historical creation of early seral habitat: fire, wind, bugs … fred swanson usda forest service...
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Historical Creation of Early Seral Habitat: Fire, Wind, Bugs …
Fred SwansonFred SwansonUSDA Forest ServiceUSDA Forest Service
Pacific Northwest Research Pacific Northwest Research StationStation
Early seral – definition issues
And we thought we have problems with old growth definitions!
Easy to talk about the archtype
Dimensions for definition:• Precursor system• Temporal - persistence• Spatial – patch size, location in environmental
gradients• Disturbance regime context
Creating early seral• Many disturbance types
• Few types commonly create big patches
• Many processes create fine patterns
Controls on disturbance effects
• Selective of vegetation structure class• Selective of species• Spatial heterogeneity – of disturbance
process, of affected ecosystem• Species dominating post-disturbance• Persistence of effects of disturbance
– biotic legacies, dispersal, soil properties change
Disturbance processes in PNW
Big patch• Fire• Forest cutting • Volcanic – tephra vs. lava flows
Small patch• Landslides – fast• Landslides – slow• Wind• Bugs• Root rot
Non-forest openings
Patchsize
Persistence of early seral (yrs)
0 50 100
small
large Mount St. HelensBlast zone – planted
Canopygap
Mount St. HelensBlast zone - unplanted
Mesic meadowsXeric
meadows
Lavaflows
Mount St. HelensPrimary succ. zone
Clearcutsfast (Yang et al) slow
Wildfire
tropics
Root rot, wind, bugs
• Part of ecosystem disturbed• Species ready to occupy the site
After Phellinus weiri Holah et al. (1997) observed:• Coast Range – shrubs dominate site• Cascades – hemlock dominates site
After Bull Run windthrow – hemlock dominates(Sinton et al 2000)
Big, homogeneous disturbance – fine-scale complexity
1995-2000
1991-1995
1988-1991
1984-1988
1977-1984
2000-2002
Stand-Replacing Disturbance
Fires
1995-2000
1991-1995
1988-1991
1984-1988
1977-1984
2000-2002
1995-2000
1991-1995
1988-1991
1984-1988
1977-1984
1972-1977
2000-2002
Stand-Replacing Disturbance
Fires Harvests
Stand-Replacing Disturbance in Western Washington, 1972-2004
Fires Harvests
1972-1977
1977-1984
1984-1988
1988-1992
1992-1996
1996-2000
2000-2002
2002-2004
Volcanic eruption
Age Class Distributions in Coastal Oregon
Source: various CLAMS analyses (Spies et al. 2007)Early seral
What we don’t know
• Character of pre-management early seral habitat
• Character of current plantations we might call early seral
“Real”, complex early seral – More or less? Probably less!
• Lack of cultural burning• Fire suppression• Reduced federal harvest• Forest encroachment in mesic meadows• Practices to hasten conifer canopy closure• Regime-scale effects – is there cumulative
loss of structural complexity and biotic diversity over multiple cuttings?
But, does harvest do the early seral creation job? Do we have more wildfire?
Closing thoughtsNext steps:• Synthesize existing knowledge of early seral
condition and function• Confer about management options and impediments• Integrate thinking/management across landscapes
and all age classes• Address geographic variation
What are the similarities/differences with development of old-growth science, policy, and management?