Fred Swanson - Historical Creation of Early Seral Habitat: Fire, Wind, Bugs

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?