Overview of Historical Range of VariabilityOverview of Historical Range of Variability

• How HRV is determined

• How HRV is used in management, especially in restoration

• Limitations

• 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 • “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

• "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

Developed By ManagersDeveloped 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

• 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

Ponderosa pine restoration examplePonderosa pine restoration example

Landscape PlanningLandscape Planning

Terminology is ConfusingTerminology is Confusing

• Related terms– Historical range of variability – Natural variability– Natural range of variation

• What do these terms have in common?

• Related terms– Historical range of variability – Natural variability– Natural range of variation

• What do these terms have in common?

Natural variabilityNatural 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

• “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

5200%

5400%

5600%

5800%

6000%

6200%

6400%

6600%

1 51 101 151 201 251 301 351 401 451 501 551 601

Time (years)

Perc

en

t o

f to

tal are

aHRV in areal extent of open old ponderosa pine forests in the Idaho Batholith

Morgan et al. 1998 Unpublished data

Premises

Premises for NV in managementPremises 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

• 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

HRV and Desired Future

Conditions

Natural Variability

Current

Range of Desired Future

Conditions Bowl, ball and plate demonstration video available on Web Site

Extreme events and desired future conditionsExtreme events and desired future conditions

• “Management variability”• Maintaining variability of disturbances within

tolerable limits

• “Management variability”• Maintaining variability of disturbances within

tolerable limits

Delineate landscape

DevelopEcosystemDiversity

Matrix

Quantifyexisting

conditions

Describe Historical

DisturbanceRegimes

Coarse FilterAdequateEcological

Representation

Check withspecies

assessments

Identify socialand economic

concerns

Determinedesired future

conditions

Implementrequiredactions

Monitor,evaluate, and adjust

Haufler et al. 1996

HRV is only part of the decision-making

process

Sources of data

Sources of data 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

• 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

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

Photograph by T.W. Swetnam

Dated fire scars in tree ringsDated fire scars in tree rings

• 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

• 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

Charcoal and pollen in lake sediments and bogs

Comparing historical and current aerial photographsComparing historical and current aerial photographs

Simulation models

HRV varies with scaleHRV varies with scale

Limitations/challengesLimitations/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

• 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

Utility

Natural variability is useful for...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

• Evaluating and assessing change

• Establishing goals for ecological restoration

• Determining desired future conditions

• Setting priorities for action

• Understanding and illustrating change

NV is less useful when 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

• Focus is on an individual species

• Historical patterns and processes are socially unacceptable

• Risk and uncertainty are high

• Biophysical conditions have changed greatly

Historical information has been used to guide managementHistorical 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)

• 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)

Utility depends on...Utility depends on...

• Social and ecological context

• Issues

• Knowledge and understanding

• Social and ecological context

• Issues

• Knowledge and understanding

Study questionsStudy 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.

• 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.

References

For further readingFor further reading

• Look at the HRV.PDF reference file available on the main Lesson 3 page

• Look at the HRV.PDF reference file available on the main Lesson 3 page