Wildland fire plays a key role in shaping natural plant communities. Managers benefit from a thorough understanding of the relationship between fire and vegetation. Multi-century fire histories provide a means to quantify past variation in fire regimes and to assess fire regime effects on ecosystem composition, structure, function and resilience. Fire histories developed from tree-ring evidence are well suited for such assessments and can be developed wherever recording trees are present. Although abundant work has been completed documenting fire regime and forest variability for many coniferous forest types, knowledge of historical fire regime variability is lacking for some widespread or high-value forest and non-forest vegetation types in the Intermountain West (USA), including persistent and seral aspen (aspen dominant or co-dominant), mountain sagebrush and Great Basin bristlecone pine.
In Fig. 1, Six fire-scarred Douglas fir trees sampled in 2006 recorded multiple fires with a mean fire free interval of 36 years from 1708-1869 – three years before the original picture was taken and the last recorded fire. Today, dense stands of spruce and fir are becoming dominant in the area in the absence of fire.
Intensive field searches are conducted to locate fire-scarred trees (living and dead) both within and in close proximity to target community types representing the range of environmental conditions encountered across the Central Great Basin Ecoregion (Utah and Nevada). Fire-scarred trees are sampled (partial cross-sections) and samples processed and dated to construct location-specific chronologies of past fire. Estimates of episodic recruitment and stand age structure are developed by sampling (cores and cross-sections) trees (or shrubs) of all size classes, and by conducting seedling inventories. Taken together, these fire and stand recruitment chronologies provide the basis for evaluating the effects of fire and fire regime variability on these plant community types in the past, and for predicting plant community stability and response to fire regime change.
In Fig. 2, Solid horizontal lines represent individual trees or groups of trees. Inverted triangles are fire years. Vertical red lines show fire-year synchrony among trees or groups from the same site. Red-yellow bands show within-site synchrony between fire years and pulses of tree establishment. Species codes are PILO = Great Basin bristlecone pine and PSME = Douglas fir.