Dave Peterson (1), Dan Fagre (2), Don McKenzie (1), Craig Allen (3), Jill Baron (3), Phillip J. van Mantgem (4), and Nate Stephenson (4)
(1) USDA Forest Service, Pacific Northwest Research Station, (2) US Geological Survey, Northern Rocky Mountain Science Center, (3) US Geological Survey, Fort Collins Science Center, (4) US Geological Survey, California Science Center
Central Rocky Mountains
Central Rocky Mountains
This region exhibits major effects of climatically induced stress, with extensive mortality in forest ecosystems
This region
exhibits major
effects
of climatically
stress,
withelevation
extensiveand
mortality
in forest
ecosystems
subjected
to prolonged
drought.
Dieback
is most induced
prominent
in lower
drier conifer
forests,
with mortality
subjected
to
prolonged
drought.
Dieback
is
most
prominent
in
lower
elevation
and
drier
conifer
forests,
with mortality
caused directly by insufficient soil moisture in combination with beetle outbreaks. Fuel accumulations throughout
caused directly
by insufficient
soil moisture
in combination
beetlewhich
outbreaks.
Fuel
accumulations
throughout
Southwestern
mountains
have created
the potential
for largewith
wildfires,
are also
linked
to ENSO cycles
(less
Southwestern
mountains
have
created
the
potential
for
large
wildfires,
which
are
also
linked
to
ENSO
cycles
(less
fires during wet El Niño, more fires during dry La Niña). Southwestern forests may be exhibiting some of the first
fires of
during
wet El of
Niño,
morechange
fires during
La Niña).
Southwestern
may whether
be exhibiting
some
of the
first
signs
the effects
climatic
in ariddry
Western
forests.
It remainsforests
to be seen
conifer
forests
with
signs of the
effects
climatic change
arid Western
forests.and
It remains
to be seen whether conifer forests with
extensive
dieback
willofregenerate
or willinconvert
to woodlands
shrublands.
extensive dieback will regenerate or will convert to woodlands and shrublands.
To date, climatic variability has had minimal effects on forests of this region, although some data suggest
To upright
date, climatic
has had
on forests
of this region,
although
somenitrogen
data suggest
that
growthvariability
of krummholz
treesminimal
may beeffects
increasing
near altitudinal
treeline.
Elevated
that upright
growth
of krummholz
may be
increasing
nearand
altitudinal
treeline.
nitrogen
deposition
at high
altitude
is alreadytrees
affecting
aquatic
systems,
may also
have a Elevated
subtle, but
long-term
deposition
at
high
altitude
is
already
affecting
aquatic
systems,
and
may
also
have
a
subtle,
but
long-term
effect on subalpine forests. Increased foliar and soil N, as well as increased microbial mineralization
have
effect
on
subalpine
forests.
Increased
foliar
and
soil
N,
as
well
as
increased
microbial
mineralization
have
been documented in high nitrogen deposition areas. Like forests throughout the West, fire exclusion has
been documented
in high
deposition
areas.
Like mixed
forestsconifer
throughout
the West, fire exclusion has
increased
stand density
andnitrogen
fuel loading
in lower
elevation
forests.
increased stand density and fuel loading in lower elevation mixed conifer forests.
Four sites in CO and WY that show increasing N concentrations and
deposition over time. Data are from the NADP program.
Forest ecosystems that are most vulnerable to prolonged drought are in arid and semiarid regions, with
Forest ecosystems that are most vulnerable to prolonged drought are in arid and semiarid regions, with
well documented dieback and stress in some Southwestern forests. In fact, insect outbreaks, elevated
well documented dieback and stress in some Southwestern forests. In fact, insect outbreaks, elevated
fuel loadings, and the potential for crown fire are common throughout the intermountain West. Not all
fuel loadings, and the potential for crown fire are common throughout the intermountain West. Not all
the news is “bad”, however. Many subalpine forests near treeline appear to be regenerating more
the news is “bad”, however. Many subalpine forests near treeline appear to be regenerating more
rapidly and growing faster in recent decades.
rapidly and growing faster in recent decades.
W et N C oncentrations
02
20
00
20
98
19
96
19
94
19
92
19
90
19
88
19
86
19
84
19
82
80
Loch Vale
Beaver Meadows
Niwot Saddle
Snowy Range
Buffalo Pass
Summaries presented here represent a range of climatic effects on forests, from most (Southwest) to
Summaries presented here represent a range of climatic effects on forests, from most (Southwest) to
least (Central Rockies) evidence of recent change.
least (Central Rockies) evidence of recent change.
19
Slope = 0.01 mg N/yr
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
19
We can estimate with some confidence how large portions of forested mountain ecosystems in the
We can estimate with some confidence how large portions of forested mountain ecosystems in the
western US will respond to a continued trend in temperature increase. The Western Mountain Initiative
western US will respond to a continued trend in temperature increase. The Western Mountain Initiative
(WMI) network has used retrospective and contemporary studies to quantify how climatic variability can
(WMI) network has used retrospective and contemporary studies to quantify how climatic variability can
increase (decrease) stress in forest ecosystems, thereby exacerbating (ameliorating) susceptibility to
increase (decrease) stress in forest ecosystems, thereby exacerbating (ameliorating) susceptibility to
subsequent stress. Data encompass a wide range of temporal scales (annual to millennial) for
subsequent stress. Data encompass a wide range of temporal scales (annual to millennial) for
mountain-dominated national parks and protected areas throughout the West.
mountain-dominated national parks and protected areas throughout the West.
American Southwest
American Southwest
mg N/L
Climate and stress in Western forests
Climate and stress in Western forests
W et N d epo sitio n
6.0
Slope1 = 0.11 kg N/ha/yr
Slope2 = 0.04 kg N/ha/yr
kg N/ha
5.0
4.0
3.0
2.0
1.0
02
20
00
20
98
19
96
19
94
19
92
19
90
19
88
19
86
19
84
19
82
19
19
80
0.0
Sierra Nevada
Sierra Nevada
Northern Rocky Mountains
Northern Rocky Mountains
Pacific Northwest
Pacific Northwest
Mixed conifer forests in the Sierra Nevada have also experienced drought stress in recent years, with
Mixed conifer
forests in
in some
the Sierra
Nevada
alsoare
experienced
stress
recent
with
considerable
mortality
areas.
Thesehave
forests
particularlydrought
susceptible
to in
large
firesyears,
because
in fire
some
areas. on
These
forests
areand
particularly
susceptibleAlso,
to large
fires because
ofconsiderable
the additionalmortality
effects of
exclusion
stand
density
fuel accumulation.
elevated
of the additional
of fire
exclusion
on stand
density
fuel accumulation.
Also,pine.
elevated
tropospheric
ozoneeffects
reduces
vigor
and increases
litterfall
in and
ponderosa
pine and Jeffrey
Finally,
tropospheric
ozone
reduces
vigor
and
increases
litterfall
in
ponderosa
pine
and
Jeffrey
pine.
Finally,
the exotic white pine blister rust has caused mortality of sugar pine and increased canopy and surface
the exotic
white pine blister
rust hasthat
caused
mortality
of sugar
pine and
increased
and surface
fuels.
Paleoecological
data suggest
a warmer
climate
may cause
treeline
to risecanopy
significantly
at
fuels.
Paleoecological
data
suggest
that
a
warmer
climate
may
cause
treeline
to
rise
significantly
at
some locations.
some locations.
Similar to the Pacific Northwest, this region also is experiencing rapid establishment of
Similar toforests
the Pacific
Northwest,
this region
also is experiencing
establishment
of
subalpine
in meadows.
Although
the location
of altitudinal rapid
treeline
has not changed
in
subalpine
forests
in
meadows.
Although
the
location
of
altitudinal
treeline
has
not
changed
response to climate, there is currently a trend of more upright growth of trees from previous in
response to
climate,form.
there is
currently
a trendand
of more
upright
growth
of trees
fromstrongly
previous
krummholz
(shrubby)
Tree
regeneration
growth
in this
location
are also
krummholz
(shrubby)
form.
Treeand
regeneration
andbeing
growth
in during
this location
also of
strongly
affected
by the
PDO, with
growth
regeneration
high
warm are
phases
PDOs
affected
by
the
PDO,
with
growth
and
regeneration
being
high
during
warm
phases
of
PDOs
(less snow) and low during cool phases (more snow). Crown fire has spread through a large
(less snow)
and
low during
coolduring
phasesthe
(more
portion
of lower
elevation
forests
past snow).
decade.Crown fire has spread through a large
portion of lower elevation forests during the past decade.
Current evidence of stress mostly exists on the east side of the Cascade Range, where large areas of
Currentforests
evidence
of stressby
mostly
exists pine
on the
eastexperienced
side of the Cascade
Range, where
areas
of
semiarid
dominated
ponderosa
have
beetle outbreaks.
Theselarge
forests
have
semiarid
forests dominated
by ponderosa
pine
have
outbreaks.
forests
have
high
stem density
and low vigor,
predisposing
them
to experienced
the effects ofbeetle
drought
on insectsThese
and large
crown
high Increased
stem density
and low vigor,
predisposing
the effects
on insects and
fires.
temperature
and periods
of lowthem
snowtohave
resultedofindrought
rapid establishment
oflarge
tree crown
fires. Increased
periods forests,
of low snow
have
resulted inisrapid
establishment
of tree of snow
seedlings
at highertemperature
elevations inand
subalpine
where
regeneration
mostly
limited by duration
seedlings
at higher
elevations
in result
subalpine
forests,
where
regeneration
is in
mostly
by duration
of snow
pack.
Periods
of lower
snow also
in faster
growth
of subalpine
trees
all butlimited
the driest
locations.
pack.
Periods of and
lower
snoware
alsostrongly
result inaffected
faster growth
subalpine
trees in
allregeneration,
but the driestespecially
locations. at
Tree
regeneration
growth
by the of
PDO,
with growth
and
Tree
regeneration
and growth
affected
by the
especially
the
highest,
coldest sites,
being are
highstrongly
during warm
phases
ofPDO,
PDO with
(lessgrowth
snow) and
and regeneration,
low during cool
phases at
the highest,
(more
snow). coldest sites, being high during warm phases of PDO (less snow) and low during cool phases
(more snow).
The majestic sugar pine (Pinus lambertiana) is declining in the Sierra
The majestic
sugar
(Pinus lambertiana)
decliningincreased
in the Sierra
Nevada,
probably
duepine
to combined
effects of airispollution,
Nevada,
probably
due
to combined
effects
of an
air introduced
pollution, increased
forest
density
resulting
from
fire exclusion,
and
pathogen
forest
density
resulting
fromgraph
fire exclusion,
and an decline
introduced
pathogen
(white
pine
blister
rust). The
shows observed
in the
(white pine
blister
The graph
shows
observed
decline
in the
Suwanee
Creek
arearust).
of Sequoia
National
Park,
with future
decline
Suwanee
Creek
area of
Sequoia
National
Park, with
future
projected
using
a matrix
model
based
on observed
growth
anddecline
projected using
demographic
rates.a matrix model based on observed growth and
demographic rates.
Summary – Forests in a Greenhouse World
Summary – Forests in a Greenhouse World
The most important effects of future increases in temperature will be:
The most important effects of future increases in temperature will be:
Altered and accelerated disturbance regimes, especially fire and insects
Altered and accelerated disturbance regimes, especially fire and insects
Changes in growth and productivity
Changes in growth and productivity
Changes in distribution and abundance of dominant species
Changes in distribution and abundance of dominant species
Even a small increase in temperature will increase area burned by wildfire throughout Western mountains. Forests whose fire cycle has been disrupted by fire
Even a small increase in temperature will increase area burned by wildfire throughout Western mountains. Forests whose fire cycle has been disrupted by fire
exclusion may burn more intensely or frequently, or both, swamping more subtle changes in growth and regeneration. Fire and all other ecological factors will
exclusion may burn more intensely or frequently, or both, swamping more subtle changes in growth and regeneration. Fire and all other ecological factors will
continue to be modulated by various modes of climatic variability, such as the PDO.
continue to be modulated by various modes of climatic variability, such as the PDO.
Effects of significant changes in the amount and seasonality of precipitation would be greater than that of temperature increase alone, because most Western
Effects of significant changes in the amount and seasonality of precipitation would be greater than that of temperature increase alone, because most Western
forests are limited by water – too little in arid locations, too much in high-snow locations. It is also possible that exotic species and multiple stressors (e.g.,
forests are limited by water – too little in arid locations, too much in high-snow locations. It is also possible that exotic species and multiple stressors (e.g.,
drought + insects + fire) will cause rapid and irreversible change in some forests. The effects of elevated CO2 and N on ecosystem productivity are “wild cards”
drought + insects + fire) will cause rapid and irreversible change in some forests. The effects of elevated CO2 and N on ecosystem productivity are “wild cards”
due to lack of empirical data on mature forests.
due to lack of empirical data on mature forests.
www.cfr.washington.edu/research.fme/wmi/
www.cfr.washington.edu/research.fme/wmi/