The effects of elk on aspen in the winter range in Rocky Mountain National Park

Abstract

National parks face problems in managing wild ungulates and their forage resources, including small park sizes and incomplete protection of winter ranges, absence of major predators, and influences from extenor management activities Our study focuses on the efTects of elk Cervus elaphus browsing on aspen Populus tremuloides in the elk winter range of Rocky Mountain National Park Elk can prevent successful regeneration of aspen by suckers, and increase the monality of established trees Here we quantify the efTect of elk on aspen in the elk winter range of the park particularly since the adoption of a policy of "natural regulation" in 1968 We collected a stratified-random sample of aspen cohorts m the elk winter range, and also inside two long-term exclosures In each cohort we tallied live and dead trees by diameter, recorded the height and percentage of stem surface covered by bark-stnpping, and estimated the date of regeneration of the cohort using increment cores We also tallied live and dead aspen suckers (young trees < 2 5 m tall) by height and the number of live and de<id branches on each sucker Aspen outside the exclosures are declining as evidenced hy 1) high mortality among established trees, including entire stands that are dead, 2) low density of live suckers, insufficient to regenerate the stand, 3) suckers that are excessively branched and seldom surviving to reach tree height, and 4) almost no cohon regeneration since adoption of natural regulation Exclosures and early photos of the elk winter range suggest these are anomalous conditions Over the last century, aspen cohorts regenerated only when there were fewer than ca 600 elk on the park's elk winter range, far fewer than the present estimated 1600 head Fire suppression, natural succession, fluctuations in beaver populations, climatic fluctuations, and other factors are of no or lesser importance than elk in the regeneration and survival of aspen cohorts on the elk winter range The decline of aspen is a concem when management is focused on the ecosystem scale rather than simply the scale of wildlife and their pnmary forage resources

Regional Assessment of Aspen Change and Spatial Variability on Decadal Time Scales

“…First, the results indicated drastically declining aspen cover in the Targhee National Forest. Similar to local-scale studies [13,15,45,46], the results indicated that 94.5% of the aspen mapped in 1920 had declined by 2005. The shorter-term change detection indicated a lesser, but still a substantial decline of 89.5%.…”

Space use and social ecology of coyotes (Canis latrans) in a high-elevation ecosystem: relative stability in a changing environment

“…In Rocky Mountain National Park, Colorado, declines of willow and aspen have been documented and attributed to high ungulate populations (Olmsted 1979;Baker et al 1997;Peinetti et al 2002). Lubow et al (2002) concluded that the park population was food-limited density dependent, likely at a higher population level than achieved under natural regulation with top predators.…”

Lichen community change in response to succession in aspen forests of the southern Rocky Mountains

“…While aspen suckers may continue to emerge within small canopy openings, their proliferation becomes increasingly limited without larger disturbance. Survival of aspen regeneration in conifer-dominated stands is often low due to increasing resource limitations and the well documented impacts of ungulate browsing (Baker et al, 1997;Hessl and Graumlich, 2002;Kay and Bartos, 2000;Ripple et al, 2001). Moreover, reduced aspen cover has resulted in limitations on further asexual reproduction: the fewer healthy trees above ground, the less likely new suckers will emerge either on a continuous basis or in a flush following disturbance (Shepperd et al, 2006).…”