Editors’ Vox is a blog from AGU’s Publications Department.

The critical zone is the thin layer of the Earth’s surface extending from the tops of trees to deep aquifers, ‘where rock meets life’. Critical zone (CZ) science explores how landscapes evolve from below the Earth’s surface to the top of trees, supporting life on Earth. It recognizes that multidisciplinary science approaches are vital to understanding the complicated flows of water, nutrients, and sediment through landscapes – processes that are fundamental to sustaining ecosystems and the services they provide to humanity.

In the September 2023 issue of Earth’s Future, a new research article proposes an approach to critical zone science that better recognizes and incorporates the role of human behavior. The authors apply this new approach in their companion paper, a study of smallholder farming communities in rural China.

We asked the authors to give an overview of the evolution of critical zone science, the major findings from their study in China, and how their research can be used.

What are ‘critical zone observatories’ and how has their focus evolved over time?

Multidisciplinary teams of Earth scientists developed holistic knowledge of natural landscapes’ evolution in the first critical zone observatories (CZO). These were specific geographic areas of the terrestrial landscape which were subject to intensive study of the hydrology, geochemistry, geomorphology, soils, and ecology in natural landscapes. These pristine natural systems are rare in our modern world. More recent CZOs have been established in landscapes degraded by human activities and have started to address important challenges including climate change, water scarcity, and food security. Five new CZOs across China revealed how farmers’ managed land impacted the CZ from shallow surface soils to deep groundwater.

CZO studies have developed sophisticated understanding of interaction of natural processes from the top of the canopy to bedrock. However, they have excluded the human influence that has a first order impact on many CZ processes in agricultural landscapes across the globe. Meanwhile, studies of agricultural landscapes by agronomists, soil scientists and social scientists have tended to focus on the top meter and field or farm scale.  We bring both together to capitalize on the integration of approaches to maximize understanding of CZ processes in human-altered environments and optimize delivery of SDGs.

Understanding human activities and their impacts on how the critical zone functions is essential for halting ecosystem degradation, delivering UN SDGs, and improving climate resilience.

We propose a new approach to CZ science for studying the human‐modified landscapes that dominate our world. To help explain why this is needed, we have re‐drawn a key diagram explaining how the critical zone works to show the role of humans. This new conceptual diagram illustrates the extensive human impacts on CZ function, providing a more realistic visual of how both human activities and natural processes shape the Earth’s critical zones. Understanding human activities and their impacts on how the critical zone functions is essential for halting ecosystem degradation, delivering UN SDGs to directly support local people, and improving the climate resilience of these landscapes and the people they sustain. 

What are the key reasons for integrating the human factor into CZS?

Agricultural landscapes have dramatically altered the Earth’s critical zone. There is a growing global need for sustainable agriculture to reduce human impacts on the environment whilst improving the local livelihoods of farmers and their communities who live and work in these stressed environments. To support local people to improve their livelihoods through more sustainable agricultural practices, we need to have a better understanding of how sustainable agricultural knowledge is produced, shared, and used between different groups including farmers, scientists, agricultural companies, and government.

Social scientists in the research team provided unique insights into how farmers actually interact with their land, including the effects of traditional farming knowledge, government training schemes, agricultural companies, and shifting land use rights. Communicating directly with farmers also provided information that helped make sense of earth science data in human-modified landscapes. Without understanding how local people actually use the land including their political and social contexts, and the cultural practices influencing land ownership and stewardship, scientists are only able to understand half of the picture.

Local knowledge is invaluable for understanding environmental science data in human-modified landscapes. Credit: Naylor et al. [2023], Figure 3c

What were the questions or goals that drove your study of smallholder farming communities in China?

Local farming practices have shaped and reshaped China’s rural landscapes through time. Many of these landscapes, and the soil and water that sustains nature, agriculture, and human livelihoods in them, have been heavily degraded through human activities. This directly impacts the ecosystems and landscapes that sustain these communities, in particular access to clean water and sanitation (SDG 6), no poverty (SDG 1), zero hunger (SDG 2), climate action (SDG 13), life on land (SDG 15), and sustainable cities and communities (SDG 11).

Changes in agricultural practices have the potential to improve ecological and social outcomes; national level policies in China have been developed to change agricultural practices to restore degraded landscapes and reduce synthetic fertilizer use. We sought to measure the effects of these policy changes on the functioning of CZOs (Paper 1). Alongside this, we sought to explore how local farmers learn, who they learn from, who they trust, their interest and capacity for learning new sustainable farming practices, and identifying key barriers to training (Paper 2). These human perspectives were crucial for identifying how best to share the findings of the CZ science.  

What were the major findings from your research?

Local farmers are adopting practices to improve resilience in degraded landscapes; interpretation of CZ science data was improved by understanding their local land management methods.

We found that learning practices and preferences varied spatially across the three studied regions, where reliance on bonding networks with family was the primary mode of learning in two of the three studied regions. This knowledge is invaluable for designing knowledge exchange activities to share CZ science and to provide sustainable agricultural training in different regions.

We identified the greatest pressures on smallholder farmers’ livelihoods, such as the cost of fertilizer. We were then able to draw links between the CZ science on nitrogen loads and fertilizer use as a major financial pressure, identifying where a policy and practice change would directly improve local livelihoods. This allowed us to better link the CZ science to SDGs.

What are some of the ways your research could be used?

Using the Anthropocene critical zone science diagram better represents human-landscape interactions in the Earth’s critical zone. This reframing allows the impacts of human activities on the Earth’s terrestrial landscapes to be readily seen – in much more clearly shows the pivotal role of humans in landscape degradation.

We demonstrated that sustainable landscape management needs both natural and social scientists to make land-use policies that work, and that are supported by local people.

We demonstrated that sustainable landscape management needs both natural and social scientists to make land-use policies that work, and that are supported by local people. A useful blueprint for transdisciplinary research approaches was created; one that directly engages with and co-develops research programs with the local communities for whom achieving UN SDGs will have the greatest benefit. This blueprint combines science, social science, local knowledge, and knowledge exchange where a transdisciplinary project research cycle and funding model have been developed that could be widely adopted by others.  This approach is suitable for addressing the global grand challenges of climate change, ecosystem collapse and planetary health necessary for resilient Earth Futures.

We recommend that future science studies in stressed agricultural landscapes use a more local approach to build trust and carry out science that better addresses pressing local environmental challenges. This requires us to study people, the residents in these landscapes, using social science and human geography approaches, alongside understanding how the landscape is functioning ecologically. This will enable environmental science to be better grounded in, informed by, and useful to local communities.

The recommended approaches from our papers can thus be used by national funding bodies such as the United States’ National Science Foundation (NSF) to help deliver their Next Generation Earth Systems Science initiative that ‘emphasizes research on the complex interconnections and feedbacks between natural and social processes.’ It can also aid delivery of global strategies such as the Food and Agriculture Organization’s (FAO) Strategic Framework 2022-2031 and key statutory policies, such as the European Union’s Soils Strategy for 2030. Our work also provides a useful case study showing the value of understanding local practices of ecosystem stewardship, local adaptation measures, and knowledge diversity in enabling climate resilient development.

—Larissa A. Naylor (larissa.naylor@glasgow.ac.uk, 0000-0002-4065-2674), University of Glasgow, United Kingdom; Jennifer A. J. Dungait  (0000-0001-9074-4174), University of Exeter and SRUC-Scotland’s Rural College, United Kingdom; Paul D. Hallett (0000-0001-7542-7832), University of Glasgow, United Kingdom; Neil Munro (0000-0001-9694-9701), University of Glasgow, United Kingdom; Alasdair Stanton (0000-0002-6237-8653), University of Glasgow, United Kingdom; and Timothy A. Quine (0000-0002-5143-5157), University of Exeter, United Kingdom

Editor’s Note: It is the policy of AGU Publications to invite the authors of selected journal articles to write a summary for Eos Editors’ Vox.

Citation: Naylor, L. A., J. A. J. Dungait, P. D. Hallett, N. Munro, A. Stanton, and T. A. Quine (2023), Earth’s critical zone remains a mystery without its people, Eos, 104, https://doi.org/10.1029/2023EO235025. Published on 19 September 2023.
he logo for the United Nations Sustainable Development Goal 2 is at left. To its right is the following text: The research reported here supports Sustainable Development Goal 2. AGU is committed to supporting the United Nations 2030 Agenda for Sustainable Development, which provides a shared blueprint for peace and prosperity for people and the planet, now and into the future.
This article does not represent the opinion of AGU, Eos, or any of its affiliates. It is solely the opinion of the author(s).
Text © 2023. The authors. CC BY-NC-ND 3.0
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