Fire History and Dendrochronology

Photo by Daniel Heffernan

Agenda: Last class of 2013

• Notes on 4/26• Fire history lecture• Break• Lab• Done!• Credits- Debra Kennard,

Laboratory of Tree Ring Research, H. D. Grissino’s Ultimate Tree Ring website

• Provides a benchmark by which we can measure change (e.g. estimating the effects of past fire exclusion helps us predict the future)

• Can serve as a guide for determining appropriate burn intervals for management plans

• Informs designation of desired future conditions, or references for restoration

The Importance of Fire history

Fire history is the study of the chronology of fire events over time, providing detailed information

about a forest’s historical fire regime

Restoration- to what?

Why?

How do we know what

the “natural” or historical fire regime

is for a given

ecosystem?

Fire Regime Attributes

FrequencySeverity

AreaType

IntensitySeveritySynergy

Distribution of ecosystems in S. Florida

From Fire Effects on Flora (Brown and Smith 2000).

How do we determine

the attributes of a historical fire regime?

Depends on what is available:

Paleoecological: Analysis of stratified lake or bog/soil sediments for charcoal; pollen analysis

Gleaning Fire History Information

• Historical records or folklore (natives, explorers, settlers)• Vegetation or stand age class distributions • Photographs, remote sensing: Chronosequence (e.g. LANDSAT)

Gleaning Fire History Information

Dendrochronology• dendro: tree. • chronology: study of time

• “Dendrochronology examines events through time that are recorded in the tree ring ‐structure or can be dated by tree rings.”

• Speer, J. 2010. Fundamentals of Tree Ring Research‐ . The University of Arizona Press

Applications of Dendrochronology

• Ecology: insect outbreaks, forest demographics and growth patterns

• Climatology: past droughts or cold periods • Geology: past earthquakes, volcanic

eruptions • Anthropology: past construction, habitation,

and abandonment of societies• Fire history!

Dendrochonology for Fire History = Dendropyrochronology

• Fires that damage cambium leave a scar

• Fire occurrence is determined by estimating the year of fires based on tree rings and location fire scars.

• Can also be used to determine fire intensity, fire seasonality, extent, and associated climatic patterns. • Takes advantage of variability in

annual growth rings (complacent vs. sensitive species)

• A diagram showing the tree rings of a "ring porous" tree species, such as oak (Quercus spp.) and elm (Ulmus spp.) (growth is to the right) (photo © LTRR).

Close-up photographs of conifer tree rings showing different types and rates of tree growth (photo © LTRR).

A close-up photograph of an individual tree ring showing the earlywood (larger cells) and latewood (smaller cells), as well as a resin duct (growth is from bottom to top) (photo © LTRR).

What does dendropyrochronology tell you?

• Frequency• Season• Areal extent?• Severity?• Years of fires?• Synergy with

climate, other disturbances

• Fire Return Interval: length of time between one fire and the next/previous fire

• Mean FRI: avg. of above

Terms

Example application of fire history studies: climate relationships

• PIPO Fire history reconstructions show that fires correlated with climate oscillations—wet/dry

A. SW Annual Precip.

B. Four Corners Drought Index (PDSI)

Niño3 SST (ENSO)

SOI (ENSO)

Superposed Epoch Analysis(SEA) of fire years at Archuleta Mesa (Brown and Wu 2005)

Years of fires: Depends on knowing a date! Or does it?

Increment cores taken from Douglas-fir (Pseudotsuga menziesii) trees growing on Mt. Graham in southeastern Arizona (photo © H.D. Grissino-Mayer).

Cross-Dating

• Matching of ring width patterns between specimens used to identify the exact year in which a ring was formed

• Useful when no known date is available; ring width patterns in a dead wood sample can be “overlapped” on (live) samples with known dates

• Accounts for tree ring anomalies• Extends fire histories back into the past, much further than

even the oldest living tree

But trees grow at different rates, even in the same stand!

• Skeleton Plotting: accounts for the fact “trees in a homogenous stand or forest usually exhibit the same relative pattern of growth variation through time, BUT

• Often have absolute growth rates that differ substantially due to living in different microsites” (Laboratory of Tree Ring Research, T. Veblen, AZ)

Skeleton Plotting

General Procedures• Mark relatively narrow rings on graph paper– the

narrower the ring, the taller the line• Match these patterns between samples• Account for missing or false rings• Date your sample• Identify fire years• Create Master Fire Chronology

Example of Master Fire Chronology for ponderosa/Doug-fir forests of Boulder, CO

Group 1

Group 2

Limitations of tree-ring analysis for fire history

• Cannot be used in areas without trees, or where trees are killed by fire (Pinyon-juniper woodlands, sand pine scrub)- it will only provide date of last fire

• Conservative estimate: Fire scars may be healed-over, some trees might not record a given fire

• A large number of samples is required for cross-dating

• Sampling is destructiveSet of fire scars shown in a section taken from a sugar pine (Pinus lambertiana) growing in California (photo © A.C. Caprio).

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1813 1865 1913 1946 1986

Nu

mb

er o

f T

rees

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f T

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Sca

rred

(%

) % Trees scarred

No. of trees

Limitations, challenges, cont.

• The record gets worse the further back in time you go

• And the larger the area sampled, the greater number of scars you’ll find (for a while)

Results depend on the factors that influence fire behavior– where & how you

sample matters!

• …and does that mean that fires occurred there more frequently, or scarred trees there more often?

Fire and Lightning Scars Across Topography

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Ravine Hilltop Knoll LowerSlope

Mid Slope UpperSlope

Ridgetop

Fire Scars

Lightning Scars

Some trees scar more easily than others…

…and evidence may be better preserved in certain microenvironments

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N E S W

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PSME

PIPO

Despite these limitations,

fire history data is widely used to characterize fire regimes, and provides

the basis for many management frameworks.

Class Challenge:

Use what you know (fire behavior, fuels, plant ecology) to infer the fire regime of this forest

What you will do

• Lab Exercise in pairs• Hand-in by end of class• Have a look at the samples• Extra Credit-- Go to:

http://www.ltrr.arizona.edu/skeletonplot/SkeletonPlot19.htm (review the tutorial)

• Do the Crossdating: Skeleton Plot for Yourself exercise