Vegetational and Climatic History of the Pacific Northwest

1
Vegetational and Climatic History of the Pacific
Northwest

• Russell Cannady

2
Method of Interest

• Palynology
• The study of pollen grains as an aid to the
  reconstruction of past plant environments.
  Relates to glaciers because the vegetational
  history of an area gives scientists a good idea
  of that areas climate

3
Whitlock

• What is known?
• - Over the last 20,000 years world has gone
  from glaciation to interglaciation.
• Why is the vegetational history significant?
• - Todays biodiversity is the legacy of the
  past
• Purpose of the paper
• - Reconstruct the vegetational and climatic
  history of the Pacific Northwest during the
  late-Quaternary period from 20 ka to the present
  day

4
How is data obtained?

• Sediment coring
• Lakes/ wetlands are the best areas
• The spatial scale of the reconstruction is
  determined by the size of the lake or wetland,
  which in turn defines the pollen-collecting area
  within the surrounding vegetation. Small- to
  medium-sized lakes (150 ha) collect pollen from
  an area of 1001,000 km2 (Jacobson and Bradshaw
  1981). The temporal resolutions of the
  reconstruction are determined by the number and
  stratigraphic spacing of pollen samples collected
  from the sediment cores (Grimm 1988). Pollen
  samples are usually taken at a stratigraphic
  interval that represents one sample for every
  3001,000 years of sediment accumulation.

5
Lets get into the results

• From 20-16ka
• - Colder than present day, 5-7C, and drier
  (about 1m less precipitation/yr known form
  presence of xerophytic taxa which indicate winter
  storms were less frequent and couldnt penetrate
  land)
• - West Olympics had tundra/parkland vegetation
  (Spruce/alder/pine/mountain and western
  hemlock/grass at high elevation)
• - Puget Trough had tundra/subalpine parkland
  vegetation (grass/tundra herbs/spruce)
• Presence of spruce significant because only
  found in mountains in eastern cascades today
• Closest modern day analog is northern Rocky
  Mountains

6
Rockys
7
Other inferrences

• Lower treeline was at higher elevation
• Upper treeline lower
• Both indicate colder climate
• information inferred from relative abundance of
  pollen grains

8
(No Transcript)
9
16-14ka

• Getting warmerbut still 2-6C below present, but
  precipitation more like today (Laurentide
  diminishing)
• Known from temperate communities to the south
• Mesophytic (wet loving) taxa in Puget Trough
  beginning to appear
• Much like subalpine western Cascades of today

10
14-10ka
11
14-10ka

• Olympic Peninsula
• - northeastern part dominated by herbs and
  shrubs
• - Drier conditions and coarse soil (glacial
  outwash) responsible for open vegetation
• - Indicative of deglaciation and warming

• Puget Trough
• Southern Puget Trough did not show signs of
  warming until 11.5ka
• By 10 ka, continued warming allowed temperate
  conifers to expand around Battle Ground Lake, and
  montane species left the region as their range
  was restricted to higher elevations.

12
The Big Picture
13
Wrapping Up

• Advance of Cordilleran ice sheet, and climatic
  factors from Laurentide ice sheet greatly
  effected the vegetation in Washington
• Vegetation responds quickly to climatic change
  (estimated around a 500yr or maybe less response
  time)
• Climate is the ultimate dictator of vegetation
  and the last glaciation is a great example of
  that

14
Sources of Error

• Core at the deepest spot
• Fire frequency/poor fire record
• Good conditions to preserve pollen
• Animal dispersion can interfere with data