The Peters Mountain mallow is a fire-dependent herbaceous plant species endemic to Peters Mountain, Virginia. Its population declined over the twentieth century, likely because of fire exclusion. We used fire-scarred trees to reconstruct the fire history of Peters Mountain (Hoss et al. 2008) and found that fires occurred frequently in the past, before fire protection became commonly practiced. The mean fire interval for the site was 2.5 years, and most fires occurred during the dormant season (spring or fall). Fire frequency is lower today. In 2005, at the time of our fieldwork, 29 years had elapsed since the last fire. The results suggest the need to reintroduce fire to restore the Peters Mountain mallow and its habitat.
In 1989, the entire known wild population of the Peters Mountain mallow (Iliamna corei Sherff.) comprised only three individuals (Baskin and Baskin 1997), making it one of the rarest plant species on earth. Apparently, the species was never abundant. When discovered in 1927, the population of the perennial herb included about 50 plants growing on thin, rocky soils among widely spaced trees (Strausbaugh and Core 1932) on the western end of Peters Mountain, Virginia. About 40 individuals remained in 1962 (Keener and Hardin 1962), and at some point thereafter the population plummeted to the low level recorded in 1989.
Autecological work (Baskin and Baskin 1997) revealed a large bank of dormant, water-impermeable mallow seeds that require heating by fire to germinate. The plants also resprout after burning, and because of their shade intolerance they need fire to maintain an open, well lit habitat. These life-history traits appear to suit the mallow to a short fire interval, likely on the order of only a few years (Hoss et al. 2008; cf. Rowe 1983). But fire prevention and suppression efforts had begun to reduce the frequency of fire in the Appalachian region by the 1940s and 1950s (Sarvis 1993). Fire exclusion is thought to have contributed to the decline of the mallow population (Caljouw et al. 1994). The Nature Conservancy purchased the habitat of the endangered Peters Mountain mallow in 1992 and began experimental burns, which resulted in a larger mallow population that has fluctuated annually in the number of individuals present (Edwards and Allen 2003). Restoring the Peters Mountain mallow and its habitat requires an understanding of the historic fire regime(s) under which the plants throve.
A study of fire history on Peters Mountain
We cut and dated cross-sections from 73 fire-scarred pine trees within a 40 ha area surrounding the mallows. We also cored all the trees growing in two plots that were situated near the mallows to illuminate how changing fire activity affected tree establishment in the vicinity of the mallows. Hoss et al. (2008) report the study in detail.
The trees recorded 53 fires during the period 1794-2005. Between 1867 (the first year with two or more scarred trees) and 1976 (the last year recording a fire), the mean fire interval was 2.5 years. That is, at least part (but not
necessarily all) of the area burned every 2-3 years. We also calculated a more conservative estimate of fire frequency: large fires that scarred at least 25% of the trees across the study area occurred about every 12.5 years. Most (93.6%) of the fire scars formed while the trees were dormant (i.e., scars are positioned between the annual rings), suggesting that the fires occurred during the spring or fall; fires rarely burn in the Appalachian Mountains during winter (Lafon et al. 2005).
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Fire frequency remained high through the 1940s, then declined …