Fire Ecology of Pacific Northwest Forests

1
Fire Ecology of Pacific Northwest Forests

• ESC 322
• Forest Ecosystems
• James K. Agee
• University of Washington

2
What Well Cover Today

• Fire Adaptations of Plants and Animals
• Fire Regimes The Concept
• Examples of PNW Fire Regimes
• High Severity
• Mixed Severity
• Low Severity

3
Fire Adaptations

• Behavioral - animals
• Morphological plants and animals

4
Behavioral Adaptations

• Life Goes On
• Kites in Northern Australia Feathered Creatures
  at Risk
• Snakes, Lizards, Insects all Vulnerable

5
Most Animals Are Mobile
Direct Effects are Minimal
Move Away or Safe Sites
6
Morphological Adaptations
Xenomelanophila miranda Mating on charred juniper
Barbeque Beetle Merimna atrata Infrared
sensors on abdomen
7
Plant Have Many Adaptations

• Some Serve to Help the Species Persist
• Some Help the Plant Survive

8
Soil Seed Bank

• Plants with Dormant Seed that requires
  scarification
• Ceanothus snowbrush, others
• Ribes - gooseberry

9
Canopy Seed Bank
Cones in Trees or Shrubs

• Lodgepole pine
• Monterey pine
• Montezuma pine
• Sand pine
• Jack pine
• Black spruce
• Aleppo pine
• Many more

10
Canopy Seed Bank in Shrubs

• Banksia Australia
• Seeds open when burned
• Kermit the Frog style

11
Rapid Development

• Longleaf pine of southeast U.S.
• Looks like perennial grass for years
• Needles protect apical meristem
• Meristem then grows fast above scorch height

12
Sprouting

• Aspen sprouts form root suckers

13
Sprouting from Crown
Crown sprouts

• Interior live oak
• Dormant buds sprout
• If crown damage severe, root crown sprouts, too

Root Crown
14
The Famous Lignotuber

• Woody tuber
• Has buds and nutrients and water
• Stimulated to sprout when top killed

Stems were here
Soil surface
Roots were here
15
Lignotuber in Chamise

• California chaparral
• About 1.5 years after fire
• Sprouters Big advantage over seeder species
• Height of seeder species at same age
• Resilient to 2 quick fires

16
Alligator juniper

• One of few sprouting juniper species
• Lignotuber obvious
• Sprouts if top-killed

17
Many Herbs Well-Adapted
8 months After a Fire

• Meristem tissue at or below ground
• Tops cure (brown) every year
• Late season fires do little damage

18
Thick Bark

• Adaptation to Frequent Fire
• Insulates cambium
• Better than asbestos
• Tc 2.9 x2 where
• Tc time to cambium kill (minutes)
• X bark thickness (cm)

19
Fire Regimes

• Based on Severity (Effect) of Fire
• A function of plant adaptations fire characters
• Fire Characters frequency, intensity, extent,
  season, synergism
• Three major fire regimes

20
Forests of the West
Canada

• Colors represent broad forest types
• Gold/Orange are dry Forests
• Dark Green and Red are moist or cool forests

United States
Mexico
21
Historical Fire Regimes of the Pacific Northwest

• High (Lethal) Severity
• Infrequent (100 yrs) and stand-replacing
• Mixed (Moderate) Severity
• Less frequent (25-75 yrs) and a mix of severities
• Low (Non-lethal) Severity
• Frequent (5-15 yrs) but low intensity

22
Fire Regimes Vary by Environment
Warm
Cold
Wet Dry
23
Three Forest Examples
24
Western Hemlock/Douglas-fir

• Warm and wet
• High severity fire regime (200-400 yr fire return
  interval)
• Covered much of region west of Cascades

25
Stand Development Sequence

• Yr 1 - trees dying
• Yr 3 - stand initiation
• Yr 20 - continues
• Yr 100 stem exclusion
• Yr 200 understory reinitiation
• Yr 500 old growth

26
Fire Kill All Trees

• Drought, lightning, and east wind
• Severe surface plus crown fires
• Only 15 biomass consumed
• Opens growing space for Douglas-fir

27
Age 20
Douglas-fir

• The only period that Douglas-fir establishes
• Need open growing conditions
• Lives 750 years so will be a dominant the whole
  time

Lens cap
Western hemlock
28
Age 100
Dense canopy

• Stem Exclusion
• Self-thinning
• Simple structure
• Low plant/animal diversity

Little light to forest floor
29
Age 200

• Old growth stands blending
• Douglas-fir still dominant

Age 200
Age 500
30
Age 200
Gaps created by treefall allow light to reach
forest floor
Shade-tolerant understory (hemlock) responds
31
Age 500 Classic Old Growth
Huge Douglas-fir Trees
Huge Douglas-fir Logs
Rip Van Winkle
32
Fire Regime Shifts to South

• Central Oregon Cascades into Northern California
• Mixed Severity Fire Regime
• Note patch size smaller and severity is variable
  across the landscape

Douglas-fir forest
Warner Creek Fire
33
Red Fir Mixed Severity
34
A Mixed Effect
1978

• 1978 Entire area except foreground has burned
  or is burning
• 1986 Result is a mix of low-, moderate- and
  high-severity patches mixed together at local
  scale

1986
35
Low Severity Patches

• Mature red firs have thick bark
• Withstand light surface fires

36
Result is a Low Thin

• Only small
• understory trees killed
• Canopy undisturbed
• Typically about 1/3
• of area burned

37
Moderate Severity patches

• Longer flame lengths
• Kill understory trees and some overstory trees
• Opens some growing space but residual stand
  provides shelter

38
Canopy is Thinned

• Fire consumes AND creates coarse woody debris
• Mixed-severity fire regimes have highest
  consistent levels of CWD

39
Seedlings Encouraged

• Thermal buffering and shade of residual stand
  good for red fir regeneration
• Highest in moderate severity patches

40
High Severity Patches

• Stand replacement
• Few survivors, much coarse woody debris
• Local scale 5-50 ha

41
Some Areas Become Brush

• Lack of lodgepole pine seed source
• Too harsh for red fir
• Dominated by ceanothus and other shrubs and herbs
  for decades

42
Landscape Diversity
Moderate Severity

• Local fire variability creates even-aged and
  multi-aged patches
• Local scale

High Severity
Low Severity
43
Diversity Maintained Over Time
Fire just shown

• Landscape structure, species composition, and
  pattern is regulated by fire

Fire about 50 years ago
44
Ponderosa Pine - Low Severity
45
Ponderosa Pine Forests

• Species has a Large Range
• Pure ponderosa pine,
• or Mixed conifer
• Douglas-fir
• Grand fir
• White fir

46
Historical Conditions

• Small Even-aged Groups
• 50-150 trees/hectare
• Oldest groups (see arrow) killed by bark beetles

47
Western Pine Beetle

• Small Group Tree Killer
• Attacks Trees of Low Resistance
• In historical forests, these were the oldest
  groups

48
Examples of Historic Pine Forest
Small trees are a result of fire exclusion
Thick Bark
Wide Spacing
Tall Crowns
49
What Maintained Open Structure?

• Frequent, Low Intensity Forest Fires
• Leave History with Fire Scars
• Up to 30 Scars on One Tree

Thick bark protects most of cambium
50
Ignition Sources

• People and Lightning
• Dry lightning common in western U.S.
• Native Americans also burned dry forests
• protect villages
• encourage herbs and shrubs

51
Fire Scar Cross Section

• Each fire kills several cm of cambium
• Subsequent annual growth begins to cover scar
• Next fire repeats process
• Fires about every 10 years on this sample

52
Fire Exclusion Removed Fire

• Effective suppression of wildfire began 1900 in
  most U.S. pine forest
• Fire killed small trees
• Therefore fire was bad

53
Unintended Consequences

• Yosemite Valley in California Sierra Nevada in
  1860
• Same view 100 years later
• Pine and oaks replaced by incense-cedar and white
  fir

1860
1960
1960
54
Pine Forest - 50 Years of Change
Low Fire Hazard
1909
1927
High Fire Hazard
1948
1938
55
Fires Get Bigger and More Severe

• Fire decline until after World War II
• Mechanization/Air support help
• Fuel buildup becomes too widespread for control
  of all fires

56
Friendly Flame Becomes a Demon

• Fires escape initial attack
• Historical fires large but of low severity
• Todays fires large but of high severity

57
With Frequent Fire
With Fire Exclusion
58
Reduce Fuel and Fire Behavior
Open Crowns No Crown Fire
No Ladder fuels No Torching
Low surface fuels Low Flame Length
59
A Solution Will Take Time