Vegetation response to Rocky Mountain National Park’s elk and vegetation management plan: Analysis of 2008–2018 data
Authors: Gage Edward , Zeigenfuss Linda , Abouelezz Hanem , Konkowski Allison , Cooper David , Johnson Therese 
Published: June 2023

Rocky Mountain National Park (RMNP) developed the Elk and Vegetation Management Plan (EVMP) to address well-documented declines in the ecological condition of aspen stands and riparian communities from high levels of elk herbivory. The EVMP aims to reduce the impacts of elk on vegetation and restore the natural range of variability in the elk population and affected plant communities, including preventing the loss of aspen clones within high elk-use areas, restoring montane riparian willow cover and height within suitable habitat, and reducing of levels of elk grazing on herbaceous vegetation. The EVMP described a range of management actions including reductions in the size of the elk herd and the installation of fencing to reduce herbivory levels and facilitate recovery in degraded communities. The EVMP established a monitoring protocol in focal communities to assess progress towards these vegetation goals and facilitate adaptive management. RMNP has collected data quantifying biomass offtake in upland herbaceous and riparian communities, willow height and cover, and aspen stand structure and regeneration periodically since implementation of the plan began in 2008. This report summarizes the results of analyses of EVMP data collected from 2008–2018, the last year comprehensive measurements were made. The EVMP was developed with a focus on the primary elk winter range in the upper montane zone on the east side of RMNP. The plan distinguishes core elk winter range, where elk concentrate during winter, and noncore winter range areas that typically have less elk use. Data were also collected in the Kawuneeche Valley in the headwaters of the Colorado River on the west side of the park, an area supporting extensive wet meadows and areas once dominated by willow. Data were also collected to investigate the effects of wildland fires that burned through the winter range in 2012 to determine the potential for using fire as a management tool to achieve EVMP goals. The overwintering elk population in the park has declined, from its peak of 1,500 animals in 2001, and over the course of EVMP implementation, from 614 animals in 2009 to 124 animals in 2019. Declines in the overwintering elk population may be best explained by increased cow elk harvest outside of the park, and, most notably, by a change in seasonal migration patterns and habitat use that have elk moving to lower elevation wintering areas following the fall rut. In sites in aspen communities, stand structure was changed little or declined across sampling periods in unfenced plots with continued patterns of little regeneration and recruitment and steady progression toward stands dominated by large-diameter trees. However, there was a progression towards taller sapling heights inside fenced plots and recruitment of small diameter tree-sized stems. Fencing had large and positive effects on aspen stand structure, with different patterns observed in fenced and unfenced core winter range and noncore winter range. Increased recruitment was observed across the winter range but occurred mainly inside fenced plots. Aspen stem counts varied between time periods and in relation to wildfire, with fenced and burned plots on the core winter range having higher stem counts by 2018 than unfenced and unburned plots. Willow height and cover increased over time in sampled sites, but positive trends were generally restricted to sites in fenced areas. Willow height also increased on noncore (all unfenced) winter range sites. Willow in unfenced core winter range sites had only minor increase in height from baseline (2008 for most sites) to 2018, but willow in fenced plots had greater height increases over the same time period. Noncore winter range willow sites had modest height increases over the 10-yr period. Mean willow cover increased nearly 5-fold compared to baseline conditions within the core winter range fenced areas and roughly 1.5-fold in noncore winter range. Willow cover was greater in unfenced than fenced plots at baseline, but the pattern was reversed in 2013 and 2018. The highest cover occurred in 2018 in fenced core winter range plots (mean = 70.8%) and unfenced noncore winter range plots (mean = 68.6%). Mean cover increased from 14.6% at baseline to 25.3% in 2013 and 70.8% in 2018 in fenced core winter range plots. Mean willow cover changed little in unfenced core winter range plots between baseline and 2018, although the range of cover values increased over time, and willow cover increases were modest in the noncore winter range. Fencing reduced or eliminated browsing from plots located inside fences, but offtake varied widely among unfenced plots. Patterns of willow browse intensity differed management subgroups (e.g., core and noncore winter range), and generally showed a downward trend between baseline and 2018 measurements. Herbaceous offtake in upland communities was measured in the first sample period (baseline–2013) to assess levels of grazing on herbaceous vegetation, however it was determined that the associated EVMP objectives had been achieved so measurements were discontinued after 2013. Continued monitoring of upland shrubs indicated no shift from herbaceous dominated to shrub dominated communities after 2013. Noncore upland plots had higher shrub cover than core winter range plots across all time periods, but most differences between year and core/noncore had low probability of effect. Cover for individual species varied over time and winter range plots. Moose presence has increased in winter range aspen and willow sites over the past decade, while beaver presence at our monitoring sites has decreased. Results indicate that RMNP is making progress toward the vegetation objectives set out in the EVMP, however positive trends were most pronounced in plots protected from ungulate herbivory through fencing. Aspen recruitment was greatest in fenced plots. Likewise, trajectories of willow height and cover were positive in fenced winter range plots. Results demonstrate that fencing is an effective means of improving condition in aspen and willow habitats. Changes outside the fences were slower and less pronounced than inside the fences, however, the positive (if small) increases in willow height and cover and aspen regeneration as well as decreases in upland herbaceous offtake, indicate that decreased wintering elk populations are also contributing to improvement of habitat conditions on the elk winter range. In the Kawuneeche Valley, which has not traditionally been heavily used by overwintering elk but does experience summer elk and moose use, poor and declining habitat condition were recorded in unfenced willow and aspen sites.