This month's story is brought to you by Neil Gifford, Conservation Director for the Albany Pine Bush Preserve Commission and NAFSE Community Representative. Neil describes their journey towards implementing growing season prescribed fires and the challenges and successes along the way. Enjoy, and thanks Neil!
A New Rx: Creating safer and more effective fires in the WUI
After decades of suppression, implementing ecologically meaningful fire in the Albany Pine Bush urban landscape was particularly challenging until we modified how and when we implemented prescribed burns.
The Albany Pine Bush Preserve Commission began using prescribed fire in 1991 with the guidance of The Nature Conservancy and the watchful cooperation of the NY State Department of Environmental Conservation. The goals were to restore globally-rare, inland pitch pine-scrub oak barrens, and recover the endangered Karner blue butterfly. Similarly to many other parts of the Northeast, spring and fall dormant season fires were most numerous, and therefore believed to be the most beneficial to our conservation goals. However, decades of accumulated fuels and flammable pine barrens plants made dormant season prescribed fires intense and flashy, commonly producing rapid rates-of-spread and flame lengths of 10-30 feet.
Despite this fireline intensity, few of these fires resulted in severity sufficient enough to reduce invasive woody growth, consume litter and duff, expose mineral soil, or foster recruitment of native grasses and wildflowers needed by the Karner blue. This behavior, coupled with the complexity of burning in a heavily developed landscape, meant individual burns needed to be small (2-10 acres) to ensure safe operations and 100% mop-up by dark. Small burns proved feasible, but resulted in limited contiguous burned acres in any given year and little benefit in fuel reduction or habitat restoration at the desired scale.
After a small escape during a dormant season fire in 1999, it became clear that we needed to find a more effective way to approach our fire management program. Specifically, we needed to increase fire severity (aka reaction intensity) by reducing rates-of-spread and increasing residence time. Considering that growing season fires occurred periodically in the past, and that UMass-Amherst research showed woody shrub vulnerability to post leaf-out fires, we suspected growing season treatments might be effective for our purposes. However, we doubted our ability generate the fire behavior we desired as well as appropriately manage smoke in the growing season given our typical summer weather and the live fuel moisture that comes with it. The 1999 escape led to changes in the program, including a decision to mechanically rearrange dense barrens fuels as a pretreatment to dormant season fire. These changes brought about an interesting hypothesis. Could burning these mechanically-treated areas after green-up generate the fire behavior and range of effects we were looking for?
To investigate this potential, we teamed up with the New York Field Office of the U.S. Fish and Wildlife Service. They were able to use their hydroaxe to mow an eight-acre scrub oak thicket in June 2003. On July 29, we attempted our first growing season “mow+burn” treatment on one half of the treated acres. With light winds and relative humidity in the high 30s, we set a test fire to observe combustion, consumption and smoke behavior (to ensure appropriate lift and dispersal). Considering the fuel arrangement within the unit, it was not expected to result in either significant combustion or consumption. With nearly two months regrowth, the live-to-dead ratio was approximately 1:3 with a 24 to 36 inch resprouting shrub layer (primarily scrub oaks and heaths). The fire behavior was favorable, and in fact the fuels in the test site burned extremely well. Topography proved to be the main factor influencing fire behavior, and with ROS at the maximum acceptable limits, the test fire was extinguished. While the active flaming front was easily put out, the scrub oak mowing slash continued to smolder for over an hour. It was apparent that while we achieved prolonged residence time, we had not reduced the ROS.
On July 31, with light winds (1-5 mph) and higher RH (upper-40s), we again attempted to burn these 4 acres. Following improvements to the 8-10 foot firebreak, raked to mineral soil, ignition began at 12:30 p.m. Fire spread and behavior was favorable, and the fuels burned very well, but rates of spread were much slower than we experienced on the 29th. Flame lengths were ~20 feet for the head fire and 2-4 feet for the backing and flanking fires, respectively. Considering this was an experiment, ignition proceeded cautiously, and it took two hours to ignite the four-acre site using narrow strip/head fires progressively across the unit. To expedite ignition in subsequent growing season mow+burn treatments, ignition incorporated multiple, simultaneous parallel flanking fires. Burning under higher relative humidity (40-55%) also allowed us to use unmowed fuels and the associated moisture of extinction to help slow and/or stop the flaming front. Without mowing slash, advancing fires would quickly diminish or extinguish altogether.
In the past, untreated pine barrens fuels would not carry growing season fire under approved prescriptions. In comparison, these mow+burn fires resulted in approximately 90% consumption of all fuels. The cured slash drives fire behavior, generating heat sufficient to preheat and ignite both dead and live fuels. The anticipation of more difficult smoke management did not materialize. Due to the moisture content of live fuels, we expected growing season burning to generate more eye-level smoke than dormant season fires. However, the exact opposite was observed as combined radiative and convective heat generated sufficient vertical lift to adequately disperse smoke.
Relative to both dormant season fires and untreated growing season burns, this and many subsequent growing season mow+burn treatments met or exceeded our objectives. Specifically, the technique has proven effective in largely eliminating mowed slash, reducing litter and duff, and exposing mineral soil. Post-season evaluations suggest several growing seasons are necessary for woody shrubs to recover from the combined “double stress” of being mowed and burned in a single growing season. The reduced shrub canopy provided for increased grass and wildflower cover. Mature pitch pine mortality was high with the initial four-acre burn, with 50% (10 trees) completely senescent one year after the burn. We were able to reduce this mortality to 13% in subsequent treatments by leaving an approximately six-foot buffer of unmowed fuels around pitch pine trees. Lastly, burning under higher humidity in the growing season allowed for the safe use of light wind speeds (0-2mph), and when combined with better smoke dispersal, provided more in-prescription burn days. This allowed us to successfully burn adjacent units over the course of the burn season and create larger contiguous burned areas, more characteristic of the historic fire regime. This ultimately reduced fuels and improved wildlife habitat at a meaningful scale.
Since implementing this technique in 2004, we have not only increased our annual area burned, but we have observed many significant ecological benefits. In addition to the good response of on-site native grasses and wildflowers, these treatments enabled post-burn lupine (Karner blue butterfly obligate host plant) interseeding. Exposing mineral soil stimulated abundant pitch pine recruitment, which had been rarely observed following repeated dormant season fires. Wildlife response has also been significant with dramatic increases in Karner blue butterfly populations and abundant young forest/shrubland birds including American woodcock, prairie warbler, field sparrow, and brown thrasher. Several species of rare obligate pine barrens moths and butterflies have been rediscovered in these sites after nearly 20 years of presumed extirpation.
In the long-term, we anticipate that growing season mow+burn will help restore fire-suppressed pitch pine-scrub oak barrens. We anticipate a 10-year average fire frequency maintenance regime, using a mix of dormant and growing season fire. The new, two-phased prescription may have been just what the doctor ordered for conserving Albany’s globally-rare pitch pine-scrub oak barrens and recovering endangered wildlife, ultimately maintaining a condition worthy of its National Natural Landmark status.