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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.

Fuel

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

Photos: NPS

Example:

Drought-induced conifer mortality, Sequoia National Park, CA, Oct., 2015

CD Allen

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

Allen et al., 2010

Ignitions – key variables include:

- Cause (lightning, human)

- Quantity

- Location

- Timing (season)

Changing Environmental Drivers of Fire Regimes

Ignitions

# Ignitions by Cause

Balch et al., PNAS 2017

Ignitions

Balch et al., PNAS 2017

Fire Regime Changes: Frequency & Warming

Westerling 2016

Fire Regime Changes: Frequency & Warming

Westerling 2016

Fire Regime Changes - Area Burned

Westerling 2016

Fire Regime Changes: Area Burned

Abatzoglou & Williams 2016

Westerling 2016

Fire Regime Changes - Seasonality

Westerling 2016

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.

Photo: C.D. Allen

CD Allen

Day 1 effects, Las Conchas Fire. Photo taken 2 months later, Aug. 2011

Photo: C.D. Allen

Day 1 effects, Las Conchas Fire. Photo taken 2 months later, Aug. 2011

Tipping Points: Watershed

Effects

Photo: C.D. Allen

Tipping Points: Vegetation Changes

Post-fire type conversion from forest to shrubland, Dalton Fire (near Pecos) Photo: CD Allen

Tipping Points: Human Communities & Society

Changing fire is causing impacts to:

- lives & health

- homes & property

- water supplies

- economies, etc…

Ignitions

Balch et al., PNAS 2017

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.

NASA Earth Observatory

map by Robert Simmon

Aboveground Woody Biomass

Gatlinburg Fire

2016\

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…

Aug, 2011 Oct, 2015

What comes next… ?

Photos: Collin Haffey

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)