Early Seral Ecosystem Creation And Dynamics


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Early Seral Ecosystem Creation And Dynamics

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Early Seral Ecosystem Creation And Dynamics

  1. 1. Early Seral Ecosystem Creation and Dynamics Thomas Spies PNW Research Station
  2. 2. Topics <ul><li>What is early seral? </li></ul><ul><li>Disturbance effects </li></ul><ul><li>Successional pathways </li></ul><ul><li>Regional patterns and trends </li></ul>
  3. 4. His ES High Severity Fire Mixed-Severity Fire
  4. 5. A Definition <ul><li>An stage in forest succession that is the immediate product of a disturbance that removes most of the canopy cover </li></ul><ul><ul><li>Less than 20% canopy cover remaining </li></ul></ul><ul><ul><li>Large enough patch for light-demanding vegetation to establish </li></ul></ul><ul><ul><li>Contains biological legacies from previous forest </li></ul></ul><ul><ul><li>Short lived, depending site productivity </li></ul></ul>
  5. 6. Components of Early Seral <ul><li>Loss of tree canopy </li></ul><ul><li>And reduction or loss one or more of following: </li></ul><ul><ul><li>Standing trees </li></ul></ul><ul><ul><li>Understory vegetation </li></ul></ul><ul><ul><li>Forest floor litter </li></ul></ul><ul><ul><li>Large woody debris </li></ul></ul><ul><ul><li>Soil organic matter </li></ul></ul><ul><ul><li>Tree roots </li></ul></ul>
  6. 7. Disturbances that create early seral ecosystems vary in their effects on ecosystem structure Structural Element Wind Fire Landslide Clear cut/Burn Canopy foliage X X X X Standing Trees X x X X LWD X X/ x Understory vegetation X X X Forest Floor X X X OM Soil x X x Roots x
  7. 8. 0 20 Low Mod High Tree Canopy Closure (%) Dead and Live Biological Legacies Wildfire Windthrow Landslide Early Seral Based on What Remains Retention Systems
  8. 9. Blowdown, Bull Run Watershed
  9. 10. HOH Fire Tillamook Fire High Severity Wildfire Yacolt Burn
  10. 11. Landslides in Coast Range Photo by Rob Pabst
  11. 12. Long-lived early seral related to land-use history and site conditions
  12. 13. Early Seral on Intensively Managed Forest Land
  13. 14. Gap Disturbances
  14. 15. Gap Height Diameter/Ht Ratio = 1.0 Diameter/Ht Ratio = 0.5 Gap Size Effect Dense Conifer Forests ES plant species begin to appear ES plant species infrequent
  15. 16. Gap diameter/canopy ht ratio Number of Gaps Most natural gaps are too small for early successional conditions
  16. 17. Fire as a gap process in dry, fire-prone forests
  17. 18. Historical dynamics of fire and succession in Ponderosa Pine R. Van Pelt Time Zero 20 yrs 40 yrs 60 yrs 80 yrs Fire Suppression
  18. 19. ES ES ES ESES Successional Pathways ES
  19. 20. ES ES ES
  20. 21. Early seral creation in the Biscuit Fire
  21. 22. Biscuit Fire Crown Damage by Vegetation Cover Class <ul><li>Median crown damage was 74% </li></ul><ul><ul><li>96% for shrub/regen </li></ul></ul><ul><ul><li>88% for hardwoods </li></ul></ul><ul><ul><li>62% small conifers </li></ul></ul><ul><ul><li>53% mixed small and large conifers </li></ul></ul><ul><ul><li>32% large conifers (>20 inches dbh) </li></ul></ul>Thompson and Spies In Press (ES)
  22. 23. Historical Range of Variability Oregon Coast Range % of Landscape Early Seral: 10-25% Old Growth: 35-60% % of Landscape Probability
  23. 24. Wildfire Conversion of Old Forest to Early Successional 1993-2003 Percent Loss of Older Forest on a Decadal Basis By Province Based on Moeur and Spies et al. 2005 3.1 % ( incl BB and DL) 3.6 % 3 % 9.5 % 2.3 % 0.4 % 0 % 0 % 0 % 1.4 % 0 %
  24. 26. Conclusions <ul><li>All ES Share the same element: Loss of tree canopy cover to low levels (e.g. <20%) </li></ul><ul><li>Disturbances produce different kinds of ES vegetation </li></ul><ul><li>A transitory stage that lasts 15 ~ 30 years depending on site productivity and vegetation type </li></ul>
  25. 27. Conclusions <ul><li>Gaps have limited capacity to create ES in wetter forests </li></ul><ul><li>Small disturbance patches are more effective ES in dry forest types than in wetter types </li></ul><ul><li>ES can arise at any stage in succession </li></ul>
  26. 28. Conclusions <ul><li>Rate of ES creation has varied over time </li></ul><ul><li>Amount of diverse ES is declining in wetter forests across all ownerships </li></ul><ul><li>ES created by intensive forest management is not the same as that created by natural disturbances </li></ul>