Historical Range of Variability

by

Ellen Wohl

• LAST REVIEWED: 26 November 2019
• LAST MODIFIED: 26 November 2019
• DOI: 10.1093/obo/9780199363445-0001

Introduction

Historical range of variability (HRV) describes the conditions of a natural system prior to intensive human alteration of that system. In this context, a natural system can be an ecosystem or a particular component of an ecosystem. Ecosystem components can be quite diverse, including the population of a species or geographic range of a species; an aspect of the disturbance regime, such as the frequency, severity, and spatial extent of wildfire or drought; or physicochemical parameters, such as water chemistry. Regardless of the component to which HRV is applied, the intent is to understand the range of variations in relevant parameters in the absence of human influence on the system. With respect to environmental science, deviations from HRV are taken as evidence of human influence on the system under consideration, and resource management is designed to maintain systems within HRV or within a socially preferred range based on HRV. The concept of HRV was initially developed by ecologists working in North America, and it was applied to understanding ecosystem characteristics prior to European settlement of a region. Although HRV was first mentioned in the early to mid-1990s, the idea of using historical conditions as a reference for ecosystem management goes back much further. HRV built on this earlier work by explicitly considering spatial and temporal variability of system components and processes. Systems exhibit variability through time because conditions change in response to disturbances. The concepts of Disturbance Regime and HRV are thus closely coupled. The assumption underlying HRV is that a system exhibits characteristic behavior and complexity when disturbances occur with a characteristic behavior through time. If human activities alter the disturbance regime, the system changes so as to exceed the bounds described by HRV. HRV is now used by scholars in diverse disciplines, and it is sometimes defined for very different time periods. HRV has been used, for example, to refer to variability during the recent past and intensive human alteration of the system. Consequently, it is important to understand the manner in which HRV is being defined in any particular study. HRV is also referred to as range of natural variability and reference variability. Regardless of the phrase used, the underlying concept represents some of the most fundamental questions we can ask in environmental science: What is the natural range of variability in a system, and in what manner have human activities altered this range?

General Overviews

The works in this section provide overviews and introductions to the concept of historical range of variability. Cissel, et al. 1994 and Morgan, et al. 1994 are two of the earliest papers to explicitly describe HRV; many earlier papers describe the ideas underpinning the approach, but they use slightly different terminology. Within five years, the existing literature on HRV had expanded sufficiently to allow Aplet and Keeton 1999 and Landres, et al. 1999 to describe more published examples of using HRV in ecosystem management, as well as citing many more published studies. Veblen 2003 provides a more recent summary of HRV in the context of managing forested ecosystems, largely based on knowledge of past disturbance regimes and forest age structure as reconstructed from tree-ring records. The use of tree rings to understand fire regimes and forest structure remains the single most commonly applied use of HRV in environmental management, as evidenced in Keane, et al. 2009. Keane and colleagues give increasing attention to some of the limitations in applying HRV in a management context, given the thorough documentation of warming climate, as well as increasingly widespread exotic species invasions and changes in land cover by expanding human populations. Higgs, et al. 2014 reviews the diverse uses of historical knowledge in restoration ecology. Wiens, et al. 2012 provides a thorough review of the history and applications of HRV, as well as some of the challenges in using this concept in a time of rapid climate and ecosystem changes. Potential limitations of applying HRV knowledge to ecosystem management are explored in more detail in the papers cited under Limitations of HRV.

• Aplet, G. H., and W. S. Keeton. 1999. Application of historical range of variability concepts to biodiversity conservation. In Practical approaches to the conservation of biological diversity. Edited by R. K. Baydack, H. Campa, and J. B. Haufler, 71–86. Washington, DC: Island.

  This book chapter concisely and clearly reviews the definition of HRV, the various components of an ecosystem that constitute HRV, applications of HRV in the context of ecosystem management, and the challenges to characterizing HRV.

• Cissel, J. H., F. J. Swanson, W. A. McKee, and A. L. Burditt. 1994. Using the past to plan the future in the Pacific Northwest. Journal of Forestry 92.30–31: 46.

  Brief introduction to the use of HRV in ecosystem management; contrasts HRV-based management and directed ecosystem manipulation using an example from the Pacific Northwest; provides useful examples of diverse components of ecosystem management at different spatial scales.

• Higgs, E., D. A. Falk, A. Guerrini, et al. 2014. The changing role of history in restoration ecology. Frontiers in Ecology and the Environment 12.9: 499–506.

  DOI: 10.1890/110267

  Useful overview of the diverse roles played by historical knowledge in ecological restoration; in particular, historical knowledge can guide scientific interpretation, help to identify important ecological legacies, and influence management choices under changing environmental conditions.

• Keane, R. E., P. F. Hessburg, P. B. Landres, and F. J. Swanson. 2009. The use of historical range and variability (HRV) in landscape management. Forest Ecology and Management 258.7: 1025–1037.

  DOI: 10.1016/j.foreco.2009.05.035

  Effective and thorough overview of past and present uses of HRV for ecosystem management, methods used to quantify HRV, and benefits and limitations of HRV; the authors also speculate on future uses of HRV, given climate warming, exotic species invasions, and increasing land development.

• Landres, P. B., P. Morgan, and F. J. Swanson. 1999. Overview and use of natural variability concepts in managing ecological systems. Ecological Applications 9.4: 1179–1188.

  An invited paper in an issue with several papers on historical range of variability; reviews use of two key concepts in management use of natural variability: that past conditions and processes provide context for contemporary ecosystem management, and that disturbance-driven spatial and temporal variability is a vital ecosystem attribute. Effective summary of conceptual basis for HRV.

• Morgan, P., G. H. Aplet, J. B. Haufler, H. C. Humphries, M. M. Moore, and W. D. Wilson. 1994. Historical range of variability: A useful tool for evaluating ecosystem change. Journal of Sustainable Forestry 2.1–2: 87–111.

  DOI: 10.1300/J091v02n01_04

  A foundational paper that lays out the key concepts (such as importance of spatial and temporal scale), questions, methods, limitations, and usefulness of HRV, especially in the context of forest ecosystems.

• Veblen, T. T. 2003. Historic range of variability of mountain forest ecosystems: Concepts and applications. Forestry Chronicle 79.2: 223–226.

  DOI: 10.5558/tfc79223-2

  The author uses examples of inferring historical disturbance ecology in forest ecosystems of the US Rockies and southern Andes. The examples illustrate the importance of site-specific information for understanding the persistent effect of infrequent but extreme disturbances that continue to shape the landscape and its potential response to future conditions.

• Wiens, J. A., G. D. Hayward, H. D. Safford, and C. M. Giffen, eds. 2012. Historical environmental variation in conservation and natural resource management. Chichester, UK: Wiley-Blackwell.

  Reviews the use of historical ecology in the context of management and conservation; thorough treatment that includes chapters on the theoretical and conceptual background of HRV, applications to resource management, specific challenges to using HRV in a time of changing climate, modeling HRV, and multiple case studies.