Aspen recruitment in the Yellowstone region linked to reduced herbivory after large carnivore restoration

May combine two claims.

Following the 1995-96 reintroduction of gray wolves, browsing decreased and sapling recruitment increased in Yellowstone National Park.

“Following the 1995-96 reintroduction of gray wolves (Canis lupus), browsing decreased and sapling recruitment increased in Yellowstone National Park.”

May combine two claims.

The percentage of the northern Yellowstone elk herd wintering inside the park was high prior to 1995 (mean 83% for 1927-1994), then declined sharply after the return of wolves (P < 0.01).

“The percentage of the northern Yellowstone elk herd wintering inside the park was high prior to 1995 (mean 83% for 1927-1994), then declined sharply after the return of wolves (P < 0.01, Fig. 4a).”

May combine two claims.

Recent aspen surveys confirmed a lack of young trees, which was evidence of a distinct gap in recruitment between mature trees and a new cohort of young aspen.

“These conditions were confirmed in our recent aspen surveys by a lack of young trees, which was evidence of a distinct gap in recruitment between mature trees and a new cohort of young aspen.”

May combine two claims.

Most aspen saplings grew taller than 1 m within the last decade, as browsing decreased (after 2004).

“Most aspen saplings grew taller than 1 m within the last decade, as browsing decreased (after 2004; Table 2, Fig. 3).”

May combine two claims.

Summer browsing rates in all areas were low on average, but much greater in some individual stands (range 0-65%).

“Summer browsing rates in all areas were low on average (Table 2), but much greater in some individual stands (range 0-65%).”

May combine two claims.

In addition to cervids, some areas had livestock or bison, but inclusion of these scat counts did not improve the regression model.

“In addition to cervids, some areas had livestock or bison, but inclusion of these scat counts did not improve the regression model.”

May combine two claims.

Young aspen with high browsing rates were consistently short, while those with less browsing were taller and more variable, regardless of growth rates.

“Instead, young aspen with high browsing rates were consistently short, while those with less browsing were taller and more variable, regardless of growth rates.”

May combine two claims.

Elk counts in the lower Madison Valley (HD 360 and 362) increased strongly during the study period, while counts of the Madison Headwaters elk in the park and Gallatin Canyon elk near the park decreased.

“Elk counts in the lower Madison Valley (HD 360 and 362) increased strongly during the study period, while counts of the Madison Headwaters elk in the park and Gallatin Canyon elk near the park decreased (Appendix S1: Fig. S3).”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Cattle accounted for 20% of all scat piles in the GNF Northern Range (at Joe Brown and Sphinx Creeks), and 23% in Sunlight/Crandall.

“Cattle accounted for 20% of all scat piles in the GNF Northern Range (at Joe Brown and Sphinx Creeks), and 23% in Sunlight/ Crandall.”

May combine two claims.

Browsing was positively correlated with elk density (r2 = 0.58, P < 0.01, n = 25), supporting the hypothesis that the recent reduction in browsing was linked to changes in elk density and distribution.

“Browsing was positively correlated with elk density (Fig. 3b, r 2 = 0.58, P < 0.01, n = 25), supporting the hypothesis that the recent reduction in browsing was linked to changes in elk density and distribution.”

• AssumptionRests on an assumption: Mean elk counts represent the average browsing pressure on aspen during the two time periods, as suppression or release of aspen recruitment results from a pattern of browsing over time, not a single year.

May combine two claims.

The change in aspen recruitment has been widespread but uneven, with much new recruitment in most but not all study areas.

“This change has been widespread but uneven, with much new recruitment in most but not all study areas (Fig. 2b).”

May combine two claims.

Dome Mountain WMA had a different history of elk use, and aspen stands had a continuous multi-age structure with no past gap in recruitment; therefore, this area was not included in the regression analysis of browsing and recruitment.

“Dome Mountain WMA had a different history of elk use, and aspen stands had a continuous multi-age structure with no past gap in recruitment; therefore, this area was not included in the regression analysis of browsing and recruitment (Fig. 2b).”

May combine two claims.

Following the return of wolves to the Yellowstone region in 1995-96, browsing of young aspen decreased and aspen recruitment increased in three elk winter ranges, outside as well as inside the park.

“Following the return of wolves to the Yellowstone region in 1995-96, browsing of young aspen decreased and aspen recruitment increased in three elk winter ranges, outside as well as inside the park (Fig. 2a).”

May combine two claims.

In 2011-15, rates of recruitment varied widely by study area and were distributed along a gradient of browsing intensity, with a strong inverse relationship between browsing and aspen recruitment (P < 0.01).

“In 2011-15, however, rates of recruitment varied widely by study area and were distributed along a gradient of browsing intensity, with a strong inverse relationship between browsing and aspen recruitment (Fig. 2b, P < 0.01).”

May combine two claims.

All areas surveyed in 1997-98 had high annual browsing rates (84-100%) and very low rates of aspen recruitment; few plots had any saplings, and these were all outside the park.

“All areas surveyed in 1997-98 had high annual browsing rates (84-100%) and very low rates of aspen recruitment (Fig. 2a); few plots had any saplings, and these were all outside the park.”

May combine two claims.

The percentage of the entire northern range herd north of Dome Mountain (count units 66, 67, 68) in the annual elk count increased during 1998-2015 (P < 0.01) and was about 30-50% of the total herd after 2005.

“The percentage of the entire northern range herd north of Dome Mountain (count units 66, 67, 68) in the annual elk count increased during the study period 1998-2015 (P < 0.01) and was about 30-50% of the total herd after 2005.”

May combine two claims.

In Dome Mountain WMA browsing was heavy and bark was stripped from saplings, indicating a recent increase in herbivory, the opposite of other study areas.

“By contrast, in Dome Mountain WMA browsing was heavy and bark was stripped from saplings, indicating a recent increase in herbivory (Keigley and Frisina 2008), the opposite of other study areas.”

• cites Keigley and Frisina 2008Not checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Bison accounted for 42% of all scat piles in the YNP Northern Range, and 1.4% at Eagle Creek.

“Bison accounted for 42% of all scat piles in the YNP Northern Range, and 1.4% at Eagle Creek.”

May combine two claims.

Sunlight/Crandall and GNF Northern Range had some aspen recruitment in the 1970s, and evidence of this was also found in Taylor Fork where some stands had trees 12-20 cm dbh, but lacked smaller trees.

“Sunlight/Crandall and GNF Northern Range had some aspen recruitment in the 1970s (Larsen and Ripple 2003), and we found evidence of this as well in Taylor Fork where some stands had trees 12-20 cm dbh, but lacked smaller trees.”

• cites Larsen and Ripple 2003Not checked yet

  Not checked in the free run.

• AssumptionRests on an assumption: Hunting has been much more restricted in Teepee Creek basin than in Taylor Fork.

May combine two claims.

Total elk counts decreased, but most of the decrease was inside the park.

“Total elk counts decreased, but most of the decrease was inside the park (Appendix S1: Fig. S2).”

May combine two claims.

Aerial counts in 2013 and 2015 found 77% of northern Yellowstone elk wintering north of the park, and the lowest numbers ever recorded (915 elk in 2013) inside the park.

“Aerial counts in 2013 and 2015 found 77% of northern Yellowstone elk wintering north of the park, and the lowest numbers ever recorded (915 elk in 2013) inside the park (Canfield 2014, Wyman andSmith 2015).”

• cites Canfield 2014Not checked yet

  Not checked in the free run.

• cites Wyman and Smith 2015Not checked yet

  Not checked in the free run.

May combine two claims.

We found strong increases in recruitment with browsing rates of 40-50% of top leaders, and moderate increases with browsing of 50-60% of leaders.

“while we found strong increases in recruitment with browsing rates of 40-50% of top leaders, and moderate increases with browsing of 50-60% of leaders (Fig. 2).”

May combine two claims.

Although the total number of elk wintering north of the park did not significantly change, since about 2005 most have been migrating to the area north of Dome Mountain.

“Although the total number of elk wintering north of the park did not significantly change, since about 2005 most have been migrating to the area north of Dome Mountain (Fig. 5)”

May combine two claims.

Our finding is that aspen are likely to be suppressed by browsing where elk densities exceed about 4 elk/km2, consistent with previous research in other areas and with other recent work in Yellowstone.

“Our finding that aspen are likely to be suppressed by browsing where elk densities exceed about 4 elk/km 2 (Figs. 2, 3b) is consistent with previous research in other areas, and with other recent work in Yellowstone (Beschta et al. 2018).”

• cites Beschta et al. 2018Not checked yet

  Not checked in the free run.

May combine two claims.

Annual counts north of Dome Mountain generally increased until the late 1990s, then remained high after wolf reintroduction as elk counts decreased elsewhere.

“Annual counts there generally increased until the late 1990s, then remained high after wolf reintroduction as elk counts decreased elsewhere (Fig. 5, Appendix S1: Fig. S2).”

May combine two claims.

In 2015, almost all stands in the GNF Northern Range contained large numbers of saplings that had grown tall in the previous decade, with low to moderate rates of browsing on average.

“and in 2015, we found that almost all stands in the GNF Northern Range contained large numbers of saplings that had grown tall in the previous decade, with low to moderate rates of browsing on average (Fig. 2b, Table 2).”

May combine two claims.

Some stands were heavily browsed by bison, but the effect was not ubiquitous.

“Some stands were heavily browsed by bison, but the effect was not ubiquitous.”

May combine two claims.

Elk counts in the Sunlight/Crandall Range did not decrease as much as in other study areas, as hunting was reduced to compensate for predation and low elk recruitment.

“Elk counts in the Sunlight/Crandall Range did not decrease as much as in other study areas (Appendix S1: Fig. S1c), as hunting was reduced to compensate for predation and low elk recruitment.”

May combine two claims.

The drought ended by 2007 and hunting was greatly reduced, yet the northern Yellowstone elk herd continued to decrease to low densities inside the park.

“The drought ended by 2007 and hunting was greatly reduced, yet the northern Yellowstone elk herd continued to decrease to low densities inside the park.”

May combine two claims.

Rather than again increasing as before, elk continued to decrease, with large harvests outside the park and comparable numbers killed by wolves inside.

“Rather than again increasing as before, elk continued to decrease, with large harvests outside the park and comparable numbers killed by wolves inside (Fig. 4b).”

May combine two claims.

Predation replaced starvation as the leading cause of elk calf mortality, and the previous starvation cycles were essentially eliminated.

“Predation replaced starvation as the leading cause of elk calf mortality (Barber-Meyer et al. 2008), and the previous starvation cycles were essentially eliminated.”

• cites Barber-Meyer et al. 2008Not checked yet

  Not checked in the free run.

May combine two claims.

In subsequent years, thousands of female elk of prime breeding age were killed by hunters north of the park, a greater impact than that of wolves.

“In subsequent years, thousands of female elk of prime breeding age were killed by hunters north of the park, a greater impact than that of wolves (Fig. 4b).”

May combine two claims.

Although cattle are known to suppress aspen, and we found evidence of this in some stands, our results confirmed that elk were the primary browsers affecting aspen.

“Although cattle are known to suppress aspen, and we found evidence of this in some stands, our results confirmed that elk were the primary browsers affecting aspen (Bork et al. 2013).”

• cites Bork et al. 2013Not checked yet

  Not checked in the free run.

May combine two claims.

Elk numbers north of the park remained fairly stable, while decreasing in the park.

“However, elk numbers north of the park remained fairly stable, while decreasing in the park (Fig. 4a, 5, Appendix S1: Fig. S2a, S2b).”

May combine two claims.

Although herbivory prevented recruitment in some aspen stands frequented by bison, this browsing did not result in a general suppression of young aspen in the YNP Northern Range, or the Eagle Creek area, as demonstrated by this and other recent aspen studies.

“Although herbivory prevented recruitment in some aspen stands frequented by bison (Bork et al. 2013), this browsing did not result in a general suppression of young aspen in the YNP Northern Range, or the Eagle Creek area, as demonstrated by this and other recent aspen studies (Runyon et al. 2014, Painter et al. 2015, Klaptosky 2016).”

• cites Bork et al. 2013Not checked yet

  Not checked in the free run.

• cites Runyon et al. 2014Not checked yet

  Not checked in the free run.

• cites Painter et al. 2015Not checked yet

  Not checked in the free run.

May combine two claims.

Aspen may have benefited from reduced cattle grazing in the Crandall Creek area, but livestock grazing was unchanged in most areas.

“Aspen may have benefited from reduced cattle grazing in the Crandall Creek area (Painter 2013), but livestock grazing was unchanged in most areas.”

• cites Painter 2013Not checked yet

  Not checked in the free run.

May combine two claims.

Late hunt permits were greatly reduced after 2005, and none were issued after 2010.

“Late hunt permits were greatly reduced after 2005, and none were issued after 2010.”

May combine two claims.

Surveys of aspen both in and out of Yellowstone National Park found reduced herbivory within the last decade, despite climate trends unfavorable for aspen.

“Surveys of aspen both in and out of the park found reduced herbivory and increased aspen recruitment within the last decade, despite climate trends unfavorable for aspen.”

• AssumptionRests on an assumption: Climate trends in the Yellowstone region were unfavorable for aspen during the last decade.

May combine two claims.

In winter ranges in and near the park, browsing generally decreased and aspen recruitment increased.

“In winter ranges in and near the park, browsing generally decreased and aspen recruitment increased.”

May combine two claims.

Surveys of aspen both in and out of Yellowstone National Park found increased aspen recruitment within the last decade, despite climate trends unfavorable for aspen.

“Surveys of aspen both in and out of the park found reduced herbivory and increased aspen recruitment within the last decade, despite climate trends unfavorable for aspen.”

• AssumptionRests on an assumption: Climate trends in the Yellowstone region were unfavorable for aspen during the last decade.

May combine two claims.

Elk use of the Dome Mountain WMA area has increased, beginning to suppress young aspen there.

“Elk use of the Dome Mountain WMA area has increased, beginning to suppress young aspen there.”

May combine two claims.

Mean and variance of elk counts between 1978-1994 and 2005-2015 were significantly different for Gardiner Basin (mean, P = 0.04; variance, P < 0.01) and north of Dome Mt. (mean, P < 0.01; variance, P = 0.01), but not for the combined total.

“Mean and variance between the time periods were significantly different for Gardiner Basin (mean, P = 0.04; variance, P < 0.01) and north of Dome Mt. (mean, P < 0.01; variance, P = 0.01), but not for the combined total.”

May combine two claims.

In some places such as Daly Creek, intensive browsing by elk continued and aspen were still suppressed.

“Yet, in some places such as Daly Creek, intensive browsing by elk continued and aspen were still suppressed.”

May combine two claims.

Changes in elk density and distribution were influenced by predators, as well as human hunters.

“Changes in elk density and distribution were influenced by predators, as well as human hunters.”

May combine two claims.

Quaking aspen recruitment during the 1980s-90s was suppressed by Rocky Mountain elk herbivory on winter ranges in the Yellowstone region, and saplings (young aspen taller than 2 m) were rare.

“Quaking aspen (Populus tremuloides) recruitment during the 1980s-90s was suppressed by Rocky Mountain elk (Cervus canadensis) herbivory on winter ranges in the Yellowstone region, and saplings (young aspen taller than 2 m) were rare.”

• cites Romme et al. 1995Not checked yet

  Not checked in the free run.

• cites Ripple andLarsen 2000Not checked yet

  Not checked in the free run.

May combine two claims.

In northern Yellowstone, the winter elk hunt (Gardiner Late Elk Hunt) that affected elk migrating from the park was greatly reduced in 2006 and ended in 2010.

“In northern Yellowstone, the winter elk hunt (Gardiner Late Elk Hunt) that affected elk migrating from the park was greatly reduced in 2006 and ended in 2010 (Eberhardt et al. 2007, White et al. 2012).”

• cites Eberhardt et al. 2007Not checked yet

  Not checked in the free run.

• cites White et al. 2012Not checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Outside of parks, human hunters may also influence elk density and behavior, possibly resulting in synergistic effects by predators and hunters on herbivores and plant communities.

“Outside of parks, human hunters may also influence elk density and behavior (Proffitt et al. 2013), possibly resulting in synergistic effects by predators and hunters on herbivores and plant communities.”

• cites Proffitt et al. 2013Not checked yet

  Not checked in the free run.

May combine two claims.

After wolves were extirpated in the 1920s and other predators were greatly reduced, browsing by elk was intensive and aspen stands in the northern Yellowstone elk winter range failed to recruit new trees.

“After wolves were extirpated in the 1920s and other predators were greatly reduced, browsing by elk was intensive and aspen stands in the northern Yellowstone elk winter range (northern range) failed to recruit new trees (Romme et al. 1995, Ripple andLarsen 2000).”

• cites Romme et al. 1995Not checked yet

  Not checked in the free run.

• cites Ripple andLarsen 2000Not checked yet

  Not checked in the free run.

May combine two claims.

These changes were associated with reduced herbivory, consistent with a trophic cascade whereby wolves, combined with bears and cougars, benefited aspen through effects on elk density or behavior.

“These changes were associated with reduced herbivory, consistent with a trophic cascade whereby wolves, combined with bears (Ursus spp.) and cougars (Puma concolor), benefited aspen through effects on elk density or behavior (Hernandez and Laundre 2005, Hamlin et al. 2009, Peterson et al. 2014, Beschta and Ripple 2016).”

• cites Hernandez and Laundre 2005Not checked yet

  Not checked in the free run.

• cites Hamlin et al. 2009Not checked yet

  Not checked in the free run.

• cites Peterson et al. 2014Not checked yet

  Not checked in the free run.

May combine two claims.

Young aspen in the 1990s typically were browsed heavily and <1 m tall, so the presence of aspen saplings, defined as young aspen taller than 2 m, was an indication of significant change.

“Young aspen in the 1990s typically were browsed heavily, and <1 m tall, so the presence of aspen saplings, defined as young aspen taller than 2 m, was an indication of significant change (Romme et al. 1995, Kay 2001, Larsen and Ripple 2005, Winnie 2012, Painter et al. 2014).”

• cites Romme et al. 1995Not checked yet

  Not checked in the free run.

• cites Kay 2001Not checked yet

  Not checked in the free run.

• cites Larsen and Ripple 2005Not checked yet

  Not checked in the free run.

• AssumptionRests on an assumption: Two meters is the height at which young aspen typically escape from elk browsing.

May combine two claims.

Although elk in the park were culled to reduce their impacts, young aspen rarely grew above the reach of elk.

“Although elk in the park were culled to reduce their impacts, young aspen rarely grew above the reach of elk (YNP 1997, Barmore 2003, Wagner 2006).”

• cites YNP 1997Not checked yet

  Not checked in the free run.

• cites Barmore 2003Not checked yet

  Not checked in the free run.

• cites Wagner 2006Not checked yet

  Not checked in the free run.

Classified as probably not a substantial claim. May combine two claims.

Fire stimulates new aspen sprouts and seedlings, but intensive herbivory may suppress growth of these new sprouts, as happened in northern Yellowstone after the fires of 1988.

“Fire stimulates new aspen sprouts and seedlings, but intensive herbivory may suppress growth of these new sprouts, as happened in northern Yellowstone after the fires of 1988 (Romme et al. 1995, YNP 1997, Halofsky et al. 2008, Hansen et al. 2016, Smith et al. 2016).”

• cites Romme et al. 1995Not checked yet

  Not checked in the free run.

• cites YNP 1997Not checked yet

  Not checked in the free run.

• cites Halofsky et al. 2008Not checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing).

Trophic effects of predators may be weakened by human influences such as predator control, forage subsidies, and livestock grazing.

“Alternatively, trophic effects of predators may be weakened by human influences such as predator control, forage subsidies, and livestock grazing (Muhly et al. 2013, Wilmers andLevi 2013).”

• cites Muhly et al. 2013Not checked yet

  Not checked in the free run.

• cites Wilmers andLevi 2013Not checked yet

  Not checked in the free run.

May combine two claims.

Wolves colonized the Gallatin Canyon Range in 1997 and the Sunlight/Crandall Range in 1998, and hunting subsequently was reduced in response to decreases in these herds.

“Wolves colonized the Gallatin Canyon Range in 1997 (Appendix S1: Fig. S1) and the Sunlight/Crandall Range in 1998 (USFWS 2000-2011, Creel and Winnie 2005, Hamlin et al. 2009), and hunting subsequently was reduced (Appendix S1: Fig. S1) in response to decreases in these herds (WGFD 1980-2014, Hamlin and Cunningham 2009).”

• cites USFWS 2000-2011Not checked yet

  Not checked in the free run.

• cites Creel and Winnie 2005Not checked yet

  Not checked in the free run.

• cites Hamlin et al. 2009Not checked yet

  Not checked in the free run.

May combine two claims.

During the first two decades after the return of wolves in 1995-96, elk densities decreased in northern YNP, and an increasing number of aspen stands produced saplings (young aspen >2 m in height), an indication that some aspen were escaping from browsing.

“During the first two decades after the return of wolves in 1995-96, elk densities decreased in northern YNP, and an increasing number of aspen stands produced saplings (young aspen >2 m in height), an indication that some aspen were escaping from browsing (Ripple and Beschta 2007, 2012, Painter et al. 2014, 2015, Klaptosky 2016, Beschta et al. 2018).”

• cites Ripple and Beschta 2007, 2012Not checked yet

  Not checked in the free run.

• cites Painter et al. 2014, 2015Not checked yet

  Not checked in the free run.

• cites Klaptosky 2016Not checked yet

  Not checked in the free run.

May combine two claims.

Rocky Mountain elk forage on young aspen in fall and winter, and high levels of herbivory by elk can suppress heights of young aspen.

“Rocky Mountain elk (wapiti, Cervus canadensis) forage on young aspen in fall and winter, and high levels of herbivory by elk can suppress heights of young aspen.”

• cites Romme et al. 1995Not checked yet

  Not checked in the free run.

• cites White et al. 1998Not checked yet

  Not checked in the free run.

• cites Barmore 2003Not checked yet

  Not checked in the free run.

May combine two claims.

This process over time can result in a loss of understory aspen and shrubs in aspen stands, and eventually loss of entire stands, as old trees die and are not replaced.

“This process over time can result in a loss of understory aspen and shrubs in aspen stands, and eventually loss of entire stands, as old trees die and are not replaced (Romme et al. 1995, White et al. 1998, Barmore 2003, Smith et al. 2016).”

• cites Romme et al. 1995Not checked yet

  Not checked in the free run.

• cites White et al. 1998Not checked yet

  Not checked in the free run.

• cites Barmore 2003Not checked yet

  Not checked in the free run.

May combine two claims.

As elk increased to high numbers in the 1980-90s, more elk migrated to winter ranges north, west, and east of the park, suppressing young aspen there.

“As elk increased to high numbers in the 1980-90s, more elk migrated to winter ranges north, west, and east of the park (Houston 1982, Rudd et al. 1983, Lemke et al. 1998), suppressing young aspen there (St. John 1995, Kay 2001, Larsen and Ripple 2005).”

• cites Houston 1982Not checked yet

  Not checked in the free run.

• cites Rudd et al. 1983Not checked yet

  Not checked in the free run.

• cites Lemke et al. 1998Not checked yet

  Not checked in the free run.

Probably not a substantial claim: may not pass S3 (load-bearing).

Many elk in the Yellowstone region spend summer in high-elevation meadows in or near the park, migrating in winter to lower ranges outside the park.

“Some elk remain inside YNP during winter, but many elk in the Yellowstone region spend summer in high-elevation meadows in or near the park, migrating in winter to lower ranges outside the park (Lovaas 1970, Craighead et al. 1972, Houston 1982, Rudd et al. 1983, Hamlin et al. 2009).”

• cites Lovaas 1970Not checked yet

  Not checked in the free run.

• cites Craighead et al. 1972Not checked yet

  Not checked in the free run.

• cites Houston 1982Not checked yet

  Not checked in the free run.

May combine two claims.

Human hunters outside the park also took many elk before 2006, but similar harvests previously had not been sufficient to limit the northern Yellowstone herd.

“Human hunters outside the park also took many elk before 2006 (Vucetich et al. 2005, Eberhardt et al. 2007), but similar harvests previously had not been sufficient to limit the northern Yellowstone herd (Lemke et al. 1998, White andGarrott 2005).”

• cites Vucetich et al. 2005Not checked yet

  Not checked in the free run.

• cites Eberhardt et al. 2007Not checked yet

  Not checked in the free run.

• cites Lemke et al. 1998Not checked yet

  Not checked in the free run.

May combine two claims.

Young aspen in these ranges were suppressed by browsing in the 1980s-90s, but after the return of wolves in the late 1990s, elk densities and distributions changed.

“Young aspen in these ranges were suppressed by browsing in the 1980s-90s, but after the return of wolves in the late 1990s, elk densities and distributions changed (Hamlin et al. 2009, Christianson andCreel 2014).”

• cites Hamlin et al. 2009Not checked yet

  Not checked in the free run.

• cites Christianson andCreel 2014Not checked yet

  Not checked in the free run.

May combine two claims.

Culling in the park ended in 1968, and elk herds grew to record numbers in the 1980s-90s, expanding beyond the park boundary and suppressing aspen recruitment in winter ranges both inside and outside the park.

“Culling in the park ended in 1968, and elk herds grew to record numbers in the 1980s-90s (Coughenour and Singer 1996), expanding beyond the park boundary and suppressing aspen recruitment in winter ranges both inside and outside the park (St. John 1995, Kay 2001, Larsen and Ripple 2003, 2005, Halofsky and Ripple 2008).”

• cites Coughenour and Singer 1996Not checked yet

  Not checked in the free run.

• cites St. John 1995Not checked yet

  Not checked in the free run.

• cites Kay 2001Not checked yet

  Not checked in the free run.

May combine two claims.

Estimates of past browsing from growth histories of the tallest young aspen were consistent with other methods, confirming these estimates and the downward trend they demonstrate.

“Estimates of past browsing from growth histories of the tallest young aspen were consistent with other methods, confirming these estimates and the downward trend they demonstrate.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

This correction raised the highest browsing rate in 1997-98 to 100% and provided an estimate more comparable to other sampling methods, but did not affect the significance of any statistical tests.

“This raised the highest browsing rate in 1997-98 to 100% and provided an estimate more comparable to other sampling methods, but did not affect the significance of any statistical tests.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Scat transects provided an index of ungulate density in an area but not within an aspen stand.

“Scat transects were located with sparse ground cover and low slope, in xeric grassland or open forest edges, providing an index of ungulate density in an area but not within an aspen stand.”

May combine two claims.

Estimates of browsing in random plots vs. the five tallest in each stand were very similar in 1997-99 for the YNP East sector, in 2011 for Sunlight/Crandall, and in 2011 and 2012 for YNP (regression slope = 1.02, r2 = 0.99, P < 0.01, n = 4 study areas, summarizing 130 sample plots).

“Estimates of browsing in random plots vs. the five tallest in each stand were very similar in 1997-99 for the YNP East sector, in 2011 for Sunlight/Crandall, and in 2011 and 2012 for YNP (regression slope = 1.02, r 2 = 0.99, P < 0.01, n = 4 study areas, summarizing 130 sample plots; see Appendix S1: Table S3, Fig. S4).”

Probably not a substantial claim: may not pass S3 (load-bearing).

To correct bias in the 1997-98 data, 10 percentage points were added to browsing rates from 1997-98, based on the finding of 13% new sprouts in YNP Northern Range in 2012.

“To correct this bias in the 1997-98 data, we added 10 percentage points to browsing rates from 1997-98, based on our finding of 13% new sprouts in YNP Northern Range in 2012.”

Probably not a substantial claim: may not pass S3 (load-bearing).

For density calculations only, a correction factor of 1.32 was used to compensate for elk missed in the counts.

“For density calculations only, a correction factor of 1.32 was used to compensate for elk missed in the counts (Eberhardt et al. 2007).”

• cites Eberhardt et al. 2007Not checked yet

  Not checked in the free run.

May combine two claims.

When elk numbers were high in the 1990s, browsing was intense, young aspen were consistently short, and aspen trees were decreasing in winter ranges in the Yellowstone region.

“When elk numbers were high in the 1990s, browsing was intense, young aspen were consistently short (Fig. 2a), and aspen trees were decreasing in winter ranges in the Yellowstone region (St. John 1995, Kay 2001, Larsen and Ripple 2005).”

• cites St. John 1995Not checked yet

  Not checked in the free run.

• cites Kay 2001Not checked yet

  Not checked in the free run.

• cites Larsen and Ripple 2005Not checked yet

  Not checked in the free run.

May combine two claims.

Changes in browsing and aspen recruitment followed the reduction and redistribution of elk herds, which was influenced by predators, interacting with the effects of human hunters.

“Thus, changes in browsing and aspen recruitment followed the reduction and redistribution of elk herds, which was influenced by predators, interacting with the effects of human hunters (Fig. 4; Eberhardt et al. 2007, Hamlin et al. 2009, White et al. 2012, Creel et al. 2013, White and Garrott 2013).”

• cites Eberhardt et al. 2007Not checked yet

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• cites Hamlin et al. 2009Not checked yet

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• cites White et al. 2012Not checked yet

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May combine two claims.

Changing elk distribution and an uneven release from browsing explain these results, but climate does not.

“Changing elk distribution and an uneven release from browsing explain these results, but climate does not.”

May combine two claims.

The measurement of growth nodes represented the time since the stand began to be released from browsing, as suppressed stands typically had no young aspen >1 m.

“This measurement represented the time since the stand began to be released from browsing, as suppressed stands typically had no young aspen >1 m (Kay 2001, Larsen andRipple 2005).”

• cites Kay 2001Not checked yet

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• cites Larsen andRipple 2005Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The combination of random sampling plots and the five tallest in a stand gave two different perspectives on young aspen dynamics, one the population average and the other providing the earliest indicators of new height growth.

“The combination of random sampling plots and the five tallest in a stand gave two different perspectives on young aspen dynamics, one the population average (comparable to data from 1998) and the other providing the earliest indicators of new height growth.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Since young aspen in these areas have only recently begun growing taller, it is likely that recruitment rates will increase over time as the ecosystem responds to the new browsing regime.

“Since young aspen in these areas have only recently begun growing taller, it is likely that recruitment rates will increase over time as the ecosystem responds to the new browsing regime.”

May combine two claims.

Painter et al. tested the prediction that sites with greatest growth rates would have tallest young aspen, but found no significant relationship between annual height growth increment and height of young aspen in northern YNP.

“Painter et al. (2014Painter et al. ( , 2015) ) tested this prediction, but found no significant relationship between annual height growth increment and height of young aspen in northern YNP.”

• cites Painter et al. (2014Not checked yet

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• cites [2015]Not checked yet

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May combine two claims.

The increase in aspen saplings on elk winter ranges in and near the park breaks the historical pattern of suppressed aspen recruitment, strongly suggesting that aspen have been a beneficiary of wolf reintroduction.

“The increase in aspen saplings on elk winter ranges in and near the park breaks the historical pattern of suppressed aspen recruitment, strongly suggesting that aspen have been a “beneficiary” of wolf reintroduction (Klaptosky 2016).”

• cites Klaptosky 2016Not checked yet

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May combine two claims.

Browsing rate estimates made in 2012 for the years 2005, 2006, and 2010, using plant architecture of the five tallest young aspen, were very close to direct measurements made in 2006 and 2010, verifying this method.

“Browsing rate estimates made in 2012 for the years 2005, 2006, and 2010, using plant architecture of the five tallest young aspen, were very close to direct measurements made in 2006 and 2010, verifying this method (Fig. 3a).”

May combine two claims.

The recruitment gap demonstrated that there was a period of low recruitment, but then something changed recently, resulting in new saplings.

“This gap demonstrated that there was a period of low recruitment, but then something changed recently, resulting in new saplings (Table 2).”

Probably not a substantial claim: may not pass S3 (load-bearing).

These climate trends have adversely affected aspen elsewhere in the western United States.

“These climate trends have adversely affected aspen elsewhere in the western United States (Rogers and Mittanck 2014).”

• cites Rogers and Mittanck 2014Not checked yet

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May combine two claims.

Although ranges and migration routes of Yellowstone elk remained the same after wolf reintroduction, the proportions of the herds wintering in or near the park decreased, even as harvest near the park decreased.

“Although ranges and migration routes of Yellowstone elk remained the same after wolf reintroduction (Mao et al. 2005, White et al. 2010), the proportions of the herds wintering in or near the park decreased (Fig. 4a), even as harvest near the park decreased (Appendix S1: Fig. S1).”

• cites Mao et al. 2005Not checked yet

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• cites White et al. 2010Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

Olmsted estimated that herbivory of more than 30% of annual twig production could reduce stand densities.

“Olmsted (1979) estimated that herbivory of more than 30% of annual twig production could reduce stand densities”

• cites Olmsted (1979)Not checked yet

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May combine two claims.

This explains the aspen stand conditions found there in 2015, with dense thickets of saplings and no gap in age and size distribution, but many saplings were stripped of bark and shorter aspen were heavily browsed.

“This explains the aspen stand conditions found there in 2015, with dense thickets of saplings and no gap in age and size distribution, but many saplings were stripped of bark and shorter aspen were heavily browsed.”

May combine two claims.

Elk recruitment was strong in surrounding areas with fewer predators, suggesting predation as a primary cause of the decrease.

“Elk recruitment was strong in surrounding areas with fewer predators, suggesting predation as a primary cause of the decrease (Hamlin and Cunningham 2009, Cunningham et al. 2010, Middleton et al. 2013, Christianson and Creel 2014).”

• cites Hamlin and Cunningham 2009Not checked yet

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• cites Cunningham et al. 2010Not checked yet

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• cites Middleton et al. 2013Not checked yet

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Classified as probably not a substantial claim. May combine two claims.

White et al. found that aspen recruitment in Rocky Mountain national parks in the United States and Canada was suppressed by elk browsing, except where predation by wolves was moderate to high and elk densities moderate to low, <4 elk/km2.

“White et al. (1998White et al. ( , 2003) ) found that aspen recruitment in Rocky Mountain national parks in the United States and Canada was suppressed by elk browsing, except where predation by wolves was moderate to high and elk densities moderate to low, <4 elk/km 2 .”

• cites White et al. (1998Not checked yet

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• cites [2003]Not checked yet

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May combine two claims.

Although total elk numbers since about 2005 have been comparable to the lows of the 1960s, this similarity was only superficial, as elk densities in the park have been much lower recently than in the 1960s.

“Although total elk numbers since about 2005 have been comparable to the lows of the 1960s (Appendix S1: Fig. S1a), this similarity was only superficial, as elk densities in the park have been much lower recently than in the 1960s (Houston 1982).”

• cites Houston 1982Not checked yet

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May combine two claims.

More elk have been wintering in these lower valleys, and resident (non-migratory) elk there have increased.

“More elk have been wintering in these lower valleys, and resident (non-migratory) elk there have increased (Hamlin andCunningham 2009, Wilmers andLevi 2013).”

• cites Hamlin and Cunningham 2009Not checked yet

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• cites Wilmers and Levi 2013Not checked yet

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May combine two claims.

Increases in height or recruitment have been documented not only for aspen, but also for cottonwood, willow, thinleaf alder, and other shrubs.

“Responses from woody forage plants might be expected to follow, and increases in height or recruitment have been documented not only for aspen, but also for cottonwood (Populus spp.), willow (Salix spp.), thinleaf alder (Alnus incana spp.tenuifolia), and other shrubs (Beschta and Ripple 2016).”

• cites Beschta and Ripple 2016Not checked yet

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May combine two claims.

A 2006 study found patchy new growth of saplings, but in most stands young aspen still were suppressed.

“A 2006 study found patchy new growth of saplings, but in most stands young aspen still were suppressed (Kimble et al. 2011).”

• cites Kimble et al. 2011Not checked yet

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May combine two claims.

Few elk migrated north of Dome Mountain until the winter after the 1988 fires, when many elk starved and unusual numbers left the park.

“Few elk migrated north of Dome Mountain until the winter after the 1988 fires (Lemke et al. 1998, NRC 2002), when many elk starved and unusual numbers left the park (Appendix S1: Fig. S2c, S2d).”

• cites Lemke et al. 1998Not checked yet

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• cites NRC 2002Not checked yet

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May combine two claims.

Consistent with trends in the northern range, elk counts decreased markedly in the Gallatin Canyon range following the return of wolves, while in the valley of the lower Madison River to the west, elk numbers increased 240% between 1994 and 2008.

“Consistent with trends in the northern range, elk counts decreased markedly in the Gallatin Canyon range following the return of wolves (Appendix S1: Figs.S1b, S3), while in the valley of the lower Madison River to the west, elk numbers increased 240% between 1994 and 2008 (Hamlin and Cunningham 2009).”

• cites Hamlin and Cunningham 2009Not checked yet

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May combine two claims.

Inside YNP, elk densities were very high in the 1990s, so a larger reduction was required to reach a density at which reduced browsing was possible, compared to areas outside the park where hunting was already limiting elk density.

“Inside YNP, elk densities were very high in the 1990s (White et al. 1998, Wagner 2006, Painter et al. 2015), so a larger reduction was required to reach a density at which reduced browsing was possible (Fig. 3b), compared to areas outside the park where hunting was already limiting elk density.”

• cites White et al. 1998Not checked yet

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• cites Wagner 2006Not checked yet

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• cites Painter et al. 2015Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Close to the park, elk recruitment, population densities, and harvests have decreased, while high elk densities in these other areas have caused concern about disease transmission, range damage, and competition with cattle.

“Close to the park, elk recruitment, population densities, and harvests have decreased, while high elk densities in these other areas have caused concern about disease transmission, range damage, and competition with cattle (Haggerty and Travis 2006, Dickson 2014, Proffitt et al. 2015).”

• cites Haggerty and Travis 2006Not checked yet

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• cites Dickson 2014Not checked yet

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• cites Proffitt et al. 2015Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

Other researchers have confirmed that high rates of aspen herbivory consistently suppressed aspen recruitment except where elk densities were relatively low.

“Other researchers have confirmed that high rates of aspen herbivory consistently suppressed aspen recruitment except where elk densities were relatively low (Durham andMarlow 2010, Rogers andMittanck 2014).”

• cites Durham and Marlow 2010Not checked yet

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• cites Rogers and Mittanck 2014Not checked yet

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May combine two claims.

Our findings, and those of other published research, provide compelling evidence that browsing intensity has been the dominant factor affecting aspen recruitment in the Yellowstone region, while the alternative hypothesis, based on climate and productivity, results in predictions not supported by the data.

“Our findings, and those of other published research, provide compelling evidence that browsing intensity has been the dominant factor affecting aspen recruitment in the Yellowstone region, while the alternative hypothesis, based on climate and productivity, results in predictions not supported by the data.”

Classified as probably not a substantial claim.

Wildlife managers attributed these changes in elk populations primarily to predation and emigration.

“Wildlife managers attributed these changes in elk populations primarily to predation and emigration (Hamlin and Cunningham 2009, Cunningham et al. 2010, Middleton et al. 2013).”

• cites Hamlin and Cunningham 2009Not checked yet

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• cites Cunningham et al. 2010Not checked yet

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• cites Middleton et al. 2013Not checked yet

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May combine two claims.

Predation by bears and cougars also increased, adding to the effects of wolves.

“Predation by bears and cougars also increased, adding to the effects of wolves (Barber-Meyer et al. 2008, Garrott et al. 2009, Hamlin et al. 2009).”

• cites Barber-Meyer et al. 2008Not checked yet

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• cites Garrott et al. 2009Not checked yet

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• cites Hamlin et al. 2009Not checked yet

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May combine two claims.

The northern Yellowstone elk herd following the restoration of wolves is an example of a switch from bottom-up to top-down limitation, first by hunters and predators, then primarily by predators.

“The northern Yellowstone elk herd following the restoration of wolves is an example of a switch from bottom-up to top-down limitation, first by hunters and predators, then primarily by predators (White and Garrott 2005, Eberhardt et al. 2007, White and Garrott 2013).”

• cites White and Garrott 2005Not checked yet

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• cites Eberhardt et al. 2007Not checked yet

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• cites White and Garrott 2013Not checked yet

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May combine two claims.

As wolves recolonized, most elk returned to the same portion of winter range each year, but some changed.

“As wolves recolonized, most elk returned to the same portion of winter range each year, but some changed (Gower et al. 2009b, Hamlin and Cunningham 2009, White et al. 2010).”

• cites Gower et al. 2009bNot checked yet

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• cites Hamlin and Cunningham 2009Not checked yet

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• cites White et al. 2010Not checked yet

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May combine two claims.

This herd had previously been regulated by hunting, and when wolves returned may already have been near the low density at which browsing was moderated.

“This herd had previously been regulated by hunting (WGFD 1980(WGFD -2014)), and when wolves returned may already have been near the low density at which browsing was moderated (Fig. 3b).”

• cites WGFD 1980-2014Not checked yet

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May combine two claims.

In the severe winter of 1997, many elk died of starvation, so predation from a small population of wolves made little difference.

“For example, in the severe winter of 1997, many elk died of starvation, so predation from a small population of wolves made little difference.”

May combine two claims.

The Madison Headwaters elk herd in central Yellowstone also was reduced by predation following wolf reintroduction, as was the Gallatin Canyon herd.

“The Madison Headwaters elk herd in central Yellowstone (Appendix S1: Fig. S3) also was reduced by predation following wolf reintroduction (Garrott et al. 2009, White et al. 2009), as was the Gallatin Canyon herd (Hamlin et al. 2009).”

• cites Garrott et al. 2009Not checked yet

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• cites White et al. 2009Not checked yet

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• cites Hamlin et al. 2009Not checked yet

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May combine two claims.

After wolf restoration, predators culled elk in the park, combining with the effect of hunters outside the park.

“After wolf restoration, predators culled elk in the park, combining with the effect of hunters outside the park (Fig. 4b).”

May combine two claims.

Greater predation in the park and recent limitations on hunting have increased benefits and reduced risks for elk migrating out of the park.

“Greater predation in the park and recent limitations on hunting have increased benefits and reduced risks for elk migrating out of the park (Hamlin et al. 2009, White et al. 2012).”

• cites Hamlin et al. 2009Not checked yet

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• cites White et al. 2012Not checked yet

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May combine two claims.

In the Sunlight/Crandall Range, many stands with new recruitment were away from open areas where elk tend to congregate, a pattern that can be explained by a greater tendency for elk to group together, thereby reducing foraging in peripheral locations.

“For example, in the Sunlight/Crandall Range, many stands with new recruitment were away from open areas where elk tend to congregate, a pattern that can be explained by a greater tendency for elk to group together (Gower et al. 2009a, White et al. 2012), thereby reducing foraging in peripheral locations.”

• cites Gower et al. 2009aNot checked yet

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• cites White et al. 2012Not checked yet

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May combine two claims.

In the Gallatin Canyon Range, risk from hunting can explain differences between Daly Creek inside the park with high browsing rates, compared to Taylor Fork which was open to hunters and had much lower browsing rates and lower scat density.

“In the Gallatin Canyon Range, risk from hunting (Proffitt et al. 2013) can explain differences between Daly Creek inside the park with high browsing rates (Winnie 2012), compared to Taylor Fork which was open to hunters and had much lower browsing rates and lower scat density (Fig. 2b, Table 2).”

• cites Proffitt et al. 2013Not checked yet

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• cites Winnie 2012Not checked yet

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May combine two claims.

Smaller changes were sufficient to reduce browsing pressure to a level at which aspen recruitment was possible, as previously occurred in the 1970s.

“Smaller changes were sufficient to reduce browsing pressure to a level at which aspen recruitment was possible, as previously occurred in the 1970s.”

May combine two claims.

Starvation limited elk numbers in the 1980s, with large die-offs in severe winters followed by increases.

“However, starvation limited elk numbers in the 1980s, with large die-offs in severe winters followed by increases (Coughenour and Singer 1996).”

• cites Coughenour and Singer 1996Not checked yet

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May combine two claims.

The consequences of large carnivore restoration in Yellowstone continue to unfold, with cascading effects over large scales, as prey balance the pressures of predation and hunting with other environmental factors.

“The consequences of large carnivore restoration in Yellowstone continue to unfold, with cascading effects over large scales, as prey balance the pressures of predation and hunting with other environmental factors.”

Classified as probably not a substantial claim.

This hypothesis was supported by evidence from aspen surveys and elk counts.

“This hypothesis was supported by evidence from aspen surveys and elk counts.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

With browsing reduced so that aspen recruitment is no longer suppressed, these ecosystem processes may be restored, and future fires may stimulate regeneration and expansion of aspen stands in Yellowstone.

“With browsing reduced so that aspen recruitment is no longer suppressed, these ecosystem processes may be restored, and future fires may stimulate regeneration and expansion of aspen stands in Yellowstone (Ripple andBeschta 2004, Halofsky et al. 2008).”

• cites Ripple and Beschta 2004Not checked yet

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• cites Halofsky et al. 2008Not checked yet

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May combine two claims.

Warmer and drier conditions may result in less aspen on winter ranges over the long term, possibly with elevational changes in aspen distribution.

“Warmer and drier conditions, however, may result in less aspen on winter ranges over the long term, possibly with elevational changes in aspen distribution (Brodie et al. 2011, Hanna and Kulakowski 2012, Worrall et al. 2013, Romme and Turner 2015, Hansen et al. 2016).”

• cites Brodie et al. 2011Not checked yet

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• cites Hanna and Kulakowski 2012Not checked yet

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• cites Worrall et al. 2013Not checked yet

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May combine two claims.

As elk densities have decreased more in some areas than others, spatial variation in browsing has increased, resulting in a patchy increase in aspen recruitment.

“As elk densities have decreased more in some areas than others, spatial variation in browsing has increased, resulting in a patchy increase in aspen recruitment.”

May combine two claims.

Behavioral responses to predators and human hunters may have influenced elk range selection, foraging, and use of habitat.

“In addition to direct mortality of elk, behavioral responses to predators and human hunters may have influenced elk range selection, foraging, and use of habitat.”