increasingly happening within the industrial development reduces the damage of future developments on existing bio-
sector, with countries being supported to draft appropriate diversity in the newly developed areas (e.g., taking a species-
legislation and build capacity for implementation (e.g., the based target; this could be done by minimizing the extent of
COMBO Project; http://combo-africa.org). In addition, as is new roads in close proximity to PAs); remediation increases
the case for all conservation actions, effective monitoring, the biodiversity values associated with new human impact
independent evaluation, and sanctions are required over the (e.g., for an ecosystem-based target; this could be done
long term to ensure compliance with agreed-on targets and through clean-up of new pollution in fished coastal areas);
actions at all levels (table 2). and offsetting improves biodiversity over the current status
quo in ways or locations not associated with a particular new
Categorizing conservation actions within the framework.  The fram- impact (e.g., for an ecosystem target by mangrove reseeding
ing of global conservation efforts in terms of a mitigation or for a species-based target by the eradication of invasives).
hierarchy, for all human impacts on biodiversity, is novel. Any entities causing new or ongoing biodiversity damage at
However, the interventions constituting the different com- the local, national, or international level (from road building
ponents of such a hierarchy—at the international, national, to nontarget-fishing impacts to climate change) would need
landscape and project levels—are already in place. Presently, to demonstrate how they were investing in conservation in a
we know that most of the terrestrial environment is exposed way that would appropriately balance that damage in order
to some form of human impact (Watson et  al. 2016a) and to meet the goals and targets set out at the same spatiotem-
that no area of the world’s oceans remains free from human poral scale and institutional level as the damage.
pressures (Halpern et  al. 2015). The options for avoiding Current protection status of terrestrial ecoregions is
intact biodiversity (devoid of significant human impact) being mapped in order to prioritize conservation actions
are already significantly constrained by the current human (Dinerstein et al. 2017). Similar mapping efforts have begun
footprint. The benefits of complete retention of large intact for forest restoration opportunities (Potapov et  al. 2017).
areas of wilderness are self-evident to many conservationists Maps such as these could provide the roadmap for global

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 Forum

biodiversity conservation being called for by scientists by the Commonwealth Scholarship Commission in the
(Watson and Venter 2017), and they could guide avoidance, United Kingdom, and the University of Oxford with a PhD
mitigation, and restoration activities, as well as highlight scholarship no. NZCR-2015-174. JWB is s­ upported through
opportunities for offsetting, within the mitigation hierarchy. a Marie Skłodowska-Curie Fellowship no. 655497 and
For example, the effectiveness of the remediation step is acknowledges the Danish National Research Foundation
open to question, with evidence suggesting that man-made for funding the Center for Macroecology, Evolution and
or restored ecosystems do not reach the levels of ecological Climate grant no. DNRF96. PFEA is supported by the
functionality of natural systems (Moreno-Mateos et al. 2012). Natural Environment Research Council no. NE/N005457/1.
At the project level, costing each step at a level that reflects DG is supported by a PhD scholarship from the Science
biodiversity gains and losses (with associated uncertain- Sciences without Borders Program no. CNPq/Brazil, grant
ties) could incentivize developers to move up the hierarchy, no. 246619/2012-0.
because avoiding sensitive sites could be made significantly
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