Rocky Mountain National Park Research Articles

Constraints on willow seedling survival in a Rocky Mountain Montane floodplain

To identify potential constraints on willow (Salix spp.) seedling establishment in montane riparian communities in Rocky Mountain National Park, Colorado, USA we established a controlled experiment to examine the effects of soil texture and elevation above river stage on willow seedling survival. We followed seedling survival rates over two summers in paired course- and fine-textured plots established at three elevations on study area point bars. Patterns of seedling survival changed over the course of the study, and after two growing seasons, greater seedling survival rates were observed in fine-textured plots and plots occurring at high and intermediate elevations. Our results indicate that both soil water availability and scour by spring floods influence the spatial and temporal patterns of willow seedling survival on point bars along small-order montane streams.

Controls on Willow Cutting Survival in a Montane Riparian Area

To provide information to guide restoration of montane riparian willow communities, we investigated factors influencing the survival of prerooted and unrooted mountain willow (Salix monticola Bebb) cuttings in 2 degraded montane riparian areas in Rocky Mountain National Park, Colorado. We planted cuttings across a gradient of water table depths and soil textures and evaluated their survival using logistic regression analysis. Our results indicate that depth to groundwater was a critical factor influencing survival of both rooted and unrooted cuttings. We found that few cuttings (7.8% rooted, 3.9% unrooted) survived where summer water table depths exceeded approximately 90 cm. Soil texture was not a significant factor in our logistic models, potentially because of low silt and clay fractions in our plots. Rooted cuttings survived at a higher rate than unrooted cuttings after 1 (55.8% vs. 36.5%, P < 0.001) and 2 (44.5% vs. 26.1%, P < 0.001) years of growth. We conclude that, when combined with appropriate hydrologic data, the use of rooted cuttings represents an effective technique to restore and revegetate degraded montane riparian ecosystems.

EFFECTS OF ELK HERBIVORY ON VEGETATION AND NITROGEN PROCESSES

We used 35-year and 4-year ungulate exclosures to determine the effects of elk (Cervus elaphus) herbivory on above-ground and below-ground production and soil fertility on the elk winter range in Rocky Mountain National Park (RMNP), Colorado, USA. We used paired grazed and ungrazed plots to evaluate ungulate herbivory effects in short and tall willow (Salix spp.), aspen (Populus spp.), and upland grass/shrub vegetation associations. We measured nitrogen (N) fluxes (litter deposition, fecal and urinary deposition from elk, movements of N by elk, N mineralization, soil N availability, elk consumption rates) within the elk winter, above-ground and below-ground N pools (herbaceous, shrub and root biomass, %N in plants, roots, and soil), and N fluxes on and off the elk winter range (seasonal movement of N by elk). Nitrogen mineralization and soil nitrate (NO3) pools were reduced in the short willow community (P = 0.07 and 0.10, respectively; n = 4 sites) in grazed plots, but not in the upland grass/shrub community or tall willow sites (P >0.10). Annual growth of willows was reduced by 98% in grazed plots, relative to 35-year exclosures, and 66% relative to 4-year exclosures. Thus, height, canopy size, and litter biomass of willows were reduced, and N yield of willows was 64% less in grazed plots. We evaluated movement of N by elk among 6 major vegetation associations and found that elk grazed more and bedded less in willow vegetation association compared to mixed conifer, mesic meadow, and grassland/shrub associations (P = 0.014, 0.001, and 0.026, respectively), suggesting that elk herbivory and movement led to a net loss of N in the willow vegetation association. Elk spent less total time in willows than mesic meadow association, yet they consumed large amounts of willow plant biomass. We recommend management of elk numbers and elk herbivory that takes into consideration impacts to N process function, as negative effects from current levels of herbivory were observed in ≥1 of 3 vegetation associations studied.

Adaptive recreation planning and climate change: a contingent visitation approach

This paper applies a contingent visitation analysis to estimate the effects of changes in climate and resource variables on nature-based recreation demand. A visitor survey at Rocky Mountain National Park included descriptions of hypothetical climate scenarios (depicting both weather- and resource-related variables), and questions about how respondents' visitation behavior would change contingent upon the scenarios. Survey responses are used to estimate the impact of climate change on park visitation and to test for the relative significance among climate scenarios and resource variables. A relatively small proportion of respondents indicated that their visitation behavior would change under the hypothetical climate scenarios, and the net effect on visitation is slightly positive. Both direct (weather-related) and indirect (resource-related) climate scenario variables are found to be statistically significant determinants of contingent expected changes in visitation. The results of the contingent visitation analysis are compared with the results of a regression analysis of historic visitation and climate variation for methodological assessment, and we find that they are in close agreement.

A breath of bad air

A breath of bad air

A Breath of Bad Air

A Breath of Bad Air

A fire history from tree rings in a high-elevation forest of Rocky Mountain National Park

Historical fire patterns in a subalpine forest of Rocky Mountain National Park were quantified from an analysis of forest stand ages and fire-scarred trees. A comparatively detailed sample of 3461 tree cores and 212 fire scars was collected from a 9200-ha study area north of Estes Park, Colorado. A total of 41 fire events were identified in the record. Annually precise fire dates, beginning in 1533, include 22 high-severity crown fires, 7 low-severity surface fires, and 8 mixed-severity events with both surface and crown fire components. Fire rotation was estimated for both surface fires (7587 years) and crown fires (346 years). Fire rotation did not appear to vary with fuel characteristics associated with topographical differences in the study area. Fires larger than 300 ha were few, but they determined a large proportion of the area burned since 1700 and were significantly correlated with a reconstructed index of summer drought. Low fire activity in the 20th century was associated with decreased severity and frequency of drought episodes. Long fire rotations preclude definitive conclusions regarding the effects of fire suppression in the 20th century, but relationships between high-severity fires, fuels, and drought suggest that climatic variability remains the primary influence on fire cycles in high-elevation ecosystems of the southern Rocky Mountains.

Arapaho Placenames in Colorado: Indigenous Mapping, White Remaking

AbstractIndigenous Arapaho placenames for the area around the present Rocky Mountain National Park have been recovered through archival research. Those names reveal a clear pattern of naming on the landscape. Human-use and human-history-oriented names occur especially often in the lowland valleys, while mountain peaks tend to be named with reference to sacred and mythological aspects of Arapaho traditional culture. The Arapaho. toponymically occupied the lowlands with their own presence, while leaving the highlands ontologically more distant and “exotic.” Ironically, the same pattern of naming occurred when Euro-American conservationists began recording and assigning Arapaho names to the landscape as they struggled to establish Rocky Mountain National Park and draw tourists, with sacred Arapaho names being selected for their exoticism and assigned to mountain locations while virtually all traces of Arapaho use and history in the area were removed in the lowlands and replaced by Euro- American names.The naming process also reveals interesting struggles between local control of naming and nationwide regulation on the part of the USGS, as well as changing perceptions of the space of Rocky Mountain National Park as a zone of resource extraction, a tourist attraction, an urban wildlands refuge, and a wilderness. The particular Arapaho names chosen (by Whites) for the landscape indirectly reflect all of these tensions.

Soil characteristics of Rocky Mountain National Park grasslands invaded by Melilotus officinalis and M. alba

AbstractAim Invasion of nitrogen‐fixing non‐native plant species may alter soil resources and impact native plant communities. Altered soils may be the driving mechanism that provides a suitable environment to facilitate future invasions and decrease native biodiversity. We hypothesized that Melilotus invasion would increase nitrogen availability and produce soil microclimate and biochemical changes, which could in turn alter plant species composition in a montane grassland community.Location Our research addressed the effects of white and yellow sweet clover (Melilotus officinalis and M. alba) invasion on soil characteristics and nitrogen processes in the montane grasslands in Rocky Mountain National Park.Methods We sampled soil in replicate sites of Melilotus‐invaded and control (non‐invaded) patches within disturbed areas in montane grassland habitats. Soil composites were analysed for available nitrogen, net nitrogen mineralization, moisture, carbon/nitrogen (C : N ratio), texture, organic matter and pH. Data were recorded at three sample dates during the growing seasons of 1998 and 1999.Results Contrary to our expectations, we observed lower nitrogen availability and mineralization in invaded patches, and differences in soil moisture content and soil C : N. Soil C : N ratios were higher in invaded plots, in spite of the fact that Melilotus had the lowest C : N ratios of other plant tissue analysed in this study.Main conclusions These findings provide land managers of natural areas with a better perspective on the possibilities of nitrogen‐fixing species impact on soil nutrient levels.

Controls on Willow Cutting Survival in a Montane Riparian Area

To provide information to guide restoration of montane riparian willow communities, we investigated factors influencing the survival of prerooted and unrooted mountain willow (Salix monticola Bebb) cuttings in 2 degraded montane riparian areas in Rocky Mountain National Park, Colorado. We planted cuttings across a gradient of water table depths and soil textures and evaluated their survival using logistic regression analysis. Our results indicate that depth to groundwater was a critical factor influencing survival of both rooted and unrooted cuttings. We found that few cuttings (7.8% rooted, 3.9% unrooted) survived where summer water table depths exceeded approximately 90 cm. Soil texture was not a significant factor in our logistic models, potentially because of low silt and clay fractions in our plots. Rooted cuttings survived at a higher rate than unrooted cuttings after 1 (55.8% vs. 36.5%, P &lt; 0.001) and 2 (44.5% vs. 26.1%, P &lt; 0.001) years of growth. We conclude that, when combined with appropriate hydrologic data, the use of rooted cuttings represents an effective technique to restore and revegetate degraded montane riparian ecosystems.

DISTURBANCE AND STAND DYNAMICS IN PONDEROSA PINE FORESTS IN ROCKY MOUNTAIN NATIONAL PARK, USA

Fire is thought to be the dominant disturbance agent in pure ponderosa pine (Pinus ponderosa Laws.) forests, but fire severity and disturbances other than fire, and the effects of these events over time, have rarely been analyzed. We first created systematic criteria to (1) identify the causes of tree regeneration and mortality events and (2) classify the severity of these events. These criteria were then applied to understand the effect of events on ponderosa pine forests in Rocky Mountain National Park (RMNP), Colorado.For each of nine intensive study plots sampled in the pure ponderosa pine zone of RMNP, we mapped and dated live and dead trees and the spatial extent of fire and non‐fire events using dendrochronology. Events were identified using evidence of disturbance agents, such as blue‐stain fungus in the case of mountain pine beetles, fire scars, and climatic reconstructions. Disturbance severity was classified based on amounts and spatial distribution of regeneration, mortality, and survivors. We studied the temporal and spatial relationships between events and tree age structures to determine historical and contemporary stand dynamics.We identified 103 events among the nine study plots; 97% of these events were fire. High‐severity events were 7% of events, 2% of events were mixed‐severity, and the other 70% were low‐severity. The severity of 20% of events could not be determined. All but one of the high‐severity events were fire. In seven plots, at least one crown fire occurred within the last 300 years. In RMNP, pre‐EuroAmerican settlement crown fires led to dense, even‐aged stands. Subsequent surface fires killed some trees and facilitated the regeneration of others, leading to less dense, uneven‐aged stands after ∼200–300 years. Climate may be the cause or co‐cause of one or two regeneration pulses within the last 300 years, but most regeneration and mortality is associated with fire. The historical occurrence of crown fires, as well as surface fires, in pure ponderosa pine forests in RMNP indicates that the fire regime is more variable than previously thought. Suppression of crown fires, though not completely possible, would move the fire regime outside its historical range of natural variability.Corresponding Editor: D. R. Strong

Genetic Variability and Its Ecological Implications in the Clonal Plant Carex scopulorum Holm. in Colorado Tundra

We assayed the amount and distribution of genetic variability in the clonal polyploid plant Carex scopulorum var. scopulorum. We used 5 polymorphic protein loci to sample 7 populations on the tundra in Rocky Mountain National Park, Colorado, U.S.A. Carex has levels of variability comparable to those found in nonclonal species. In the loci studied, transmission is disomic, as in diploid species. Of 148 tillers tested, 59.5% had different 5-locus genotypes. The distributions of genotypes fit Hardy-Weinberg expectations at 4 loci in most populations. These results suggest that there is significant cross-pollination and establishment by seed in this tundra plant. There were significant differences in allele frequencies between adjacent populations occupying wet versus moist environments at alcohol dehydrogenase, an enzyme known to be relevant to metabolism under oxygen-limiting conditions. There was no relationship between geographic distance and genetic distance at the scale we studied.

Recent ecological and biogeochemical changes in alpine lakes of Rocky Mountain National Park (Colorado, USA): a response to anthropogenic nitrogen deposition

ABSTRACTDated sediment cores from five alpine lakes (&gt;3200 m asl) in Rocky Mountain National Park (Colorado Front Range, USA) record near‐synchronous stratigraphic changes that are believed to reflect ecological and biogeochemical responses to enhanced nitrogen deposition from anthropogenic sources. Changes in sediment proxies include progressive increases in the frequencies of mesotrophic planktonic diatom taxa and diatom concentrations, coupled with depletions of sediment δ15N and C : N values. These trends are especially pronounced since approximately 1950. The most conspicuous diatoms to expand in recent decades are Asterionella formosa and Fragilaria crotonensis. Down‐core species changes are corroborated by a year‐long sediment trap experiment from one of the lakes, which reveals high frequencies of these two taxa during autumn and winter months, the interval of peak annual limnetic []. Although all lakes record recent changes, the amplitude of stratigraphic shifts is greater in lakes east of the Continental Divide relative to those on the western slope, implying that most nitrogen enrichment originates from urban, industrial and agricultural sources east of the Rocky Mountains. Deviations from natural trajectories of lake ontogeny are illustrated by canonical correspondence analysis, which constrains the diatom record as a response to changes in nitrogen biogeochemistry. These results indicate that modest rates of anthropogenic nitrogen deposition are fully capable of inducing directional biological and biogeochemical shifts in relatively pristine ecosystems.

Invasion by Sweet Clover (Melilotus) in Montane Grasslands, Rocky Mountain National Park

Exotic (nonnative) invasion, often fostered by anthropogenic disturbances, can be detrimental to the biodiversity of indigenous plant communities. We examined the impact of two exotic species, Melilotus officinalis and M. alba (yellow and white sweet clover) in the montane grassland community in Rocky Mountain National Park to determine (1) whether native and exotic plant diversity differs between patches within grasslands that are invaded by Melilotus species and patches that are not invaded (control patches) and (2) whether the presence of Melilotus species are associated with specific exotic species. Variables that were recorded included species richness, species composition, and percent cover in invaded and control patches at multiple spatial scales. The results showed that more exotic, annual/biennial, and forb species occurred within patches invaded by Melilotus species, while more native, perennial, and grass species occurred in nearby control patches. Moreover, the invaded patches had several exotic species that were not found in control patches, whereas certain native species were only found in control patches. In some instances, the presence of Melilotus in the native community appeared unrelated to disturbance; some colonies were in seemingly undisturbed meadows well beyond disturbance edges. The data also showed that Melilotus species spread beyond original mapped boundaries in a span of two seasons.

Model-based assessment of aspen responses to elk herbivory in Rocky Mountain National Park, USA.

In Rocky Mountain National Park (RMNP), aspen (Populus tremuloides Michx.) has been observed to be declining on elk (Cervus elaphus nelsoni) winter range for many decades. To support elk management decisions, the SAVANNA ecosystem model was adapted to explore interactions between elk herbivory and aspen dynamics. The simulated probability of successful vegetative regeneration for senescent aspen stands declines sharply when elk densities reach levels of 3-5 elk/km2, depending on model assumptions for the seasonal duration of elk foraging activities. For aspen stands with a substantial component of younger trees, the simulated regeneration probability declines more continuously with increasing elk density, dropping below 50% from densities at 8-14 elk/km2. At the landscape scale, simulated aspen regeneration probability under a scenario of extensive seasonal use was little affected by elk population level, when this level was above 300-600 elk (25%-50% current population) over the ca. 107 km2 winter range. This was because elk distribution was highly aggregated, so that a high density of elk occupied certain areas, even at low population levels overall. At approximately current elk population levels (1000-1200 elk), only 35%-45% of senescent aspen stands are simulated as having at least a 90% probability of regeneration, nearly all of them located on the periphery of the winter range. Successful management for aspen persistence on core winter range will likely require some combination of elk population reduction, management of elk distribution, and fencing to protect aspen suckers from elk browsing.

Wolf mountains: a history of wolves along the Great Divide

Situating the wolf in the history of Canadian national parks, Karen Jones considers changing ideas of nature and wilderness and competing visions of the North American West. Wolf Mountains: A History of Wolves along the Great Divide is essentially a work of environmental history, treating the land as an actor in the historical process. This controversial study examines the tumultuous relationship between humans and wolves in four Rocky Mountain parks. By comparing the distinctive lupine histories of specific national parks with anecdotes and narratives of wolves from Aboriginals and early Europeans from the nineteenth and twentieth centuries, important shifts in attitude and policy are clearly shown. Drawing on published scholarly research, archived newspapers, records from environmental groups, U.S. and Canadian park records, first-hand accounts from explorers and trappers, and scientific interviews with park staff and biologists, this book contributes enormously to our understanding of the relationship between wolves and humans.

Influence of elk grazing on soil properties in Rocky Mountain National Park

We used three 35-year exclosures to examine the effects of high elk populations on a variety of soil properties in three vegetation types: upland sagebrush, aspen, and meadow. Grazing and hoof action by elk significantly increased bulk density (from 0.87 kg/l ungrazed to 0.94 kg/l grazed), with greater effects on soils with fewer rocks. Grazing substantially reduced extractable calcium, magnesium, potassium and phosphorus in the sagebrush type, but not in the aspen or meadow types. The only grazing effect on pH came in aspen types, where grazing prevented aspen establishment, and kept soil pH about 0.7 units higher than under aspen inside the exclosures. Grazing had no overall effect on total soil C and N across all exclosures and vegetation types. The availability of soil nitrogen, indexed by in-field resin bags and net mineralization in soil cores, showed little overall effect of grazing. Limited data on soil leaching indicated a possibility of strong increases in nitrate leaching with grazing for an aspen vegetation type at one exclosure. Although we found little effect of grazing on soil N supply, we note that N fertilization doubled the production of grasses and shrubs; if grazing eventually led to changes in soil N supply, species composition and growth would likely change.

Do ungulates accelerate or decelerate nitrogen cycling?

Nitrogen (N) is an essential nutrient for plants and animals, and N may be limiting in many western US grassland and shrubland ungulate winter ranges. Ungulates may influence N pools and they may alter N inputs and outputs (losses) to the ecosystem in a number of ways. In this paper we compare the ecosystem effects of ungulate herbivory in two western national parks, Rocky Mountain National Park (RMNP), Colorado, and Yellowstone National Park (YNP), Wyoming. We compare ungulate herbivory effects on N pools, N fluxes, N yields, and plant productivity in the context of the accelerating and decelerating nutrient cycling scenarios [Ecology 79 (1998) 165]. We concluded that the YNP grasslands fit the accelerating nutrient cycling scenario for ungulate herbivory: in response to grazing, grassland plant species abundance was largely unaltered, net annual aboveground primary productivity (NAPP) was stimulated (except during drought), consumption of key N-rich forages by ungulates was moderate and their abundance was sustained, soil N mineralization rates doubled, N pools increased, aboveground N yield increased, and N concentrations increased in most grassland plant species. Grazing in grasslands in RMNP resulted in no consistent detectable acceleration or deceleration of nutrient cycling. Grazing effects in short willow and aspen vegetation types in RMNP fit the decelerating nutrient cycling scenario of Ritchie et al. [Ecology 79 (1998) 165]. Key N-rich forages declined due to herbivory (willows, aspen, herbaceous vegetation). Aboveground production declined, soil N mineralization rates declined, N pools declined (NO 3 − pools were 30% that of ungrazed controls), and aboveground N yield declined. We believe that the higher ungulate densities and rates of plant consumption in RMNP, large declines in N-rich forage plants, and possibly a tendency of ungulates to move N from willow and aspen vegetation types to other types in RMNP, contributed to deceleration of nutrient cycling in two vegetation types in RMNP compared to acceleration in grasslands in YNP.

Predation risk and the functional response of elk–aspen herbivory

Hypotheses for trembling aspen ( Populus tremuloides) decline in Rocky Mountain national parks include long-term high herbivory by elk ( Cervus elaphus), decreased disturbance, climate change, and long-term low elk herbivory. Predation theory, as applied to herbivores, was used to describe alternative functional responses predicted by each hypothesis. Further, we postulated that elk behavioral patterns resulting from predation risk could also influence aspen herbivory. We tested predictions by sampling aspen density and browsing conditions in spatially separate watersheds in the Canadian Rockies, with three areas in each of three elk density levels (<2, 2–4, >4 elk/km 2), and in each of four tree cover classes: recently disturbed (<25 years ago), and low, moderate, and high. Plot elk use was indexed with pellet group counts classed by habitat patch type, aspen condition (open or thicket), and different distances from trails or park boundaries used by predators, hunters, or park visitors. The herbivory rate on aspen saplings (>1 m height and <1 cm diameter at breast height, DBH) fitted the predictions of a Type 2 functional response (e.g. increased rate of herbivory with decreased sapling density). The Type 2 response appeared to result from low elk use in dense aspen thickets when predation risk is high. An interaction effect in the tree cover×elk density factorial analysis indicated that recent disturbances (<25 years) have incrementally increased the number of aspen saplings, but did not cause a major shift to an abundant sapling state in areas of high and moderate elk density. These results best supported the predictions of the low elk herbivory hypothesis. Anthropogenic burning combined with human and carnivore predation effects on elk (behavioral and numeric) appeared to be important in aspen’s long-term persistence, and its recent decline.

Carbon dynamics of pristine and hydrologically modified fens in the southern Rocky Mountains

We measured water table levels, above- and below-ground plant production, and CO2and CH4emissions for five fens in Rocky Mountain National Park, Colorado, to determine whether a water diversion project was adversely affecting carbon cycling. Two fens were located beneath the water diversion, and three fens were located in an adjacent pristine watershed. The diversion lowered water table levels in one fen, while the other fen was not hydrologically modified. Total NPP (net primary production) for all sites ranged from 130 to 316 g C·m–2·year–1, with a mean of 217 g C·m–2·year–1, and belowground NPP accounted for ~60% of the total. Maximum CO2emissions for pristine fens ranged between 170 and 273 mg CO2-C·m–2·h–1, with annual emissions of 230–388 g CO2-C·m–2·year–1. However, the hydrologically modified fen had maximum CO2emissions of 457 mg CO2-C·m–2·h–1and had an annual flux of 573 g CO2-C·m–2·year–1. Maximum CH4emissions ranged from 3 to 25 mg CH4-C·m–2·h–1, with annual emissions of 9–61 g CH4-C·m–2·year–1. The water diversion structure lowered water tables, increased CO2, decreased CH4and NPP, and resulted in the site likely becoming a net source of carbon.Key words: peatlands, fens, CO2, CH4, hydrology, Rocky Mountains, Rocky Mountain National Park, plant production.