After long-term decline, are aspen recovering in northern Yellowstone?

“Changes in the behavior or movements of elk, in combination with reduced elk density, may also have contributed to release of aspen from herbivory (White et al., 2003, 2009; Fortin et al., 2005; Hebblewhite et al., 2005; Mao et al., 2005; Gude et al., 2006; Muhly et al., 2010).”

“…al., 2003; Beschta, 2005; Beyer et al., 2007; Wolf et al., 2007), but heights and canopy cover of these plants increased in portions of the northern range following wolf reintroduction (Smith and Tyers, 2008; Tercek et al., 2010; Baril et al., 2011; Ripple and Beschta, 2012b; Ripple et al., 2014).”

“Kauffman et al. (2010), using different methods, did not find evidence of reduced browsing or aspen recovery and concluded that no trophic cascade benefiting aspen had yet begun.”

“Some researchers have argued that these factors were more important than predation as causes of elk decline prior to 2006 (Vucetich et al., 2005; Eberhardt et al., 2007).”

“4) (Wilmers and Getz, 2005; McMenamin et al., 2008; Frank et al., 2013), and in northern YNP every winter from 2000 to 2010 had snow accumulations below average.”

“…such as serviceberry (Amelanchier alnifolia) were suppressed by intensive herbivory (Kay, 1990; NRC, 2002; Singer et al., 2003; Beschta, 2005; Beyer et al., 2007; Wolf et al., 2007), but heights and canopy cover of these plants increased in portions of the northern range following wolf…”

“In some places willow heights are now influenced more by abiotic factors such as water and soil conditions than by browsing (Bilyeu et al., 2008; Tercek et al., 2010; Marshall et al., 2013), evidence of a significant reduction in herbivory (Singer et al.”

“In some places willow heights are now influenced more by abiotic factors such as water and soil conditions than by browsing (Bilyeu et al., 2008; Tercek et al., 2010; Marshall et al., 2013), evidence of a significant reduction in herbivory (Singer et al., 2003; Hebblewhite and Smith, 2010).”

“Researchers in some other portions of the Yellowstone ecosystem have not found such changes (Kimble et al., 2011; Winnie, 2012), however, aspen recruitment increased after 2005 in the Eagle Creek area north of the park boundary following a decrease in browsing (Runyon et al., 2014), similar to what…”

“Although a broadening release of aspen in both riparian and upland aspen stands currently appears to be underway (Painter et al., 2014, 2015), there is considerable variability as to where and when aspen recovery has begun occur.”

“…there is debate about the exact mechanisms by which wolves affect their main prey, elk (Cervus elaphus) (Kauffman et al. 2007; Middleton et al. 2013), and how widespread the cascading effects on vegetation have been (Kauffman et al. 2010, but see Painter et al. 2014 for the most recent analyses).”

“…in aspen recruitment represents a fundamental shift in aspen dynamics, because recruitment of new aspen trees declined and virtually ceased by the mid-20th century due to intensive herbivory by elk (Ripple and Larsen 2000, Kauffman et al. 2010, Beschta and Ripple 2013, Painter et al. 2014).”

“Browsing effects depend on ungulate behavior and population size, which varies over time; a substantial decline in Yellowstone elk numbers between 1997 and 2014 (Smith et al., 2015) has been linked to increased aspen-ramet heights in mature stands (Painter et al., 2014).”

“Where this occurs, indirect effects on stream morphology (Beschta & Ripple 2012), woody plants (Painter et al., 2014) and berry production (Ripple et al. 2014b) have been observed as well as for a suite of animals including medium-sized ungulates (e.g. White-tailed Deer, Odocoileus virginianus, and…”

“…young aspen (< 200 cm in height) and overstory trees (typically> 20 cm in diameter at breast height) was characteristic of aspen stands across the northern range due to the historical suppression of young plants by elk (Larsen and Ripple, 2005; Ripple and Beschta, 2007; Painter et al., 2014).”

“However, the annual SWE was below average most years after 1997, consistent with the fact that the region was in a drought (Painter et al., 2014).”

“An inverse relationship between browsing intensity and height of young woody plants is central to the trophic cascade hypotheses, as it clearly identifies the mechanism via which top-down pressure ensues (Beyer et al. 2007; Painter et al. 2014).”

“In fact, willow recovery, like aspen recovery, began in the early 2000s during a time of drought (McMenamin et al. 2008, Painter et al. 2014) and has continued under a long-term warming and drying trend.”

“This ongoing recovery started slowly but has nevertheless increased in strength over time (Painter et al., 2014; Beschta et al., 2018).”

“Painter et al. (2014) and Rooney (2001) came to this same conclusion.”

“…from across a stand will always be greater than the average height of young aspen measured in a small 20 m 2 plot, such as that used by Brice et al. Painter et al. (2014, 2015) subsequently addressed this issue by measuring, in conjunction with 5T sampling, young aspen heights in random plots for…”

“…trend of aspen recovery, we randomly sampled aspen stands across northern YNP and compared results with two previous surveys of aspen in these same stands: (1) in 1997 – 98 (Larsen and Ripple, 2003) shortly after the 1995 – 96 introduction of wolves, and (2) in 2012 (Painter et al., 2014, 2015).”

“…to establish and grow above the upper browse level of elk in the northern winter range of Yellowstone National Park (Beschta and Ripple, 2010, 2016; Painter et al. 2014), as well as in Banff National Park (Hebblewhite and Smith, 2010; White et al., 2015), Jasper National Park (Beschta and Ripple,…”