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Fire History from Tree Rings

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Fire History from Tree Rings. Justification: Wildfires in Montana and Idaho …. Justification: Wildfires in Florida and Georgia …. Justification: Wildfires in California …. Justification: Wildfires in Arizona …. Justification: Wildfires in Arizona ….

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The fire-scar record from tree rings.

ponderosa pine, El Malpais National Monument, New Mexico

Southwestern white pine and ponderosa pine, Mt. Graham, Arizona

The fire-scar record from tree rings.

Giant sequoia stump, Sequoia National Park, California

The fire-scar record from tree rings.

Table Mountain pine snag, Brush Mountain, Virginia

The fire-scar record from tree rings.

Catface on Table Mountain pine log, Reddish Knob, Virginia

The fire-scar record from tree rings.

Fire scars on freshly-cut Table Mountain pine, Brush Mountain, Virginia

The fire-scar record from tree rings.

Fire scars on ponderosa pine, El Malpais National Monument, New Mexico

The fire-scar record from tree rings.

Fire scars on sugar pine, Sequoia National Park, California

The fire-scar record from tree rings.

Fire scars on giant sequoia, Sequoia National Park, California

Seasonality of past fires from tree rings.

Fire scar on southwestern white pine, Mt. Graham, Arizona

Seasonality of past fires from tree rings.

Detail of fire scar on ponderosa pine, El Malpais National Monument, New Mexico

Fire regimes:
  • Fire frequency: how often
    • Mean Fire Return Interval, Weibull Median Probability Interval
  • Fire seasonality: when fires occur throughout the year
    • Early season versus late season
  • Fire severity: effects on forests
    • Age structure, stand composition, stand structure
  • Fire extent: spatial aspects
    • Patchy fires versus landscape level fires
  • Fire variability: changes in fire over time and space
    • Climatic or human-driven?
Each line = 1 tree

Sample IDs

Dash lines = non-recorder years

Begin/end symbology

Each tic = fire scar

Solid lines = recorder years

Composite axis

Interpreting Fire History Charts

Years on x-axis

Period of Reliability: 1896 to 1944



Pines Oaks

Mountain Otherlaurel hardwoods

Stand Age, Structure, and Composition

  • Standard 50 x 20 m plot but greater spatial coverageis available using numerous smaller circular plots
  • Inventory all tree species, measure dbh
  • Core, crossdate/age all trees ≥ 5 cm dbh
  • Inventory all saplings < 5 cm dbh,> 50 cm ht
  • Inventory seedlings in 10 x 20 msubplot
  • Collect sections from 20 mountainlaurel stems
  • Measure depth to mineral soil at20 random locations

50 m

20 m

Cohort establishment with surviving trees, then little fire for 30 years = possible moderate severity fire in 1853

Fires abruptly terminate after the 1926 and 1932 fires with establishment of the Jefferson National Forest in 1934.

Brush Mountain Fire History

Period of Reliability: 1758–1934

All fires:

MEI: 3 yrs; LEI: 1 yr; UEI: 8 yrs

Widespread fires:

MEI: 8 yrs; LEI: 2 yrs; UEI: 19 yrs

90% early, 10% late season

Oak and yellow pine decline, replacement by fire intolerant species: eastern white pine, eastern hemlock, red maple

Fires abruptly terminate after the 1929 fire with establishment of Great Smoky Mountains National Park in 1934.

Gold Mine Trail Fire History

Period of Reliability: 1850–1929

All fires:

MEI: 2 yrs; LEI: 1 yr; UEI: 4 yrs

Widespread fires:

MEI: 5 yrs; LEI: 2 yrs; UEI: 9 yrs

60% early, 40% late season

All Sites, 1825–1934

All fires:WMPI = 2 yrs, range 1 to 3 yrs

Widespread fires:WMPI = 8 yrs, range 2 to 17 yrs

Seasonality:73% dormant, early season

All Sites, 1935–2006

All fires:WMPI = 4 yrs, range 1 to 6 yrs

Widespread fires:No area wide fires post 1934

Seasonality:50% dormant, early season

Gold Mine Trail

Rabbit Creek Trail

Pine Mountain



Basically, tree-ring based fire history studies can be performed in nearly all forested temperate environments, even in subtropical environments and at higher elevations (despite fire being uncommon).

Big Pine Key

MFI = mean fire interval; WMPI = Weibull median probability interval; SD = standard deviation

No Name Key

Analyzing the Climate/Wildfire Relationship:
  • Done using Superposed Epoch Analysis
  • Originally developed to study the preconditioning controls of natural events. Examples?
  • First “stacks” all fire events one on top of the other.
  • Then takes climate prior to, during, and after fire events, averages them together. For example: 5 years before event, the event year itself, and then 5 years after = 11 year window.
  • Where does climate information come from before climate records were kept?
  • Then uses bootstrapping methods to develop robust confidence intervals to determine which years in the window of years are statistically significant.
  • The years after the event have nothing to do with the fire event itself, but help establish if a pattern exists in climate.
Changing fire regimes?
  • Relationship between drought and fire activity deteriorates between 1775 and 1825 during major climate transition in the Southwest.
Changing fire seasonality?
  • Related to climate change!
  • Late season monsoon was non-existent prior to 1800 allowing July and August fires.
  • After 1800, monsoon kicks in, shifting fires to earlier in the season.