| Grand Canyon Fire Ecology |
|
|
|
Research sponsored by the Joint Fire Science Program (JFSP) http://jfsp.nifc.gov/
Panorama of the Grand Canyon from Timp Point on the North
Rim. Photo by Dan Binkley There are three parts of our Grand Canyon Fire Ecology Research:
Project #1A: Mixed-Severity Fire Regime in a High-Elevation Forest: Grand Canyon, ArizonaSummary:Fire regime characteristics of high-elevation forest on the North Rim of the Grand Canyon, Arizona, were reconstructed from fire scar analysis, remote sensing, tree age, and forest structure measurements, a first attempt at detailed reconstruction of the transition from surface to stand-replacing fire patterns in the Southwest. Tree densities and fire-/non-fire-initiated groups were highly mixed over the landscape, so distinct fire-created stands could not be delineated from satellite imagery or the oldest available aerial photos. Surface fires were common from 1700 to 1879 in the 11,000 acre site, especially on S and W aspects. Fire dates frequently coincided with fire dates measured at study sites at lower elevation, suggesting that pre-1880 fire sizes may have been very large. Large fires, those scarring 25% or more of the sample trees, were relatively infrequent, averaging 31 years between burns. Four of the five major regional fire years occurred in the 1700’s, followed by a 94-year gap until 1879. Fires typically occurred in significantly dry years (Palmer Drought Stress Index), with severe drought in major regional fire years. Currently the forest is predominantly spruce-fir, mixed conifer, and aspen. In contrast, dendroecological reconstruction of past forest structure showed that the forest in 1880 was very open, corresponding closely with historical (1910) accounts of severe fires leaving partially denuded landscapes. Age structure and species composition were used to classify sampling points into fire-initiated and non-fire-initiated groups. Tree groups on nearly 60% of the plots were fire-initiated; the oldest such groups appeared to have originated after severe fires in 1782 or 1785. In 1880, all fire-initiated groups were less than 100 years old and nearly 25% of the groups were less than 20 years old. Non-fire-initiated groups were significantly older (oldest 262 years in 1880), dominated by ponderosa pine, Douglas-fir, or white fir, and occurred preferentially on S and W slopes. The mixed-severity fire regime, transitioning from lower-elevation surface fires to mixed surface and stand-replacing fire at higher elevations, appeared not to have been stable over the temporal and spatial scales of this study. Information about historical fire regime and forest structure is valuable for managers but the information is probably less specific and stable for high-elevation forests than for low-elevation ponderosa pine forests.
Fire chart for 132 fire-scarred trees from the Little Park
study site, a high-elevation landscape of mixed forests at Grand Canyon National
Park. Detailed information:
Project #1B: Changes in Canopy Fuels and Potential Fire Behavior 1880-2040: Grand Canyon, ArizonaSummary:We applied detailed forest reconstructions measured on broad-scale plot grids to initialize forest simulation modeling in 1880 and modeled spatially explicit changes in canopy fuels (crown biomass, crown bulk density, species composition) and potential fire behavior (crowning index) through 2040, a 160-year period. The study sites spanned a 547 yard (500 meter) elevational gradient from ponderosa pine forest through higher-elevation mixed conifer, aspen, and spruce-fir forests on the North Rim of Grand Canyon National Park in northern Arizona. The simulations were relatively accurate, as assessed by comparing the simulation output in the year 2000 with field data collected in 1997-2001, because a regionally calibrated simulator was used (Central Rockies variant of the Forest Vegetation Simulator) and because we added regeneration by species and density in the correct historical sequence. Crown biomass increased at all sites, rising an average of 122% at the low-elevation sites and 279% at the high-elevation sites. The intermediate-elevation site, where mixed conifer vegetation predominated, began with the highest crown biomass in 1880 but had the lowest increase through 2040 (39%). Crown bulk density increased roughly in parallel with crown biomass; however, density values were considered less accurate in non-contemporary dates because they were based on assumptions about crown volume. Species composition of canopy fuels was consistent at low elevation (ponderosa pine) but shifted strongly toward mesic species at higher elevations, where ponderosa pine declined in absolute as well as relative terms. Potential crown fire behavior was assessed with the Nexus model in terms of crowning index (CI), the windspeed required to sustain active canopy burning. CI values decreased 23% to 80% over the modeled period. Canopy fuel and CI values were mapped across the entire North Rim landscape. At a threshold windspeed of 28 mph (45 km/hr), only 6% of the landscape was susceptible to active crown fire in 1880 but 33% was susceptible by 2000. Implications of the changes over time and space include altered contemporary habitats and the high likelihood of rapid, broad-scale disturbance by fire or other agents. If managers choose to intervene to reduce canopy fuel mass and continuity, actions should be guided by the distinct ecological and geographic attributes of the different forest types.
Detailed information:
Project #2: Fire Use Over a Southwestern Elevational Gradient: Effects of 2003 FiresSummary:
Detailed information:
View Final ReportFire Use Over a Southwestern Elevational Gradient: Effect of 2003 Fires, H1200040002
Ponderosa pines on Rainbow Plateau Last updated: December 13, 2007 |
||||||||||||
