Methods for Distinguishing Aspen Seedlings from Suckers in the Field

Abstract

<jats:title>Abstract</jats:title> <jats:p>Quaking aspen is a common component of postdisturbance landscapes, in part because of its ability to regenerate via asexual suckers. Previously viewed as exceedingly rare in the western United States, sexual seedling establishment is increasingly seen as another important natural regeneration pathway for aspen, because sexual regeneration increases genetic diversity and facilitates long-distance dispersal. However, aspen seedling research is hampered by difficulties in visually distinguishing seedlings from suckers in the field, and few resources exist to guide managers and researchers. We present methods for distinguishing aspen seedlings from aspen suckers, suitable for use in field studies. Using these methods, we achieved 99 percent predictive accuracy in a recently burned area in southern Utah, although accuracy decreased to 90 percent following one summer’s growth, as seedlings and suckers became more similar in appearance.</jats:p> <jats:p>Study Implication: Sexual regeneration may play an important role in aspen’s response to climate change, as it increases genetic diversity and adaptive capacity, and allows aspen populations and their ecological associates to better track changing climate through increased dispersal distances. The methods we present allow managers and researchers to accurately identify aspen seedling populations, which can then be protected and monitored through time to better understand aspen demography and the factors limiting establishment and survival of new clones. Aspen seedling ecology is an area with many knowledge gaps currently, and these methods remove a barrier that has hindered research in the past.</jats:p>

Low‐density aspen seedling establishment is widespread following recent wildfires in the western United States

“…Within this area, using the Historic Fire Database (Weber, 2020) we identified every wildfire that burned in 2018 Accepted Article 1) over 20 ha; 2) on U.S. Forest Service public land; and 3) in areas that contained pre-fire aspen (Ellenwood et al, 2015). We restricted our candidate fires to those that burned in 2018 to ensure accurate differentiation of seedlings from suckers, before these two regeneration types became indistinguishable (Kreider et al, 2020). Due to time constraints, we did not survey two fires in the study region, both of which were ˂80 ha.…”

“…Each plot consisted of a 50x2 m belt transect. In June-August 2020, we censused all aspen seedlings within each plot, distinguishing them from suckers using non-destructive methods detailed by Kreider et al (2020) that were shown to be 96% accurate. We excavated the first aspen seedling found in each fire footprint; specimens can be viewed at the Intermountain Herbarium at Utah State University or online at http://intermountainbiota.org.…”

“…We restricted our candidate fires to those that burned in 2018 to ensure accurate differentiation of seedlings from suckers, before these two regeneration types became indistinguishable (Kreider et al. 2020). Because of time constraints, we did not survey two fires in the study region, both of which were <80 ha.…”

“…Though seedling establishment is considered more common in the wetter climate of Canada and the eastern United States (Landhäusser et al 2019), the prevailing assumption in the conterminous western United States for much of the 20th century was that sexual reproduction in aspen was exceedingly rare because of prohibitively arid climate (Kay 1993). Compounding this was the fact that aspen seedlings are not easily differentiated from suckers (Kreider et al 2020), and regenerating aspen stems are frequently assumed to be exclusively asexual. However, several occurrences of widespread aspen seedling regeneration after fires in the western United States (e.g., Kay 1993, Romme et al 1997, along with genetic evidence suggesting recent seedling establishment (Mock et al 2008), have led to the recent realization that sexual regeneration is more common than once thought (Long and Mock 2012).…”

“…Compounding this was the fact that aspen seedlings are not easily differentiated from suckers (Kreider et al, 2020), and regenerating aspen stems are frequently assumed to be exclusively asexual.…”