Transcript Document

Pacific Northwest Forests
Under a Changing Climate:
Climate, ecosystem impacts, and adaptation
Jeremy S. Littell
CSES Climate Impacts Group
University of Washington
Four main climate impacts on forests will change
the nature of vegetation and habitat:
• Changes in tree growth, productivity, and carbon uptake
• Changes in species biogeography and forest composition
• Changes in disturbance rate, severity (fire, insects,
pathogens)
• Changes in forest hydrology and ecohydrology
Water balance and forest impacts
• Water balance deficit
is
the difference between
atmospheric demand for water and
the water available to satisfy that
demand
• As deficit increases, tree growth
and regeneration typically become
more limited
• Different tree species have
different tolerances
• Fuel moisture declines
As temperature increases, potential
evapotranspiration increases nonlinearly if precipitation does not
change.
McCabe and Wolock 2002.
Linda Brubaker, Chris Earle (UW)
Four main climate impacts on forests:
Changes in tree growth,
productivity, and carbon uptake
High elevation / northern mountain hemlock
Photo: J. Littell
Low elevation / southern mountain hemlock
Photo: C. Webber
Interior ponderosa pine
Photo: C. Woodhouse
Climatic change and tree growth responses
Winter limited forests: longer, warmer growing seasons, shorter snowpack duration = growth increase
Mid elevation forests: warmer summers, lower snow pack = growth depends on precipitation change
Water limited forests: warmer summers, potentially less summer precipitation = large growth decrease
Olympic and Coast
Range Forests
(Maritime Climate)
Sea level
Cascades Forests
Eastern Cascades Forests
Basin and Range Forests
(Continental Climate)
Snow / winter temp
limited forests
9000-11000 ft
Mixed limiting factors
Water limited forests
Can forests be managed to
sequester more carbon?
• Longer rotations would be required
to realize benefits
Storage: <100 Mg/ha Uptake: ~5-10
• Managing fire in forests
(suppression, fuel management) may conflict with restoration /
resilience goals for fire-adapted
forests
• Potential market for carbon credits,
but accountability is problematic
and ecological and economic risks
non-zero (disturbance)
Storage: >600 Mg/ha Uptake: ~1
• Sequestration at best is a fraction
(10-30%?) of emissions
A1B
B1
CSIRO_MK3
HADCM3 MIROC3_MEDRES
A2
percent
Percent Change in Vegetation Carbon
2070-2099 vs. 1961-1990.
Neilson et al.
Carbon storage and sequestration in NW temperate
Forests
• Sometimes decades are required for net ecosystem productivity to
recoup losses from respiration.
• Real gains in carbon storage become apparent > 70yr.
Data: Pregitzer and Euskirchen, 2004
October 22, 2008
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Four main climate impacts on forests:
Changes in species biogeography
and forest composition
Forest communities are dynamic: species
dissociate and re-asemble through time
Cedar
Douglas-fir
Alder
Pines
Historical
Dynamic global vegetation models:
Neilson, et al.
A2 (warmer)
A1B (moderate)
CSIRO_MK3
HADCM3
MIROC3_MEDRES
ecophysiology,carbon, climate, and disturbance
December 1, 2008
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B1 (cooler)
Stephenson, 1990
December 1, 2008
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Stephenson, 1990
?
?
HP
GR
EC
BR
BT
Biterroot LALY 3 mm pith = 1977
TN
WR
SM
ZR
Projected suitability changes: lodgepole pine
Data: Rehfeldt et al.
Projected suitability changes: lodgepole pine
Data: Rehfeldt et al.
Climate is not the only limiting factor
Four main climate impacts on forests:
Changes in disturbance rate, severity
(fire, insects, pathogens)
Area burned in 11 Western states, 19162007*
Littell and Westerling,
Warm
PDOin prep
Period of postsettlement fire
Cool
PDO
Period of active fire suppression
and fuel accumulation
Warm PDO
Period of fire
increase
After Mote 1999
Is PDO really
fire “climate?”
• Mechanism relating
PDO to fire in the
PNW less clear
than, e.g., ENSO in
the SW
(interannual)
• Difficult to separate
from fire
suppression without
clear climatic
mechanism
Fire Area Burned and Summer Hydroclimate:
A Non-linear Relationship in the 20th Century
WA, OR, ID, and MT
NIFC
Cool,
WET
Warm,
DRY
Ecosystem vegetation influences fire-climate
relationships
• Fuels drying in
northern/mountain ecosystems
(forests):
– Climate relationships largely year of
fire, primarily growing season water
deficit
– Secondarily, similar relationships in
year prior
• Vegetation facilitation in arid
ecosystem (woodlands,
shrublands, grasslands):
– Climate relationships largely year
prior to fire, primarily cool, wet winters
– Secondarily, dry growing season year
of fire
Littell, McKenzie, Peterson, and Westerling. In press, Ecological Applications.
Projections of future PNW area burned
• Historical average:
425,000 acres
– 2020s: 0.8 million
– 2040s: 1.4 million
– 2080s: 1.8 million
• Probability of a year
>> 2 million acres:
–
–
–
–
Historical: 5%
2020s: 5% (1 in 20)
2040s: 17% (~1 in 6)
2080s: 47% (~1 in 2)
Best model (tie): summer precip + summer temp
OR summer water balance deficit
Littell et al. 2009, in review
A1B
B1
CSIRO_MK3
HADCM3 MIROC3_MEDRES
A2
percent
Percent Change Biomass consumed by Fire
2051-2100 vs. 1951-2000.
Neilson et al.
Insects: Mountain Pine
Beetle (and others)
• Two ways climate affects forest
vulnerability:
– Insects’ life cycle:
Mountain pine beetle mortality in whitebark pine, Yellowstone.
Jane Pargiter, 2007.
• failure of cold temperatures
decrease winter mortality
• Increased temperature
decreases generation time
– Trees’ resistance:
• Increased summer temperature
and decreased precipitation
decrease resistance
• Some insects more closely tied
to climate than others:
– Mountain pine beetle
– Western spruce budworm
Kawuneeche Valley Mountain Pine Beetle Kill at Farview Curve by
Fort Photo / © All rights reserved
December 1, 2008
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Projected suitability changes: lodgepole pine
Data: Rehfeldt et al.
Blister rust, Foxtail pine
Photo: Deems Burton
Disease
• Changes in climate affect:
– Tree susceptibility
– Pathogen ranges
– Pathogen survivorship
• Likely that increased
stress in many tree
species will increase
infection rate and mortality
Zirkel Wilderness, CO
Agnes Creek, Glacier Peak Wilderness, North Cascades, WA
Planning for climatic change in PNW
forests
Some vegetation research needs
• Genetic variability and climatic
tolerance within species and across
biogeographical ranges
• CO2, water use efficiency, and
ecological consequences at local
scales
• Prediction of future assemblages in real
world conditions (not potential
vegetation, not probability of species
occurrence, but with disturbance and
competition)
• Improved understanding of direct
climate limitations on seedling
establishment, esp. after disturbance
• Process-based disturbance forecasting
in ecosystems where disturbance is
currently rare
Uncertainty, science, and adaptation in forests
• Uncertainty about impacts of climate change on
forests is not the only barrier to adaptation, nor is it
necessarily the biggest….
• Once we have a handle on the basic climatic
mechanisms and what the future likely holds, it’s time
to look at other barriers while the science proceeds/
• Barriers to adaptation include scientific uncertainty,
but are comparable now to institutional barriers at
multiple levels:
–
–
–
–
–
Will to change agency mandate and flexibility
Leadership and coordination in forest management agencies
Legal (ESA, NEPA, NWFP)
Public mistrust of agency intent
Resource limitations (money, personnel)
Some concluding thoughts
•
Planning around vegetation types and
communities will be forced by nature to
become more dynamic as assemblages
erode and accrete.
•
Monitoring tree growth, establishment,
and mortality together provide the clues
to the nature of climate impacts as they
happen.
•
Extreme events - novel disturbances, or
combinations of disturbances, will
accelerate species turnover, landscape
evolution.
•
Science to support future decisions in
the wake of big disturbances therefore
needs to accelerate too…
Thanks!
Questions?
[email protected]
More information on Columbia
basin and PNW climate
impacts and planning for
climate change is available
from::
www.cses.washington.edu/cig