Aspen Restoration in the Eastern Sierra Nevada: Effectiveness of Prescribed Fire and Conifer Removal

Abstract

Aspen (Populus tremuloides Michx.) comprises only a small fraction (1 %) of the Sierra Nevada landscape, yet contributes significant biological diversity to this range. In an effort to rejuvenate declining aspen stands, the Bureau of Land Management conducted conifer removal in three sites (2004 to 2006) and prescribed fire in two sites (2007). The goal of this study was to evaluate the efficacy of these treatments. In each site, aspen densities in three regeneration size classes were measured in treated and untreated transects before and up to five years post-treatment. Five years after treatment, two of the three conifer removal sites showed significant improvement over controls in the density of total stems and two of three regeneration size classes. The third site did not show significant gains over controls in any size class and experienced significant aspen overstory mortality three years after treatment, which was attributed to sunscald and advanced age at the time of treatment. Three years after treatment, the two prescribed fire sites showed significant increases in total stem density and two regeneration size classes, but also exhibited significant stem mortality, which was likely due to a combination of herbivory and drought. Overall, both treatments can be effective, but future treatments should incorporate methods to reduce post-treatment mortality of residual aspen and new sprouts.

Evolving paradigms of aspen ecology and management: impacts of stand condition and fire severity on vegetation dynamics

“…Comparing aspen sprout densities between treatments and wildfire.-Aspen sprout densities were compared between revitalization treatments (conifer removal and prescribed fire; see Krasnow et al 2012) and wildfire of low, moderate, and high severity. Sprout densities in each transect or plot for each year of measurement were converted to stems per hectare and comparisons were made both before and up to five years post treatment or wildfire.…”

“…Aspen are often associated with riparian areas or mesic sites with low slope angle, though upland stands are also present. Early European settlement in this area occurred after the 1860s and was concentrated in cattle ranches on the valley floor and a few boom-mining areas such as Bodie, which is 25 km from the Virginia Creek and Green Creek study sites (for aspen revitalization treatment stand descriptions for Virginia Creek and Green Creek sites, see Krasnow et al 2012). The Silver Creek, Wet Meadow, and Black Mountain study areas are mixed aspen-conifer forest, comprised primarily (90% of stems) of two species: aspen and Jeffery pine (Pinus jefferyi Balf.).…”

“…If aspen regeneration is a management goal, it will likely be better met by using managed wildfires to burn rather than attempting to conduct a prescribed fire (unless high-intensity prescribed fire is possible). In areas where allowing managed wildfires may not be socially acceptable, revitalization treatments such as conifer removal may be a viable alternative , Jones et al 2005, Krasnow et al 2012.…”

“…In each transect, live aspen stems were measured in the following four size classes (SC) before treatment and up to five years after treatment: SC1 ¼ height less than 0.45 m, SC2 ¼ height 0.45 m to 1.5 m, SC3 ¼ height above 1.5 m and diameter at breast height (dbh) less than 2.5 cm, and SC4 ¼ height above 1.5 m and dbh greater than 2.5 cm (Jones et al 2005). Conifer removal sites were measured prior to treatment and annually thereafter for 5 years (though not measured in 2008) and prescribed fire sites were measured before treatment and annually thereafter for three years (Table 1; for more details on the treatments, see Krasnow et al 2012). …”

“…Historically, it had been assumed that aspen sexual reproduction was exceedingly rare (Ellison 1943, Mueggler 1988, Romme et al 2005, clones were thousands of years old (Einspahr andWinton 1976, McDonough 1985), stands were always successional to conifers (Baker 1925), and that genetic diversity was low. However, numerous aspen seedlings have been found after disturbance in recent years (Turner et al 2003, Landhäusser et al 2010, Krasnow et al 2012, Fairweather et al 2014) and a growing number of studies have shown that aspen stands contain much more genetic diversity than once assumed (Jelinski and Cheliak 1992, Hipkins and Kitzmiller 2004, Mock et al 2008, De Woody et al 2009), indicating that seedling establishment is likely more common than once thought, and that many stands are not as ancient as once assumed. Measured by its range alone, aspen could be considered the most successful disperser in North America.…”