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Overview of Historical Range of Variability

Overview of Historical Range of Variability. How HRV is determined How HRV is used in management, especially in restoration Limitations. "Ecosystems are not defined so much by the objects they contain as by the processes that regulate them" -- Christensen et al. 1989

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Overview of Historical Range of Variability

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  1. Overview of Historical Range of Variability • How HRV is determined • How HRV is used in management, especially in restoration • Limitations

  2. "Ecosystems are not defined so much by the objects they contain as by the processes that regulate them" -- Christensen et al. 1989 • “Human-generated changes must be constrained because nature has functional, historical and evolutionary limits. Nature has a range of ways to be, but there is a limit to those ways, and therefore, human changes must be within those limits.” -- Christensen et al. 1996 • “Management should strive to retain critical types and ranges of natural variation in resource systems to maintain their resiliency.” -- Holling and Meffe 1996

  3. Developed By Managers • Searching for a legally defensible approach to conservation of biological diversity • Premised on current ecological understanding • Now central to sustainability, ecological integrity, and ecological restoration • Now included in USFS planning regulations

  4. Ponderosa pine restoration example

  5. Landscape Planning

  6. Terminology is Confusing • Related terms • Historical range of variability • Natural variability • Natural range of variation • What do these terms have in common?

  7. Natural variability • “The ecological conditions and their variability over space and time relatively unaffected by people…within a period of time and geographical area appropriate to an expressed goal.” • Related terms: historical range of variability, reference variability -- Landres et al. 1999

  8. HRV in areal extent of open old ponderosa pine forests in the Idaho Batholith Morgan et al. 1998 Unpublished data

  9. Premises

  10. Premises for NV in management • Disturbance structures ecosystems • Variability is important • Anthropogenic change decreases viability • Fewer subsidies to systems within bounds • Past is clue to the future • Coarse filter • Reference • Context and guidance Landres et al. 1999

  11. HRV and Desired Future Conditions

  12. Current Natural Variability Range of Desired Future Conditions Bowl, ball and plate demonstration video available on Web Site

  13. Extreme events and desired future conditions • “Management variability” • Maintaining variability of disturbances within tolerable limits

  14. Identify social and economic concerns Quantify existing conditions HRV is only part of the decision-making process Implement required actions Develop Ecosystem Diversity Matrix Determine desired future conditions Delineate landscape Coarse Filter Adequate Ecological Representation Monitor, evaluate, and adjust Describe Historical Disturbance Regimes Check with species assessments Haufler et al. 1996

  15. Sources of data

  16. Sources of data • Natural archives • Tree rings (fire scars, climate, defoliators) • Pollen, macrofossils, and charcoal from bog and lake sediments and pack rat middens • Soil phytoliths • Human archives • Old maps, repeat photographs, journals, long-term and early data • Models and expert opinions

  17. The sources, time frames, and spatial resolution of available data vary greatly

  18. The fire scars in this partial cross-section of ponderosa pine tree have been dated. The fire interval between fires can be determined by counting the annual rings between scars. In fire history studies, this is done for many trees Dated fire scars in tree rings Photograph by T.W. Swetnam

  19. Charcoal and pollen in lake sediments and bogs

  20. Comparing historical and current aerial photographs

  21. Simulation models

  22. HRV varies with scale

  23. Limitations/challenges • Extrapolating from points to landscapes • HRV varies with scale • Integrating space AND time • Long time series for large areas • Models of landscape change • Understanding complex systems • Changing climate

  24. Utility

  25. Natural variability is useful for... • Evaluating and assessing change • Establishing goals for ecological restoration • Determining desired future conditions • Setting priorities for action • Understanding and illustrating change

  26. NV is less useful when • Focus is on an individual species • Historical patterns and processes are socially unacceptable • Risk and uncertainty are high • Biophysical conditions have changed greatly

  27. Historical information has been used to guide management • Colorado River (Poff et al. 1997) • Everglades (Harwell 1997) • Forests in the Midwest (Mladenoff and Pastor 1993), Southwest (Moore et al. 1999), and Northwest (Lesica 1996, Lertzman et al. 1997, Hessburg et al. 1999) • National Forests in Idaho (USDA 2000b)

  28. Utility depends on... • Social and ecological context • Issues • Knowledge and understanding

  29. Study questions • Define the terms used in HRV and NV: historical, natural, range, variability • Why are our estimates of HRV more uncertain the further we go back in time or out into the future? • Give two examples each of natural and human archives that are used to derive HRV estimates • Find a description of a case study where HRV has been either estimated or used in management. Provide a complete reference to the written document or web site.

  30. References

  31. For further reading • Look at the HRV.PDF reference file available on the main Lesson 3 page

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