Forest Insects & Wildland Fire

Ann M. Lynch, Ph.D.

US Forest Service, Rocky Mountain Research Station, &

University of Arizona, Laboratory of Tree-Ring Research

photo: Pavlo Vakhrushev

The most frightening sound in the forest is:

a.

The howl of

the WOLF

The most frightening sound in the forest is:

a.

The howl of

the WOLF

b.

The growl of

the GRIZZLY

The most frightening sound in the forest is:

a.

The howl of

the WOLF

b.

The growl of

the GRIZZLY

c.

The belch

of the

BARK

BEETLE

The most frightening sound in the forest is:

a.

The howl of

the WOLF

b.

The growl of

the GRIZZLY

c.

The belch

of the

BARK

BEETLE

d.

The

crackle of

FIRE

Insects and fire

• Ecological disturbance agents

• Social perceptions

c.

The belch

of the

BARK

BEETLE

d.

The

crackle of

FIRE

HUMAN PERCEPTIONS OF INSECT & FIRE DISTURBANCES

Historically, insects

damage larger area than

wildfire, but wildfire is

perceived as more

significant.

Contemporary insect and

fire events are both

thought to be anomalous,

yet the fire events are

considered greater

catastrophes.

Why?

Human perceptions are complicated, but

… FIRE BEATS BUGS ANY DAY

Fire is an immediate crisis, but we have time to do

something about insect outbreaks

Up in smoke is worse than dead and decaying

Insects are living organisms that have (a few)

inherent rights, fire is an agent of the devil

Human perceptions are complicated, but

… FIRE BEATS BUGS ANY DAY

Fire is an immediate crisis, but we have time to do

something about insect outbreaks

Up in smoke is worse than dead and decaying

Insects are living organisms that have inherent

rights, fire is an agent of the devil

The primary difference is risk to lives & property…

David McNew/Getty Images. Show

Low AZ during Rodeo-Chedeski Fire

Insects do

not threaten

imminent

harm to

people or

their homes.

City of Denver in a haze of smoke from the Hayman wildfires. View of city

photographed from the west looking east.

Pat Shannahan (photo)/The

Arizona Republic. Rodeo Fire

AZCentral.com

Wildfires sweep

across Texas,

four dead

Smoke City

FOREST INSECTS & WILDLAND FIRE

Fire effects on insects

Insect effects on fire

Fire & insects as disturbance agents

3400 species/ac (PNW old-growth forest)

124,000,000 to 455,000,000 arthropods/ac of soil 5” deep (estimates

from various ecosystems)

°C General effect

46 kill 62% of bugs of 10 min, 83% in 30 min

60 kill almost all bugs in 10 min

100 drive off moisture

300 smoldering fire

K.Chief lecture: fire effects in sagebrush steppe, Nevada

The majority of arthropods present in wildland

fires die

photo: Pavlo Vakhrushev

INSECT RESPONSE TO FIRE

Pyro bugs: attracted by flames & smoke: some wood

borers (Monochamus beetles, siricid wasps,

parasitoids of wood borers & bark beetles)

Attack fire-damaged trees:

Wood borers

Some bark beetles: fir engraver

Douglas-fir beetle

turpentine beetles

many BB in ponderosa pine &

southern pines

Can initiate expansive outbreaks beyond fire-damaged areas:

Douglas-fir beetle NOT: mountain pine beetle

fir engraver spruce beetle

May have a synergistic interaction with fire:

Pandora moth

INSECT ACTIVITY AFTER FIRE

Why bark beetles attack fire-damaged trees

Ips beetle attack on fire-damaged

red pine (Ayers et al. 1999)

Tree defenses are weakened

Reduced sap flow in damaged area

Reduced sap flow if crown or roots are damaged

Altered sap chemistry

Insects attracted to injured trees

Increased brood success for some species

Roundheaded pine beetle attack and pitch

tubes on drought-stressed ponderosa pine

(photo: Lynch 2009, Santa Catalina Mtns AZ)

POST-FIRE MORTALITY FROM BARK BEETLES

Risk factors

• Tree & bark beetle species

• Canopy consumption

• Canopy scorch

• Bole scorch

• Tree diameter ( ↑ or ↓ varies by

species & region)

• Burn season

• Root damage (difficult to asses)

• Pre-fire vigor

• Post-fire precipitation

• Pre-fire BB population levels

INSECT RESPONSE TO FIRE

red turpentine beetle in fire-damaged

ponderosa pine (A. Eglitis)

P(bark beetle outbreak after fire)

tree species/veg type

Douglas-fir

Ponderosa pine

Englemann spruce

& spruce-fir

lodgepole pine

from Joel McMillin, USFS R3 Flagstaff

POST-FIRE MORTALITY FROM BARK BEETLES

Key papers. Note: the literature mostly addresses tree- and stand-level

effects, NOT landscape-level effects

1) Breece et al. 2008. Prescribed fire effects on bark beetle activity and

tree mortality in southwestern ponderosa pine forests. Forest Ecology

and Management 255: 119-128.

2) McHugh et al. 2003. Bark beetle attacks on ponderosa pine following

fire in northern Arizona. Environmental Entomology 32: 510-522.

3) Ryan and Amman. 1996. Bark beetle activity and delayed tree mortality

in the Greater Yellowstone Area following the 1988 fires. Ecological

Implications of Fire in Greater Yellowstone, IAWF.

4) Sieg et al. 2006. Best predictors for postfire mortality of ponderosa

pine trees in the intermountain West. Forest Science 52: 718-728.

5) Youngblood et al. 2009. Delayed conifer mortality after fuel reduction

trreatments: interactive effects of fuel, fire intensity, and bark beetles.

Ecological Applications 19: 321-337.

FOREST INSECTS & WILDLAND FIRE

Fire effects on insects

Insect effects on fire

Fire & insects as disturbance agents

Insects are not known to start fires or to put out fires

But they do alter:

fuel complexes species composition

stand structure stand densities

… which in turn affect fire:

behavior intensity

risk hazard

rates of spread

transition from surface to canopy

regimes

Key paper: Jenkins et al. 2008. Bark beetles, fuels, fires and implications for

forest management in the Intermountain West. Forest Ecology and Management

254: 16-34.

Photo: Bob Oakes, USFS

“Conventional wisdom”

is plentiful, but in

actuality these effects

are poorly understood

and data are sparse

From NFPA video

A Christmas tree that has

been well-watered, ignited at

floor level.

www.nfpa.org

Watered

10 sec

45 sec

From NFPA video

Dry vs watered Christmas

trees with ignition at the

bottom

www.nfpa.org

Watered Dry

10 sec

45 sec

Initiation

energy

May 2002

Piñon mortality from pinyon ips

Photos: Craig Allen

October 2004

FUEL

EFFECTS OF A TREE-KILLING INSECT OUTBREAK ON FUELS

EFFECTS OF A TREE-KILLING INSECT OUTBREAK ON FUELS

Time frame Effect

months Reduced foliar moisture content

“Red” patches in green forest

months-years Increased amount & continuity of fine

surface fuels

Reduced canopy bulk density

Years Reduced canopy bulk density

Increased duff volume

Increased herbaceous fuels

years-

decades;

onset &

duration

variable

High-extreme amounts of down

coarse woody debris

Increased live surface fuels

Reduced crown base height

Altered micro-climates

decades Jackstraw logs + fine flashy fuels

spotting distance & ignition

ability to transition from

surface to canopy

ability to sustain canopy fire

surface fire intensity

EFFECTS OF AN EXTENDED DEFOLIATOR INSECT OUTBREAK ON FUELS (more

speculative than the previous table; dependent upon outbreak duration & severity)

Time frame Effect

Months-years

Reduced foliar moisture content (dead needles, increased air-flow)

Reduced canopy fuels

Some species: reduced lower canopy fuels

Increased amount & continuity of fine surface fuels

Increased duff volume

Increased herbaceous fuels

Years-decades;

onset &

duration

variable

Reduced canopy bulk density

Increased amounts of CWD

Increased live surface fuels

Reduced crown base height

Altered micro-climates

Years-decades Jackstraw stems, if mortality is high

Increased grass/shrub/regen canopies

FOREST INSECTS & WILDLAND FIRE

Insects

Insect effects on fire

Fire effects on insects

INSECTS & FIRE AS DISTURBANCE AGENTS

SIMILARITIES IN INSECTS & AND FIRE AS DISTURBANCE AGENTS

Mortality events

Patchy

Mixed-severity

Regimes are described in similar terms

risk & hazard

return intervals

intensity

control and manage

Extreme events are rare

Target-specific vs everything goes: Insects attack trees of

specific species and size classes. Canopy fires are not

so selective.

Post-event succession: generally, bark beetle outbreaks

take out old, large, seed-bearing trees, and in mixed-age

& -species stands leave shade-tolerant understory.

Surface fires take out younger, smaller, non-seed

producing trees, and in mixed-species stands leave the

larger seed-prducing components. Canopy fires take

everything or nearly so in large patches, leaving

opportunities for colonizing vegetation.

Temporal frameworks: outbreak duration varies by insect

species; most are short but some may be lengthy. Fires

are usually of short duration.

Nutrient cycling, carbon destination

Wildlife habitat, snow melt, hydrologic effects, blah blah

ECOLOGICAL DIFFERENCES BETWEEN

INSECT OUTBREAKS & FIRE

blah

Initiation

energy

Do catastrophic insect

outbreaks lead to

catastrophic wildfires?

FIRE: Crown fire initiation depends on:

• crown base height

• surface fire intensity

• ability to transition surface-to-crown

Crown fire spread depends on:

• crown bulk density

• wind speed

• slope

INSECTS: Outbreak effects are often transitory

CLIMATE : Usually, wind & drought drive

BUT:

Insect outbreaks can last many years, increasing

the potential for drought, heat, wind, insect

damage, and fire to coincide

The same area can be subject to repeated,

prolonged activity

Once blowdown occurs, the “canopy” is the

jackstrawed timber`

Surface fuel connectivity

Rare events (perfect storms)

Long-term lag effects?

Do catastrophic insect

outbreaks lead to

catastrophic wildfires?

Do catastrophic insect

outbreaks lead to

catastrophic wildfires?

Data are sparse; evidence says

NO

But, STAND STRUCTURE may

affect P(an area burning in a fire)

after long-term lags… given that

there is a fire, as this is not an effect

on P(ignition)

MATTERS OF ASSOCIATION & INFLUENCE

ASSOCIATION & INFLUENCES ARE INEVITABLE

Fire regimes influence forest structure & species

composition

Insect populations influence forest structure &

species composition

\ an association between fire regimes and

insect outbreak regimes is inevitable

CONCLUSIONS FROM SPARSE DATA:

Insect effects on stand structure much more important than

mortality effects on fuels

Insects & fire are often influenced by similar factors

Associations between outbreaks & P(burning) may occur with

long-term post-outbreak lags

Key papers:

Bigler et al. 2005. Multiple disturbance interactions and drought

influence fire severity in Rocky Mountain subalpine forests.

Ecology 86: 3018-3029

Jenkins et al. 2008. Bark beetles, fuels, fires and implications for

forest management in the Intermountain West. Forest Ecology

and Management 254: 16-34.

Lynch H.J. et al. 2006. The influence of previous mountain pine

beetle (Dendroctonus ponderosae) activity on the 1988

Yellowstone fires. Ecosystems 9: 1318-1327.

Fire exclusion favors: shade-tolerant tree species

multi-storied canopies

high-density and highly-stocked stands

It would be difficult to write a better silvicultural

prescription to favor western spruce budworm,

Douglas-fir tussock moth, and other defoliators in

mixed-conifer forests.

INSECT RESPONSE TO FIRE EXCLUSION

Monument Canyon

Los Griegos

Mean P

erc

ent S

acrr

ed

Num

ber

of T

rees R

ecord

ing O

utb

reaks

East Fork

1750 1800 1850 1900 1950

0

5

10

15

20

25

30

35

1750 1800 1850 1900 1950

0

5

10

15

20

25

30

35

40

0

25

50

75

100

0

25

50

75

100

Frijoles Canyon

1750 1800 1850 1900 1950

0

5

10

15

20

25

30

0

25

50

75

100

Canada Bonito

0

25

50

75

100

1750 1800 1850 1900 1950

0

5

10

15

20

25

1750 1800 1850 1900 1950

0

5

10

15

20

25

30

35

0

25

50

75

100

Red: Moving period fire occurrence

Green: WSBW outbreak time series

Has budworm replaced fire as the

primary disturbance agent?

WSBW reconstruction:

Jemez Mountains, New Mexico

RECOMMENDED READINGS

Bond M.L., Lee D.E., Bradley C.M., Hanson C.T. 2009. Influence of pre-fire tree mortality on fire severity in conifer forests of

the San Bernardino Mountains, California. The Open Forest Science Journal 2009 2: 41-47.

Breece et al. 2008. Prescribed fire effects on bark beetle activity and tree mortality in southwestern ponderosa pine forests.

Forest Ecology and Management 255: 119-128.

Brown, J.K. 1975. Fire cycles and community dynamics in lodgepole pine forests. In: Management of Lodgepole Pine

Ecosystems.

Bulaon B.M. 2003. Douglas-fir beetle surveys of the fires of 2000 in the Northern Region. USDA Forest Service, Northern

Region, Forest Health Protection, Report 03-2, 10 p.

Jenkins M.J., Hebertson E., Page W., Jorgensen C.A. 2008. Bark beetles, fuels, fires and implications for forest management

in the Intermountain West. Forest Ecology and Management 254: 16-34.

Klutsch J.G. et al. 2009. Stand characteristics and downed wood debris accumulations associated with a mountain pine

beetle (Dendroctonus ponderosae Hopkins) outbreak in Colorado. Forest Ecology and Management 258: 641-649.

McHugh et al. 2003. Bark beetle attacks on ponderosa pine following fire in northern Arizona. Environmental Entomology 32:

510-522.

Ryan and Amman. 1996. Bark beetle activity and delayed tree mortality in the Greater Yellowstone Area following the 1988

fires. Ecological Implications of Fire in Greater Yellowstone, IAWF.

Sieg et al. 2006. Best predictors for postfire mortality of ponderosa pine trees in the intermountain West. Forest Science 52:

718-728.

White et al. 1997, Flammability of Christmas trees and other vegetation. Proceedings of the International Conference on Fire

Safety, Volume Twenty-Four 1997, www.fpl.fs.fed.us/documnts/pdf1997/white97b.pdf.

Youngblood et al. 2009. Delayed conifer mortality after fuel reduction treatments: interactive effects of fuel, fire intensity, and

bark beetles. Ecological Applications 19: 321-337.

A SHORT PRIMER ON FOREST INSECT PESTS

Insects

Damage

Outbreak dynamics

This info not

presented in

lecture

Ponderosa pine mortality from Arizona five-spined ips,

Horsethief Basin, Arizona. Photo by Joel McMillin

A SHORT PRIMER ON INSECT PESTS

Insects moths & butterflies

Damage beetles

Outbreaks flies

aphids, scales, cicadas

bees, ants, & wasps

thrips

crickets, grasshoppers, mantids

20

additional

orders

HEXAPODA

1.a. Winged, ... 2

1.b. Wingless ... 9

2.a Wings membranous, ... 3

2.b Front wings hardened or leathery, ... 18

3.a With 1 pair of wings, ... 4

3.b With 2 pairs of wings, ... 24

4.a Pronotum extending back over abdomen, ... 5

4.b Pronotum not as above, ... 37

5.a Abdomen with threadlike caudal filaments, ... 6

5.b Abdomen without threadlike caudal filaments, ... 63

6.a Antennae long and conspicouous, ... 7

6.b Antennae short, bristlelike, ... 87

7.a Tarsi nearly always 5-segmented, mouthparts haustellate, ... 8

7.b Tarsi 2- or 3-segmented, mouthparts variables, ... 141

8.a. Mouthparts mandibulate, ... ....................................... Psocoptera

8.b. Mouthparts haustellate, .............................................. Homoptera

Hemimetabolous or holometabolous?

Egg » » Nymph » » Adult

or

Egg » » Larva » » Pupa » » Adult

Egg » » Nymph 1 » » Nymph 2 » » Nymph 3 » » Nymph 4 » » Adult

or

Egg » » Larva 1 » » Larva 2 » » Larva 3 » » Pupa » » Adult

A SHORT PRIMER ON INSECT PESTS

Insects moths & butterflies

Damage beetles

Outbreaks flies

aphids, scales, cicadas

bees, ants, & wasps

thrips

crickets, grasshoppers, mantids

HEXAPODA

1.a. Winged, ... 2

1.b. Wingless ... 9

2.a Wings membranous, ... 3

2.b Front wings hardened or leathery, ... 18

3.a With 1 pair of wings, ... 4

3.b With 2 pairs of wings, ... 24

4.a Pronotum extending back over abdomen, ... 5

4.b Pronotum not as above, ... 37

5.a Abdomen with threadlike caudal filaments, ... 6

5.b Abdomen without threadlike caudal filaments, ... 63

6.a Antennae long and conspicouous, ... 7

6.b Antennae short, bristlelike, ... 87

7.a Tarsi nearly always 5-segmented, mouthparts haustellate, ... 8

7.b Tarsi 2- or 3-segmented, mouthparts variables, ... 141

8.a. Mouthparts mandibulate, ... ....................................... Psocoptera

8.b. Mouthparts haustellate, .............................................. Homoptera

Hemimetabolous or holometabolous?

Egg » » Nymph » » Adult

or

Egg » » Larva » » Pupa » » Adult

Egg » » Nymph 1 » » Nymph 2 » » Nymph 3 » » Nymph 4 » » Adult

or

Egg » » Larva 1 » » Larva 2 » » Larva 3 » » Pupa » » Adult

majority of

wildland

tree pests

A SHORT PRIMER ON INSECT PESTS

Insects

Damage Type vs. effects on trees

Outbreaks

A SHORT PRIMER ON INSECT PESTS

Insects

Damage: Type defoliators (leaf chewers)

Outbreaks phloem fluid feeders (sap-suckers)

phloem tissue feeders (incl. bark beetles)

wood borers

… many others

A SHORT PRIMER ON INSECT PESTS

Insects

Damage: Type defoliators (leaf chewers)

Outbreaks phloem fluid feeders (sap-suckers)

phloem tissue feeders (incl. bark beetles)

wood borers

… many others

A SHORT PRIMER ON INSECT PESTS

Insects

Damage: Type defoliators (leaf chewers)

Outbreaks phloem fluid feeders (sap-suckers)

phloem tissue feeders (incl. bark beetles)

wood borers

… many others

bark beetle mortality in ponderosa pine, Tonto NF, Joel McMillin

A SHORT PRIMER ON INSECT PESTS

Insects

Damage: Type defoliators (leaf chewers)

Outbreaks phloem fluid feeders (sap-suckers)

phloem tissue feeders (incl. bark beetles)

wood borers

… many others

Generality: for the most part, certain types of insects cause certain

types of damage

Insects Damage

moths defoliators (leaf chewers)

aphids, adelgids phloem fluid feeders (sap-suckers)

bark beetles phloem tissue feeders

beetles, ants wood borers

many all the above & many others

A SHORT PRIMER ON INSECT

PESTS

Insects

Damage: Effects on trees

Outbreaks Is it lethal?

mortality-causing vs.

non-fatal damage

A SHORT PRIMER

ON INSECT PESTS

Insects

Damage

Outbreak &

population dynamics

Semivoltine

univoltine

multivoltine

Asaro & Berisford. 2001. Env. Entomol. 30: 776.

Nantucket pine tip moth trap catches,

Georgia piedmont.

A SHORT PRIMER

ON INSECT PESTS

Insects

Damage

Outbreak &

population dynamics

semivoltine

univoltine

multivoltine

“aggressive” population dynamics

The 1990s spruce beetle

outbreak in Alaska progressed

from single trees to scattered

mortality to >90% mortality for

the entire Kenai Peninsula

A SHORT PRIMER

ON INSECT PESTS

Insects

Damage

Outbreak &

population dynamics

cyclic, eruptive, non-outbreak

0

50

100

150

200

250

300

350

400

450

500

1 51 101 151 201 251

year

rela

tive p

op

ula

tio

n d

en

sit

y

food resource

parasites

predators

disease

weather

phenology