By: Hannah E. Birgé and Becca A. Bevans, University of Nebraska Lincoln, USA
As a cryptic system occurring in an opaque medium, it’s easy to ignore the belowground in natural resources management until it’s too late. Soil functioning contributes to essential ecosystem services, including regulation of the atmosphere and climate, primary (including agricultural) production, waste processing, decomposition, nutrient conservation, water purification, erosion control, medical resources, pest control, and disease mitigation. The soil system also influences the aboveground through feedbacks. Management that ignores these feedbacks in the pursuit of generating a single ecosystem service may inadvertently alter the very soil processes that underpin the long-term generation of the desired services.
This outcome is easily identified in retrospect, but often difficult to predict. Immediate soil responses to management occurring in this opaque matrix are often ignored, and many monitoring plans fail to capture slow feedbacks, such as declining biodiversity. The effects of these slow feedbacks may be felt only when shifting environmental conditions reveal a loss of response diversity, potentially triggering a non-linear (or threshold) response by the system being managed. The question of when and how to test soil responses to management in the interest of long-term ecosystem service production formed the premise of our paper, “Adaptive Management for Ecosystem Services”, which we co-authored with Craig R. Allen, David G. Angeler, Sara G. Baer, and Diana H. Wall for a special issue in The Journal of Environmental Management.
The Dust Bowl provides a familiar example of how mismanagement, leading to lost soil functioning, undermines ecosystem service production. In the early 20th century, European settlers in the U.S. Great Plains extensively replaced deep-rooted, drought tolerant perennial grassland species with drought intolerant wheat crops. They were spurred on in part by the 1909 U.S. Bureau of Soils announcement that “The soil is the one indestructible, immutable asset that the nation possesses. It is the one resource that cannot be exhausted; that cannot be used up.” This broad-scale removal of perennial prairie plants in the Great Plains starved belowground biota, and left large expanses of bareground exposed during much of the year. An intense drought in the 1930s finally triggered the Dust Bowl. As is common in desertification events, a stochastic event was the proximate cause of system collapse while previously altered system feedbacks were likely the ultimate drivers, making it difficult to disentangle the individual drivers of system state change. The Dust Bowl displaced 100 million hectares of topsoil and left 500,000 people homeless. Yet desertification is not only a historical problem: current annual global economic losses due to desertification are roughly US $3 trillion (~3-5% of global GDP).
Salinization is another example of the unintended consequences of feedbacks between natural resources management and belowground response. In Western Australia, the replacement of native woody vegetation with shallow-rooted wheat crops has mobilized groundwater to the soil surface –moving through salt deposits on its way up. Evaporation and infiltration of impure irrigation water often leaves behind saline deposits on the soil surface. In zones where groundwater recharge is high and mean annual precipitation is low, salinity may not be mobilized back to deeper soil, negatively affecting crop productivity and biological activity in the soil surface. Salinization remains an ongoing problem in Australia and throughout the planet. Nearly 50% of global agricultural soils face some risk of salinization, at a global annual cost of ~$12 billion.
On a smaller scale, issues like mycorrhizal fungi scarcity, pathogen loading, and legacy nutrient loading in the soil can frustrate expected management outcomes. But these are just a few examples of the many possible soil-related management impediments and, crucially, all of them are invisible to the naked eye. How, then, can a manager with limited time, money, and equipment probe the interior of the soil to prevent unwanted feedbacks arising from the soil system while continuing to produce desired ecosystem services?
Adaptive management, we argue, may provide the answer. Adaptive management is a management approach that applies the scientific method to a management problem. We should note that all natural resources managers are adaptive: if something goes wrong, good managers adjust!
Adaptive management was originally designed for the aboveground, but provided us with a starting point for a soil adaptive management framework. Our approach gives natural resources managers a roadmap to determine when and how they should probe the belowground to reduce uncertainty in their management program. When results from an adaptive management cycle focused on the aboveground do not match hypothesized outcomes, managers can implement a simultaneous adaptive management loop focusing on soil variables, by first deciding what factors within the soil may be affecting their management plans (formulate hypotheses), researching and determining methods for altering those processes (develop a testing plan), and finally, implementing their plan by applying the management treatment and monitoring the effects. Tests need not be expensive or labor-intensive; we suggest several tests that are inexpensive and relatively easy to perform on a large scale. In this way, system thresholds are less likely to be inadvertently ignored (or accelerated!) by a management plan.
Adaptive management for soils provides another tool enabling natural resources specialists to identify and address uncertainty arising from the soil system in a methodical and focused way. Like any tool, it will not be applicable in every context (i.e., when certainty is high, or there is little controllability and replicated experiments are infeasible), but it does enable further testing, leading to a greater understanding and appreciation of the roles belowground systems play in regulating essential ecosystem services, and how they perform those services. Avoiding system thresholds does not need to be a mysterious process; implementing adaptive management for soils can help managers to access desired ecosystem services without undermining the process that support them.