Abstract and Figures

The coastal temperate rainforests of South and North America are part of the most biomass dense forest biome on the planet. They are also subject to rapid climatic shifts and, subsequently, new disturbance processes – snow loss-driven mortality and the emergence of fire in historically non-fire-exposed areas. Here, we compare and contrast Southern and Northern Hemisphere coastal temperate rainforests of the Americas, two of the largest examples of the biome, via synthesis of current literature, future climate expectations and new downscaling of a global fire model. In terms of snow loss, a rapid decline in winter snow is leading to mass mortality of certain conifer species in the Northern Hemisphere rainforests. High-elevation Southern Hemisphere forests, which are beginning to see similar declines in snow, may be vulnerable in the future, especially bogs and high-water content soils. Southern Hemisphere forests are seeing the invasion of fire as an ecological force at mid-to-high latitudes, a shift not yet observed in the north but which may become more prominent with ongoing climate change. We suggest that research should focus on the flammability of seral vegetation and bogs under future climate scenarios in both regions. By comparing these two drivers of change across similar gradients in the Northern and Southern Hemispheres, this work points to the potential for emerging change in unexpected places in both regions. There is a clear benefit to conceptualising the coastal temperate rainforests of the Americas as two examples of the biome which can inform the other, as change is proceeding in similar directions but at different rates in each region.
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Emergent freeze and re disturbance dynamics in
temperate rainforests
Department of Integrative Biology, University of Colorado, Denver, 1151 Arapahoe St., Denver, Colorado
80204, USA (Email: brian.buma@ucdenver.edu);
Universitat Aut
onoma de Barcelona, Cerdanyola del
es, Spain;
Department of Natural Resources & Environmental Science, University of Nevada Reno,
Reno, Nevada;
Department of Geography, Portland State University, Portland, Oregon, USA;
Area Research, BC Ministry of Forests, Lands, Natural Resource Operations, and Rural Development,
Nanaimo, British Columbia, Canada;
Alaska Coastal Rainforest Center, University of Alaska Southeast,
Juneau, Alaska;
Institute for Natural Resources, Oregon State University, Portland;
Geos Institute,
Ashland, Oregon;
Alaska Department of Fish and Game, Wildlife Conservation Division, Douglas;
USDA Forest Service, PNW Research Station;
Juneau Greens, Juneau, Alaska;
Agriculture and
Natural Resources Division, University of California Cooperative Extension; and
Bren School of
Environmental Science & Management, University of California, Santa Barbara, California, USA
Abstract The coastal temperate rainforests of South and North America are part of the most biomass dense for-
est biome on the planet. They are also subject to rapid climatic shifts and, subsequently, new disturbance processes
snow loss-driven mortality and the emergence of re in historically non-re-exposed areas. Here, we compare
and contrast Southern and Northern Hemisphere coastal temperate rainforests of the Americas, two of the largest
examples of the biome, via synthesis of current literature, future climate expectations and new downscaling of a
global re model. In terms of snow loss, a rapid decline in winter snow is leading to mass mortality of certain coni-
fer species in the Northern Hemisphere rainforests. High-elevation Southern Hemisphere forests, which are begin-
ning to see similar declines in snow, may be vulnerable in the future, especially bogs and high-water content soils.
Southern Hemisphere forests are seeing the invasion of re as an ecological force at mid-to-high latitudes, a shift
not yet observed in the north but which may become more prominent with ongoing climate change. We suggest
that research should focus on the ammability of seral vegetation and bogs under future climate scenarios in both
regions. By comparing these two drivers of change across similar gradients in the Northern and Southern Hemi-
spheres, this work points to the potential for emerging change in unexpected places in both regions. There is a clear
benet to conceptualising the coastal temperate rainforests of the Americas as two examples of the biome which
can inform the other, as change is proceeding in similar directions but at different rates in each region.
Abstract in Spanish is available with online material.
Key words: climate change, coastal temperate rainforest, emerging disturbance regimes, re, snow loss.
Climate change is affecting global forests in multiple
ways, often by altering the abiotic conditions forests
experience. Direct effects include increasing water
stress and associated drought-induced tree mortality
(Adams et al. 2009; Holz et al. 2017), CO
tion (Bolker et al. 1995) or lengthening of the grow-
ing season (Cleland et al. 2007), with these effects
leading to altered productivity and/or range shifts
(Krapek & Buma 2018). These changes may be
punctuated, resulting from the crossing of climatic
thresholds that drive major ecological changes related
to species physiological tolerances (e.g. Allen et al.
2010). The existence of environmental thresholds
may also cause shifts in or intensication of distur-
bance regimes (Brooks et al. 2004; Veblen et al.
2011; Buma 2015; Millar & Stephenson 2015),
which can lead to sudden changes in ecosystem type
when disturbance severity or frequency exceeds spe-
cies, community and ecosystem tolerances (Buma &
Wessman 2011). As a result, signicant shifts in eco-
logical relationships such as the establishment of
*Corresponding author.
Accepted for publication February 2019.
© 2019 Ecological Society of Australia doi:10.1111/aec.12751
Austral Ecology (2019) ,
novel functional relationships (Gilman et al. 2010) or
the formation of no-analogue communities (Williams
& Jackson 2007) are widely anticipated.
Precipitation including its phase, amount, intensity
and timing is one such climate factor expected to
potentially drive signicant, threshold-like change. The
phase of precipitation (snow or rain) represents only a
small shift in winter temperatures but results in a very
large change in the physical environment that forests
inhabit. For example, the loss of a winter snowpack
results in decreased soil insulation in winter (Groffman
et al. 2001), loss of nival habitat (Pauli et al. 2013),
altered plant communities (Bannister et al. 2005) and
reduced summer streamows (e.g. Mote 2003), among
other factors. Changes in the amount and timing of
precipitation also have major impacts. Several research-
ers have focused on forest health in relation to precipi-
tation-associated physiological stress (Anderegg et al.
2013), winter high ow/summer low ow events (Sur-
eet & Tullos 2013), and erosion and ooding severity
and timing (Klos et al. 2014).
Fire is also a well-known driver of rapid threshold-
like change. Fire is a major disturbance agent in most
of the worlds forests (Rundel 1981; Scott 2000),
burning ~348 Mha annually (Bowman et al. 2009;
Giglio et al. 2013) and inuencing vegetation (He
et al. 2016), soil (Certini 2014), and a host of other
ecological aspects of forest ecosystems. Fire occur-
rence responds rapidly due to climate or anthro-
pogenic activity (Doerr & Sant
ın 2016). Because of its
near ubiquity, re can be difcult to disentangle from
the baseline functioning of the forest (Pausas & Keeley
2009). When excluded via modelling, it is apparent
that whole biome distributions likely result from the
presence (or absence) of re (Bond et al. 2005). Antic-
ipating changes to re regimes especially the emer-
gence of re in areas where it was not historically
present, or rare enough to not be an evolutionary force
is important for management, conservation and pre-
diction of future ecosystem dynamics and functioning.
Both snow loss and re regime shifts are major con-
cerns to forest managers, conservationists, researchers
and culture bearers in forests worldwide. Here, we illus-
trate how the loss of snow and the emergence of re
may act as important agents of change. We focus on
coastal temperate rainforests, a globally important biome
that holds an immense amount of carbon in relatively
intact forests (Keith et al. 2009), where snow loss is pro-
ceeding faster than anywhere else globally and where the
re regime is expected to intensify or even emerge in
areas where it was previously essentially absent.
The objectives of this review are to (i) synthesise and
describe the signicance of crossing precipitation and
re thresholds to the ecology and functioning of this
globally important forest biome; (ii) discuss the spa-
tial pattern of potential change within the regions;
and (iii) use the analysis of drivers of the new distur-
bances in this ecosystem to anticipate new dynamics
in other temperate rainforest systems. We hope to
draw attention to the benets of considering the
southern and northern coastal temperate rainforest as
two regions which can inform each other via direct
Coastal temperate rainforests (hereafter CTRFs) are
globally important as the most carbon-dense forested
areas on the planet, containing upwards of 1867 tons
(Australian CTRFs, Keith et al. 2009), a
result of generally low rates of decomposition, low
water stress, moderate climate and relatively long
growing seasons. They provide a multitude of ecosys-
tem services, from signicant cultural resources to
wildlife habitat, and function as the headwaters of
globally signicant sheries (Brandt et al. 2014;
Rodriguez-Echeverry et al. 2018). These regions are
also associated with high endemic biodiversity (e.g.
South American forests) in terms of nonvascular
plants and lichens (DellaSala 2011) and relatively
low levels of human development in many places.
Despite occurring across a wide range of latitudes
(~30°north to south), CTRFs have relatively consis-
tent, moderate climate conditions due to their close
proximity to the ocean (Alaback 1991; DellaSala
2011; Fig. 1). The mild, consistent climatic condi-
tions favour evergreen tree species, ne-scale, infre-
quent disturbances and generally older, late-
successional forests over much of the landscape.
Average annual temperatures range between 4 and
12°C, with annual precipitation from as low as 1.5 m
to as high as 5 m or more in some areas (DellaSala
2011). The historic disturbance regime was domi-
nated by relatively frequent tectonic activity, land-
slides, windstorms, ne-scale tree mortality and
infrequent res (Veblen & Alaback 1996; Buma &
Barrett 2015; Holz et al. 2016). Although observed
and projected absolute warming rates in CTRFs are
not as high as in polar or high-latitude interior
regions, warming temperatures are crossing key cli-
matic and ecological thresholds (Veblen et al. 2011;
Shanley et al. 2015), notably: (i) a phase change from
snow to rain as mean winter temperatures cross the
0°C threshold and (ii) the emergence or increased
role of re on the landscape (e.g. see DellaSala et al.
The snow-to-rain transition is an abrupt physical
threshold driven directly by temperature. This
doi:10.1111/aec.12751 © 2019 Ecological Society of Australia
fundamental shift in hydrology inuences a variety of
ecosystem properties and underlying processes,
including subnival habitat (Pauli et al. 2013) and
snow disturbance dynamics (Hennon et al. 2016).
Large areas of high-latitude CTRFs are at or near
the 0°C isotherm during winter, meaning that precip-
itation usually falls as snow. This climatological loca-
tion makes CTRF snow regimes especially vulnerable
to a loss of days below freezing given even minimal
warming (Meehl et al. 2004), as illustrated by the
crossing of the snow-to-rain threshold already
reported in portions of the biome (Buma 2018).
Historically, re in CTRFs was very infrequent,
although large in extent, at lower latitudes (~40°
50°) but very rare at higher latitudes (>55°) due to
climatological constraints, especially the relatively wet
summer periods and limited natural ignition sources
(Veblen & Alaback 1996; Kitzberger et al. 2016).
Areas with continuous human habitation had a more
frequent re regime associated with land manage-
ment (Hoffman et al. 2016; M
endez et al. 2016),
though many mid- to high-latitude locations had re
return intervals >100010 000 years (Veblen & Ala-
back 1996; Gavin et al. 2003). At lower latitudes, re
was rare but a signicant driver of landscape pattern
(e.g. Washington State, USA, Agee 1993; Gavin
et al. 2007). Paleoecological records from the higher
latitude portions of North Americas CTRF (>54°N)
have recorded essentially no charcoal since approxi-
mately 7500 years before present and no widespread
res since the Holocene Climatic Optimum (Baichtal
et al. 2008). The anticipated general increase in re
activity at temperate latitudes worldwide, where fuel
is abundant, is tied to lower moisture availability
resulting from predicted higher temperatures,
reduced precipitation and/or longer re season
Fig. 1. The North Pacic coastal temperate rainforest (panel a) and the South Pacic CTR (panel b). The focus of the
comparison is on the perhumid and seasonal zones of both forests. Biome map from DellaSala (2011).
© 2019 Ecological Society of Australia doi:10.1111/aec.12751
(Westerling et al. 2006; Bowman et al. 2009; Moritz
et al. 2012; Abatzoglou et al. 2017). In addition,
increasing temperatures generate higher water decits
(via increased evapotranspiration) even under poten-
tially increased rainfall at higher latitudes. The lack
of historical re exposure combined with a likely
increase in future re activity makes CTRFs poten-
tially vulnerable to novel change.
In sum, the particular climate and disturbance
state spacein CTRFs makes them an ideal biome
for studying how climate change-induced shifts in
winter precipitation phase and the emergence of re
have direct and indirect, long-lasting consequences
for ecosystem structure and function. Coastal tem-
perate rainforests can serve as model systems for
developing predictions about future changes in other
forested regions, which are expected to undergo simi-
lar snow-to-rain and re regime shifts in the future
(Bowman et al. 2014; Holz et al. 2016).
We take advantage of the fact that the two largest
examples of the biome, the North Paciccoastal
temperate rainforest (NPCTR) of North America
and the South Pacic coastal temperate rainforests
(SPCTR) of Chilean South America (27.3 and
12.5 million ha, respectively), together represent
50.7% of all global temperate rainforests (DellaSala
2011). We focus on the perhumid and seasonal
portions, which straddle the snowrain and re-pre-
sence/absence thresholds (Fig. 1; Veblen & Alaback
1996). Parallel characteristics result from adjacency
to the highly moderating, cool Pacicmaritime
environment and continuously wet conditions that
favour dense, contiguous evergreen forests (needle-
leaf in the Northern Hemisphere and broadleaf in
the Southern Hemisphere) and a large abundance
of temperate, peat-accumulating wetlands in areas
of poor drainage. Both have high carbon (C)
stocks, with slightly more in the Northern than the
Southern Hemisphere (NPCTR: 568794 tons
,SPCTR:326571 tons C ha
; studies
synthesised in Keith et al. 2009). Both regions of
the CTRF exhibit a gradient of human impacts,
from signicant development/land cover change at
lower latitudes to more intact landscapes at higher
latitudes (DellaSala 2011). While the higher lati-
tude areas are certainly impacted by extensive his-
torical logging, often targeting large trees and
vulnerable portions of the ecosystem (ood plain/ri-
parian zones; Albert & Schoen 2013) with impor-
tant negative impacts on sh, wildlife and habitat
(Beier et al. 2008a), they still retain relatively high
value in regard to cultural resources and biodiver-
sity among other ecosystem services (Brandt et al.
2014; Rodriguez-Echeverry et al. 2018). The long
northsouth latitudinal extent of these CTRFs
means that climate change is asynchronous across
this gradient, with poleward regions warming faster
and equatorward regions experiencing more rapid
precipitation changes (IPCC 2014).
In contrast to many other well-studied biomes
experiencing rapid changes in precipitation regimes
and re dynamics (e.g. Serreze et al. 2000), CTRFs
are useful study systems in that climate change
impacts can be examined concurrently and compara-
tively in both the Northern and Southern Hemi-
spheres. A threshold may be crossed earlier in one
region than the other, providing insights into how the
slower changing area might respond. Comparative
studies can provide a more robust test for hypothe-
sised mechanisms and an indication of potential cli-
mate change impacts on local climatology and
ecosystem responses to these and to other distur-
bances (Alaback 1991). We take advantage of that
cross-comparison in the following discussion.
Among the most visible environmental changes asso-
ciated with a warming climate in these two regions
are the reduced depth, extent and persistence of
snow as average winter temperatures cross the rain
snow threshold of 0°C (Fig. 2). In CTRFs, where
precipitation is ample year-round, precipitation phase
and subsequent routing of runoff play important
roles in forest functioning (Bisbing et al. 2016); this
change in phase may be a more signicant shift than
any absolute change in the overall amount or season-
ality. Because the CTRF regions have historically
occurred along the 0°C isotherm in winter, the num-
ber of snow-covered days, there is decreasing faster
than in any other biome (Meehl et al. 2004). Cur-
rently, the rainsnow boundary bisects the NPCTR,
starting at approximately 2000 m by 50
N and
reaching sea level around 57
N (Shanley et al.
2015). The more maritime southern SPCTR in
Patagonia is generally already above this threshold at
low elevations, and snow is transient in those areas,
though areas at higher latitudes and elevations do
remain snow and ice covered. While, to our knowl-
edge, no research has been done on long-term
changes in snow persistence in those higher elevation
areas of the SPCTR, satellite-based observations in
the Andes just north of the region (from ~28°to
36.5°S) identied signicant declines in duration of
snow persistence, approaching 23% per year, with
the rate of snow loss highest at higher latitudes
(Saavedra et al. 2018). Additionally, various ice caps
in the region have been retreating rapidly over the
last several decades, attributed to warming and sub-
sequent raising of the 0°C isotherm (Davies & Glas-
ser 2012), and this is expected to continue over the
next decades (Fig. 2). Thus, research of climate
doi:10.1111/aec.12751 © 2019 Ecological Society of Australia
change effects on the rainsnow threshold in the
NPCTR may be instructive to the less studied snow
dynamic SPCTR.
Observed effects of snow loss
The crossing of the rainsnow threshold can have
signicant ecological effects, especially among species
adapted to reliable winter snow environments. In the
NPCTR, yellow-cedar (Callitropsis nootkatensis)is
experiencing extensive mortality over 9°of latitude
(>400 000 ha; Buma et al. 2017). This species has a
competitive strategy of ne root growth in the early
spring when supplies of nitrogen are abundant in
upper soil layers (Hennon et al. 2016); however, ne
root death can occur during subfreezing weather
events when snow is no longer present (Hennon
et al. 2016). Snow is an effective insulator for soils,
buffering soil temperatures from atmospheric vari-
ability; a lack of snow generally leads to colder soils
in winter months (Groffman et al. 2001) and an
overall increase in soil temperature variability (Jungq-
vist et al. 2014). Even in a warming climate with less
snow, sporadic cold weather events have persisted in
portions of the NPCTR (Beier et al. 2008b; Buma
2018), driving continued tree mortality. Ongoing
mortality is likely to lead to shifts in community com-
position to a smaller suite of species more tolerant of
snow-free winter conditions (Oakes et al. 2014). But,
tree mortality is not the only effect of increasing soil
freezing. Mobilisation of contaminants (Mohanty
Fig. 2. Anticipated shifts in winter snow threshold in the South Pacic CTR (SPCTR) and North Pacic coastal temperate
rainforest (NPCTR) using the HadGEM2-ES (RCP 8.5) climate model/emission scenario. No areas are expected to shift
from above to below freezing. Due to substantial lower elevation/slope areas in the NPCTR, the spatial extent of change is
large. In the SPCTR, shifts are likely along the higher altitudinal range edge throughout the forest, and the inset shows a sub-
section in detail to illustrate this pattern. Climate data from Hijmans et al. (2005) at 1-km resolution, HadGEM2-ES GCM.
© 2019 Ecological Society of Australia doi:10.1111/aec.12751
et al. 2014) and microbial communities (Larsen et al.
2002) can drive signicant changes to nutrient
cycling (Fitzhugh et al. 2001; Urakawa et al. 2014).
These changes, triggered by increasing freezethaw
dynamics in soils, may have signicant downstream
effects as well.
There are multiple pathways by which snow loss
might cause continued plant mortality in the NPCTR
and at higher elevations in SPCTR forests. Climate
change is altering the phenology of forest species, lead-
ing to increased risk of cold-related damage in a war-
mer world (Gu et al. 2008; Rigby & Porporato 2008).
The general ecological strategy of early spring activity
as a means to gain competitive advantage is wide-
spread (Polgar & Primack 2011). Apart from root
freezing, warmer temperatures speed plant develop-
ment earlier each year, making them vulnerable to
frost (Gu et al. 2008). Increased cold damage associ-
ated with climate warming and earlier spring pheno-
logical development is well recognised (Gu et al. 2008;
Inouye 2008) and is typically associated with above-
ground bud mortality. Broadscale damage to sensitive
bud tissue has already been noted in a variety of loca-
tions (Inouye 2008). The threat of root freezing due to
a lack of snow has not been generally quantied out-
side of NPCTR, but it is expected to be a signicant
factor in areas where snow cover will shift from contin-
uous to transient in temperate zones (Bannister et al.
2005). The risk would be highest in areas of the land-
scape prone to shallow rooting habits (e.g. wetlands
and bogs). The most vulnerable species are likely to be
those adapted to early-onset seasonal growth that his-
torically occurred under reliable cover of snow.
It is possible that subfreezing-induced damages
could decline after the transitional period, when tem-
peratures rise above the freezethaw boundary
(Henry 2008, Buma 2018), but this is dependent on
freezing probability corresponding to average temper-
atures as they have in the past. Given the topography
of both regions, with signicantly colder areas located
in close geographic proximity to these ecosystems
(on the eastern sides of the Andes in South America
and Coast Mountains of the United States and
Canada), it is unclear whether that relationship will
hold (Beier et al. 2008b). Areas of historically thin
snowpack and winter temperature slightly below
freezing in the SPCTR should be monitored for plant
stress, root mortality and other emerging dynamics
suggested by the NPCTR decline.
The combination of decreasing winter snowpack
resulting from precipitation phase change, earlier
snowmelt and thaw, and increasing springsummer
evaporative demand (e.g. vapour pressure decit) over
longer, rainfall-free growing seasons is likely to result
in an increase in the prevalence of re in certain por-
tions of CTRFs (Westerling et al. 2006; Littell et al.
2010; Moritz et al. 2012). As noted, the historic
importance of re in CTRFs has been relatively low,
ranging from a nearly nonexistent re regime at higher
latitudes (Gavin et al. 2003) to infrequent, though
stand-replacing, res at lower latitudes (Agee 1993;
Veblen & Alaback 1996; Holz et al. 2012; Walsh et al.
2015; Hoffman et al. 2016; Fig. 3). Although there is
a substantial amount of highly contiguous vegetation
that may act as fuel for a re in CTRFs, vegetation is
typically too wet to burn, and natural ignitions are very
infrequent, as lighting is rare and generally accompa-
nied by rain. Overall, re across both CTRF regions
has historically been driven by the conuence of atmo-
spheric circulation patterns cycling at multiple tempo-
ral scales (Whitlock et al. 2008; Littell et al. 2010;
Holz et al. 2017) and human presence (Hoffman et al.
2016; M
endez et al. 2016).
Under climate change projections, the poleward
portions (>55 °N and >50
S) of both the NPCTR
and the SPCTR are expected to experience signi-
cant annual warming, lower snowpack, a potential
increase in springsummer drought (Veblen et al.
2011) and increasing moisture decits (4050% at
~60°N; Hauer 2010). As a result, the equatorward
portions of CTRFs are expected to become more
ammable throughout the re season (e.g. summer;
Fig. 4), leading to more ammable conditions (Littell
et al. 2010; Sheehan et al. 2015). Additionally, war-
mer coastal ocean temperatures are likely to create
the potential for more ignitions via increased light-
ning activity (Garreaud et al. 2014). In several of the
drier and mountainous areas in the SPCTR,
increases in lightning-set res have been observed in
recent decades (Veblen et al. 2011), and increases in
the frequency of dry, warm periods have been linked
to global climate warming and ozone depletion in
Antarctica (Holz & Veblen 2011; Holz et al. 2017).
Recent research has identied the southern SPCTR
as an area where wildres might invadeas soon as
~2039 if ignitions are provided (Moritz et al. 2012).
Downscaled re projections
Unlike global data related to the winter snowrain
temperature threshold (e.g. Meehl et al. 2004; Buma
et al. 2017), comparable, high spatial-resolution re
modelling studies do not currently exist for northern
and southern CTRFs. For the purposes of this syn-
thesis, we used the global modelling framework of
Moritz et al. (2012) to evaluate changes in climate-
driven probability of re across these regions. This
framework integrates global re datasets (NASA
MODIS missions) and environmental covariates
doi:10.1111/aec.12751 © 2019 Ecological Society of Australia
representing re-conducive climate conditions over
the reference period 19712000 to determine re
climate relationships and assess the likelihood of re
under ongoing climate change. We used the frame-
work to build spatial statistical models of relative
changes to re probability that describe the long-
term potential of re occurrence over the period
20712100. Using methods based on Moritz et al.
(2012), we used projected changes in temperature
seasonality, precipitation of the driest month and
annual precipitation to describe potential alterations
in the probability of re over 0.5°latitudinal bands
across CTRFs (Fig. 5). Projected future climate
data were obtained from the WorldClim CMIP5
HadGEM2-ES (RCP 8.5; Hijmans et al. 2005,
updated to CMIP5 in 2017) for the study region
(for full details, see Appendix S1S3).
Because the scope of this synthesis is focused on
relative changes, modelling was limited to the Hadley
climate projection. The Hadley model performed the
best in aggregate when compared to climate-precipi-
tation values for ve other GCMs at the seasonal
level for the North Pacic forest region (SNAP
2009). To check the assumption that the climatere
relationships quantied in Moritz et al. (2012) would
remain valid with the Hadley climatic dataset, corre-
lations between the WorldClim CMIP5 HadGEM2-
ES data (used here) and CMIP3 data used in Moritz
et al. (2012) were computed. We found very high
Spearman rank coefcients for the variables used in
the model (>0.9; Appendix S3) and considered the
climatere relationships from the Moritz et al.
(2012) ensemble re model suitable to assess poten-
tial relative alterations in the CTRFslikelihood of
Fig. 3. Yearly burned area, cumulative burned area (per 0.25
) and per cent burned (mean fraction of each pixel burned per
) from 1997 to 2016 in the South Pacic CTR and North Pacic coastal temperate rainforest. Fire statistics come from the
Global Fire Emissions Database version 4 (Giglio et al. 2013).
© 2019 Ecological Society of Australia doi:10.1111/aec.12751
re for the period 20712100 driven by HadGEM2-
ES climate projections. The purpose of this exercise
was not to predict absolute changes in re probability
but rather to identify the portions of each region
likely to see the largest relative change. For further
details associated with this modelling methodology,
see Appendix S1 and Moritz et al. (2012).
While the frequency of dry, warm conditions
increases at low latitudes in both regions (where the
majority of re modelling work has been concen-
trated, for example Littell et al. 2010), the modelling
results suggest that the central latitude portions of
the biome in both hemispheres will see the largest
relative increase in climate-driven re probability.
This is primarily due to projected changes in dry sea-
son precipitation (Fig. 5). The more equatorward
portions of the biome will likely have higher rates of
re due to their higher baseline rates. However, a lar-
ger relative increase in re activity indicates a more
substantial departure from historical norms and is
thus worth noting for future estimates of CTRF
It should also be noted that these models are based
on broadscale climatic trends and reect general cli-
matere relationships; the actual occurrence and
behaviour of res at regional and local scales is a
result of ner scale weather patterns, topo-edaphic
gradients and vegetation-re feedbacks as well.
Effects of re regime changes in the NPCTR
Fires have occurred historically in the southern and
central portions of the NPCTR but with highly
Fig. 4. Projected precipitation change. Relative change in summer precipitation (dened as warmest quarter of the year) by
2070 for the North Pacic coastal temperate rainforest (left) and the South Pacic CTR (right) using the HadGEM2-ES
(RCP 8.5) climate model/emission scenario. Climate data from Hijmans et al. (2005) at 1-km resolution, HadGEM2-ES
GCM (updated to CMIP5, see http://www.worldclim.org).
doi:10.1111/aec.12751 © 2019 Ecological Society of Australia
Fig. 5. Relative change in re probability projected as a function of the major climate drivers in the North Pacic coastal tem-
perate rainforest (NPCTR; top) and the South Pacic CTR (SPCTR; bottom) using the 2070 HadGEM2-ES (RCP 8.5) climate
model/emission scenario. A negative (green or blue) value indicates the driver is expected to change in a direction that reduces
relative re probability, and a positive value (orange or red) indicates an increase in re probability. Agreement between predic-
tors: 100% indicates the three drivers had similar signs (i.e. all were positive), whereas 67% indicates that two-thirds were in
agreement for either an increase (I) or a decrease (D) in re probability. In general, there is strong agreement that re frequency
will increase throughout the SPCTR. Expectations are mixed in the NPCTR, but generally an increase is expected further north
than historical res. The extreme southern portion of the NPCTR is not modelled due to a lack of climate data at the proper
scale; for climate locations used to create the probability graphs, see Fig. S1. Note differences of scale of axes and legends.
© 2019 Ecological Society of Australia doi:10.1111/aec.12751
variable return intervals (3003000+years, Fig. 4)
and spatial heterogeneity due to variable ignitions
and climatic conditions (Hoffman et al. 2018). Thin-
barked, non-serotinous species dominate CTRFs,
and re-adapted species are generally absent (Veblen
& Alaback 1996). In the southern NPCTR (<55
where re has an infrequent but more signicant role
(Agee 1993; Tepley et al. 2013; Whitlock et al.
2014), a few seral thick-barked species occur (e.g.
Douglas-r, Pseudotsuga menziesii) that can survive
low-to-moderate re intensities (Agee 1993).
Anticipating the effects of both increasing and
emerging re (at lower and higher latitudes, respec-
tively) is critical (Littell et al. 2010). Theory suggests
that in wet systems, where ammability declines as
forest structure develops, the introduction of re-
conducive conditions can lead to a cycle of increasing
re extents and subsequent widespread ecological
changes. This positive feedback occurs because
increases in the spatial extent and connectivity of the
more ammable, early seral vegetation after each re
event lead, subsequently, to more extensive res.
Given sufcient ignition opportunities and a climate
conducive to periodic re (Perry et al. 2012), rapid
and persistent threshold-like changes can occur when
forests at the landscape scale cross critical am-
mable-connectivity thresholds and any re event is
likely to spread over the majority of the landscape.
Increased NPCTR ammability associated with early
successional species can lead to positive re-vegeta-
tion feedbacks (Agee & Huff 1987) due to highly
ammable early successional ne fuels that dry
rapidly even in the relatively short re season com-
mon to the regions climate. Thus, the emergence or
acceleration of re regimes is a signicant concern
and changes projected here should be considered
conservative estimates. Recent events in mesic forest
stands in the southern portions of the NPCTR (e.g.
Eagle Creek Fire in the Columbia Gorge Scenic Area
in Oregon and Norse Peak Fire in Washington, from
a human ignition) remind us that the transformation
of these forests by re is likely as a potential result of
the warming regional climate. To this point, the his-
torical and already-underway expansion of re into
the SPCTR is instructive for the NPCTR.
The expansion of re in the SPCTR
The expansion of re is well documented in the
SPCTR. Historically, humans were the ignition
source for most SPCTR res (Holz et al. 2016), with
ignitions occurring primarily at the warmest and dri-
est equatorward edge. Since the 1970s, there has
been an increase in lightning-ignited res in the
northern and central regions of the SPCTR (Veblen
et al. 2011), attributed to environmental shifts
associated with climate change (Thompson et al.
2011, IPCC 2014, Garreaud et al. 2014). As biomass
is not limiting and the climate is becoming more
conducive to re, the occurrence of re is increas-
ingly ignition limited (Paritsis et al. 2013). Emerging
res tied to climate change and increasing variability
in climate have already been transforming ecological
composition, structure and function, particularly in
re-sensitive Pilgerodendron forests (Holz & Veblen
2009; Bannister et al. 2012). These species are
mostly re sensitive, and the landscape has been rela-
tively nonammable historically but is becoming
less so today.
In addition to climate change driving increases in
re probability, tree plantations in the SPCTR have
the potential to increase re risk. Pine and euca-
lypts plantations, like other plantations in the
southern NPCTR (Zald & Dunn 2018), facilitate
re spread due to homogeneous patch structure
and connectivity, which in turn can result in higher
re frequency and severity (McWethy et al. 2018;
Paritsis et al. 2018). While many historical and
recent large res in Chile occurred just north of
the CTRF region in the more Mediterranean cen-
tral valley, there are plantations of Eucalypts in the
SPCTR as far south as 42
on Isla Chilo
e, and at
the Patagonian dry forest/steppe ecotone lodgepole
pine (Pinus contorta var. latifolia), a re-associated
species has established from plantations even fur-
ther south (at least 45.5
; Taylor et al. 2017).
There are concerns that invasion by re-adapted
species may alter the water balance, fuel type (Tng
et al. 2012) and fuel structures (Cobar-Carranza
et al. 2014) of the region.
When res do occur, they can cause signicant
changes to forests and have the potential to initiate
positive feedbacks that drive further increases in re
frequency (e.g. Paritsis et al. 2013; Taylor et al.
2017). In the SPCTR, invasion of shade intolerant
Sphagnum species can result in subsequent waterlog-
ging of the habitat due to an overall decline in evapo-
transpiration (D
ıaz et al. 2007). Sphagnum mosses,
which dominate wetlands in the NPCTR as well,
acidify substrates, outcompete tree seedlings, trans-
form the plant community and potentially lock the
system into an alternative stable state (Kitzberger
et al. 2016; Zaret & Holz 2016). Preliminary results
suggest that: (i) water table and substrate interact
and best explain patterns in post-re tree seedling
abundance and plant community; (ii) small seedling
abundance is best explained by water-table height
and plant community type (Zaret & Holz 2016); and
(iii) ne-fuel bric peats are more likely to support a
high-frequency, low-severity re regime given an
amenable climate for re resulting in a positive feed-
back between re and vegetation ammability (Holz
2009, Kitzberger et al. 2016).
doi:10.1111/aec.12751 © 2019 Ecological Society of Australia
10 B. BU M A ET AL.
This observation of a rapid ecosystem shift trig-
gered by the emergence of re and explained by the
expansion of more ammable, early seral vegetation
coupled with increasingly favourable climates for re
is clearly instructive to the NPCTR. It also echoes
observations from paleoecological reconstructions in
temperate New Zealand (Perry et al. 2012) and
recent events in Tasmanian temperate rainforests,
where unprecedented res in 2015 and 2016 burned
re-sensitive trees as well as vast tracks of peatland
and alpine vegetation (~105 000 ha) during the driest
season on record (Marris 2016). That the largest rel-
ative change in re probability is not anticipated at
the equatorward edge of the biome, but rather in the
middle and at higher latitudes, is an unexpected nd-
ing and suggests research should consider emerging
re regimes beyond the drier, equatorward extents
typically considered where adaptations to re are
minimal and resilience potentially low. The story of
re emergence clearly illustrates the value of linking
the NPCTR and the SPCTR in a single analysis, as
physical drivers are changing in similar directions,
but at different times, in both areas the emergence
of re in the south is a valuable case study for the
forests in the north.
Much of the concern regarding climate change-dri-
ven mortality centres on changes at the trailing
(lower latitude or elevation; Parmesan & Yohe 2003)
or leading edges (higher latitude or higher elevation;
Mason et al. 2015) of species and biome distribu-
tions. Generally, discussion in temperate regions has
focused on increasing temperatures and declining
precipitation on the southern boundary, as both are
known to strongly structure species range edges and
biome extents. At broad scales, species and biomes
do generally track long-term climate conditions such
as mean winter temperatures or annual water bal-
ance, though there may be lag after major climatic
shifts (e.g. Ice Ages) due to slow migration rates
(Krapek & Buma 2018). In the future, however,
there is the potential for thresholds in speciestoler-
ances to be crossed elsewhere within the current
range of a forest ecosystem, because climate warming
and precipitation changes are not synchronous and
occur at different rates. Edgesof climatic tolerance
may emerge within central portions of a range due to
the intersection of climatic trends with important
physical thresholds or biological tolerances.
The NPCTR and SPCTR regions demonstrate sig-
nicant, climate change-driven changes occurring near
the geographic middle of a biome not just on the
lower latitude portions. Loss of snow is causing the
most signicant ecological changes in the geographic
middle of the NPCTR, where snow was reliably pre-
sent but winter mean temperatures were near 0°
(Buma et al. 2017). Higher elevations of the SPCTR
and surrounding ecosystems are likely to be similarly
susceptible in the future, as snow loss (although mini-
mal in absolute terms) is reported in the central por-
tion (Fig. 2). Further research on the role of snowpack
changes in determining species ranges is a signicant
need (Pauli et al. 2013), either via direct mortality as
in the case of yellow-cedar or via interactions with
other stressors and disturbance agents (e.g. Poulos
2014). Similarly, the highest increase in relative re
likelihood is in the geographic middle latitudes of the
biome in both hemispheres, where re was historically
rare and species are not well adapted to re (this anal-
ysis, Fig. 5). Fire may emerge in unexpected loca-
tions, and the emergence rather than simple
intensication is also a major research need, espe-
cially in landscapes where theory suggests rapid trans-
formations due to seral changes in ammability.
Temperate rainforests, by virtue of their long lati-
tudinal extent, exemplify these emerging edge phe-
nomena at both the species and ecosystem levels.
This suggests that climate change monitoring in a
variety of regions should focus not only on leading or
lagging edges, but also emerging edges driven by cli-
matic shifts like precipitation phase.
The objectives of this synthesis and review were to
draw attention to emerging disturbance phenomena
in the coastal temperate rainforests of the Pacic
Coast, discuss the causes and effects of those phe-
nomena and utilise the cross-hemispheric comparison
to enable more general predictions about change
than can be done from single-system studies. This
comparative examination of climateecosystem rela-
tionships across hemispheres of the CTRFs provides
a framework within which to hypothesise the nature,
geographic location and potential effects of emergent
disturbances within similar systems.
The counter-intuitive nature of the processes being
observed root freezing due to warming and re in
wet forests makes their prediction more difcult but
the broad nature of the changes underway underlines
the signicance of these emergent trends. In particu-
lar, the sensitivity of forests to root freezing mortality
in areas where snow will become transient should be
investigated in other systems, especially those prone
to late spring cold events. Emergence of re, or
increases in re frequency and/or intensity, may con-
strain survival and self-replacement of dominant spe-
cies, leading to long-lasting shifts in community
composition or landscape structure, or the establish-
ment of alternative ecosystem states. Both are
© 2019 Ecological Society of Australia doi:10.1111/aec.12751
resulting in community simplication by acting as l-
ters selective removal of freeze-susceptible trees and
selection for more re-tolerant species; longer term
implications of this shift clearly need more research.
Temperate rainforests are undergoing novel change
largely driven by climate change. Change in these
systems is particularly important given the two
regions we examined are well recognised for their
global biodiversity importance and relative intactness,
which provides opportunities to proactively respond
to emerging conditions relative to highly disturbed
areas. Their role as major storehouses of carbon at
the global scale underlines the importance of these
shifts. Finally, the use of coastal temperate rainforests
as early indicators of change is valuable and can lead
to predictive capabilities for similar functional groups
and responses in forests elsewhere.
This paper emerged from an invited symposium at
the International Association for Landscape Ecology
in Portland, Oregon, 2015. The authors would like
to thank all participants in that session for their
Abatzoglou J. T., Kolden C. A., Williams A. P., Lutz J. A. &
Smith A. M. S. (2017) Climatic inuences on interannual
variability in regional burn severity across western US
forests. Int. J. Wildl. Fire 26, 26975.
Adams H. D., Guardiola-Claramonte M., Barron-Gafford G.
A. et al. (2009) Temperature sensitivity of drought-
induced tree mortality portends increased regional die-off
under global-change-type drought. PNAS 106, 70636.
Agee J. K. (1993) Fire Ecology of Pacic Northwest Forests.
Island Press, Washington.
Agee J. K. & Huff M. H. (1987) Fuel succession in a western
hemlock/Douglas-r forest. Can. J. For. Res. 17, 697704.
Alaback P. B. (1991) Comparative ecology of temperate
rainforests of the Americas along analogous climatic
gradients. Rev. Chil. Hist. Nat. 64, 399412.
Albert D. M. & Schoen J. W. (2013) Use of historical logging
patterns to identify disproportionately logged ecosystems
within temperate rainforests of southeastern Alaska.
Conserv. Biol. 27, 77484.
Allen C. D., Macalady A. K., Chenchouni H. et al. (2010) A
global overview of drought and heat-induced tree mortality
reveals emerging climate change risks for forests. For. Ecol.
Manage. 259, 66084.
Anderegg W. R., Plavcov
a L., Anderegg L. D., Hacke U. G.,
Berry J. A. & Field C. B. (2013) Droughts legacy:
multiyear hydraulic deterioration underlies widespread
aspen forest die-off and portends increased future risk.
Glob. Change Biol. 19, 118896.
Baichtal J. F., Crockford S. J. & Carlson R. J. (2008) Possible
evidence of warmer, drier conditions during the early
Holocene of southern Southeast Alaska from shell-bearing
marine and peat deposits. Poster. Alaska Anthropological
Association annual meeting poster.
Bannister P., Maegli T., Dickinson K. J. et al. (2005) Will loss
of snow cover during climatic warming expose New
Zealand alpine plants to increased frost damage? Oecologia
144, 24556.
Bannister J. R., Donoso P. J. & Bauhus J. (2012) Persistence of
the slow growing conifer Pilgerodendron uviferum in old-
growth and re-disturbed southern bog forests. Ecosystems
15, 115872.
Beier C. M., Patterson T. M. & Chapin F. S. (2008a)
Ecosystem services and emergent vulnerability in managed
ecosystems: a geospatial decision-support tool. Ecosystems
11, 92338.
Beier C. M., Sink S. E., Hennon P. E., DAmore D. V. &
Juday G. P. (2008b) Twentieth-century warming and the
dendroclimatology of declining yellow-cedar forests in
southeastern Alaska. Can. J. For. Res. 38, 131934.
Bisbing S. M., Cooper D. J., DAmore D. V. & Marshall K.
N. (2016) Determinants of conifer distributions across
peatland to forest gradients in the coastal temperate
rainforest of southeast Alaska. Ecohydrology 9, 35467.
Bolker B. M., Pacala S. W., Bazzaz F. A., Canham C. D. &
Levin S. A. (1995) Species diversity and ecosystem
response to carbon dioxide fertilization: conclusions from a
temperate forest model. Glob. Change Biol. 1, 37381.
Bond W. J., Woodward F. I. & Midgley G. F. (2005) The
global distribution of ecosystems in a world without re.
New Phytol. 165, 52538.
Bowman D. M., Balch J. K., Artaxo P. et al. (2009) Fire in the
earth system. Science 324, 4814.
Bowman D. M., Murphy B. P., Neyland D. L. J., Williamson
G. J. & Prior L. D. (2014) Abrupt re regime change may
cause landscape-wide loss of mature obligate seeder
forests. Glob. Change Biol. 20, 100815.
Brandt P., Abson D. J., DellaSala D. A., Feller R. & von
Wehrden H. (2014) Multifunctionality and biodiversity:
ecosystem services in temperate rainforests of the Pacic
Northwest, USA. Biol. Cons. 169, 36271.
Brooks M. L., DAntonio C. M., Richardson D. M. et al.
(2004) Effects of invasive alien plants on re regimes.
Bioscience 54, 67788.
Buma B. (2015) Disturbance interactions: characterization,
prediction, and the potential for cascading effects.
Ecosphere 6, 115.
Buma B. (2018) Transitional climate mortality: slower warming
may result in increased climate-induced mortality in some
systems. Ecosphere 9, e02170.
Buma B. & Barrett T. M. (2015) Spatial and topographic
trends in forest expansion and biomass change, from
regional to local scales. Glob. Change Biol. 21, 344554.
Buma B. & Wessman C. A. (2011) Disturbance interactions can
impact resilience mechanisms of forests. Ecosphere 2, 113.
Buma B., Hennon P. E., Harrington C. A. et al. (2017)
Emerging broad-scale mortality driven by climate warming
and loss of snowpack. Glob. Change Biol. 23, 290314.
Certini G. (2014) Fire as a soil-forming factor. Ambio 43, 1915.
Cleland E. E., Chuine I., Menzel A., Mooney H. A. &
Schwartz M. D. (2007) Shifting plant phenology in
response to global change. Trends Ecol. Evol. 22, 35765.
Cobar-Carranza A. J., Garcia R. A., Pauchard A. & Pena E.
(2014) Effect of Pinus contorta invasion on forest fuel
properties and its potential implications on the re regime
of Araucaria araucana and Nothofagus antarctica forests.
Biol. Invasions 16, 227391.
doi:10.1111/aec.12751 © 2019 Ecological Society of Australia
12 B. BU M A ET AL.
Davies B. J. & Glasser N. F. (2012) Accelerating shrinkage of
Patagonian glaciers from the Little Ice Age (~1870 AD) to
2011. J. Glaciol. 58, 106384.
DellaSala D. A. (2011) Temperate and Boreal Rainforests of the
World: Ecology and Conservation. Island Press, Washington.
DellaSala D. A., Brandt P., Koopman M. et al. (2018) Climate
change may trigger broad shifts in North Americas Pacic
Coastal rainforests. In: The Encyclopedia of the Anthropocene
(eds D. A. DellaSala & M. I. Goldstein), vol. 2pp. 233
44. Elsevier,Oxford.
ıaz M. F., Bigelow S. & Armesto J. J. (2007) Alteration of
the hydrologic cycle due to forest clearing and its
consequences for rainforest succession. For. Ecol. Manage.
244, 3240.
Doerr S. H. & Sant
ın C. (2016) Global trends in wildre and
its impacts: perceptions versus realities in a changing
world. Phil. Trans. R. Soc. B 371, 20150345.
Fitzhugh R. D., Driscoll C. T., Groffman P. M., Tierney G.
L., Fahey T. J. & Hardy J. P. (2001) Effects of soil
freezing disturbance on soil solution nitrogen, phosphorus,
and carbon chemistry in a northern hardwood ecosystem.
Biogeochemistry 56, 21538.
Garreaud R. D., Gabriela Nicora M., B
urgesser R. E. &
E. E. (2014) Lightning in western Patagonia. J. Geophys.
Res. Atmos. 119, 447185.
Gavin D. G., Brubaker L. B. & Lertzman K. P. (2003)
Holocene re history of a coastal temperate rain forest
based on soil charcoal radiocarbon dates. Ecology 84, 186
Gavin D. G., Hallet D. J., Hu F. S., Lertzman K. P., Prichard
S. J., Brown K. J., Lynch J. A., Bartlein P. & Peterson D.
L. (2007) Forest re and climate change in western North
America: insights from sediment charcoal records. Front.
Ecol. Environ. 5, 499506.
Giglio L., Randerson J. T. & Werf G. R. (2013) Analysis of
daily, monthly, and annual burned area using the fourth-
generation global re emissions database (GFED4). J.
Geophys. Res. Biogeosci. 118, 31728.
Gilman S. E., Urban M. C., Tewksbury J., Gilchrist G. W. &
Holt R. D. (2010) A framework for community
interactions under climate change. Trends Ecol. Evol. 25,
Groffman P. M., Driscoll C. T., Fahey T. J., Hardy J. P.,
Fitzhugh R. D. & Tierney G. L. (2001) Colder soils in
a warmer world: a snow manipulation study in a
northern hardwood forest ecosystem. Biogeochemistry 56,
Gu L., Hanson P. J., Post W. M. et al. (2008) The 2007
eastern US spring freeze: increased cold damage in a
warming world? Bioscience 58, 25362.
Hauer J. B. (2010) Climate Change: Anticipated Effects on
Ecosystem Services and Potential Actions by the Alaska Region,
US Forest Service. Ecosystem Management Research
Institute, Seeley Lake.
He T., Belcher C. M., Lamont B. B. & Lim S. L. (2016) A
350-million-year legacy of re adaptation among conifers.
J. Ecol. 104, 35263.
Hennon P. E., McKenzie C. M., DAmore D. et al. (2016) A
climate adaptation strategy for conservation and
management of yellow cedar in Alaska. Gen. Tech. Rep.
PNW-GTR-917. U.S. Department of Agriculture, Forest
Service, Pacic Northwest Research Station, Portland.
Henry H. A. (2008) Climate change and soil freezing
dynamics: historical trends and projected changes. Clim
Change,87, 42134.
Hijmans R. J., Cameron S. E., Parra J. L., Jones P. G. & Jarvis
A. (2005) Very high-resolution interpolated climate surfaces
for global land areas. Int. J. Climatol. 25, 196578.
Hoffman K. M., Gavin D. G., Lertzman K. P., Smith D. J. &
Starzomski B. M. (2016) 13,000 years of re history
derived from soil charcoal in a British Columbia coastal
temperate rain forest. Ecosphere 7, e01415.
Hoffman K. M., Trant A. J., Nijland W. & Starzomski B. M.
(2018) Ecological legacies of re detected using plot-level
measurements and LiDAR in an old growth coastal
temperate rainforest. For. Ecol. Manage. 424, 1120.
Holz C. A. (2009) Climatic and human inuences on re
regimes and forest dynamics in temperate rainforests in
southern Chile (Doctoral dissertation). University of
Colorado, Boulder.
Holz A. & Veblen T. T. (2009) Pilgerodendron uviferum: the
southernmost tree-ring re recorder species. Ecoscience 16,
Holz A. & Veblen T. T. (2011) Variability in the Southern
Annular Mode determines wildre activity in Patagonia.
Geophys. Res. Lett. 38, L14710.
Holz A., Haberle S., Veblen T. T., De Pol-Holz R. &
Southon J. (2012) Fire history in western Patagonia from
paired tree-ring re-scar and charcoal records. Clim. Past
8, 451.
Holz A., M
endez C., Borrero L., Prieto A., Torrej
on F. &
Maldonado A. (2016) Fires: the main human impact on
past environments in Patagonia. PAGES Mag. 2, 723.
Holz A., Paritsis J., Mundo I. A. et al. (2017) Southern
Annular Mode drives multicentury wildre activity in
southern South America. Proc. Natl Acad. Sci. USA 114,
Inouye D. W. (2008) Effects of climate change on phenology,
frost damage, and oral abundance of montane
wildowers. Ecology 89, 35362.
IPCC (2014) Climate change 2014: synthesis report. In:
Contribution of Working Groups I, II and III to the Fifth
Assessment Report of the Intergovernmental Panel on Climate
Change (Core Writing Team, R. K. Pachauri & L. A.
Meyer eds) 151 pp. IPCC, Geneva.
Jungqvist G., Oni S. K., Teutschbein C. & Futter M. N.
(2014) Effect of climate change on soil temperature in
Swedish boreal forests. PLoS ONE 9, e93957.
Keith H., Mackey B. G. & Lindenmayer D. B. (2009) Re-
evaluation of forest biomass carbon stocks and lessons
from the worlds most carbon-dense forests. Proc. Natl
Acad. Sci. USA 106, 1163540.
Kitzberger T., Perry G. L. W., Paritsis J. et al. (2016) Fire
vegetation feedbacks and alternative states: common
mechanisms of temperate forest vulnerability to re in
southern South America and New Zealand. N. Z. J. Bot.
54, 24772.
Klos P. Z., Link T. E. & Abatzoglou J. T. (2014) Extent of the
rain-snow transition zone in the western US under historic
and projected climate. Geophys. Res. Lett. 41, 45608.
Krapek J. & Buma B. (2018) Limited stand expansion by a
long-lived conifer at a leading northern range edge, despite
available habitat. J. Ecol. 106, 91124.
Larsen K. S., Jonasson S. & Michelsen A. (2002) Repeated
freeze-thaw cycles and their effects on biological
processes in two arctic ecosystem types. Appl. Soil Ecol.
21, 18795.
Littell J. S., Oneil E. E., McKenzie D. et al. (2010) Forest
ecosystems, disturbance, and climatic change in
Washington State, USA. Clim. Change. 102, 12958.
© 2019 Ecological Society of Australia doi:10.1111/aec.12751
Marris E. (2016) Tasmanian bushres threaten iconic ancient
forests. Nature 530, 1378.
Mason S. C., Palmer G., Fox R. et al. (2015) Geographical
range margins of many taxonomic groups continue to shift
polewards. Biol. J. Lin. Soc. 115, 58697.
McWethy D. B., Pauchard A., Garcia R. A. et al. (2018)
Landscape drivers of recent re activity (20012017) in
south central Chile. PLoS ONE 13, e0201195.
Meehl G. A., Tebaldi C. & Nychka D. (2004) Changes in frost
days in simulations of twenty-rst century climate. Clim.
Dyn. 23, 495511.
endez C., de Porras M. E., Maldonado A., Reyes O., Nuevo
Delaunay A. & Garc
ıa J. L. (2016) Human effects in
Holocene re dynamics of central western Patagonia (~44
S, Chile). Front. Ecol. Evol. 4, 100.
Millar C. I. & Stephenson N. L. (2015) Temperate forest
health in an era of emerging mega disturbance. Science
349, 8236.
Mohanty S. K., Saiers J. E. & Ryan J. N. (2014) Colloid-
facilitated mobilization of metals by freeze-thaw cycles.
Environ. Sci. Technol. 48, 97784.
Moritz M. A., Parisien M. A., Batllori E. et al. (2012) Climate
change and disruptions to global re activity. Ecosphere 3,
Mote P. W. (2003) Trends in snow water equivalent in the
Pacic Northwest and their climatic causes. Geophys. Res.
Lett. 30, 14.
Oakes L. E., Hennon P. E., OHara K. L. & Dirzo R. (2014)
Long-term vegetation changes in a temperate forest
impacted by climate change. Ecosphere 5, 128.
Paritsis J., Holz A., Veblen T. T. & Litzbeerger T. (2013)
Habitat distribution modeling reveals vegetation
ammability and land use as drivers of wildre in SW
Patagonia. Ecosphere 4, 120.
Paritsis J., Landesmann J. B., Kitzberger T. et al. (2018) Pine
plantations and invasion alter fuel structure and potential
re behavior in a Patagonian forest-steppe ecotone. Forests
9, 117.
Parmesan C. & Yohe G. (2003) A globally coherent ngerprint
of climate change impacts across natural systems. Nature
421, 37.
Pauli J. N., Zuckerberg B., Whiteman J. P. & Porter W. (2013)
The subnivium: a deteriorating seasonal refugium. Front.
Ecol. Environ. 11, 2607.
Pausas J. G. & Keeley J. E. (2009) A burning story: the role of
re in the history of life. Bioscience 59, 593601.
Perry G. L., Wilmshurst J. M., McGlone M. S., McWethy
D. B. & Whitlock C. (2012) Explaining re-driven
landscape transformation during the Initial Burning
Period of New Zealands prehistory. Glob. Change Biol.
18, 160921.
Polgar C. A. & Primack R. B. (2011) Leaf-out phenology of
temperate woody plants: from trees to ecosystems. New
Phytol. 191, 92641.
Poulos H. M. (2014) Tree mortality from a short-duration
freezing event and global-change-type drought in a
Southwestern pi~
non-juniper woodland, USA. PeerJ 2, e404.
Rigby J. R. & Porporato A. (2008) Spring frost risk in a
changing climate. Geophys. Res. Lett. 35, L12703.
Rodriguez-Echeverry J., Echeverria C., Oyarzun C. & Morales
L. (2018) Impact of land-use change on biodiversity and
ecosystem services in the Chilean temperate forests.
Landscape Ecol. 33, 43953.
Rundel P. W. (1981) Fire as an ecological factor. In:
Physiological Plant Ecology I (eds O. L. Lange, P. S. Nobel,
C. B. Osmond & H. Ziegler) pp. 50138. Springer, Berlin,
Saavedra F. A., Kampf S. K., Fassnacht S. R. & Sibold J. S.
(2018) Changes in Andes snow cover from MODIS data,
20002016. Cryosphere 12, 102746.
Scott A. C. (2000) The pre-quaternary history of re.
Palaeogeogr. Palaeoclimatol. Palaeoecol. 164, 281329.
Serreze M. C., Walsh J. E., Chapin F. S. et al. (2000)
Observational evidence of recent change in the northern
high-latitude environment. Clim. Change. 46, 159207.
Shanley C. S., Pyare S., Goldstein M. I. et al. (2015)
Climate change implications in the northern coastal
temperate rainforest of North America. Clim. Change.
130, 15570.
Sheehan T., Bachelet D. & Ferschweiler K. (2015) Projected
major re and vegetation changes in the Pacic Northwest
of the conterminous United States under selected CMIP5
climate futures. Ecol. Model. 317, 1629.
SNAP (2009) Validating SNAP climate models. Scenarios
Network for Arctic Planning. SNRAS Misc Pub No 2009-
03. [Cited 1 May 2018.] Available from URL: https://
Sureet C. G. & Tullos D. (2013) Variability in effect of
climate change on rain-on-snow peak ow events in a
temperate climate. J. Hydrol. 479, 2434.
Taylor K. R., Maxwell B. D., McWethy D. B., Pauchard A.,
Nunez M. A. & Whitlock C. (2017) Pinus contorta
invasions increase wildre fuel loads and may create a
positive feedback with re. Ecology 98, 67887.
Tepley A. J., Swanson F. J. & Spies T. A. (2013) Fire-
mediated pathways of stand development in Douglas-r/
western hemlock forests of the Pacic Northwest, USA.
Ecology 94, 172943.
Thompson A. M., Oltmans S. J., Tarasick D. W., von der
Gathen P., Smit H. G. & Witte, J. C. (2011) Strategic
ozone sounding networks: Review of design and
accomplishments. Atmos. Environ.,45, 214563.
Tng D. Y. P., Williamson G. J., Jordan G. J. & Bowman D.
M. J. S. (2012) Giant eucalyptsglobally unique re-
adapted rain-forest trees? New Phytol. 196, 100114.
Urakawa R., Shibata H., Kuroiwa M. et al. (2014) Effects of
freeze-thaw cycles resulting from winter climate change on
soil nitrogen cycling in ten temperate forest ecosystems
throughout the Japanese archipelago. Soil Biol. Biogeochem.
74, 8294.
Veblen T. T. & Alaback P. B. (1996) A comparative review of
forest dynamics and disturbance in the temperate
rainforests of North and South America. In: High-latitude
Rainforests and Associated Ecosystems of the West Coast of the
Americas: Climate, Hydrology, Ecology, and Conservation (eds
R. G. Lawford, P. B. Alaback & E. Fuentes) pp. 173213.
Springer-Verlag, New York.
Veblen T. T., Holz A., Paritsis J., Raffaele E., Kitzberger T. &
Blackhall M. (2011) Adapting to global environmental
change in Patagonia: what role for disturbance ecology?
Austral Ecol. 36, 891903.
Walsh M. K., Marlon J. R., Goring S. J., Brown K. J. & Gavin
D. G. (2015) A regional perspective on Holocene re
climatehuman interactions in the Pacic Northwest of
North America. Ann. Assoc. Am. Geogr. 105, 113557.
Westerling A. L., Hidalgo H. G., Cayan D. R. & Swetnam T.
W. (2006) Warming and earlier spring increase western
US forest wildre activity. Science 313, 9403.
Whitlock C., Marlon J., Briles C., Brunelle A., Long C. &
Bartlein P. (2008) Long-term relations among re, fuel,
doi:10.1111/aec.12751 © 2019 Ecological Society of Australia
14 B. BU M A ET AL.
and climate in the north-western US based on lake-
sediment studies. Int. J. Wildl. Fire 17, 7283.
Whitlock C., McWethy D. B., Tepley A. J. et al. (2014) Past and
present vulnerability of closed-canopy temperate forests to
altered re regimes: a comparison of the Pacic Northwest,
New Zealand, and Patagonia. Bioscience 65, 15163.
Williams J. W. & Jackson S. T. (2007) Novel climates, no-
analog communities, and ecological surprises. Front. Ecol.
Environ. 5, 47582.
Zald H. S. J. & Dunn C. J. (2018) Severe re weather and
intensive forest management increase re severity in a
multi-ownership landscape. Ecol. Appl. 28, 106880.
Zaret K. & Holz A. (2016) Seedling performance of
Pilgerodendron uviferum (Cipr
es de las Guaitecas) in a
burned peatland, lower baker river watershed: implications
for restoration. VIII Southern Connection Congress. Punta
Arenas, Chile.
Additional supporting information may/can be found
online in the supporting information tab for this
Appendix S1. Fire modelling.
Appendix S2. Red dots depict the xycoordinates
used to extract the values of each bioclimatic variable
in each region.
Appendix S3. Spearman rank correlation coef-
cient between WorldClim CMIP5 HadGEM2-ES
(RCP8.5; Hijmans et al. 2005) and the CMIP3 cli-
mate projections used to build the ensemble re mod-
els in the Moritz et al. (2012) global re framework.
© 2019 Ecological Society of Australia doi:10.1111/aec.12751
... While IRA fish and wildlife habitat values have been documented on the TNF [40], our study is the first to quantify the C Land 2022, 11, 717 14 of 18 stock value of IRAs, which contain over half the entire C stock on the TNF. Importantly, the C stock within IRA POGs (and POGs generally) are likely to remain relatively stable compared to the interior of Alaska and the southern extent of the North Pacific coastal temperate rainforest biome subject to more extreme climate change [41][42][43]. ...
... The maritime climate and intact forests of the TNF have climate refugia properties compared to more extreme climatic zones in the interior of Alaska and temperate rainforests further south [41][42][43], thereby offering a relatively stable C reservoir. However, due to declining late-season snow cover that prevents late-winter root freezing, yellow-cedar is experiencing a range contraction, and is a climate-sensitive focal species [44]. ...
... Those areas should be candidates for proforestation [37] to restore carbon stocks over time. Thus, a climate-smart strategy centered on sequestration and accumulation of C is generally essential to addressing the climate crisis [37] and would offer co-benefits, including a host of ecosystem services derived from C dense forests [48] as well as potential climate refugia [41][42][43]. ...
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The 6.7 M ha Tongass National Forest in southeast Alaska, USA, supports a world-class salmon fishery, is one of the world’s most intact temperate rainforests, and is recognized for exceptional levels of carbon stored in woody biomass. We quantified biomass and soil organic carbon (C) by land use designation, Inventoried Roadless Areas (IRAs), young and productive old-growth forests (POGs), and 77 priority watersheds. We used published timber harvest volumes (roundwood) to estimate C stock change across five time periods from early historical (1909–1951) through future (2022–2100). Total soil organic and woody biomass C in the Tongass was 2.7 Pg, representing ~20% of the total forest C stock in the entire national forest system, the equivalent of 1.5 times the 2019 US greenhouse gas emissions. IRAs account for just over half the C, with 48% stored in POGs. Nearly 15% of all C is within T77 watersheds, >80% of which overlaps with IRAs, with half of that overlapping with POGs. Young growth accounted for only ~5% of the total C stock. Nearly two centuries of historical and projected logging would release an estimated 69.5 Mt CO2e, equivalent to the cumulative emissions of ~15 million vehicles. Previously logged forests within IRAs should be allowed to recover carbon stock via proforestation. Tongass old growth, IRAs, and priority watersheds deserve stepped-up protection as natural climate solutions.
... Non-growing season climate and interactions with extreme events can also drive change. Warming winter temperatures, are leading to reduced snowpack levels (Groisman et al., 2004;Knowles et al., 2006), with consequences for water supply from spring snowmelt runoff (Stewart et al., 2004) and species that rely on persistent snow cover in late-winter as protection from thaw-freeze events (Buma et al., 2019). Species sensitive to winter climate include yellow-cedar [Callitropsis nootkatensis (D. ...
... However, across coastal temperate rainforests globally, warming temperatures are crossing key climatic and ecological thresholds (Veblen et al., 2011;Shanley et al., 2015). Along the Pacific coast of North America, average annual temperatures range from 4 to 12 • C (DellaSala, 2011), and importantly winter temperatures exist near the rain-tosnow threshold (−2 to 2 • C) (Buma et al., 2019). Therefore, although changes in temperature in coastal regions have not been as extreme as other high-latitude regions, small changes in temperature have had significant impacts (Buma, 2018;Buma et al., 2019). ...
... Along the Pacific coast of North America, average annual temperatures range from 4 to 12 • C (DellaSala, 2011), and importantly winter temperatures exist near the rain-tosnow threshold (−2 to 2 • C) (Buma et al., 2019). Therefore, although changes in temperature in coastal regions have not been as extreme as other high-latitude regions, small changes in temperature have had significant impacts (Buma, 2018;Buma et al., 2019). ...
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Old-growth forests in the Pacific Northwest are being fundamentally altered by climate change. A primary example of this is yellow-cedar (Callitropsis nootkatensis ), a culturally and economically important species, which has suffered widespread decline across its range since the beginning of the twentieth century. We used tree rings to compare the climate-growth response of yellow-cedar to two co-occurring species; western hemlock ( Tsuga heterophylla ) and Sitka spruce ( Picea sitchensis ), in an old-growth forest on Haida Gwaii, Canada, to better understand the unique climatic drivers of a species that is declining across its range. We developed three species-specific chronologies spanning 560–770 years, reconstructing a long-term record of species growth and dynamics over time. The climate is strongly influenced by the Pacific Decadal Oscillation (PDO), a multi-decadal pattern of ocean-atmospheric climate variability. Climate varied across three time periods that have coincided with major shifts in the PDO during the twentieth century [1901–1945 (neutral/positive), 1946–1976 (negative) and 1977–2015 (positive)]. Conditions were significantly warmer and wetter during positive phases, with the greatest maximum temperatures in the most recent period. We used complimentary methods of comparison, including Morlet wavelet analysis, Pearson correlations, and linear-mixed effects modeling to investigate the relations between climate and species growth. All three species exhibited multi-decadal frequency variation, strongest for yellow-cedar, suggesting the influence of the PDO. Consistent with this, the strength and direction of climate-growth correlations varied among PDO phases. Growing season temperature in the year of ring formation was strongly positively correlated to yellow-cedar and western hemlock growth, most significantly in the latter two time periods, representing a release from a temperature limitation. Sitka spruce growth was only weakly associated with climate. Yellow-cedar responded negatively to winter temperature from 1977 to 2015, consistent with the decline mechanism. Increased yellow-cedar mortality has been linked to warmer winters and snow loss. This study provides new insights into yellow-cedar decline, finding the first evidence of decline-related growth patterns in an apparently healthy, productive coastal temperate rainforest.
... The Pacific Northwest (PNW) contains the largest seasonal temperate rainforests in the world [22] and despite only slight increases in the area burned (before 2020), major shifts in future fire activity have been projected [28][29][30][31]. Discerning these trends is difficult owing to the episodic nature of wildfire events [32], the size and severity of these disturbances [33], and striking climatic gradients. ...
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Nearly 0.8 million hectares of land were burned in the North American Pacific Northwest (PNW) over two weeks under record-breaking fuel aridity and winds during the extraordinary 2020 fire season, representing a rare example of megafires in forests west of the Cascade Mountains. We quantified the relative influence of weather, vegetation, and topography on patterns of high burn severity (>75% tree mortality) among five synchronous megafires in the western Cascade Mountains. Despite the conventional wisdom in climate-limited fire regimes that regional drivers (e.g., extreme aridity, and synoptic winds) overwhelm local controls on vegetation mortality patterns (e.g., vegetation structure and topography), we hypothesized that local controls remain important influences on burn severity patterns in these rugged forested landscapes. To study these influences, we developed remotely sensed fire extent and burn severity maps for two distinct weather periods, thereby isolating the effect of extreme east winds on drivers of burn severity. Our results confirm that wind was the major driver of the 2020 megafires, but also that both vegetation structure and topography significantly affect burn severity patterns even under extreme fuel aridity and winds. Early-seral forests primarily concentrated on private lands, burned more severely than their older and taller counterparts, over the entire megafire event regardless of topography. Meanwhile, mature stands burned severely only under extreme winds and especially on steeper slopes. Although climate change and land-use legacies may prime temperate rainforests to burn more frequently and at higher severities than has been historically observed, our work suggests that future high-severity megafires are only likely to occur during coinciding periods of heat, fuel aridity, and extreme winds.
... In southeast Alaska, southwest New Zealand, and Chilean Patagonia, these forests are amongst the densest and biomass-rich biomes worldwide (DellaSala, 2011). These forests experience frequent disturbances (Johnstone et al., 2016) such as earthquakes, windstorms, volcanic eruptions, and landslides (Buma et al., 2019;Korup et al., 2019;Sommerfeld et al., 2018); such forest disturbances, in turn, alter the susceptibility to slope failure in feedback (Buma & Johnson, 2015;Scheidl et al., 2020). The susceptibility to shallow landslides can increase the following deforestation because of limited root reinforcement (Schwarz et al., 2010;Sidle, 1991), altered soil infiltration, and permeability rates. ...
... At the other extreme, transfer to the wet, maritime climate of the contorta garden led to the highest absolute survival for all populations, and water availability appears to be a significant driver of P. contorta success. Local declines are likely in portions of the species' distribution where, despite predicted increases in precipitation (Mahony et al., 2017), concurrent temperature increases will change the timing and type of precipitation (e.g., from snow-to rain-dominated precipitation; Buma et al., 2019) and thus growing-season water availability. Given that drought is expected to become increasingly common across its range (Coops & Waring, 2011;Mahony et al., 2020), drought adaptation may be key to local P. contorta population persistence. ...
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Aim Climate change poses significant challenges for tree species, which are slow to adapt and migrate. Insight into genetic and phenotypic variation under current landscape conditions can be used to gauge persistence potential to future conditions and determine conservation priorities, but landscape effects have been minimally tested in trees. Here, we use Pinus contorta, one of the most widely distributed conifers in North America, to evaluate the influence of landscape heterogeneity on genetic structure as well as the magnitude of local adaptation versus phenotypic plasticity in a widespread tree species. Location Western North America. Methods We paired landscape genetics with fully reciprocal in situ common gardens to evaluate landscape influence on neutral and adaptive variation across all subspecies of P. contorta. Results Landscape barriers alone play a minor role in limiting gene flow, creating marginal geographically‐based structure. Local climate determines population performance, with survival highest at home but growth greatest in mild climates (e.g., warm, wet). Survival of two of the three populations tested was consistent with patterns of local adaptation documented for P. contorta, while growth was indicative of plasticity for populations grown under novel conditions and suggesting that some populations are not currently occupying their climatic optimum. Main Conclusions Our findings provide insight into the role of the landscape in shaping population genetic structure in a widespread tree species as well as the potential response of local populations to novel conditions, knowledge critical to understanding how widely distributed species may respond to climate change. Geographically based genetic structure and reduced survival under water‐limited conditions may make some populations of widespread tree species more vulnerable to local maladaptation and extirpation. However, genetically diverse and phenotypically plastic populations of widespread trees, such as many of the P. contorta populations sampled and tested here, likely possess high persistence potential.
... Moist forests historically characterized by infrequent wildfire are projected to experience significant increases in wildfire frequency before the end of the century as a result of climate change and anthropogenic activities [1][2][3]. Many of these forests are not adapted to rapid shifts in disturbance regimes and future wildfire could lead to irreversible changes in vegetation structure and composition [4][5][6][7]. ...
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Characterizing wildfire regimes where wildfires are uncommon is challenged by a lack of empirical information. Moreover, climate change is projected to lead to increasingly frequent wildfires and additional annual area burned in forests historically characterized by long fire return intervals. Western Oregon and Washington, USA (westside) have experienced few large wildfires (fires greater than 100 hectares) the past century and are characterized to infrequent large fires with return intervals greater than 500 years. We evaluated impacts of climate change on wildfire hazard in a major urban watershed outside Portland, OR, USA. We simulated wildfire occurrence and fire regime characteristics under contemporary conditions (1992–2015) and four mid-century (2040–2069) scenarios using Representative Concentration Pathway (RCP) 8.5. Simulated mid-century fire seasons expanded in most scenarios, in some cases by nearly two months. In all scenarios, average fire size and frequency projections increased significantly. Fire regime characteristics under the hottest and driest mid-century scenarios illustrate novel disturbance regimes which could result in permanent changes to forest structure and composition and the provision of ecosystem services. Managers and planners can use the range of modeled outputs and simulation results to inform robust strategies for climate adaptation and risk mitigation.
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Dense tree stands and high wind speeds characterize the temperate rainforests of southern Chilean Patagonia, where landslides frequently strip hillslopes of soils, rock, and biomass. Assuming that wind loads on trees promote slope instability, we explore the role of forest cover and wind speed in predicting landslides with a hierarchical Bayesian logistic regression. We find that higher crown openness and wind speeds credibly predict higher probabilities of detecting landslides regardless of topographic location, though much better in low‐order channels and on midslope locations than on open slopes. Wind speed has less predictive power in areas that were impacted by tephra fall from recent volcanic eruptions, while the influence of forest cover in terms of crown openness remains.
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In recent decades large fires have affected communities throughout central and southern Chile with great social and ecological consequences. Despite this high fire activity, the controls and drivers and the spatiotemporal pattern of fires are not well understood. To identify the large-scale trends and drivers of recent fire activity across six regions in south-central Chile (~32-40˚S40˚S Latitude) we evaluated MODIS satellite-derived fire detections and compared this data with Chilean Forest Service records for the period 2001-2017. MODIS burned area estimates provide a spatially and temporally comprehensive record of fire activity across an important bioclimatic transition zone between dry Mediterranean shrublands/ sclerophyllous forests and wetter deciduous-broadleaf evergreen forests. Results suggest fire activity was highly variable in any given year, with no statistically significant trend in the number of fires or mean annual area burned. Evaluation of the variables associated with spa-tiotemporal patterns of fire for the 2001-2017 period indicate vegetation type, biophysical conditions (e.g., elevation, slope), mean annual and seasonal climatic conditions (e.g., precipitation) and mean population density have the greatest influence on the probability of fire occurrence and burned area for any given year. Both the number of fires and annual area burned were greatest in warmer, biomass-rich lowland Bío-Bío and Araucanía regions. Resource selection analyses indicate fire 'preferentially' occurs in exotic plantation forests, mixed native-exotic forests, native sclerophyll forests, pasture lands and matorral, vegetation types that all provide abundant, flammable and connected biomass for burning. Structurally and compositionally homogenous exotic plantation forests may promote fire spread greater than native deciduous-Nothofagaceae forests which were once widespread in the southern parts of the study area. In the future, the coincidence of warmer and drier conditions in landscapes dominated by flammable and fuel-rich forest plantations and mixed native-exotic and sclerophyll forests are likely to further promote large fires in south-central Chile.
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Many studies have examined how fuels, topography, climate, and fire weather influence fire severity. Less is known about how different forest management practices influence fire severity in multi‐owner landscapes, despite costly and controversial suppression of wildfires that do not acknowledge ownership boundaries. In 2013, the Douglas Complex burned over 19,000 ha of Oregon & California Railroad (O&C) lands in Southwestern Oregon, USA. O&C lands are composed of a checkerboard of private industrial and federal forestland (Bureau of Land Management, BLM) with contrasting management objectives, providing a unique experimental landscape to understand how different management practices influence wildfire severity. Leveraging Landsat based estimates of fire severity (Relative differenced Normalized Burn Ratio, RdNBR) and geospatial data on fire progression, weather, topography, pre‐fire forest conditions, and land ownership, we asked (1) what is the relative importance of different variables driving fire severity, and (2) is intensive plantation forestry associated with higher fire severity? Using Random Forest ensemble machine learning, we found daily fire weather was the most important predictor of fire severity, followed by stand age and ownership, followed by topographic features. Estimates of pre‐fire forest biomass were not an important predictor of fire severity. Adjusting for all other predictor variables in a general least squares model incorporating spatial autocorrelation, mean predicted RdNBR was higher on private industrial forests (RdNBR 521.85 ± 18.67 [mean ± SE]) vs. BLM forests (398.87 ± 18.23) with a much greater proportion of older forests. Our findings suggest intensive plantation forestry characterized by young forests and spatially homogenized fuels, rather than pre‐fire biomass, were significant drivers of wildfire severity. This has implications for perceptions of wildfire risk, shared fire management responsibilities, and developing fire resilience for multiple objectives in multi‐owner landscapes.
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The potential for climate change to cause mass tree mortality in forested systems by pushing environmental conditions past physiological tolerance thresholds is well documented. Less well studied is damage and mortality associated with climatic transitions, where mortality is less on either side of the transition; the shift from freezing winter conditions to thawed winter conditions in temperate and high latitudes is a clear example. “Transitional climate mortality” is sporadic, but widespread, associated with exposure to mortality during these climatic transitions, and triggered by proximal weather events like a hard freeze after a period of above freezing temperatures. Interestingly, this suggests that slower warming could result in more intensive mortality because of extended exposure to potential mortality events. The concept is tested using a well‐studied species (Callitropsis nootkatensis) on the US/Canadian Pacific coast. To identify the transitional mortality zone, statistical modeling combined with a current mortality map and bioclimatic variables was used. This process identified the −5° to 0°C zone (mean temperature of the coldest month) as particularly associated with transitional mortality. Weather station data from multiple locations were used to validate observations. Four GCMs (General Circulation Model) and two future warming scenarios (representative concentration pathway 2.6 and 8.5) were used to estimate time and spatial extent of exposure at broad scales; slower warming results in more intensive cumulative exposure than faster warming. Finally, by combining the observed mortality zone with weather station data a generalizable binomial model was tested as a means to estimate potential future mortality. This model is applicable to any system where the transitional mortality zone (e.g., temperature range) and the frequency of proximal mortality triggers are known. This type of mortality phenomena has been understudied but may be a large driver of future forest change, given the frequency of mortality events and the ubiquity of the freeze–thaw transition across temperate systems globally.
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The Andes span a length of 7000 km and are important for sustaining regional water supplies. Snow variability across this region has not been studied in detail due to sparse and unevenly distributed instrumental climate data. We calculated snow persistence (SP) as the fraction of time with snow cover for each year between 2000 and 2016 from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite sensors (500 m, 8-day maximum snow cover extent). This analysis is conducted between 8 and 36° S due to high frequency of cloud (> 30 % of the time) south and north of this range. We ran Mann–Kendall and Theil–Sens analyses to identify areas with significant changes in SP and snowline (the line at lower elevation where SP = 20 %). We evaluated how these trends relate to temperature and precipitation from Modern-Era Retrospective Analysis for Research and Applications-2 (MERRA2) and University of Delaware datasets and climate indices as El Niño–Southern Oscillation (ENSO), Southern Annular Mode (SAM), and Pacific Decadal Oscillation (PDO). Areas north of 29° S have limited snow cover, and few trends in snow persistence were detected. A large area (34 370 km2) with persistent snow cover between 29 and 36° S experienced a significant loss of snow cover (2–5 fewer days of snow year−1). Snow loss was more pronounced (62 % of the area with significant trends) on the east side of the Andes. We also found a significant increase in the elevation of the snowline at 10–30 m year−1 south of 29–30° S. Decreasing SP correlates with decreasing precipitation and increasing temperature, and the magnitudes of these correlations vary with latitude and elevation. ENSO climate indices better predicted SP conditions north of 31° S, whereas the SAM better predicted SP south of 31° S.
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Planted and invading non-native plant species can alter fire regimes through changes in fuel loads and in the structure and continuity of fuels, potentially modifying the flammability of native plant communities. Such changes are not easily predicted and deserve system-specific studies. In several regions of the southern hemisphere, exotic pines have been extensively planted in native treeless areas for forestry purposes and have subsequently invaded the native environments. However, studies evaluating alterations in flammability caused by pines in Patagonia are scarce. In the forest-steppe ecotone of northwestern Patagonia, we evaluated fine fuels structure and simulated fire behavior in the native shrubby steppe, pine plantations, pine invasions, and mechanically removed invasions to establish the relative ecological vulnerability of these forestry and invasion scenarios to fire. We found that pine plantations and their subsequent invasion in the Patagonian shrubby steppe produced sharp changes in fine fuel amount and its vertical and horizontal continuity. These changes in fuel properties have the potential to affect fire behavior, increasing fire intensity by almost 30 times. Pruning of basal branches in plantations may substantially reduce fire hazard by lowering the probability of fire crowning, and mechanical removal of invasion seems effective in restoring original fuel structure in the native community. The current expansion of pine plantations and subsequent invasions acting synergistically with climate warming and increased human ignitions warrant a highly vulnerable landscape in the near future for northwestern Patagonia if no management actions are undertaken.
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ContextLand-use change impacts biodiversity and ecosystem services, which are intrinsically related. There is a serious lack of knowledge concerning on how land-use change affects this relationship at landscape level, where the greatest impacts have been reported. A proper knowledge of that relationship would provide crucial information for planning conservation strategies. The forest landscape of southern Chile, which includes Valdivian Temperate Forest, has been designated as a hotspot for biodiversity conservation. However, this landscape has been transformed by land-use change. Objective We evaluated the impact of land-use change on the spatial patterns of the diversity of native forest habitat and the influence of these impacts on the provision of the ecosystem services water supply, erosion control, and organic matter accumulation from 1986 to 2011. Methods The evaluation, at the landscape level, was carried out using satellite images, landscape metrics, spatially explicit models and generalized linear models. Results: We found that the area loss of native forest habitat was 12%, the number patches of native forest habitat increased more than 150% and the Shannon diversity index decreased by 0.20. The largest decrease in the provision of services was recorded for erosion control (346%), and the smallest for water supply (11%). Conclusions The loss of provision of the ecosystem services can be explained by the interaction between the area loss, increase in the number patches and diversity loss. We recommend that the conservation planning strategies should consider the current landscape configuration, complemented with land-use planning.
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The Southern Annular Mode (SAM) is the main driver of climate variability at mid to high latitudes in the Southern Hemisphere, affecting wildfire activity, which in turn pollutes the air and contributes to human health problems and mortality, and potentially provides strong feedback to the climate system through emissions and land cover changes. Here we report the largest Southern Hemisphere network of annually resolved tree ring fire histories, consisting of 1,767 fire-scarred trees from 97 sites (from 22 °S to 54 °S) in southern South America (SAS), to quantify the coupling of SAM and regional wildfire variability using recently created multicentury proxy indices of SAM for the years 1531–2010 AD. We show that at interan-nual time scales, as well as at multidecadal time scales across 37–54 °S, latitudinal gradient elevated wildfire activity is synchronous with positive phases of the SAM over the years 1665–1995. Positive phases of the SAM are associated primarily with warm conditions in these biomass-rich forests, in which widespread fire activity depends on fuel desiccation. Climate modeling studies indicate that greenhouse gases will force SAM into its positive phase even if stratospheric ozone returns to normal levels, so that climate conditions conducive to widespread fire activity in SAS will continue throughout the 21st century. fire scars | climate modes | AAO | synchrony | warming
Vegetation succession following fire disturbances has long been of interest in ecology, but the evolution of landscape pattern and structure following low-severity ground fires is poorly understood. In coastal temperate rainforest ecosystems historic fire disturbances are not well documented and time since the most recent fire is largely unknown. We sampled 6000 tree cores from 27 forest plots that burned 124 years ago and 11 plots with no recent history of fire (within the last 1000 years) to understand the legacies of fire on forest stand structure in a British Columbia high-latitude coastal temperate rainforest. We assessed the timing and spatial extent of historic fires with a 700 year fire history reconstruction built from fire scars, and applied light detection and ranging (LiDAR) to ground-truth plot-level measurements. We sampled an additional 32 plots with known fire histories to validate the ability of LiDAR to detect and characterize historic fire legacies. In total, we sampled 70 plots for stem density, stand structure, and stand composition. Trees in burned plots were significantly taller, and the mean stem density was less than half that of unburned plots despite 124 years since the most recent fire. LiDAR analyses had similar results and also showed that burned plots had lower canopy cover and greater canopy complexity. Field-based measurements are still required to resolve differences in community structure and composition in our temperate rainforest study area. However, LiDAR may be an important tool to bridge the spatial information offered by plot-level measurements to larger area characterizations in the future. Our comparative analyses provide an improved understanding of fire legacies and temperate rainforest structure, which increases our ability to detect fire disturbances in heterogeneous forests and is important for forest resource management and conservation.
In an era of rapid climate change, understanding the natural capacity of species' ranges to track shifting climatic niches is a critical research and conservation need. Because species do not move across the landscape through empty space, but instead have to migrate through existing biotic communities, basic dispersal ecology and biotic interactions are important considerations beyond simple climate niche tracking. Yellow-cedar (Callitropsis nootkatensis), a long-lived conifer of the North Pacific coastal temperate rainforest region, is thought to be undergoing a continued natural range expansion in southeast Alaska. At the same time, yellow-cedar's trailing edge is approaching its leading edge in the region, due to climate-induced root injury leading to widespread mortality over the past century. To examine the current dispersal capacity of yellow-cedar at its leading range edge, and potential for the species' leading edge to stay ahead of its trailing edge, we characterized recent yellow-cedar stand development near Juneau, Alaska, and surveyed the spread of yellow-cedar seedlings just beyond existing stand boundaries. Despite suitable habitat beyond stand edges, stand expansion appears limited in recent decades to centuries. Large quantities of seed are germinating within stands and just beyond boundaries, but seedlings are not developing to maturity. Furthermore, c. 100-200-year-old yellow-cedar trees are located abruptly at stand boundaries, indicating stand expansion is in a period of stasis with a last pulse at the end of the Little Ice Age climate period. Vegetative regeneration is common across stands and may be an adaptive strategy for this long-lived tree to persist on the landscape until conditions are favourable for successful seedling recruitment, leading to an overall punctuated migration and colonization of new landscapes. Synthesis. Species ranges do not always respond linearly to shifting climatic conditions. Instead, successful colonization of new habitat may be tied to episodic, threshold-related landscape phenomena, dispersal ability, and competition with existing plant communities.