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Historical Creation of Early Seral Habitat: Fire, Wind, Bugs … Fred Swanson USDA Forest Service Pacific Northwest Research Station
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 large Mount St. Helens Blast zone – planted Mount St. Helens Blast zone - unplanted Mount St. Helens Primary succ. zone Lava flows Patch size Wildfire Clearcuts fast (Yang et al) slow Xeric meadows Mesic meadows Canopy gap small 0 50 100 tropics Persistence of early seral (yrs)
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)
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
Early seral Age Class Distributions in Coastal Oregon Source: various CLAMS analyses (Spies et al. 2007)
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 thoughts Next 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?