Climate and 20th century establishment in alpine treeline ecotones of the western USA [Jeremy Littell]


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Climate and 20th century establishment in alpine treeline ecotones of the western USA. Presented by Jeremy Littell at the "Perth II: Global Change and the World's Mountains" conference in Perth, Scotland in September 2010.

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Climate and 20th century establishment in alpine treeline ecotones of the western USA [Jeremy Littell]

  1. 1. Climate and 20th century establishment in alpine treeline ecotones of the western USA Jeremy Littell1, Greg Pederson2, Matt Germino3, L. J. Graumlich4 1Climate Impacts Group, University of Washington 2USGS Northern Rocky Mountain Science Center; 3Department of Biological Sciences, Idaho State University; 4University of Washington College of the EnvironmentHigh Five II Missoula, MT 27 Jun 2010 Climate Science in the Public Interest
  2. 2. Treeline • Ecotone where forest shifts to some Photo: Andrea Lloyd other vegetation – Boreal treeline / forest to tundra – Alpine treeline / forest to tundra or meadow – Lower treeline / forest to steppe~grassland • Limiting factors often related to climate:Absaroka-Beartooth wilderness, MT – Temperature: min. / max. / annual – Growing season length: GDD / snow free – Soil moisture • Limiting mechanisms – Physical --> life history – Physical --> carbon fixation – Physical --> carbon storageBoulder Valley, SW MT
  3. 3. What is the role of climate in seedlingestablishment in the alpine treeline ecotone?• Climatic correlates of tree germination, seedling survival, growth, mortality: mere hints• Ecophysiologically, the mechanisms related to establishment affected by climate are often more complex• Not stationary in time or place
  4. 4. Establishment is a Demographic Bottleneck • In many years, there are many germinants, but in most years most germinants die.Survivorship for three treeline species,Tetons, Beartooths, and Snowy Range.Maher & Germino, 2006. • In the first few years, there is very high mortality. • Successful establishment – is increasingly confined to favorable microsites with time Larix lyallii
  5. 5. What is a favorable microsite?Range of sky exposures occupied by emergent (top panel)or older (seedlings and juveniles; bottom panel) individuals ofsubalpine fir, Engelmann spruce, and whitebark pine in the Teton,Beartooth and Medicine Bow Mountains. Maher & Germino, 2006.
  6. 6. Sky Exposure• Affects radiative cooling at night and thus probability of frost in microsites• Affects daytime radiation• Photoinhibition
  7. 7. TN SN •Climatic gradient in winter snowpack •9 sites 1950m – 3300m •Seedling census – 6 x 50m transects •Established tree ages (cores) •Seedling and sapling ages (sections) •1 year air and surface temperatureLittell, Germino,Pederson, Graumlich in prep
  8. 8. Site climate• Hobos placed year prior; 1 or 4 hrly – Two air temperature, two surface temperature per site• Gives monthly lapse rate (AT) and also snow pack duration (ST)
  9. 9. Herb 2 None 5 4 Grass 11 Sedge 8 53 Rock 15 Conifer sapling 16 Tree Woodn ~ 2000 dates, including~ 400 established trees
  10. 10. Successful establishment appears episodic within sites, sometimes synchronous across sitesEstablishment Count
  11. 11. Site climatologies • Daily / hourly hobo observations • Monthly lapse with valley stations • Extrapolate for period of record: – Tmax, Tmin – Degree days – Snowpack duration
  12. 12. Establishment, climate, and…what else…?• Years of high establishment • AND – most establishment qualitatively relate to still within 10m – 40m of favorable climate…but many existing treeline ways to fail
  13. 13. • Hydrologic model (VIC) to calculate SWE (but at 6km averaged over site)• Anomalies are good, but mean is probably cold.• Trends evident
  14. 14. Role of extreme events
  15. 15.