Wildfire Helps Rare Plants on White Mountain National Forest

The first individual of Douglas' knotweed found on Rattlesnake Mountain.
The first individual of Douglas' knotweed found on Rattlesnake Mountain.

Burned area with fern-leaved false foxglove.
Burned area with fern-leaved false foxglove.

Fern-leaved false foxglove.
Fern-leaved false foxglove.

Rare plant surveys re-discover a rare plant on Rattlesnake Mountain in area burned over by 2008 wildfire. The populations of two other rare plant species in this area increased dramatically.

Douglas' knotweed (Polygonum douglasii) is a slender and inconspicuous member of the buckwheat family. Recent botanical survey efforts at Rattlesnake Mountain were unsuccessful in relocating this elusive annual. It is one of a dozen or so state or regionally rare plant species that grow on the rocky summit, exposed ledges, or enriched forests at this popular rock-climbing venue in Rumney, New Hampshire. Rattlesnake Mountain has been the site of several wildfires in the past and numerous fire adapted species and natural communities have developed. For another rare species, piled-up sedge (Carex cumulata), population numbers seem to be directly tied to fire events. Following wildfire events, the population increases to hundreds of plants but as conditions stabilize and the shrubs and trees leaf out and re-colonize the population declines into the tens of plants.

In May of 2008, the summit and upper ledges of Rattlesnake Mountain in Rumney, New Hampshire on the Pemigewassett Ranger District was the site of a wildfire. Once the fire was extinguished and the concerns for public and firefighter safety were quelled, the ecological benefits of this fire could be surveyed and analyzed. From the base of the mountain it was clear that much of the understory and some of the overstory woody vegetation had been killed or only top-killed. U.S. Forest Service botanists conducted surveys of the burned area in 2009, and expected to find populations of the fire adapted species increased. The degree of population increases was startling!

Piled-up sedge (Carex cumulate) was found in multiple locations throughout the burned area and in many previously shaded locations where it had not been previously documented. Population numbers were up dramatically. A survey in 2006 located only 30 plants, but the 2009 survey found well over 1,000 plants with multiple flowering culms on each plant. The ecological benefit of the wildfire was not limited to this species. Another plant species, fern-leaved false foxglove (Aureolaria pedicularia var. intercedens), with its bright yellow flowers was clearly visible throughout the burned area. Prior to the wildfire it occurred only in the most exposed ledge-top locations, but was now found in many previously forested sites. The greatest botanical discovery during the post fire surveys was multiple sub-populations of Douglas' knotweed (Polygonum douglasii). Whether these plants emerged in response to the wildfire or the exposure to increased direct sunlight as a result of removal of competing vegetation is unclear, but a total over 600 individual stems were counted.

From an ecological perspective, the wildfire was a great success. In the absence of fire disturbance, a few individuals hang on at only the most suitable locations. After a fire they rely on significant seed reserves in the soil that allow them to effectively re-colonize previously inhospitable locations. In the years following the fire when the populations are large, massive amounts of seed are produced and deposited into the soil. Some of these seeds will continue to germinate and grow while conditions are suitable. Some seed will not immediate germinate, but will be naturally incorporated into the soil seed bank, remaining dormant awaiting the next wildfire event.

When the next wildfire event at Rattlesnake Mountain will occur is unknown. In an effort to ensure the future presence of these species on Rattlesnake Mountain, the New England Wild Flower Society will be collecting seed of these disturbance dependent species over the next two to three years. These seeds will be cleaned, dried and stored in the New England Plant Conservation Program regional seed bank. The preservation of the seeds in this manner lengthens the viability of the collected seed. It is unclear how long seed of each of these species remains viable in the soil. The stored seeds are an insurance policy in case the interval between this fire and the next is too great for the soil seed bank to produce the next generation of plants.