Interactions Between Fire and Plant

Invasions Under a Warming Climate

in the Sierra Nevada Bioregion

Matt Brooks, Robert Klinger, Jan van Wagtendonk

U.S. Geological Survey

Western Ecological Research Center

Yosemite Field Station

Presentation Outline

• Conceptual framework for

climate x fire x invasive

plant interactions

• Variation among multiple

invaders and over time

• Collective implications of

a warming climate

• Ways to potentially get

ahead of the curve

climate

vegetation fire regimes

Temperatures and

precipitation affect growing

conditions (e.g. soil moisture

levels), which in turn affect

vegetation characteristics

lightning affects ignition

distributions

wind, temp, RH, and precipitation

(i.e. fire weather) affect fire

spread rates

Fuels affect ignition rates and

fire behavior and fire regimes

Fire behavior and fire regimes

affect vegetation distributions

The Fire/Climate Triangle

A Fire Triangle For The Modern Era?

climate

fire regimesnon-native plants

Nonnative Plants

Fuels

Fire Regime

Native Plants

+ –

–

Brooks et al. 2004

Invasive Plant / Fire Regime Cycle

The Invasive Plant / Fire Regime Cycle is

Influence by Many Interacting Factors

• Climate

• Vegetation (native and non-native)

• Fire regimes

• Climate x vegetation

• Climate x fire regimes

• Vegetation x fire regimes

• Climate x vegetation x fire regimes

IPCC 2001

Climate

Climate

0

20

40

60

80

100

120

140

160

J F M A M J J A S O N D J

Month

Wate

r (m

m)

0

10

20

30

40

50

60

70

80

0 C

WS

PET

AET

TMP

Nitrogen deposition?

0 10 20 30 40 50 60 70 80 90 100

Miles East of San Joaquin River

Yosemite National Park

Elevational Limits of

Vegetation Zones

- 13,000

- 12,000

- 11,000

- 10,000

- 9,000

- 8,000

- 7,000

- 6,000

- 5,000

- 4,000

- 3,000

- 2,000

- 1,000

35”

10”

20”

Live oak

Foothill pine

Chaparral

Blue oak

Giant sequoia

White fir

Sugar pine

Incense-cedar

Ponderosa pine

Western white pine

Red fir

Lodgepole pine

25”

Ele

vat

ion (

feet

)

50-

40-

30-

20-

10-

Whitebark pine

Mountain hemlock

Jeffrey pine

10”

VE

RN

AL

FA

LL

35”

Grasses

Valley

Grassland

Great Basin

Woodland

Lower

Montane

Forest

50”

Upper

Montane

Forest

35”

Subalpine

Forest

35” 30”

Foothill

Woodland Pre

cip

itati

on

(in

)

10”

Alpine

Meadow

25”

Vegetation Zones

Alpine

Subalpine

Upper Montane

Lower Montane

Foothill

Patterns of Plant Invasions

• Statewide estimate ≈ 1050

– ≈ 16%

• Sierra Nevada estimate

– No comprehensive inventory

– ≈ 250 -300 species (≈ 24% -

29%)

• Most are herbaceous

species (= fine fuels)

• Most concentrated in lower

elevations (grasslands, oak

woodlands) and areas of

anthropogenic use

Sources:

Rejmanek and Randall (1994)

Randall et al. (1998)

Gerlach et al. 2001

Keeley et al. 2003

Klinger et al. 2006

Invasion Process

Four general phases

Colonization

Establishment

Spread

Equilibrium

Time

Distribution and/or

Abundance Transformer species

= species that

significantly alter

ecosystem

structure/processes

Fire Regimes

Vegtype Seasonality FRI Area Complexity Intensity Severity Type

Chaparral Dry Moderate Large Low High High Crown

Woodland Dry Short Large Low Low Low Surface

Mix Conifer Dry Short Large Low High Moderate Surface

White Fir Dry Short Large Multiple Moderate Low Multiple

Red Fir Dry Moderate Moderate Multiple Multiple Multiple Multiple

Jeffrey Pine Dry Moderate Small Low Low Low Surface

Lodge Pine Dry Long Small Low Multiple Multiple Multiple

WB Pine Dry Long Small Low Low Low Surface

Meadow Dry Moderate Moderate High Multiple Multiple Surface

PJ Dry Long Small Low Low Multiple Surface

0 10 20 30 40 50 60 70 80 90 100

Miles East of San Joaquin River

Yosemite National Park

Elevational Limits of

Vegetation Zones

- 13,000

- 12,000

- 11,000

- 10,000

- 9,000

- 8,000

- 7,000

- 6,000

- 5,000

- 4,000

- 3,000

- 2,000

- 1,000

35”

10”

20”

Live oak

Foothill pine

Chaparral

Blue oak

Giant sequoia

White fir

Sugar pine

Incense-cedar

Ponderosa pine

Western white pine

Red fir

Lodgepole pine

25”

Ele

vat

ion (

feet

)

50-

40-

30-

20-

10-

Whitebark pine

Mountain hemlock

Jeffrey pine

10”

VE

RN

AL

FA

LL

35”

Grasses

Valley

Grassland

Great Basin

Woodland

Lower

Montane

Forest

50”

Upper

Montane

Forest

35”

Subalpine

Forest

35” 30”

Foothill

Woodland Pre

cip

itati

on

(in

)

10”

Alpine

Meadow

25”

shrublands and woodlands

moving upslope replacing forests

forests moving above

current treeline

Predictions of vegetation shifts

with a warming climate

Climate x Vegetation

Alpine

Subalpine

Upper Montane

Lower Montane

Foothill

Climate x Vegetation

Climate x Invasive Plants:

the Contemporary Version

Four general phases

Colonization

Establishment

Spread

Equilibrium

Time

Distribution and/or

Abundance

Climate

Four general phases

Colonization

Establishment

Spread

Equilibrium

Time

Distribution and/or

Abundance

Climate

Climate x Invasive Plants:

the Warmer Version

• Longer growing season and milder conditions at higher elevations could:– Open niches

– Increase the species pool

– Increase chances of establishment of transformer species

Invasion x Elevation Relationship

30004000

50006000

70008000

9000

10000

11000

Elevation

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Spe

cies

30004000

50006000

70008000

9000

10000

11000

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Y = exp(3.191+0.666*elevation-0.034*elevation̂ 2)r = 0.972

• Mooney et al. 1986

• Schwartz et al. 1996

• Keeley et al. 2003

• D’Antonio et al. 2004

• Klinger et al. 2006

• Climate has acted as a filter to

invasions

• Decreased diversity and

abundance of invasive plants

with increased elevation

• Climate change could “lower

the mountaintop” and improve

conditions for invasions at

higher elevations

…increased probability

of ignition?

Climate x Fire Regimes

• Temperature

• Precipitation

• RH

• Wind

• Lightning

Warming climate =

• Upslope shift in

vegetation

• Drier fuels

• Longer fire

season

Native Plants

Fuels

Fire Regime

Climate Topography

Climate x Vegetation x Fire

the one stable factorvariable factors

Currently, environmental gradients have more influence than

fire on presence of non-natives

NRI Plots

Unburned Burned0

100

200

300

400

Nu

mb

er

of

Plo

ts

PresentNot Present

Alien Species

TNC Plots

Unburned Burned0

50

100

150

200

Nu

mb

er

of

Plo

ts

PresentNot Present

Alien Species

Klinger et al. 2006

… but this may change as a

warming climate reduces

environmental limitations,

especially at lower elevations

Post-fire succession itself can also suppress non-natives

(Klinger et al. 2006)

0 10 20 30 40 50

Years Post-burn

0

1

2

3

4

5

6

7

Alie

n S

pecie

s

0 10 20 30 40 50

0

1

2

3

4

5

6

7

0 10 20 30 40 50

Years Post-burn

0

3

6

9

12

15

18

21

24

27

30

Alie

n C

over

(%)

0 10 20 30 40 50

0

3

6

9

12

15

18

21

24

27

30

…but this pattern can be affected by initial burn

severity, with higher severity associated with longer

dominance of non-natives postfire (Keeley et al. 2003)

600 1000 1500 2000 2400

Elevation (m)

010

20

30

40

50

60

De

nsity

Response Curves

brorub brotec erocic

The Dilemma Of Multiple Invaders

• Three species comprise

>90% total herbaceous

biomass

• Individualistic species

responses

• Overlapping but shifting

abundance peaks along

environmental gradients

• Individual and cumulative

effects along gradients

B. rubens E. cicutarium B. tectorum

Distribution with elevation

In the Mojave DesertInsights From The

2005 Mojave Fires

• Erodium cicutarium peaks

at drier end of precipitation

gradient

• Bromus rubens peaks at

intermediate part of

precipitation gradient

• Bromus tectorum has

monotonic increase along

precipitation gradient

-8 -6 -4 -2 0 2 4 6 8 10

Precipitation (Residuals)

010

20

30

40

50

De

nsity

Response Curves

brorub brotec erocic

Relationship of

Non-natives with

Precipitation

Transformer species exploiting a broad range of precipitation

E. cicutarium B. rubens B. tectorum

Distribution with rainfall

In the Mojave Desert

-1.0 1.0

-1.0

1.0

Elevation

SlopeAspect

RdNBR

Monsoon

Late Dry

Early Wet

Late Wet

EarlyDry

ENV. VARIABLES

SAMPLES

2006 2007 2008

Relative Dominance Varies Over Time Postfire

Shifting patterns of

dominance among postfire

years is driven by rainfall in

the Mojave Desert

Alien Grass

2006 2007 2008

0

10

20

30

40

50

60

70

80

90

100

Ste

ms

(%)

Alien Forbs

Seeded

Control

Condition

2006 2007 2008

0

10

20

30

40

50

60

70

80

90

100

Ste

ms

(%)

Native Grass

2006 2007 2008

0

10

20

30

40

50

60

70

80

90

100

Ste

ms

(%)

Native Forbs

Seeded

Control

Condition

2006 2007 2008

0

10

20

30

40

50

60

70

80

90

100

Ste

ms

(%)

2007

2008

2006

Non-natives May Themselves Alter Succession

Strong negative relationship between native diversity and density of non-natives

0 100 200 300 400 500 600 700

Density

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

E (

1/D

)

0 100 200 300 400 500 600 700

Density

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

E (

1/D

)

0 1 2 3 4 5

Non-native density (log)

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Seedlin

g D

ensi

ty (

log)

0 1 2 3 4 5

Non-native density (log)

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Seedlin

g D

ensi

ty (

log)

Strong negative relationship between native woody seedling density and density of non-natives

Effects of Repeated Spring Fires

in the Sierra Nevada%

of b

iom

ass

100

50

0

1980 1981 1982 1983

spring

fire

Native forbs

Non-native forbs

Non-native grasses

spring

fire

spring

fire redrawn from Parsons and Stohlgren 1989

redrawn from Parsons and Stohlgren 1989

Effects of Repeated Fall Fires

in the Sierra Nevada%

of bio

mass

100

50

0

1980 1981 1982 1983

Native forbs

Non-native forbs

Non-native grasses

fall

fire

fall

fire

fall

fire

1980

pre-

burn

1983

3x

burned

1983

unburned

control

1980

pre-

burn

1983

3x

burned

1983

unburned

control

spring burn increasers fall burn increasers

Erodium botrys 0 16 0 Centauria melitensis 0 46 0.1

Trifolium microcephalum* 1 11 0.1 Lotus subpinnatus* 0 11 0

Siline gallica 0 8 0.1 Siline gallica 0 5 0.1

Lotus subpinnatus* 0 7 0 Hypochoeris glabra 0 5 0.1

Festuca megalura 0.1 6 0Orthocarpus

attenuatus*0 4 0

Centauria melitensis 0 2 0.1

spring burn decreasers fall burn decreasers

Avena fatua 77 12 39 Avena fatua 90 5 39

Bromus diandrus 13 1 12 Bromus diandrus 11 0.2 12

Relative Biomass of Herbaceous Species

redrawn from Parsons and Stohlgren 1989

* Native species (all others are non-native species)

1980

pre-

burn

1983

3x

burned

1983

unburned

control

1980

pre-

burn

1983

3x

burned

1983

unburned

control

spring burn increasers fall burn increasers

Erodium botrys 0 16 0 Centauria melitensis 0 46 0.1

Trifolium microcephalum* 1 11 0.1 Lotus subpinnatus* 0 11 0

Siline gallica 0 8 0.1 Siline gallica 0 5 0.1

Lotus subpinnatus* 0 7 0 Hypochoeris glabra 0 5 0.1

Festuca megalura 0.1 6 0Orthocarpus

attenuatus*0 4 0

Centauria melitensis 0 2 0.1

spring burn decreasers fall burn decreasers

Avena fatua 77 12 39 Avena fatua 90 5 39

Bromus diandrus 13 1 12 Bromus diandrus 11 0.2 12

Relative Biomass of Herbaceous Species

redrawn from Parsons and Stohlgren 1989

* Native species (all others are non-native species)

A. fatua

49%↓ due to year

A. fatua

57%↓ due to year

84%↓ due to burning 94%↓ due to burning

General Patterns In Western Ecosystems

• Fire size has increased in Mojave

and Great Basin shrublands

– Linked to climate and invasive

species

• Fire size and severity has

increased in western forests

– Linked to climate and historical

factors, not invasive species (so far)

• Increase severity, coupled with

decreased environmental

impediments to invasion, may

increase the effects of non-

natives on forest fire regimes

Which Species May Emerge at the

New Transformer Species?

• Bromus tectorum ?

• Bromus madritensis rubens?

• Cirsium vulgare?

• Arundo donax?

• Genista monspessulana?

• Cytisus scoparius?

• Tamarix spp?

• Ailanthus altissima?

• Pinus pinea?

Where are New Species Coming From?

• We look most frequently for invaders from the west of the Sierra Nevada

• Species associated with agricultural and urban areas

• Forest cover can impede upward spread of species on the western slope, but this impediment may be moving upslope

But Many of the Barbarians are at

the Eastern Gates…and a few are already in the castle

• Mojave and Great Basin species

• Forest cover which impedes upward spread on the west slope is relatively low on the east slope

• Elevation gradient is also very steep on the east side, and upslope dispersal distances are much shorter than on the west side

What Does this all Mean for

Land Management in the Sierra Nevada?

• Past experiences may be increasingly insufficient to predict future effects of land management actions (e.g. Rx fire, weed control, native spp. revegetation)

• Thus, well-intended management action may trigger unexpected and potentially undesirable outcomes?

• Example: The bighorn burns project (east side)

• Question: Will an unintended outcome of burning winter range for sheep be increased abundance of cheatgrass as the climate warms?

Getting Ahead of the Curve

Integration of prioritization

and prediction

• What species will likely

become invasive?

• What sites will likely be

heavily invaded?

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

hypper cirvul vertha rumace poapra taroff phlpra

Species

Sco

re

Underwood et al. 2004

Brooks and Klinger in press

SummaryExpect increase in

colonizing species from

both the west and east

Expect upward elevational

spread of non-native

species

Fire frequency will likely

increase in upper

elevations

Combination of

prioritization and species

distribution models may

provide some

management options