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Early Seral Ecosystem Creation And Dynamics
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Early Seral Ecosystem Creation and Dynamics
Thomas SpiesPNW Research Station
Topics• What is early seral?
• Disturbance effects
• Successional pathways
• Regional patterns and trends
His
ES
High Severity Fire
Mixed-Severity Fire
A Definition
• An stage in forest succession that is the immediate product of a disturbance that removes most of the canopy cover– Less than 20% canopy cover remaining
– Large enough patch for light-demanding vegetation to establish
– Contains biological legacies from previous forest
– Short lived, depending site productivity
Components of Early Seral
• Loss of tree canopy • And reduction or loss one
or more of following:– Standing trees
– Understory vegetation
– Forest floor litter
– Large woody debris
– Soil organic matter
– Tree roots
StructuralElement
Wind Fire Landslide Clear cut/Burn
Canopy foliage X X X XStanding Trees X x X XLWD X X/xUnderstoryvegetation X X XForest Floor X X XOM Soil x X xRoots x
Disturbances that create early seral ecosystemsvary in their effects on ecosystem structure
0 20
Low
Mod
High
Tree Canopy Closure (%)
Dea
d an
d L
ive
Bio
logi
cal L
egac
ies
Wildfire
Windthrow
Landslide
Early Seral Based on What Remains
Retention Systems
Blowdown, Bull Run Watershed
HOH Fire
Tillamook Fire
High Severity Wildfire
Yacolt Burn
Landslides in Coast Range
Photo by Rob Pabst
Long-lived early seral related to land-use history and site conditions
Early Seral on Intensively Managed Forest Land
Gap Disturbances
Gap
Height
Diameter/Ht Ratio = 1.0
Diameter/Ht Ratio = 0.5
Gap Size Effect Dense Conifer Forests
ES plant species begin to appearES plant species infrequent
Gap diameter/canopy ht ratio
Num
ber
of G
aps
Most natural gaps are too small for early successional conditions
Fire as a gap process in dry, fire-prone forests
Historical dynamics of fire and succession in Ponderosa Pine
R. Van Pelt
Time Zero
20 yrs
40 yrs
60 yrs
80 yrs
Fire Suppression
ES ES
ES
ESESSuccessional Pathways
ES
ES ES
ES
Early seral creation in the Biscuit Fire
Biscuit Fire Crown Damage byVegetation Cover Class
• Median crown damage was 74%– 96% for shrub/regen– 88% for hardwoods– 62% small conifers– 53% mixed small and large conifers– 32% large conifers (>20 inches dbh)
Thompson and Spies In Press
(ES)
Historical Range of VariabilityOregon Coast Range
% of Landscape
Early Seral: 10-25%
Old Growth: 35-60%
% of Landscape
Pro
babi
lity
3.1 % (incl BB and DL)
3.6 %
3 %9.5 %
2.3 %
0.4 %
0 %
0 %
0 %
Wildfire Conversion of Old Forest to Early Successional1993-2003
Percent Loss of Older Forest on a Decadal Basis By Province
1.4 %
0 %
Based on Moeur and Spies et al. 2005
Conclusions
• All ES Share the same element: Loss of tree canopy cover to low levels (e.g. <20%)
• Disturbances produce different kinds of ES vegetation
• A transitory stage that lasts 15 ~ 30 years depending on site productivity and vegetation type
Conclusions
• Gaps have limited capacity to create ES in wetter forests
• Small disturbance patches are more effective ES in dry forest types than in wetter types
• ES can arise at any stage in succession
Conclusions
• Rate of ES creation has varied over time
• Amount of diverse ES is declining in wetter forests across all ownerships
• ES created by intensive forest management is not the same as that created by natural disturbances