View
263
Download
0
Tags:
Embed Size (px)
DESCRIPTION
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.
Citation preview
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 Environment
Climate Science in the Public Interest High Five II Missoula, MT 27 Jun 2010
Treeline
• Ecotone where forest shifts to some 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:
– Temperature: min. / max. / annual
– Growing season length: GDD / snow free
– Soil moisture
• Limiting mechanisms
– Physical --> life history
– Physical --> carbon fixation
– Physical --> carbon storage
– Physical --> carbon utilization
– Biotic: competition / facilitation
Photo: Andrea Lloyd
Absaroka-Beartooth wilderness, MT
Boulder Valley, SW MT
What is the role of climate in seedling
establishment 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
Establishment is a
Demographic Bottleneck
• In many years, there are
many germinants, but in most
years most germinants die.
• In the first few years, there is
very high mortality.
• Successful establishment – is
increasingly confined to
favorable microsites with time
Survivorship for three treeline species,
Tetons, Beartooths, and Snowy Range.
Maher & Germino, 2006.
Larix lyallii
What is a favorable
microsite?
Range of sky exposures occupied by emergent (top panel)
or older (seedlings and juveniles; bottom panel) individuals of
subalpine fir, Engelmann spruce, and whitebark pine in the Teton,
Beartooth and Medicine Bow Mountains. Maher & Germino, 2006.
Sky Exposure
• Affects radiative cooling at
night and thus probability
of frost in microsites
• Affects daytime radiation
• Photoinhibition
•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 temperature
TN
SN
Littell, Germino,Pederson, Graumlich in prep
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)
n ~ 2000 dates, including
~ 400 established trees
53
16
15
8
11
5 4
2
Herb
None
Grass
Sedge
Rock
Conifersapling
Tree
Wood
Successful establishment appears episodic within
sites, sometimes synchronous across sites E
sta
blis
hm
ent
Count
Site climatologies
• Daily / hourly hobo
observations
• Monthly lapse with
valley stations
• Extrapolate for
period of record:
– Tmax, Tmin
– Degree days
– Snowpack
duration
Establishment, climate, and…what
else…? • Years of high establishment
qualitatively relate to
favorable climate…but many
ways to fail
• AND – most establishment
still within 10m – 40m of
existing treeline
• Hydrologic
model (VIC)
to calculate
SWE (but at
6km averaged
over site)
• Anomalies are
good, but
mean is
probably cold.
• Trends
evident
Role of extreme events