The fire-scar record from tree rings. Southwestern white pine and ponderosa pine, Mt. Graham, Arizona ponderosa pine, El Malpais National Monument, New Mexico
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?
Interpreting Fire History Charts Years on x-axis Period of Reliability: 1896 to 1944 Each line = 1 treeSample IDs Composite axis Solid lines = recorder years Each tic = fire scar Dash lines = non-recorder years Begin/end symbology
Standard 50 x 20 m plot but greater spatial coverage is available using numerous smaller circular plots Inventory all tree species, measure dbh Core, crossdate/age all trees 5 cm dbh Inventory all saplings 50 cm ht Inventory seedlings in 10 x 20 m subplot Collect sections from 20 mountain laurel stems Measure depth to mineral soil at 20 random locations Pines Oaks Mountain Other laurel hardwoods 20 m 50 m Stand Age, Structure, and Composition
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 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.
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 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.
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). BYRBYR NNKNNK
Big Pine Key No Name Key MFIWMPIRangeSD BPK (n = 36) All scarred > 10% > 25% NNK (n = 32) All scarred > 10% > 25% 6.55 6.86 8.47 9.79 10.94 5.83 6.15 7.91 9.14 10.32 2–26 2–24 4.68 4.75 4.88 5.56 5.91 MFI = mean fire interval; WMPI = Weibull median probability interval; SD = standard deviation
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.