Overview of Historical Range of Variability
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Transcript of Overview of Historical Range of Variability
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