changing environmental drivers, tipping points...
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Changing Environmental Drivers,
Tipping Points,
& Resilience
in Fire-Prone Ecosystems
Craig D. Allen
USGS New Mexico Landscapes Field Station
Los Alamos, New Mexico
INTRO
Ecosystems and associated fire regimes are always
dynamic, in the process of change.
Significant changes in fire, and associated fire-prone
ecosystems, have been emerging recently in many parts of
the US, as well as in other regions globally.
These changes in fire can be understood as responses to
changes in the ENVIRONMENTAL DRIVERS of fire and other
ecosystem patterns and processes.
Since late 1980s, rapid “tipping point”
changes to Western US landscapes
by high-severity fire & forest die-off. Las Conchas Fire, 2011
Brian Jacobs CD Allen
CD Allen
Viveashe Fire, 2000
CD Allen
These TIPPING POINT changes in fire regimes and
ecosystems can be understood as responses to gradual
or abrupt changes in the ENVIRONMENTAL DRIVERS of
fire and other ecosystem patterns and processes.
Some big, fast TIPPING POINT changes in fire regimes
and ecosystems have been SURPRISES, with major
impacts on vegetation, watersheds, people, property,
economies, etc.
Some TIPPING POINT changes in US fire regimes and
ecosystems are raising concerns about the RESILIENCE
of linked human and natural systems.
Changing Environmental Drivers of Fire Regimes
Atmospheric Conditions
Fire Weather – short term
Climate Variability & Change – longer term
Atmosphere – key variables include:
- Temperature
- Humidity
- Precipitation
(amount, intensity, seasonality, snow vs. rain, …)
- Winds
(surface, aloft)
- Atmospheric stability
- Timing, seasonality
- Changing CO2, N2, O3
Example: Tipping-point fire regime changes related to
warming in the Western US
Wiilliams et al. 2015 Westerling et al. 2006
Fire Frequency – W US Area Burned – SW US
Fuels – key fire variables include:
- Type (e.g., grass, shrub, tree)
- Quantity
- Horizontal connectivity
- Vertical structure
- Moisture content
- Fuel buildup rate (i.e., plant growth rate)
With CO2 & N2 enrichment and longer growing
season, faster growth during wet periods
- Energy content
- Content of volatile compounds
- Live vs. Dead
Changing Environmental Drivers of Fire Regimes
FUELS
Schismus arabicus
Schismus barbatus
Mediterranean grass
Bromus tectorum
cheatgrass
Cenchrus
ciliaris
buffelgrass
Bromus madritensis var.
rubens red brome
Example:
Novel ecosystems and
“grassification” of
North American deserts
Courtesy: Julio Betancourt
FIR
E
HA
ZA
RD
h
igh
lo
w
TIME
Live,
water-stressed
conifer forest,
needles with volatile
biochemicals like
terpenes
Extensive tree
mortality,
dead needles
still on trees,
but without
volatile biochemicals
Dead needles drop,
Fine surface fuels , Surface fuels drier
Surface Fire
Canopy Fire
Dead trees start to fall,
Herb and shrub and
tree regrowth,
Coarse woody
surface fuels
bark
beetl
e o
utb
reak –
fo
rest
die
-off
Bentz et al., 2009
Hypothesized changes in conifer forest fire hazard with forest die-off
Major bark beetle
outbreaks
2001 – 2010
Strongly linked to
forest drought stress
Meddens et al., 2014
Ignitions – key variables include:
- Cause (lightning, human)
- Quantity
- Location
- Timing (season)
Changing Environmental Drivers of Fire Regimes
Ignitions
Photo: Bob Parmenter, VCNP
Fire Regime Changes: Severity
This aspen tree fell with wind & broke this power-line,
starting the Las Conchas Fire in the left foreground at
1 PM on June 26, 2011. Photo 2 months later.
Photo: Jeff Dube - USFS
~1 hour after ignition, the start of the
Las Conchas Fire, June 26, 2011.
Note extreme fire activity, flame lengths >> 300
feet.
Brian Jacobs
~7 hours after ignition, early in the
Las Conchas Fire, June 26, 2011.
View from Los Alamos.
Tipping Points: Human Communities & Society
Changing fire is causing impacts to:
- lives & health
- homes & property
- water supplies
- economies, etc…
NASA Earth Observatory
map by Robert Simmon
Aboveground Woody Biomass
When dry, the substantial
woody biomass building up
in the East becomes
available to burn. Combined
with lots of WUI and human
ignitions, the risk of more
severe fires in the East like
Gatlinburg 2016 will
increase if climate and fire
weather become hotter-
drier.
These are natural response to changing environmental drivers…
As environmental drivers continue to change, we should expect more
Tipping Point surprises…
E.g., if/when hotter droughts emerge in the Eastern US,
increases in wildfire and tree mortality can be expected.
Resilience & Adaptation
Many Western US forests and landscapes are starting to
rapidly adjust to a warmer and drier climate.
As large portions of Earth rapidly
move beyond our experience, the
Historical Range of Variability (HRV)…
As large portions of Earth rapidly
move beyond our experience, the
Historical Range of Variability (HRV)…
… we increasingly will need to:
anticipate,
adapt to, and
and begin managing for
an uncertain
Future Range of Variability (FRV).
As large portions of Earth rapidly
move beyond our experience, the
Historical Range of Variability (HRV)…
… we increasingly will need to:
anticipate,
adapt to, and
and begin managing for
an uncertain
Future Range of Variability (FRV).
Lots of learning to do…
Research Priorities
How to better anticipate fire-related surprises ?
1) Determine thresholds & tipping points for environmental
drivers of big, fast changes in fire regimes & ecosystems.
- physical
- biological-ecological
- socio-economic
- particularly temperature-sensitive processes
2) Extreme climate events (e.g., extreme droughts & heat waves)
as triggers of tipping point disturbance processes.
3) Disturbance interactions & feedbacks across spatial scales.
4) “Anticipatory natural resource management for a dynamic
future.” (Bradford et al. – in review)
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