In 2015, all United Nations member states agreed to the 2030 Agenda for Sustainable Development (United Nations, 2015). The Agenda proposes 17 Sustainable Development Goals (SDGs) and 169 indicators to realise its vision of a prosperous and peaceful planet for people and nature. Goal 9 calls to “build resilient infrastructure, promote inclusive and sustainable industrialisation and foster innovation.” The term infrastructure refers to the facilities that allow humans to fulfil the need for energy (e.g., coal, wind, gas, solar, hydropower, waves, power lines, oil, and gas pipelines), water (e.g., canals, dams, pipelines), transport (e.g., ports, roads, railways), and telecommunications (e.g., internet cables) (Woetzel et al., 2016). Infrastructure development is considered a fundamental requirement to help achieve other SDGs (The Economist Intelligence Unit, 2019). Similarly, environmental goals underpin societal and economic goals (Folke et al., 2016)—as supported by the latest Intergovernmental Science-Policy Platform for Biodiversity and Ecosystem Services global assessment report (IPBES, 2019), UN Convention on Biological Diversity (Romanelli et al., 2015; Secretariat of the Convention on Biological Diversity, 2020), and UN Food and Agricultural Organisation (FAO, 2019). Balancing infrastructure development and biodiversity conservation goals is therefore central to achieve sustainable development, but also involves socio-economic and political choices on how land is used, with likely trade-offs with other objectives.

The current and ongoing global expansion in infrastructure development has been described as an “infrastructure tsunami” (Laurance, 2010) or a “global infrastructure boom” (zu Ermgassen et al., 2019b). When these infrastructure projects are implemented, usually under a spatially oriented and economic development strategy, they are referred to as “development,” “resource,” “economic,” or “growth” corridors (Nogales, 2014; Hope and Cox, 2015; Laurance et al., 2015; Reeg, 2017; Schindler and Kanai, 2019). Notable examples are the 33 corridors in Africa potentially crossing 400 protected areas (Laurance et al., 2015), or initiatives in Latin America, Asia, Europe, and Oceania (Nogales, 2014; Hope and Cox, 2015; Reeg, 2017; Sloan et al., 2019a). The Belt and Road Initiative is an example of this concept being taken to a global scale: a Chinese economic and political programme which was launched in 2013, comprising at least six interconnected corridors across the land and sea and over 15 countries in Asia and Europe (The Belt and Road Initiative, 2019), and has now has expanded to 140 countries including Sub-Saharan Africa, Latin America, and the Caribbean (The Green Belt and Road Initiative Center, 2021).

Although the term “Development corridor” has been often used as an umbrella term for these initiatives (Mulenga, 2013; Laurance et al., 2017; Enns, 2018; Collinson et al., 2019; Dong et al., 2019; Heinicke et al., 2019; Sloan et al., 2019b; Müller-Mahn, 2020), corridor terminology is diverse, not standardised, and it depends on the purpose of the corridor, the actors involved, and the stage at which it is. As such there are transport, trade, utility, agricultural, or resource corridors, among others (Nogales, 2014; Hope and Cox, 2015; The Development Coridors Partnership, 2021). Although they may start as such, in the long term these are not individual isolated projects. They usually comprise several infrastructure projects that serve to link growth nodes or anchor projects with urban centres, markets and/or points of imports and exports, such as ports. Mulenga (2013) uses the terms development corridors and economic corridors interchangeably as “the concept of using transport corridors as a means to develop the regions around the corridors.” Hope and Cox (2015) propose planning development corridor as a systematic process which may start with a transport corridor but then evolves into a more complex economic corridor as different infrastructure, programmes, plans, and policies are incorporated. Nogales (2014) agrees, but employs the term “growth corridor” and proposes to use Spatial Development Initiates (SDI) as an umbrella term for all types of corridors (i.e., an agglomeration of economic activity in a specific location where businesses gain advantages through co-location; see Reeg, 2017). Therefore, crucially, development corridors are not static entities but rather a process which evolves towards a coordinated spatial development strategy with multiple stages—each involving different objectives and stakeholders.

Here we define development corridors as large, often transnational and linear, geographical areas targeted for investment under a spatially oriented and common economic strategy towards achieving long-term sustainable development. To avoid confusion, in this article we use the term “development corridors” to refer to all corridors, but we recognise and reflect on the varied terminology and complex nature of these initiatives (see Box 1).

We propose four broad ideal stages that should be common to all development corridors: concept planning, approval, implementation, and monitoring, and evaluation (Box 1 and Figure 1A). In addition to these four stages, development corridors tend to evolve from simpler initiatives to a spectrum of different types of more complex development corridors (Nogales, 2014; Hope and Cox, 2015; Reeg, 2017). For example, a road or railway connecting key cities or trade hubs to resources is initially considered as a transport corridor and, as hard and soft infrastructure are created and other economic and non-economic dimensions are integrated into the system, it can evolve into a logistics corridor, and economic corridor or true development corridor (Box 1 and Figure 1B).

The most widely used tool to assess and mitigate the impacts of development activities on the environment at a project level is Environmental Impact Assessment (EIA), adopted as a national legal instrument by 180 countries and territories (Craik, 2019). At the strategic planning level, at least 40 countries had Strategic Environmental Assessment (SEA) legislation in place (UNEP, 2018). The scope of an SEA is broader than that of an EIA and refers to “a range of analytical and participatory approaches that aim to integrate environmental considerations into policies, plans and programmes and evaluate the interlinkages with economic and social considerations” (OECD, 2006). SEAs are thus more directly relevant to development corridors although each individual project within a corridor will need to have an EIA mandated by local regulations.

In addition to what is required by national law, the use of decision-making frameworks is becoming mainstreamed in policy for governments, lender, and multinational corporations. One such framework is the mitigation hierarchy, which guides the management of biodiversity and people impacts from development (CSBI & TBC, 2013; Bigard et al., 2017), supports corporate commitments to achieve no net loss, or net gain of biodiversity in projects’ lifecycles or commodity production (Bull and Strange, 2018; de Silva et al., 2019). Achieving no net loss for biodiversity means that the implementation of a project has not resulted in net biodiversity loss in comparison to an established baseline or counterfactual. Net gain proposes going even further so that new biodiversity is created through the life cycle of the project. The mitigation hierarchy is central to achieve these objectives and ultimately seen as a path towards better outcomes for biodiversity and people (Arlidge et al., 2018; Griffiths et al., 2019; Jones et al., 2019; Bull et al., 2020; Maron et al., 2020). It proposes four sequential but iterative stages, typically phrased as: avoid, minimise, restore, and offset. Avoid and minimise are preventive actions which focus on anticipating and preventing an impact, while restore and ecological compensation are remediative actions which aim to repair existing impacts (CSBI & TBC, 2013).

More importantly, over the past decades financial institutions have developed environmental and social performance standards, aimed to minimise the risks and maximise opportunities of their investments, some of which specifically address impacts on biodiversity and ecosystem services. A well-recognised example of such a standard is the International Finance Corporation Performance Standard 6 or IFC PS6 (IFC, 2012). To provide funding, the IFC PS6 requires that projects should assess direct impacts (direct footprint of a project), indirect impacts (not directly attributed to a project but caused indirectly by the project), and cumulative impacts (interactions between other projects in the landscape plus other external pressures) on biodiversity (IFC, 2013). IFC PS6 then requires impact mitigation measures to be put in place, such that the net outcome is no net loss and net gain for biodiversity to be achieved (IFC, 2012). PS6 is seen as an example of best practice in biodiversity impact mitigation (Narain et al., 2020). However, a study on best-practice on biodiversity safeguards for the Belt and Road Initiative’s financiers revealed that most associated lenders do not follow such best practice (Narain et al., 2020). Moreover, there is no consensus around common standards and sustainability metrics for infrastructure development, as shown in a review of 12 sustainability standards for financing infrastructure (Bennon and Sharma, 2018).

The impacts on biodiversity from the proliferation of development corridors have been highlighted for the African continent (Laurance et al., 2015), Indonesia (Sloan et al., 2019a), Papua New Guinea (Sloan et al., 2019b), and the Belt and Road Initiative (Ascensão et al., 2018; Hughes, 2019), among others, revealing significant risks for biodiversity conservation in the long-term. Although fundamentally important in raising awareness, such studies scarcely detail which methods and approaches are being used or proposed to assess impacts of these developments and recommendations on specific mitigation measures. More importantly, it is not clear the extent to which existing research on development corridors follows best practice frameworks and tools mentioned above, despite them becoming mainstream in sustainability standards and corporate commitments. Given the wide geographic scope, the global proliferation of these initiatives, and their particular complexity (i.e., many ongoing projects and numerous stakeholders involved), there is a need to better understand how they develop and, more importantly, how impacts they have on biodiversity and ecosystem services (if any) are being assessed and managed.

Here, we describe corridors from a biodiversity perspective and identify the elements of best practice in biodiversity impact mitigation, considering related ecosystem services where possible. We focus on the specific nature of these complex initiatives acknowledging that the science to understand and manage the impacts of individual infrastructure projects has many years of history (Spellerberg and Morrison, 1998) and is well-advanced, especially for roads (Coffin, 2007; Fahrig and Rytwinski, 2009; van der Ree et al., 2011; Forman et al., 2015; Bennett, 2017; Collinson et al., 2019) but also railways (Barrientos et al., 2017, 2019). Here we are particularly interested in development corridors more broadly and how impacts on biodiversity are assessed and what mitigation measures (if any) are proposed. Applying a Rapid Evidence Assessment of peer-reviewed publications on corridors and biodiversity impact mitigation, we therefore aim to: (i) understand how impacts on biodiversity and ecosystem services are assessed; (ii) document the mitigation measures proposed to manage these impacts; and (iii) assess how these approximate to best practice. We then discuss key gaps identified, explore alternatives to fill these with existing tools and approaches, and put forward policy relevant recommendations.

Of the included 271 articles, 37% (n = 100) assessed the impacts of corridors on biodiversity but only seven assessed impacts on ecosystem services. Thirty-seven per cent (n = 37) of assessments were conducted in the conception planning stage of a corridor (Figure 3). Of these 74% percent where country case studies across 33 countries (Figure 4). The reduction of studies assessing biodiversity or ecosystem services impacts from 271 to 100 articles was particularly prominent in Africa (75% reduction), Asia and Latin America (over 60% reduction each). The number of countries represented went down from 45 to 33.

Over half of studies used either ecosystems (37%) or species (25%) to measure impacts on biodiversity. Fewer publications (14%) used a mix of biodiversity metrics combining species, protected areas or other important conservation areas (e.g., Mahmoud et al., 2017; Laurance et al., n.d.; Sloan et al., 2019a). Notably, 14% of studies assessed impacts on the environment not using any specific quantitative metrics related to biodiversity. This includes measuring pollutants generated (Valentukevičiene and Ignatavičius, 2011) but not linking these to biodiversity impacts, or changes on different land uses over time which could or could not relate to biodiversity loss and degradation (Subasinghe et al., 2016). The three studies assessing impacts on ecosystem services were specifically on water quality (Valentukevičiene and Ignatavičius, 2011; Er et al., 2014) and carbon sequestration (Chen et al., 2017). There were four studies that used carbon emissions as an environmental impact metric but did not focus on ecosystem services.

Of the 100 studies assessing impacts on biodiversity and ecosystem services, 61 proposed mitigation measures. The studies that did not comply this inclusion criteria (Figure 2) only assessed trends or impacts of land use or biodiversity change but did not propose or discuss explicitly or implicitly any mitigation measures. In addition, we excluded studies that could not be found (n = 6), and those written in a language that could not be read by the authors (n = 3), leaving 52 studies to be fully read.

These final 52 studies account for 19% of the initial 271 studies on corridors. While the number of studies decreased, from 271 to 52, the geographical coverage remained similar with Europe as the second continent with more studies followed by Oceania and Africa (Figure 4). At a country level, case studies from 19 countries were excluded as they did not propose any mitigation measures leaving a total of 45 studies across 26 countries (Figure 4). 34 of these 52 publications used spatially explicit methods and modeling techniques were the most used (Figure 5). The modeling was used to assess impacts on ecosystems, species, land use or from invasive species. Seventeen studies used more simple techniques, such as assessing linear proximity and overlaps with the planned corridor footprint or overlaps with a buffer created around the corridor. Eleven studies based their impact assessment on data collected through field surveys. Non-spatial methods were qualitative assessments of impacts (10) and mainly reviews of existing research (3), with no actual quantification of impacts. Notably, two indicator prioritisation studies selected best indicators to monitor corridor performance (Zhang et al., 2017; Yogeswari and Bala Keerthana, 2019).

Sixty-two percent of the articles only assessed direct impacts on biodiversity. Those which assessed indirect impacts as well (37%) evaluated linear proximity or overlaps with buffers drawn from the main linear infrastructure of the corridor (Laurance et al., 2015; Mahmoud et al., 2017; Sloan et al., 2019b), by measuring land cover changes over time in the area of influence of the corridor (Petty et al., 2012; Villarreal et al., 2013; Wilson et al., 2013), or combining both (Heinicke et al., 2019).

The application of the mitigation hierarchy was explicitly mentioned in only two studies (Bastille-Rousseau et al., 2018; Heinicke et al., 2019). Similarly, we found no studies that assessed restoration or offsets alternatives for corridors nor any discussion or evaluation of no net loss or net gain achievement, although the existence of these approaches was briefly mentioned in some of them. There was, however, implicit use of the mitigation hierarchy in other studies proposing minimisation measures (56%) and avoidance (21%). The remaining 23% combined avoidance and minimisation measures. The main avoidance action proposed was to not develop infrastructure in important places for biodiversity (e.g., Laurance et al., 2015; Pomazkova et al., 2019). Regarding minimisation, most measures were species specific [e.g., moose (Wierzchowski et al., 2019), West African chimpanzees (Heinicke et al., 2019), elephants (Bastille-Rousseau et al., 2018), or invasive species (Liu et al., 2019)], while one study proposed minimisation measures for several species (Cserkész and Farkas, 2015). Only one study was found that assessed direct, indirect, and cumulative impacts (Lechner et al., 2017).

We find three major evidence gaps. First, less than half (37%) of the peer reviewed literature on development corridors assess impacts on biodiversity and even less so (3%) on ecosystem services. Those studies that assess impacts on biodiversity do not follow best practice as defined in this review (Table 1) and only one in 5 (19%) propose mitigation measures to address those impacts. Second, the review found only one study in South America, 10 in Africa, and 11 in Oceania which assess impacts on biodiversity. These are continents with high levels of biodiversity and also where development corridors are expanding (Laurance et al., 2015; Sloan et al., 2019a, b; Vilela et al., 2020). Third, the lack of impact assessments on ecosystem services suggests at best partial consideration of how development corridors might bring socio-economic benefits to local people. Moreover, there is evidence that infrastructure corridors can negatively impact ecosystem services (Mandle et al., 2015; Nyumba et al., 2021). In this discussion, we focus on impacts on biodiversity within development corridors from two perspectives: how impacts are assessed and how impact mitigation is approached.

No net loss or net gain goals are not only becoming increasingly mainstream for industry but also in global and national policies. Achieving positive outcomes for biodiversity and ecosystem services will likely be a critical component of the post-2020 global biodiversity framework of the Convention on Biological Diversity. In this context, Díaz et al. (2020) propose a strict no net loss goal as a highly ambitious end point that can only be achieved through a coordinated and holistic approach that considers socio-economic and environmental trade-offs.

Notwithstanding the challenges to achieve no net loss, the policies under which it could be pursued for development corridors already exist in some countries where they are ongoing or planned (Figure 6). The Global Inventory on Biodiversity Offset Policies (GIBOP), which summarises the degree to which biodiversity compensation policies and the mitigation hierarchy are embedded within national environmental policy frameworks, shows that 100 countries have or are developing biodiversity compensation and/or offset policies (Bull and Strange, 2018).

According to GIBOP, 36% of our initial 45 countries already have regulatory requirements for offsets for at least some projects in some circumstances, 38% provide guidance or have measures in place to facilitate voluntary offsetting (GIBOP, 2020), and 13% have no provisions could be found with regards to compensation/offset (Figure 6). In Africa, we know that at least 33 development corridors are or will be dissecting the continent in the next decades (Laurance et al., 2015). Yet, only three country case studies and four regional studies in Africa assessed impacts on biodiversity and proposed mitigation measures but none proposed the use of offsets despite most countries having voluntary or compulsory provisions already in place (Figure 6b). It seems urgent and necessary that future impact assessment of development corridors in peer reviewed literature consider not only best practice but also existing compulsory or voluntary policy guidance on impact mitigation at a national level.

Tools for impact assessment, such as EIA and SEA could be the conduit through which best practice and regulatory requirements are implemented at a national level. SEAs seem particularly well-suited to do this as SEAs necessarily involve stakeholders coming together to assess environmental, social, and economic risks and alternatives to development at policy, planning and programming levels. This approach is critical for responding to the transboundary nature of development corridors, while ensuring these align with broad sustainability strategies and national policies. Still, in our review only one publication focused on developing methods to improve SEAs outcomes (Ramachandran and Linde, 2011). Similarly, lessons learned from jurisdictional approaches to REDD+ (i.e., reducing emissions from deforestation and forest degradation and the role of conservation, sustainable management of forests, and enhancement of forest carbon stocks) could provide some insights into how to achieve positive outcomes from initiatives that comprise multiple projects across a landscape. Jurisdictional approaches to REDD+ were taken acknowledging that significant reductions in deforestation could not be achieved by individual projects and that success in protecting forests and climate relied on successful implementation government-led policies and programs at multiple levels (Boyd et al., 2018).