Wednesday, August 5, 2009: 10:50 AM
Grand Pavillion IV, Hyatt
Background/Question/Methods There has been considerable debate about where tree densities and fire severity have significantly increased in response to past fire suppression, stemming from the desire to appropriately restore open forest structure and associated low-severity fire regimes across fire-prone forests in the West. There is general consensus in the Rocky Mountains that some lower montane ponderosa pine-dominated forests have experienced significant increases in tree densities that may put them at risk of uncharacteristic high-severity fire, and that most high-elevation subalpine forests have experienced very little change in tree densities or fire severity. However, mid-elevation forests in the upper montane zone, which are vegetatively and topographically diverse, are not well understood in terms of effects of past fires and fire suppression on forest stand structure and the need for structural restoration. We randomly selected 40 sites in the upper montane zone (2300-2800 m) of the Colorado Front Range that reflect the relative proportion of the five main forest types characteristic of this zone in order to link past timing and severity of fire to current age structure. In each forest polygon, we cored live and dead trees to determine establishment and death dates and collected wedges from fire-scarred trees, targeting areas where fire scars would likely be found (remnant trees; rocky outcrops; changes in forest composition, structure or topography).
Results/Conclusions The majority of the sites had trees with only single fire scars, relatively few recorded fire events (<3 on average) that commonly dated to the late 1800s, suggesting relatively long fire intervals. In terms of fire effects on stand structure, about two-thirds of the sites showed distinct pulses of tree establishment (30-60% of the current stand density) within ~25 years of a fire event, low tree survival of these fire events, and low rates of tree establishment during the fire suppression era. This 1840s-90s period of high fire activity and high rates of post-fire tree establishment coincided with a period of intense drought. This study suggests that high-severity fires during the late-19th C, followed by rapid post-fire tree establishment, was common across this upper montane zone. Forest densities have not significantly increased during the fire suppression era and severe fires were common in the past, indicating that open stands and low-severity fires are inappropriate restoration goals in this area, although climate and land-use change may complicate future management objectives.
Results/Conclusions The majority of the sites had trees with only single fire scars, relatively few recorded fire events (<3 on average) that commonly dated to the late 1800s, suggesting relatively long fire intervals. In terms of fire effects on stand structure, about two-thirds of the sites showed distinct pulses of tree establishment (30-60% of the current stand density) within ~25 years of a fire event, low tree survival of these fire events, and low rates of tree establishment during the fire suppression era. This 1840s-90s period of high fire activity and high rates of post-fire tree establishment coincided with a period of intense drought. This study suggests that high-severity fires during the late-19th C, followed by rapid post-fire tree establishment, was common across this upper montane zone. Forest densities have not significantly increased during the fire suppression era and severe fires were common in the past, indicating that open stands and low-severity fires are inappropriate restoration goals in this area, although climate and land-use change may complicate future management objectives.
