Historic Range of Variability

Historic Range of Variability

Jen Costanza

Bio 255

October 14, 2005

“The balance of nature does not exist, and perhaps has never existed… the resultant confusion is remarkable”

- Charles Elton, 1930

OutlineOutline

• Background:– Equilibrium concepts vs. change and instability– Historic range of variability

• Summary of Landres et al. 1999 and Tinker et al. 2003– Ecological significance– Methods of assessing HRV– Challenges of spatial and temporal scale– Management applications

• Future work• Discussion

Context: Equilbirium and DisturbanceContext: Equilbirium and Disturbance

• Clements – early 20th Century: disturbance is unnatural and disrupts progression of succession

• Equilibrium views:– Watt 1947: unit pattern – succession manifests itself

in space and time– Bormann and Likens, Whittaker 1950s, 60s, 70s:

constant proportion of the landscape in each successional stage

• Shugart, Turner et al.: disturbance extent small and recovery interval quick = equilibrium

Perry 2002

Landscape DynamicsLandscape Dynamics

Turner et al. 1993

Yellowstone 1988

Pre-1988 Yellowstone

Disturbance can lead to stable landscapes with variability

HRV ConceptsHRV Concepts

• Historic variability of a landscape and its disturbance regime – Qualitative equilibrium

White et al. 2000

Landres et al. 1999Landres et al. 1999

Natural variability:– The ecological conditions, and the spatial and temporal

variation in these conditions, that are relatively unaffected by people, within a period of time and geographical area appropriate to an expressed goal

• The past as a means of understanding and predicting impacts of current management efforts

• A way to balance short-term efforts and long-term goals: temporal and spatial context

• Illustrates the importance of disturbance and temporal change

Using HRV to Guide ManagementUsing HRV to Guide Management

Desired Future Conditions may not correspond to Historic Range of

Variability

ChallengesChallenges

• Appropriate spatial and temporal scale• May be difficult to fully assess range of variation• Reconstructions from further back in time become

difficult• Historic variation may not be relevant under today’s

conditions• It may not always be possible to restore the historic

disturbance regime

Methods to Assess HRVMethods to Assess HRV

• Site-specific measurements, as well as data from similar systems elsewhere

• Kulakowski and Bebi 2004:– Use HRV for the Rockies to help assess likely HRV

for the Swiss Alps

• Wimberly et al. 2000:– Simulation models– With finer spatial extent, more variability

Tinker et al. 2003Tinker et al. 2003

• Use landscape metrics (pattern) as measure• Compare Yellowstone before and after 1988 fires• Also compare Yellowstone to nearby Targhee NF

before and after clearcutting• Spatial scale: Management areas• Temporal scale:

– Yellowstone: past 300 years– Targhee: 1950 and 1991

Mapping Yellowstone NPMapping Yellowstone NP

1985

Historic Maps of Yellowstone NPHistoric Maps of Yellowstone NP

0-19

20-39

40-59

60-79

80-99

1985

Burned Forest

Unburned Forest

Unburned Forest

Unburned Forest

Unburned Forest

Reclassification

1985

Unburned Forest

Unburned Forest

Burned Forest

Unburned Forest

Unburned Forest

Reclassification

1965

350

0-19

20-39

40-59

60-79

1965

330

350

0-19

20-39

40-59

1945

Unburned Forest

Burned Forest

Unburned Forest

Unburned Forest

Unburned Forest

Reclassification

1965

Other MapsOther Maps

•1995 YNP– after large 1988 fire•Targhee National Forest:

–1950s before clearcutting–1991 after clearcutting

Landscape-Scale MetricsLandscape-Scale Metrics

Class-Level MetricsClass-Level Metrics

Tinker et al. 2003 - ConclusionsTinker et al. 2003 - Conclusions

• Large, infrequent disturbances control the landscape structure and dynamics here: 1988 fires expanded the HRV– Temporal extent matters!

• Before clearcutting: Targhee NF was within the HRV for Yellowstone

• After clearcutting: Targhee NF was outside HRV• We are able to say little about how landscape

patterns affect function

Future Work - HRVFuture Work - HRV

• Additional characterization of HRV for more landscapes, at different temporal scales

• Better understanding of how scale affects HRV and the equilibrium of systems – is there any hope of generality here?

• More modeling/scenarios to determine how current efforts will affect future conditions

Questions for DiscussionQuestions for Discussion

• Is HRV a worthwhile concept? • Is HRV an appropriate management tool everywhere?• Is there any hope in developing guidelines for spatial and

temporal extent of HRV, besides whatever scale is “appropriate”?

• Is Yellowstone NP at equilibrium over the time period studied? Might the 1988 fires lead to a directional shift in landscape pattern?

• Why were many of the class-level metrics for the Targhee within the HRV for Yellowstone?

• Is landscape pattern the best metric to use in assessing HRV? Would managers want to restore the pattern or the process?

• How could we assess HRV for local landscapes in the Southeast?

• How could HRV be useful in studying climate ch. impacts?