Rocky Mountain National Park Research Articles

Rapid assessment of butterfly diversity in a montane landscape

We present the results of a rapid assessment of butterfly diversity in the 754 ha Beaver Meadows study area in Rocky Mountain National Park, Larimer County, Colorado. We measured butterfly species richness and relative abundance as part of a landscape-scale investigation of diversity patterns involving several groups of organisms. A stratified random sampling design was used to include replication in both rare and common vegetation types. We recorded 49 butterfly species from the twenty-four 0.1 ha plots that were sampled four times during June, July, and August 1996. Butterfly species richness, diversity, and uniqueness were highest in quaking aspen (Populus tremuloides Michaux) groves and wet meadows, which occupy only a small proportion of the studied landscape. This result supports the suggestion that aspen areas represent ‘hotspots’ of biological diversity in this montane landscape. Patterns of butterfly species richness were positively correlated with total vascular plant species richness (r = 0.69; P < 0.001), and native plant species richness (r = 0.64; P < 0.001). However, exotic plant species richness (r = 0.70; P < 0.001) and the cover of exotic plant species (r = 0.70; P < 0.001) were the best predictors of butterfly species richness.

Experimental Repatriation of Boreal Toad (Bufo boreas) Eggs, Metamorphs, and Adults in Rocky Mountain National Park

Experimental Repatriation of Boreal Toad (Bufo boreas) Eggs, Metamorphs, and Adults in Rocky Mountain National Park

The influence of physical soil conditions on the formation of root nodules of Melilotus officinalis in the montane zone of Rocky Mountain National Park

Exotic invasion is a key threat to native biological diversity, second only to habitat degradation. Melilotus officinalis is an exotic species that thrives in areas of anthropogenic disturbances and low nutrient availability. Typically, natural disturbance facilitates native species establishment and maintains species diversity; however, anthropogenic disturbance facilitates exotic species establishment. M. officinalis functions as a competitor in the montane communities because of its symbiosis with Rhizobium bacteria, a symbiosis that allows the plant to acquire nitrogen. Although the ability to fix nitrogen permits M. officinalis to grow in nitrogen depleted soils, the soil must have a microclimate that is favorable to symbiosis and nodulation. We analyzed abiotic soil characteristics in Rocky Mountain National Park to determine if nodulation was related to soil texture, as well as in the mid-range level of soil and temperatures. We found that nodules on plant specimens showed a positive correlation with soil moisture and temperature, and occurred in a specific range of moderate moisture and temperature. Soil texture was not correlated to nodule formation.

Fire history in high elevation subalpine forests in the Colorado Front Range

Resource managers rely on knowledge of fire history to guide management decisions, but for the subalpine zone of the Colorado Front Range little information exists on fire history documenting changes in fire regimes over the past several centuries. We examined fire history at 13 high elevation sites in the Colorado Front Range to detect long-term trends that may be related to changes in land use and/or to climatic variability. There is a high degree of spatial and temporal variation in fire regimes across sites; however, most sites exhibit an increase in fire frequency during the 20th century compared to the 19th century. We did not find any evidence that fire suppression after the creation of National Forests and Rocky Mountain National Park in the early 1900s decreased fire frequency at the highest elevations of forest cover in the Front Range. Human influences over the last 200 years have played less of a role in these high elevation subalpine forests than in the lower elevation forests of the Colorado Front Range. In the absence of effective fire exclusion in these high elevation forests, there is no basis for assuming that forest structure and fuel conditions are outside of the historic range of variability for this habitat. Fire occurrence in these high elevation sites is highly dependent on drought, which often results from La Niña events. In comparison with lower elevation ponderosa pine forests of the Front Range, fire is less dependent on increased fuel production following wet El Niño events.

Valid Threat or “Tempest in a Teapot”? An Historical Account of Tourism Development and the Canadian Rocky Mountain Parks World Heritage Site Designation

UNESCO declared the Canadian Rocky Mountain Parks of Western Canada a World Heritage Site (WHS) in 1984, based on a submission from Parks Canada, the federal agency charged with managing Canada's national park system. In the 1990s, increasing tourism development and related infrastructure in Banff National Park prompted environmentalists to express concerns regarding threats to the ecological integrity of Banff National Park and its status as part of a WHS. Parks Canada and the Town of Banff responded in various ways to the perceived threats. The criteria under which the site designation was approved, and the current state party dominated process outlined in the World Heritage Committee's Operational Guidelines, make it unlikely that the Canadian Rocky Mountain Parks will appear on UNESCO's List of World Heritage Sites in Danger. Nevertheless, significant threats to the areas's ecological integrity remain, and warrant continued attention. Recommendations made by the IUCN to make World Heritage processes more democratic, and to clarify and focus natural criteria on bio-diversity and ecological integrity, would enhance the credibility of WHS designation as a conservation tool.

Strategic highway improvements to minimize environmental impacts within the Canadian Rocky Mountain National Parks

This paper describes how strategic highway engineering improvements have been developed or adopted to mitigate the unique environmental impact highways and roads have within Canadian Rocky Mountain national parks, which are also World Heritage Sites. Three levels of strategic highway development are presented. The first is the recapitalization of existing park roads. Examples are presented from several national parks where parkways and low-volume roads were reconstructed or repaired in ways to reduce terrain impacts. The second is the development of the passing lane system on the Trans-Canada Highway in the Rocky Mountain national parks to defer twinning. The third example is the twinning of 18.6 km of the Trans-Canada Highway. Twinning represents a logical next step following the passing lane phase. This paper describes how highway engineering improvements were developed to address and mitigate numerous potential twinning impacts identified during environmental assessment. Included within the environmental mitigation measures are fencing and animal crossing structures, addressing wildlife movement, biodiversity, and mortality as well as stream, terrain, and vegetation disturbance minimization techniques. Research has found that the mitigation measures have been effective in reducing wildlife and vehicle collisions by 97%.Key words: highway, sustainable, national park, environment.

Determination of hydrologic pathways during snowmelt for alpine/subalpine basins, Rocky Mountain National Park, Colorado

Alpine/subalpine ecosystems in Rocky Mountain National Park may be sensitive to atmospherically derived acidic deposition. Two‐ and three‐component hydrograph separation analyses and correlation analyses were performed for six basins to provide insight into streamflow generation during snowmelt and to assess basin sensitivity to acidic deposition. Three‐component hydrograph separation results for five basins showed that streamflow contained from 42 to 57% direct snowmelt runoff, 37 to 54% subsurface water, and 4 to 13% direct rain runoff for the May through October 1994 study period. Subsurface contributions were 89% of total flow for the sixth basin. The reliability of hydrograph separation model assumptions was explored. Subsurface flow was positively correlated with the amount of surficial material in a basin and was negatively correlated with basin slope. Basins with extensive surficial material and shallow slopes are less susceptible to ecosystem changes due to acidic deposition than basins with less surficial material and steeper slopes. This study was initiated to expand the intensive hydrologic research that has been conducted in Loch Vale basin to a more regional scale.

Relations between basin characteristics and stream water chemistry in alpine/subalpine basins in Rocky Mountain National Park, Colorado

Relations between stream water chemistry and topographic, vegetative, and geologic characteristics of basins were evaluated for nine alpine/subalpine basins in Rocky Mountain National Park, Colorado, to identify controlling parameters and to better understand processes governing patterns in stream water chemistry. Fractional amounts of steep slopes (≥30°), unvegetated terrain, and young surficial debris within each basin were positively correlated to each other. These terrain features, which commonly occur on steep valley side slopes underlain by talus, were negatively correlated with concentrations of base cations, silica, and alkalinity and were positively correlated with nitrate, acidity, and runoff. These relations might result from the short residence times of water and limited soil development in the talus environment, which limit chemical weathering and nitrogen uptake. Steep, unvegetated terrains also tend to promote high Ca/Na ratios in stream water, probably because physical weathering rates in those areas are high. Physical weathering exposes fresh bedrock that contains interstitial calcite, which weathers relatively quickly. The fractional amounts of subalpine meadow and, to a lesser extent, old surficial debris in the basins were positively correlated to concentrations of weathering products and were negatively correlated to nitrate and acidity. These relations may reflect more opportunities for silicate weathering and nitrogen uptake in the lower‐energy environments of the valley floor, where soils are finer‐grained, older, and better developed and slopes are relatively flat. These results indicate that in alpine/subalpine basins, slope, vegetation (or lack thereof), and distribution and age of surficial materials are interrelated and can have major effects on stream water chemistry.

Sustainable Highway Development in a National Park

Sustainable highway-engineering improvements have been developed or adopted to mitigate the unique environmental impact that highways and roads have in Canadian Rocky Mountain National Parks, which are also World Heritage Sites. Three levels of sustainable highway development are presented. The first is the reconstruction or rehabilitation of park roads. Examples are presented from several national parks in which parkways and low-volume roads were reconstructed or repaired in ways that reduced impacts. The second is the development of the passing-lane system on the Trans-Canada Highway in the Rocky Mountain National Parks. The passing-lane system has extended the design service life of the two-lane highway by approximately 15 years while maintaining an acceptable level of service. The third example is the twinning of 18.6 km of the Trans-Canada Highway, which represents a logical next step in a program of sequential twinning following the passing-lane phase. Discussion includes the ways in which highway-engineering improvements were developed to address and mitigate numerous potential project impacts that were identified during environmental assessment. Included in the environmental mitigations were a series of measures such as fencing, animal-crossing structures, and underpasses to address wildlife movement, biodiversity, and mortality. Stream, terrain, and vegetation disturbance-minimization techniques also were applied. Research has found that the mitigation measures have been effective in reducing wildlife–vehicle collisions by as much as 97 percent.

Monitoring shifts in plant diversity in response to climate change: A method for landscapes

Improved sampling designs are needed to detect, monitor, and predict plant migrations and plant diversity changes caused by climate change and other human activities. We propose a methodology based on multi-scale vegetation plots established across forest ecotones which provide baseline data on patterns of plant diversity, invasions of exotic plant species, and plant migrations at landscape scales in Rocky Mountain National Park, Colorado, USA. We established forty two 1000-m2 plots in relatively homogeneous forest types and the ecotones between them on 14 vegetation transects. We found that 64% of the variance in understory species distributions at landscape scales were described generally by gradients of elevation and under-canopy solar radiation. Superimposed on broad-scale climatic gradients are small-scale gradients characterized by patches of light, pockets of fertile soil, and zones of high soil moisture. Eighteen of the 42 plots contained at least one exotic species; monitoring exotic plant invasions provides a means to assess changes in native plant diversity and plant migrations. Plant species showed weak affinities to overstory vegetation types, with 43% of the plant species found in three or more vegetation types. Replicate transects along several environmental gradients may provide the means to monitor plant diversity and species migrations at landscape scales because: (1) ecotones may play crucial roles in expanding the geophysiological ranges of many plant species; (2) low affinities of understory species to overstory forest types may predispose vegetation types to be resilient to rapid environmental change; and (3) ecotones may help buffer plant species from extirpation and extinction.

Combining binary decision tree and geostatistical methods to estimate snow distribution in a mountain watershed

We model the spatial distribution of snow across a mountain basin using an approach that combines binary decision tree and geostatistical techniques. In April 1997 and 1998, intensive snow surveys were conducted in the 6.9‐km2 Loch Vale watershed (LVWS), Rocky Mountain National Park, Colorado. Binary decision trees were used to model the large‐scale variations in snow depth, while the small‐scale variations were modeled through kriging interpolation methods. Binary decision trees related depth to the physically based independent variables of net solar radiation, elevation, slope, and vegetation cover type. These decision tree models explained 54–65% of the observed variance in the depth measurements. The tree‐based modeled depths were then subtracted from the measured depths, and the resulting residuals were spatially distributed across LVWS through kriging techniques. The kriged estimates of the residuals were added to the tree‐based modeled depths to produce a combined depth model. The combined depth estimates explained 60–85% of the variance in the measured depths. Snow densities were mapped across LVWS using regression analysis. Snow‐covered area was determined from high‐resolution aerial photographs. Combining the modeled depths and densities with a snow cover map produced estimates of the spatial distribution of snow water equivalence (SWE). This modeling approach offers improvement over previous methods of estimating SWE distribution in mountain basins.

Using multi-scale sampling and spatial cross-correlation to investigate patterns of plant species richness

Land managers need better techniques to assess exotic plant invasions. We used the cross-correlation statistic, IYZ, to test for the presence of spatial cross-correlation between pair- wise combinations of soil characteristics, topographic variables, plant species richness, and cover of vascular plants in a 754 ha study site in Rocky Mountain National Park, Colorado, U.S.A. Us- ing 25 large plots (1000 m 2 ) in five vegetation types, 8 of 12 variables showed significant spatial cross-correlation with at least one other variable, while 6 of 12 variables showed significant spatial auto-correlation. Elevation and slope showed significant spatial cross-correlation with all variables except percent cover of native and exotic species. Percent cover of native species had significant spatial cross-correlations with soil variables, but not with exotic species. This was probably because of the patchy distributions of vegetation types in the study area. At a finer resolution, using data from ten 1 m 2 subplots within each of the 1000 m 2 plots, all variables showed significant spatial auto- and cross-correlation. Large-plot sampling was more affected by topographic factors than species distribution patterns, while with finer resolution sampling, the opposite was true. However, the statistically and biologically significant spatial correlation of native and exotic species could only be detected with finer resolution sampling. We found exotic plant species invading areas with high native plant richness and cover, and in fertile soils high in nitrogen, silt, and clay. Spatial auto- and cross-correlation statistics, along with the integration of remotely sensed data and geographic information systems, are powerful new tools for evaluating the patterns and distribution of native and exotic plant species in relation to landscape structure.

Strategic highway improvements to minimize environmental impacts within the Canadian Rocky Mountain National Parks

Strategic highway improvements to minimize environmental impacts within the Canadian Rocky Mountain National Parks

Natural variability in N export from headwater catchments: snow cover controls on ecosystem N retention

The causes of natural variability in catchment scale N export need to be understood and quantified before the effects of increased N deposition in high elevation catchments can be evaluated. This study evaluates controls on the size of the leachable soil N pool concurrent with the spring hydrologic flush that is primarily responsible for the transport of N to surface water. In high elevation catchments in the western United States, sources of N during this snowmelt flush include both atmospheric N deposition stored in the snowpack until melt and mobile soil N pools, and sinks are dominated by biogeochemical processes that occur in soil under snow cover. Because soil processes may serve either as a source or sink for N, controls on the amount of inorganic N leached from soil during the snowmelt period were evaluated in the major landscape types in four catchments in Colorado. Measurements of leached N were inversely related to measurements of over-winter CO 2 flux at all sites, indicating that N was immobilized in soil heterotrophic biomass. Because over-winter soil heterotrophic activity is controlled primarily by the depth and timing of snow accumulation, the importance of these plot scale measurements to catchment scale N export were evaluated using a long-term record of winter precipitation, N deposition, and N export from Loch Vale in Rocky Mountain National Park. This data set identified a strong, linear relationship (r 2 = 0.68) between catchment scale N retention and winter snow cover, consistent with subnivean, soil based controls on the mobile N pool identified at the plot scale. These results indicate that the winter snow pack is the major control both on hydrologic N export and on soil source/sink relationships for N concurrent with this transport mechanism. The effect of winter snow cover on the fate of both atmospheric and soil N needs to be considered when evaluating potential the effects of increased N deposition on either terrestrial or aquatic ecosystems in seasonally snow-covered watersheds. In these systems, changes in surface water chemistry are likely to occur in high deposition, snow-covered sites during low snow years before terrestrial vegetation is affected.

Carbon and water relations of Salix monticola in response to winter browsing and changes in surface water hydrology: an isotopic study using δ13C and δ18O.

To ascertain whether browsing or hydrologic conditions influence the physiological performance of Salix and whether Salix and graminoids (Carex) use and possibly compete for similar water resources, we quantified the in situ seasonal patterns of plant water and carbon relations over three growing seasons. Our studies were designed to address the physiological factors which may be responsible for poor woody plant regeneration in montane riparian habitats of Rocky Mountain National Park, Colo. As these systems act to insure the delivery of fresh water to downstream users, the maintenance of their integrity is critical. We quantified plant water potentials, instantaneous rates of carbon fixation, leaf carbon isotope discrimination (Δ), leaf nitrogen content and water sources using stable isotopes of water (δ18O). The carbon and water relations of Salix were significantly affected by winter browsing by elk and in some cases by landscape position with regard to proximity to active streams. Winter browsing of Salix by elk significantly increased summer plant water potentials and integrative measures of gas exchange (Δ), though browsing did not consistently affect instantaneous rates of photosynthesis, leaf nitrogen or the sources of water used by Salix. No effect of experimental manipulations of surface water conditions on Salix physiology was observed, likely due to the mesic nature of our study period. Using a two-member linear mixing model, from δ18O values we calculated that Salix appears to rely on streams for approximately 80% of its water. In contrast, the graminoid Carex derives almost 50% of its water from rainfall, indicating divergent water source use by these two life forms. Based on these findings, winter browsing by elk improved Salix water balance possibly by altering the shoot to root ratio which in turn leads to higher water potentials and higher degrees of season-long gas exchange, while experimental damming had in general no effect on the physiological performance of Salix plants. In addition, as the water sources of Salix and Carex were significantly different, competition for water may not influence the growth, development, and regeneration of Salix. Thus, under the conditions of our study, herbivory had a positive effect on the physiological performance of Salix, but it is still unclear whether these changes in physiology transcend into improved Salix regeneration and survivorship. However, under drier environmental conditions such as lower snowpacks and lower stream flows, the browsing resistance of Salix and ecosystem regeneration may be greatly hindered because the reliance of Salix on stream water makes it vulnerable to changes in surface water and hydrological conditions.

The role of disseminated calcite in the chemical weathering of granitoid rocks

Accessory calcite, present at concentrations between 300 and 3000 mg kg −1, occurs in fresh granitoid rocks sampled from the Merced watershed in Yosemite National Park, CA, USA; Loch Vale in Rocky Mountain National Park CO USA; the Panola watershed, GA USA; and the Rio Icacos, Puerto Rico. Calcite occurs as fillings in microfractures, as disseminated grains within the silicate matrix, and as replacement of calcic cores in plagioclase. Flow-through column experiments, using de-ionized water saturated with 0.05 atm. CO 2, produced effluents from the fresh granitoid rocks that were dominated by Ca and bicarbonate and thermodynamically saturated with calcite. During reactions up to 1.7 yr, calcite dissolution progressively decreased and was superceded by steady state dissolution of silicates, principally biotite. Mass balance calculations indicate that most calcite had been removed during this time and accounted for 57–98% of the total Ca released from these rocks. Experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution. The lack of excess Ca and alkalinity indicated that calcite had been previously removed by natural weathering. The extent of Ca enrichment in watershed discharge fluxes corresponds to the amounts of calcite exposed in granitoid rocks. High Ca/Na ratios relative to plagioclase stoichiometries indicate excess Ca in the Yosemite, Loch Vale, and other alpine watersheds in the Sierra Nevada and Rocky Mountains of the western United States. This Ca enrichment correlates with strong preferential weathering of calcite relative to plagioclase in exfoliated granitoids in glaciated terrains. In contrast, Ca/Na flux ratios are comparable to or less than the Ca/Na ratios for plagioclase in the subtropical Panola and tropical Rio Icacos watersheds, in which deeply weathered regoliths exhibit concurrent losses of calcite and much larger masses of plagioclase during transport-limited weathering. These results indicate that the weathering of accessory calcite may strongly influence Ca and alkalinity fluxes from silicate rocks during and following periods of glaciation and tectonism but is much less important for older stable geomorphic surfaces.

Methane flux in subalpine wetland and unsaturated soils in the southern Rocky Mountains

Methane exchange between the atmosphere and subalpine wetland and unsaturated soils was evaluated over a 15‐month period during 1995–1996. Four vegetation community types along a moisture gradient (wetland, moist‐grassy, moist‐mossy, and dry) were included in a 100 m sampling transect situated at 3200 m elevation in Rocky Mountain National Park, Colorado. Methane fluxes and soil temperature were measured during snow‐free and snow‐covered periods, and soil moisture content was measured during snow‐free periods. The range of mean measured fluxes through all seasons (a positive value represents CH4 efflux to the atmosphere) were: 0.3 to 29.2 mmol CH4 m−2 d−1 wetland area; 0.1 to 1.8 mmol CH4 m−2 d−1, moist‐grassy area; −0.04 to 0.7 mmol CH4 m−2 d−1, moist‐mossy area; and −0.6 to 0 mmol CH4m−2 d−1, dry area. Methane efflux was significantly correlated with soil temperature (5 cm) at the continuously saturated wetland area during snow‐free periods. Consumption of atmospheric methane was significantly correlated with moisture content in the upper 5 cm of soil at the dry area. A model based on the wetland flux‐temperature relationship estimated an annual methane emission of 2.53 mol CH4 m−2 from the wetland. Estimates of annual methane flux based on field measurements at the other sites were 0.12 mol CH4 m−2, moist‐grassy area; 0.03 mol CH4 m−2, moist‐mossy area; and −0.04 mol CH4 m−2, dry area. Methane fluxes during snow‐covered periods were responsible for 25, 73, 23, and 43% of the annual fluxes at the wetland, moist‐grassy, moist‐mossy, and dry sites, respectively.

Aspen regeneration in the Colorado Front Range: differences at local and landscape scales

Elk (Cervus elaphus) populations in Rocky Mountain National Park are higher than at any time in the past century, and heavy browsing by elk may interfere with aspen (Populus tremuloides Michx.) regneration. We used aerial photographs to identify all aspen stands within Rocky Mountain National Park, and all aspen stands within the elk winter range range (defined as 2400 to 2800 m elevation) in three portions of the adjacent Roosevelt National Forest. From this population of aspen stands, we randomly selected 57 stands for evaluation of aspen regeneration. Stands that contained stems younger than 30 years and taller than 2.5 m tall were classified as regenerating suc- cessfully. Only 20% of the aspen stands in Estes Valley contained a cohort of regenerating aspen stems, whereas 45-to- 75% of aspen stands across the larger landscape of the Front Range had regenerating cohorts of aspen. Within the elk winter range of the Roosevelt National Forest, 13 of 17 aspen stands were regenerating. In the elk winter range on the east side of the Park but outside of Estes Valley, 11 of 15 aspen stands were regenerating successfully. Only a few aspen stands exist in the elk winter range on the western side of the Park, and none of the five aspen stands sampled in Kawuneeche Valley had a regenerating cohort. The lack of regeneration in Kawuneeche Valley may result from locally heavy elk use in both winter and summer. In the summer elk range at higher elevations in the Park (2800 to 3200 m), 16 of 23 stands had regenerated. At landscape scales, all locations outside of the heavily impacted Estes Valley averaged about two cohorts/stand that regenerated after the mid-1960s. All stands that lacked a regenerating cohort showed evidence of moderate-to-severe damage from elk browsing of stems. No regenerating stands showed evidence of severe browsing. We conclude that at landscape scales, regeneration within aspen stands is very common across the Front Range, except in local areas of the highest elk use where little regeneration has occurred in the past 30 years. , i i Introduction

GTNP Breeding Bird Monitoring Project: The 1999 Season

Overview: GTNP Breeding Bird Monitoring Project. 1. Following initial independent work by M. L. Cody and 3y funding from NPS, we have instigated a scheme for long-term monitoring of breeding land bird populations in a wide variety of habitats representative of the northern Rockies and the Greater Yellowstone Ecosystem (GYE). Census sites are located almost entirely within Grand Teton National Park, where a broad range of representative vegetation types is accessible within close geographic proximity. 2. Some 30 monitoring sites are established within and adjacent to the park in pristine habitat. Sites range from the Jackson Hole lowlands to subalpine and alpine sites, from meadow, sagebrush and marshland, through willow scrub, cottonwood and aspen woodlands, to lodgepole pine and spruce-fir forests. Some sites have a monitoring history of &gt; 30 y; others were established in the mid-1990's. 3. The location and accessibility of the study sites permits all to be regularly and repeatedly censused during the short (6-week) breeding season. Census sites are standardized in area (5-10 ha in size) and mapped in detail (topographic features, vegetation). Census schedules, turung, and methodological protocols will be established and maintained, providing for strictly controlled inter-site and inter-year comparisons in breeding bird populations, species composition, and densities. 4. To evaluate the local versus more regional nature of inter-year variation in bird densities, one widespread habitat (willows) is replicated and censused at locations outside GTNP, in the northern Rockies (Glacier National Park) and central Rockies (Rocky Mountain National Park). 5. The project entails only modest costs (e.g. for transportation), but the projected benefits to science, specifically to resource management, will continue to accumulate as the data base is expanded in future years. As no comparable data base or monitoring scheme exists for the region, the value of the GTNP is apparent, and ensuring its continuance is of critical importance.

Restoration of the food web of an alpine lake following fish stocking

Trout stocking in the mid‐1960s eliminated the calanoid copepod Hesperodiaptomus arcticus and other large‐bodied crustaceans such as Gammarus lacustris, Daphnia middendorffiana, and Daphnia pulex from many alpine lakes in the Rocky Mountain Parks of Canada. H. arcticus frequently dominates the plankton communities of fishless lakes, preying on rotifers and nauplius larvae. Following the extirpation of H. arcticus, rotifers and small‐bodied cyclopoid copepods dominate the zooplankton assemblages of alpine lakes.We studied the zooplankton community of Snowflake Lake, Banff National Park, from 1966 to 1995. H. arcticus was eliminated following stocking of the lake with trout in the 1960s. It failed to become reestablished after the disappearance of the fish population in the mid‐1980s. Several species of rotifers and small‐bodied crustaceans, species originally rare or absent from the plankton, became abundant following fish stocking and remained so after the fish population declined.In 1992, we reintroduced H. arcticus to Snowflake Lake. The H. arcticus population grew exponentially for 4 yr, but had not reached stable densities typical of unmanipulated alpine lakes by 1995. By 1994, however, even the small population of Hesperodiaptomus was beginning to suppress populations of rotifers, copepod nauplii, and large diatoms. Because H. arcticus is omnivorous, a simple model of cascading trophic interactions did not predict the outcome of trophic manipulations in this alpine lake.