Removal of Encroaching Conifers to Regenerate Degraded Aspen Stands in the Sierra Nevada

Abstract

Aspen is considered a keystone species, and aspen communities are critical for maintaining biodiversity in western landscapes. Inventories of aspen stand health across the Eagle Lake Ranger District (ELRD), Lassen National Forest, California, U.S.A., indicate that 77% of stands are in decline and at risk of loss as defined by almost complete loss of mature aspen with little or no regeneration. This decline is due to competition from conifers establishing within aspen stands as a result of modification of natural fire regimes coupled with excessive browsing by livestock. Restoration treatments were implemented in four aspen stands in 1999 using mechanical equipment to remove competing conifers to enhance the growth environment for aspen. Recruitment and establishment of aspen stems were measured in treated stands (removal of competing conifers) and non-treated stands (control) immediately prior to treatment and 2 and 4 years post-treatment. There was a significant increase in total aspen stem density and in two of three aspen regeneration size classes for treated stands compared to controls. Pre-treatment total aspen density was positively associated with total aspen density and density in all size classes of aspen (p < 0.001). The results demonstrate that mechanical removal of conifers is an effective treatment for restoring aspen.

Tamm Review: Management of mixed-severity fire regime forests in Oregon, Washington, and Northern California

“…In the case of relatively pure patches of aspen (Populus tremuloides), cottonwood (Populus trichocarpa & Populus fremontii), and birch (Betula papyrifera & Betula occidentalis), fire exclusion has dramatically reduced their abundance, patch sizes, and vigor (Hessburg et al, 1999a). For their influence on habitat for certain species, landscape biodiversity, and fire behavior (Kuhn et al, 2011;Shinneman et al, 2013), there are clear advantages to revitalizing existing clones and patches, or to restoring their abundance (Jones et al, 2005) near wet meadows and seeps, in areas of seasonally high water table, and in floodplain and riparian areas (Bartos and Campbell, 1998;Campbell and Bartos, 2001;Seager et al, 2013). …”

Continuous 1985–2012 Landsat Monitoring to Assess Fire Effects on Meadows in Yosemite National Park, California

“…Seed dispersal of herbaceous meadow species is inhibited by competition from forest species [57]. To counter the potential consequences of conifer encroachment, the mechanical removal of conifers has been shown to be an effective treatment for restoring meadow species such as aspen (Populus tremuloides) [58]. The season-specific analyses included in this study show that lowseverity fire may also positively influence meadows.…”

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

“…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).…”

“…Today, aspen management focuses almost exclusively on attempting to rejuvenate existing stands, primarily through conifer removal, prescribed fire, and protection from herbivory , Jones et al 2005, Bates et al 2006. Though, as our understanding of aspen ecology evolves and a warming climate threatens disturbance regimes and existing aspen populations, we need to better understand the impact and interaction of disturbance, management, and stand conditions on aspen vegetation dynamics.…”