The re-imagining of a framework for agricultural land use: A pathway for integrating agricultural practices into ecosystem services, planetary boundaries and sustainable development goals

Abstract

This paper reflects on the legacy of the Ambio papers by Sombroek et al. (1993), Turner et al. (1994), and Brussaard et al. (1997) on the study of agricultural land use and its impacts on global carbon storage and nutrient dynamics. The papers were published at a time of transition in ecology that involved the integration of humans as components of ecosystems, the formulation of the ecosystem services, and emergence of sustainability science. The papers offered new frameworks to studying agricultural land use across multiple scales in a way that captured causality from interacting components of the system. Each paper argued for more comprehensive data sets; foreseeing the power of network-based science, the potential of molecular technologies to assess biodiversity, and advances in remote sensing. The papers have contributed both conceptual framings and methodological approaches to an ongoing movement to identify a pathway to study agricultural land use and environmental change that fit within the concepts of ecosystem services, planetary boundaries and sustainable development goals.

Introduction

Agricultural land use and land use change represents one of the more pervasive and measurable impacts of humans on the environment. In the broadest sense, agricultural land use change encompasses the use of natural systems for food and fiber production (e.g., grazing, cropping, and forestry), the transition of extant systems from one system to another, and changes in the management practices for existing systems. Upwards of 50% of the Earth’s total terrestrial surface and more than 75% of ice-free terrestrial surface has been altered by human activity (Vitousek et al. 1997; Ellis and Ramankutty 2008). Agriculture represents 38% of human land use; dominated by grazing, cropping systems, and forests (Davis et al. 2019). Water use and diversion, fertilizer production and use, and management practices extend the environmental impacts of production far beyond the cumulative local effects on soils and biota (Galloway et al. 2002; Galloway et al. 2008). In short, agricultural land use affects the local ecosystem structure, function, and dynamics, interactions with adjacent land and waterways, and land-atmosphere interactions.

The paper set of Sombroek et al. (1993), Turner et al. (1994), Brussaard et al. (1997), captures the thinking about agricultural land use change at a time of transition in ecology in terms of how we frame and view questions, the advent of new technologies that allow us to address different questions, and in the types of and amount of data we deal with. The papers were part of a broader initiative in global change science that set new standards in how we address agricultural land use change and beyond. As a collection, the papers embody the thematic human enterprises of land transformation, global biogeochemistry, and the importance of biodiversity in maintaining ecosystem function presented by Vitousek et al. (1997), and provided a glimpse to the approaches that have been adopted to address questions at the center of the sustainability science movement (Kates et al. 2001).

Frameworks

The challenges presented in studying agricultural land use and land use change required a reformulation of approaches. Each of the papers worked with the information at hand, but identified the need to develop a new framework to study land use. In many ways the authors grappled with a familiar theme in science. Some years earlier O’Neill et al. (1986) had provided four guidelines or rules to work by when using models to study systems which are germane to this discussion: 1) The model must be internally consistent; 2) The model must not be adopted simply because it was successful in another field; 3) The model must agree with known properties of the system being studied; and 4) The model must be capable of testing new and testable hypotheses. In retrospect, each of the papers identified deficiencies in the traditional frameworks (read models) and the then current state of available data to implement the models, particularly with regards to Guidelines 1-3. All aspired to achieve the predictive capabilities embodied in Guideline 4.

Sombroek et al. (1993) focused on refining estimates of pools of soil organic carbon (SOC) using contemporary soils maps. They were able to provide estimates of the SOC pools that were in line earlier and contemporary ones, but were quick to point out challenges when using traditional soil classification systems. Different approaches were used for estimating area, there were different base maps, and few maps of actual land use. Moreover, the soil maps lacked credible estimates of bulk density of soil horizons and provided poor characterizations of topsoil when using data from routine soil surveys proved challenging. More importantly, the heavy reliance on the correlative relationships between organic carbon levels and related parameters to infer fertility status, organic matter turnover and biological activity affected both the estimates and the utility of the approach to meet the management aims. Challenges notwithstanding, the paper provided a template for studying soil carbon at the global scale, and highlighted the need for a more comprehensive mechanistic framework for studying soil carbon that included earth system, biological and human drivers. The paper was also one of the early calls for large-scale field programs to stimulate organic-carbon storage as a means to attenuate the consequences of the rise in atmospheric CO₂.

Turner et al. (1994) noted that the traditional approach of studying land use and ascribing single or multiple causal effects were inadequate. The challenge for Turner et al. (1994) was that the existing data sets on land cover and land covers, and the understanding of the driving forces were not sufficient for the task. To resolve this, Turner et al. (1994) proposed a two-phased approach that started with designing a common protocol for case studies to study cause-to-cover dynamics for different scenarios, followed by the development of a basic framework that includes these variables for global land use and land-cover models. The case studies would provide empirical data and theoretical assessments that are quantitatively comparable. Turner et al. (1994) recognized the need to identify a common set of independent variables and driving forces that include population, technology, economic and political structures, and cultural beliefs and attitudes. Ideally, the work would lead to the development and parameterization of models that would organize existing data on land transformation, identify mechanisms behind the changes in land use and land cover, and provide projections under different scenarios.

Brussaard et al. (1997) focused on soil biota and their importance to soil formation, nutrient dynamics and plant growth. The paper summarized the contributions of soil biota to ecosystem processes, and highlighted different modeling approaches that soil ecologists had developed to link biota to function (Hunt et al. 1987; Moore et al. 1988; de Ruiter et al. 1994). The paper adopted a philosophy that agricultural production would benefit by taking advantage of the functional benefits of a healthy soil community provides to soil formation, biogeochemical cycling and plant growth (Elliott and Coleman 1988). The paper laid out several priorities for future research, two of which stand out. First was a need to better catalog and understand the vast diversity of soil organisms. Second was the need for better formulations of functional groups to study ecosystem processes (read—reformulate how we model the systems). The molecular techniques of the time showed much promise in the quest to link species to function, and to organize species into functional groups of biota to study ecosystem processes. At the time, these techniques were being used as tools to characterize communities. Changes in community structure were inferred to affect ecosystem function.

Impacts and New Directions

Each of the papers stressed the need to develop and adopt a model or framework for studying agricultural land use, noted the inadequacies of contemporary approaches, but were solution oriented by offering pathways forward. The papers recognized that the local or system specific ecological perspective to studying agricultural ecosystems was inadequate. The impacts of agricultural land use had historically been viewed in terms of habitat loss and fragmentation, soil fertility and soil loss through wind and water erosion, nutrient run-off and its effects on aquatic systems. We witnessed a transition from this perspective to a landscape and regional view of land use, and how ecosystems function within the landscape and interact with the atmosphere. Agricultural land use was not only a local or regional issue, but was seen as a driver of many global change issues—atmospheric CO₂, reactive nitrogen, and soil loss on water quality and climate (Davis et al. 2019). The cumulative global impacts of agricultural production were recognized, but means and methods necessary to study them at this scale were in the nascent stages of development.

Three additional changes in thinking developed at the time and shortly after the papers were published that facilitated this transition. The first was the advent of the social-ecological perspective wherein humans are integral components and drivers of systems (Turner et al. 1990, 1994; Collins et al. 2011). The framework proposed by Turner et al. (1994) was explicit in this regard with inclusion of humans as both components and drivers of agricultural land use and change. The second development was that the work provided a framework for studying land use change via a systems approach that resembles and contains foundational characteristics of sustainability science (Kates et al. 2001; Clark and Dickson 2003; Clark 2007). The ecological, social, and economic contexts—the three interacting pillars of sustainability science—were stressed as important components of studies moving forward—see Figure 1 in Turner et al. (1994). The third involved the reconceptualizing ecosystem processes in terms of human needs. This included the formalization of the concepts of Ecosystem Services (MA 2005) and Planetary Boundaries (Steffen et al 2007; Rockström et al. 2009), and the establishment of the United Nations Sustainable Development Goals (United Nations 2015). While Turner et al. (1994) took a decidedly bottom-up approach through the use case studies to inform their models, as opposed to a top-down modeling approach used by many (see Steffen et al. 2007), the work nonetheless demonstrated that our understanding agricultural land use, and its impacts on human well-being and the environment are pivotal to these concepts and initiatives.

The papers also recognized the potential of new and emerging technologies and collaborative networks to help resolve the inadequacies that each identified. Our understanding of the extent and dynamics of agricultural land use has benefited from the advances in remote sensing and network science envisioned by Sombroek et al (1993) and Turner et al. (1994). Recent studies have applied these advances to the aforementioned frameworks to better understand agricultural land use and its impact on ecosystem processes (Liang et al. 2017; Davis et al. 2019).

Advances in molecular techniques really took hold shortly after Brussaard et al. (1997). The techniques were well-suited to characterize soil biota and their activities in soil formation, plant nutrient dynamics and carbon cycling in general, and under different agricultural settings. have had profound impacts on the field in the manner envisioned by Brussaard et al. (1997) and helped resolve issues raised by Stromboek et al. (1993). The genotype, to transcription, to function (read performance in the field) approach would require not only different types of information at fine resolution, but a rethinking of what information is needed and organized. Recently, Hall et al. (2018) and others see a similar need to better characterize microbial communities along microbial functional groups, akin to that made by Brussaard et al. (1997). It is not enough to characterize which genes and traits are present, but rather to understand the dynamics of gene function in relation to ecosystem processes. Ironically, given the nature of the molecular techniques, the field of soil ecology took a marked shift away from soil biota writ large to a greater focus on microbes. While great strides have been made in soil microbial ecology, and microbial-based processes in soils, soil microbiota and mesobiota received short shrift. There is now growing re-realization along the lines that Brussaard et al. (1997) made, that microbes alone do not make an ecosystem and that micro-fauna and mesofauna are important drivers of these processes as well (Grandy et al. 2016).

The work previewed the need for a change in how we structured and employed models. A clear movement in the direction of characterizing communities in ways that link presence and activity to function has developed (Cotrufo et al. 2013; Wieder et al. 2014; Hall et al. 2018). Global scale biogeochemical models are now being re-imagined to include finer scale soil biological processes, linked to soils and land use to assess carbon capture and storage potential at local, regional and global scales (Paustian et al. 2016; Lavallee et al. 2019).

Concluding Remarks

While much progress has been made over the past 20 years, the study of agricultural land use and the impacts that it has on ecosystem processes and human well-being is grappling with many of the same issues that it did when the paper set (Sombroek et al. 1993; Turner et al. 1994; Brussaard et al. 1997) was published. Standardization of data to characterize systems, refinement of data collection at spatial and temporal scales to link structural to function, and fully integrating the social and cultural dimensions of humans into the calculus are still pressing.

In many respects, the field has been transformed for the reasons discussed above and has adopted, such as their predecessors, the data and approaches at hand. What is clear is that the approaches to studying agricultural practices and land use advanced in the paper set have contributed to more than our understanding of their impacts on food production and the environment, but have helped guide and shape the debate and concepts important to sustainability science (Kates et al. 2001; Steffen et al. 2007; Biermann and Kim 2020—read ecosystem services and planetary boundaries) and are a prominent within the UN Sustainable Development Goals (UN 2015). Moving forward will require different innovative approaches and perspectives like those offered by these papers (Sombroek et al. 1993; Turner et al. 1994; Brussaard et al. 1997).

John C. Moore:

is a Professor in the Department of Ecosystem Science and Sustainability, and Director of the Natural Resource Ecology Laboratory at Colorado State University. His research interests are in the fields of soil ecology, mathematical/theoretical ecology, and the application of the theory of complex adaptive systems to teaching and learning. His research on food web structure, function and dynamics is positioned at the interfaces of community ecology, ecosystem ecology, and evolution linking species traits and adaptions to biogeochemical cycles—contributing to our understanding of how soil organisms contribute to soil formation and nutrient retention in sustainable agricultural practices in temperate regions.