Introduction
In our paper “Coupled Human and Natural Systems” (Liu et al. 2007), we developed a
timely, theoretical, and practical foundation for research on Coupled Human And Natural
Systems (CHANS). The science of CHANS builds upon, but goes beyond previous research
that linked humans and ecosystems (e.g., ecological anthropology, environmental geography,
human ecology). CHANS science uses a holistic perspective to integrate patterns and
processes that connect human and natural systems, as well as within-scale and cross-scale
interactions and feedbacks between human and natural components of such systems (Fig. 1).
Such an integrated framework is needed to understand the increased complexity of the
Anthropocene and develop innovative solutions to unprecedented global challenges.
Fig. 1
A schematic diagram of a coupled human and natural system. Arrows show interactions
and feedbacks. (courtesy of Vanessa Hull.)
Over time, key ideas in this framework, in particular cross-scale interactions and
feedbacks, also became incorporated into closely related concepts such as “social-ecological
systems” and “human-environmental systems”. All three concepts are often used interchangeably,
although formally the latter two are subsets of CHANS because CHANS includes not only
social dimensions but also many other human dimensions (e.g., economic, cultural)
that are not emphasized in the term of “social-ecological systems”. Similarly, the
CHANS framework emphasizes consideration of all aspects of nature including not only
environmental processes in the term of “human-environmental systems” but also other
dimensions (e.g., hydrological, climatic). We emphasize that the communities that
use these various concepts overlap and that the concepts involved are not in contradiction,
but simply note that the term of CHANS tends be the most encompassing. Since the publication
of original CHANS ideas, research on CHANS has grown dramatically. In this essay,
we offer a brief overview of the impact of our paper and highlight how the paper has
inspired some later work such as telecoupling (Liu et al. 2013) and metacoupling (Liu
2017).
Impact overview
This paper has been cited in many languages, on a wide variety of topics, by scholars
in many countries and from many disciplines, including ecology, land use, natural
resource management, social sciences, and sustainability science. The paper’s impact
extends well beyond citations. Indeed, citation analysis underestimates impact. The
CHANS paper was preceded by the Millennium Ecosystem Assessment1 and crystallization
of sustainability science and resilience concepts, for example, and the CHANS paper
brought these ideas together and helped link these communities. As often happens in
the history of science, frameworks like CHANS become generally accepted background
knowledge that have influence without being cited. Similarly, many later publications
adopted ideas from the CHANS paper without citing it. For instance, CHANS approaches
are now widespread in global change science (e.g., Nyström et al. 2019). A key paper
developing the link between CHANS and sustainability (Liu et al. 2015) was given the
“Sustainability Science Award” by the Ecological Society of America.
The paper also catalyzed the establishment of the “International Network of Research
on Coupled Human and Natural Systems” (CHANS-Net) to promote and facilitate communications
and collaborations between a diverse community of CHANS scholars. CHANS-Net has organized
several dozen workshops, symposia and other events at national and international scientific
meetings. Many publications have resulted from these events (e.g., Kramer et al. 2017).
CHANS-Net has also supported many young scholars (e.g., CHANS Fellows) from all over
the globe to attend, present, network, collaborate, and learn from senior scholars
at the various events.
The paper has important implications for conservation, management, and policy. For
instance, it underpins the goal of achieving human-nature harmony. This idea has been
endorsed by the Convention on Biological Diversity as the 2050 Vision “[Humans] Living
in Harmony with Nature”. The CHANS perspective also has helped generate important
information for transforming the dynamics of the habitat of a global wildlife icon—giant
pandas—from long-term loss to gradual recovery (Liu et al. 2016). Subsequently, in
2016, the giant panda was removed from the endangered species list of the International
Union for Conservation of Nature, IUCN (downgraded from endangered to vulnerable).
Traditional research on giant pandas focused on panda biology, which is needed, but
the critical force behind the panda’s endangerment was habitat loss due to human activities.
As a result, even in the flagship nature reserve for panda conservation, the panda
habitat was lost faster after the reserve’s establishment than before. CHANS research
was able to illuminate how and why humans affected panda habitat, how changes in panda
habitat prompted the Chinese government to develop new policies, how and why the new
policies altered human attitudes and behaviors, and how these feedback loops evolved
over time and across space. The findings provided unique insights into diverse human
needs, complex human-nature interactions, and win–win solutions for humans to prosper
and pandas to thrive (Liu et al. 2016).
Examples of applications
The CHANS framework has transformed the field of urban ecology and the conceptualization
of urban ecosystems as complex systems of interacting social and ecological processes
across multiple temporal and spatial scales (Alberti 2008). It inspired theoretical
advances and research design of the two US Urban Long-Term Ecological Research sites,
Phoenix and Baltimore (Pickett et al. 2020). Cities as coupled human natural systems
are gaining a new attention in the study of rapid urban evolutionary change and urban
eco-evolutionary dynamics (Alberti et al. 2020). Advances in urban ecology and eco-evolutionary
dynamic provide fertile ground to extend the CHANS framework to incorporate both urban
and evolutionary dynamics (Des Roches et al. 2020).
In rural settings, CHANS concepts have been used in a series of projects focused on
evaluating water availability, use, and quality in Canadian agricultural watersheds
(Liu et al. 2019). These projects focus on the key drivers, including hydro-climatic,
geomorphic, agricultural land management practices, and watershed governance frameworks.
The work is accomplished through field-based research, data mining, and socioeconomic
modeling. Agent-based models link human decisions related to agricultural best management
practices to biophysical conditions in the watershed and regulatory programs and frameworks.
CHANS concepts and framework also have increased tractions in aquatic systems and
at the interfaces between terrestrial and aquatic systems. For example, the CHANS
framework provides new insights into restoration and governance of ocean ecosystems
(Lubchenco and Petes 2010). Fisheries have been treated as CHANS to effectively study
and manage them in a holistic manner (Lynch and Liu 2014). Studying floodplains as
CHANS offers advantages (e.g., facilitating interdisciplinary collaborations and in-depth
disciplinary analytical examination) over the use of several other frameworks (Moritz
et al. 2016).
While the CHANS framework has been effective for bringing together those who focus
on ecology, social sciences, and natural resource management and policy, expanded
frameworks have been suggested to add more engineers, planners, and other “design”
professionals into the mix (Redman and Miller 2015). The key insight has been to view
infrastructure and technology as systems in themselves and that through their close
“coupling” with human and natural systems can better understand and effectively intervene
in the overall system. In studies of urban sustainability, this is exemplified by
the social, ecological, and technological systems approach used by the Urban Resilience
to Extremes Sustainability Research Network (Markoff et al. 2018) and many subsequent
projects (Hobbie and Grimm 2020).
From coupled to metacoupled human and natural systems
Although the framework of CHANS has had considerable impact, most CHANS research has
focused on a specific place or comparisons between a few different places. With globalization,
external forces such as international trade are becoming increasingly powerful in
shaping place-based human-nature interactions. For example, the world’s agricultural
product exports across country boundaries jumped 45-fold during 1961–2018.2 Interactions
among CHANS are increasingly important and new frameworks are needed to account for
such increasing importance of cross-boundary interactions.
To take interactions among distant CHANS into consideration, an umbrella concept—telecoupling
(human-nature interactions over distances, such as international trade, species invasion,
tourism, and human migration)—was created in 2008. While the CHANS framework drew
on the research traditions of many areas such as human ecology, social-ecological
systems, and human-environmental systems, the concept of telecoupling substantially
expanded the scope of the analysis and allowed links to traditions in the natural
sciences (e.g., teleconnection in climate change and animal migration in ecology)
and social sciences (e.g., trade in economics, world systems theory in sociology)
that emphasized actions at a distance across the world. The framework of telecoupled
human and natural systems was developed to facilitate quantitative analyses of such
linkages (Fig. 2).
Fig. 2
Five major and interrelated components of the telecoupling framework. A telecoupled
system consists of interacting coupled human and natural systems through flows. Each
coupled system includes three interrelated components: causes, effects, and agents.
Causes are reasons behind the flows, effects are consequences of the flows, and agents
are decision-making entities that facilitate or hinder the flows. A system can be
sending, receiving, and/or spillover systems, depending on the direction of a flow.
For the sake of simplicity, local couplings within a coupled system are not shown.
(from Liu et al. 2013)
The integration of socioeconomic and environmental interactions is a major difference
between the telecoupling framework and previous frameworks of distant processes such
as animal migration or human migration. Traditionally, frameworks of animal migration
largely focused on biological aspects, while frameworks of human migration mainly
focused on socioeconomic dimensions. Some work in the social sciences, in particular
environmental world systems theory, also incorporate both ecological and social systems,
but mostly see the latter as driving the former (Jorgenson 2016). The telecoupling
framework incorporates the insights on trade and the global political economy from
this tradition, but expands upon them by emphasizing multiple links and feedbacks.
Use of the telecoupling framework can help identify knowledge gaps and reveal “invisible”
and unexpected impacts. For instance, negative spillover effects on Brazil’s Cerrado
(a global savannah biodiversity hotspot) offset conservation efforts in the Amazon
(Dou et al. 2018). More specifically, the supply chain agreements (Soy Moratorium
and zero-deforestation beef agreement) protected much of the Amazon forest from being
converted from native land to food production but pushed food production to the Cerrado
region and resulted in a substantial increase of deforestation there (Dou et al. 2018).
Using the telecoupling framework can address many fundamental questions, e.g., how
do telecouplings compromise or enhance environmental sustainability and human well-being
in sending, receiving, and spillover systems? How do telecouplings amplify or offset
other forces behind environmental sustainability and human well-being? How can spillover
systems be better detected and accounted for in policy? Addressing these and other
related questions requires the incorporation of methods and insights from a variety
of disciplines such as ecology, economics, behavioral sciences, geography, sociology,
information and sensing technologies, and policy science. Telecoupling is designated
as a research priority by the Global Land Programme and featured in authoritative
reports such as the Global Assessment of Biodiversity and Ecosystem Assessment (Intergovernmental
Science-Policy Platform on Biodiversity and Ecosystem Services3) and Global Environment
Outlook.4 It has been highlighted in the news outlets such as Time magazine5 and by
high-level officials of the United Nations.6 Additionally, a number of funding agencies
support telecoupling research and education. For example, the European Union has been
supporting a PhD program on telecoupling (“COUPLED-Operationalising Telecouplings
for Solving Sustainability Challenges for Land Use”,7 with 15 PhD students in its
first cohort across Europe).
To capture interactions within and among adjacent and distant CHANS, a new integrated
framework of metacoupling (human-nature interactions within as well as between adjacent
and distant systems) has been developed (Liu 2017). The metacoupling framework consists
of the coupled human and natural system framework (intracoupling—human-nature interactions
within boundaries), the telecoupling framework, the framework of pericoupling (human-nature
interactions between adjacent systems), and the interrelationships among intracoupling,
telecoupling, and pericoupling (Fig. 3). The metacoupling framework is useful to develop
realistic understanding of the complexity of real-world phenomena. For example, the
framework is successfully applied to global marine fishing (Carlson et al. 2020),
which occurs within exclusive economic zones (EEZs, intracoupling), between adjacent
EEZs (pericoupling), and between distant EEZs (telecoupling). The framework has also
been used to evaluate impacts on the UN Sustainable Development Goals (SDGs) and targets
because human activity in one place can affect the progress toward SDG targets elsewhere
through trade and other metacouplings (Xu et al. 2020). The application of the metacoupling
framework in nexus approaches for global sustainable development has been given the
“Innovations in Sustainability Science Award” by the Ecological Society of America.8
The CHANS and expanded frameworks are tools suitable for analyzing and understanding
various human-nature nexuses across space.
Fig. 3
a A schematic diagram illustrating a focal coupled human and natural system, an adjacent
system, and a distant system, as well as their interactions (indicated by arrows)
(modified from Liu 2017 and courtesy of Shuxin Li). b Metacoupling consists of intracoupling
and intercoupling, which in turn includes pericoupling and telecoupling (from Liu
2017)
Perspectives
The initial spirit of CHANS—to provide an integrated framework while incorporating
insights from a diversity of research traditions—remains. The ongoing COVID-19 pandemic
is an obvious example—understanding requires examining the links between human and
natural systems and understanding linkages that span the globe, but that manifest
in local places as well as regionally and globally. COVID-19 is a global perturbation
experiment on metacoupled systems. It has unprecedented impacts on human health, economy,
transportation, markets, medical supplies, food distribution, and so on, and these
impacts are inequitably distributed across and within nations. On the other hand,
this is a unique learning opportunity. As the impacts from the COVID-19 episode continue
to unfold, the CHANS community should seize the opportunity to learn what a hard,
sharp shock does to a complex system.
The interrelated and daunting challenges that the world now is grappling with, including
the COVID-19 pandemic, climate change, dysfunctional food distribution, and social
inequality and injustices, require integrated approaches that are core to CHANS and
expanded frameworks. Continuing exploration and expansion of the many insights highlighted
in the initial CHANS paper can help the world better understand and address crucial
societal and environmental challenges.