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Historical Creation of Early Seral Habitat: Fire, Wind, Bugs …

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1 Historical Creation of Early Seral Habitat: Fire, Wind, Bugs …
Fred Swanson USDA Forest Service Pacific Northwest Research Station

2 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

3 Creating early seral Many disturbance types
Few types commonly create big patches Many processes create fine patterns

4 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

5 Disturbance processes in PNW
Big patch Fire Forest cutting Volcanic – tephra vs. lava flows Small patch Landslides – fast Landslides – slow Wind Bugs Root rot

6 Non-forest openings Wildfire Patch size
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 50 100 Persistence of early seral (yrs) tropics


8 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)

9 Big, homogeneous disturbance – fine-scale complexity


11 Stand-Replacing Disturbance

12 Stand-Replacing Disturbance
Fires Harvests

13 Stand-Replacing Disturbance in Western Washington, 1972-2004
Fires Harvests Volcanic eruption

14 Age Class Distributions in Coastal Oregon
Early seral Relative to HRV in the coast range, we have no shortage of early-seral forest in current landscape. Slide compares age-class distributions in current landscape (‘initial’, 1996) with HRV (300 years pre-Euro-settlement) and 100 years from now (CLAMS simulation – ignore for now). ~30% of current forest is early seral, vs. 3-12% historically. Source: various CLAMS analyses (Spies et al. 2007)

15 What we don’t know Character of pre-management early seral habitat
Character of current plantations we might call early seral

16 “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?

17 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?

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