Progress 10/01/10 to 09/30/15
Outputs
Target Audience:Target audiences include the Bureau of Land Management, foresters, fire researchers, landowners, educators, students, and the general public. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?This award was the focus of a Masters of Environmental Horticulture (MEH) report, by student Ellen Sherck. Research Scientist/Engineer Jeremy Littell and Research Associate Michael Case provided assistance with field sampling. How have the results been disseminated to communities of interest?A manuscript will be submitted for publication in a peer-reviewed journal after the close of the project. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Reconnaissance work began in Autumn 2010. Each site was thoroughly examined to identify fire-scarred trees, snags, down logs, and intact stumps. Each of these structures was inspected for number of visible scars, soundness of wood, and distance to roads and paths. Care was taken to avoid selecting trees and snags within a clear line of sight of, and not closer than one tree length from, roads or paths. Locations of features suitable for sampling were recorded using a portable GPS device. Samples were obtained by removing a partial cross-section (often referred to as a "wedge sample") from the bole of each standing tree using a chainsaw (Arno and Sneck 1977).In total, we secured samples from 40 trees, 19 at Kellett Bluff and 21 at Turn Point. All samples were transported to the Terrestrial Restoration Ecology lab (http://depts.washington.edu/relab/) at the University of Washington, where they were allowed to dry until Spring 2012. Most samples were glued onto plywood to assemble samples that were in multiple sections and to prevent breakage and loss. They were then planed and sanded with progressively finer grits (50 to 400) to obtain a smooth, polished surface (Stokes and Smiley 1968). Ideally, completed samples were sanded to the point where cell walls were clearly visible under a 10x magnification microscope so that details of fires could be determined as well as false, double, and missing growth rings (Stokes and Smiley 1968; Speer 2010). A master chronology was built from the increment cores taken from non-scarred live trees. Cores were scanned with a high-resolution digital scanner and the images imported into WinDENDRO 2012a software (http://www.regent.qc.ca/products/dendro/DENDRO.html). Ring widths were measured to the nearest 0.01 mm. The ring widths were analyzed using the Dendrochronology Program Library in R (dplR) (Bunn 2008, 2010; Bunn et al. 2015) package in R (R Core Team 2015). Once cross-section samples were prepared, we analyze them using a boom-mounted dissecting scope. Fire scar samples from live trees were visually crossdated following the methods outlined in Yamaguchi (1991) and by comparing ring width patterns to those in the master chronology. Samples from dead trees were cross-dated by numbering the rings from the outer ring to the inner ring, noting which rings were narrower or wider than expected compared to the surrounding rings, and then evaluating the fit between this set of narrow and wide rings and the master list of marker years. For each outer ring date, the putative date of each narrow and wide ring was determined. The correspondence between these dates and the master list of marker years was then calculated to determine which outer ring date had the strongest support. We identified the pith and death dates where possible, or the dates of the innermost and outermost extant rings. After determining a tree's chronology, its fire scars were assigned to the appropriate years. Fire scars were identified by the characteristic band of previously killed cambium tissue and the subsequent pattern of radial growth healing (McBride 1983; Agee 1993; Speer 2010). Data were entered into FHAES fire history software (v.2.0.1-SNAPSHOT; Brewer et al. 2015). This software is an update of the original FHX2 program for fire history analysis (Grissino-Mayer 2001). It provides a variety of descriptive statistics about fire intervals along with the ability to create fire history charts, a commonly used graphical format for displaying results. Fire return intervals were analyzed in FHAES. Each site was analyzed separately. Data were summarized across the entire period of record and for each of two time periods, historical and post-settlement. Fire intervals were analyzed using individual-tree and composite methods (Agee 1993) to better characterize fire history and to provide results comparable to similar studies (Romme 1980). Seasonality was summarized by tallying the number of fires associated with each season. Considerable evidence of past fire was found at both sites. Many of the mature Douglas-fir trees had charred bark and visible fire scars on the lower bole of the tree. In some areas, large, mature Douglas-fir trees with substantial lower limb branches were present, indicating that they grew in open conditions in the past. At Kellett Bluff, samples recorded between one and 10 fires, with a mean of 3.6 scars per sample. A total of 69 fire scars were identified across 19 samples. These fire scars represent 35 distinct fire years between 1565 and 1926. Particularly widespread fires occurred in 1895 (recorded by 10 trees), 1844 (6 trees), 1868 (4 trees), and 1883 (4 trees). The vast majority of fires occurred when the tree was dormant. Individual trees were scarred by fire on average every 40-50 years, but this ranged from 1 to 270 years. Many fire scars healed over before the next fire was recorded. The fire return interval was more than three times longer in the post-settlement period than in the historical period. Considering the site as a whole, the mean fire return interval was 13 years, but ranged from 1 to 85 years. The fire return interval was 4.5 times longer in the post-settlement period than the historical period. At Turn Point, samples recorded between one and six fires, with a mean of 3.9 scars per sample. A total of 77 fire scars were identified across 20 samples. These fire scars represent 34 distinct fire years between 1624 and 1964. Particularly widespread fires occurred in 1850 (recorded by 13 trees), 1822 (10 trees), 1868 (7 trees), and 1804 (5 trees). The vast majority of fires occurred when the tree was dormant. Individual trees were scarred by fire on average every 35-48 years, though this ranged from 2 to 180 years. The fire return interval was 25 years in the historical period but 64 years in the post-settlement period. Considering the site as a whole, the mean fire return interval was 7-11 years, but ranged from 1 to 88 years. The mean fire interval rose from 6 years in the historical period to 14 years in the post-settlement period. Recommendations: Turn Point and Kellett Bluff provide opportunities for restoring and conserving fire-maintained ecosystems in the San Juan Islands and the unique plant assemblages and species associated with them. Based on this fire history study, we suggest that the BLM: • Consider further research into stand structure and development, including multiple tree species and their spatial patterns, and the historical prevalence of forest, savanna, and grassland ecosystems. • Explore the utility of forest thinning to reduce the risk of high-intensity fires in the future. This many include opportunities to favor particular species, as occurs elsewhere in the San Juan Islands where Garry oaks are released by cutting the Douglas-fir that have overtopped them (Dunwiddie et al. 2011). • Actively pursue the application of prescribed fires on these sites. Both sites experienced fires frequently yet supported a tree component for centuries - the oldest tree in this study was more than 500 years old. A program of frequent, low-intensity fire may be critical for the long-term persistence of these trees.
Publications
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