Presentations

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Open Access
Two years of carbon dioxide enrichment on the Shortgrass Steppe of Colorado
(Colorado State University. Libraries, 1998) Ojima, D. S., author; Parton, W. J., author; Milchunas, D. G., author; Mosier, A. R., author; LeCain, D. R., author; Morgan, J. A., author; SGS-LTER, Colorado State University, publisher
This study assessed how doubling the CO2 concentration over present levels affects the growth and physiology of shortgrass steppe vegetation in eastern Colorado. In March, 1997, six open-top chambers (OTCs) were installed on native shortgrass steppe in NE Colorado, USA. Three grass species make up about 88% of the above-ground biomass of this ecosystem; Bouteloua gracilis (C4), Pascopyrum smithii (C3) and Stipa comata (C3). More than 20 other grass and forb species also occur here. CO2 was injected into three OTCs to raise the concentration to 720 ppm, approximately twice that in the three ambient chambers. Three non-chambered plots were established to evaluate chamber effects. The air temperature in the chambers averaged 2° C warmer than outside. During 1997 and 1998 significant chamber and CO2 effects were detected. Averaging over the two years, above-ground production in the ambient chambers was 22% greater than that in unchambered plots, probably due to warmer spring temperatures in the chambers. Production under elevated CO2 averaged 35% greater than that in ambient OTCs. Significant growth increases occurred for both C3 and C4 grasses and forbs in 1998. These CO2 -induced growth increases were primarily due to improved water status. Soil water content was often higher in elevated CO2 chambers. Leaf water potentials were generally higher in plants grown at elevated CO2 compared to ambient chambers. Leaf intercellular CO2 photosynthesis response curves indicated neither P. smithii nor B. gracilis leaves were saturated with CO2 at 360 ppm. Photosynthetic capacity of both species was reduced in plants grown at elevated CO2, although this response was much stronger in the the C3 species, P. smithii. Results suggest that future CO2 enrichment will lead to growth enhancements in both C3 and C4 grasses of the shortgrass steppe.
Open Access
Inter-annual differences in abundance of thirteen-lined ground squirrels (Spermophilus tridecemlineatus) in Colorado Shortgrass Steppe
(Colorado State University. Libraries, 1999) Stapp, Paul, author; Hanni, David, author; Lindquist, Mark, author; SGS-LTER, Colorado State University, publisher
We live-trapped thirteen-lined ground squirrels (Spermophilus tridecemlineatus) on three grassland and three saltbush-dominated sites in June and July 1999 to estimate population densities in representative vegetation types in shortgrass steppe, and to describe changes in population structure and body weight during their summer active period. We also compared population densities in 1999 to estimates from 1995, the last time that ground squirrel populations were surveyed on the SGS-LTER site in north-central Colorado. As in 1995, most squirrels captured in June 1999 were adults; the near absence of juveniles in June 1999 compared to the earlier study suggested that reproduction was delayed this year. Juveniles comprised > 70% of individuals captured in both habitats in July 1999, and were especially numerous on grassland sites. However, in contrast to 1995, when squirrels much more common in saltbush habitats, squirrels were significantly (2-3X) more abundant on grassland webs in 1999. The difference in population densities between habitats in 1995 vs. 1999 was unexpected because both years had similarly high early-season precipitation, and presumably, similar vegetation. Moreover, there were no consistent differences in the abundance of arthropod prey between years that could readily explain the differences in squirrel abundance. Additional long-term studies of ecology and population dynamics of thirteen-lined ground squirrels in shortgrass steppe will be necessary to identify the factors that determine patterns of abundance of this critical species over time.
Open Access
A multi-scale assessment of beetle diversity and landscape properties
(Colorado State University. Libraries, 1999) Wiens, John A., author; Hoffman, Aaron L., author; SGS-LTER, Colorado State University, publisher
The issue of scale is important in ecology. Many studies have indicated that ecological patterns can vary with the grain and extent of the study, and thus it is difficult to extrapolate from fine to coarse scales. Furthermore, habitats are generally not homogenous, so interactions between an organism and its environment, as well as the scale at which they are examined, are primary factors underlying the patterns or processes being studied. This study has many facets, but we are particularly interested in how spatial patterns of beetle species richness and environmental variables change with scale. Other questions address whether there are spatial scales where correlations between beetle abundance and environmental measures peak? Identifying such scales should provide insights to the processes responsible for the observed patterns.
Open Access
Arthropod studies on the Shortgrass Steppe LTER: past, present and future
(Colorado State University. Libraries, 2000) Hartley, Laurel M., author; Kaplan, Nicole E., author; Lindquist, Mark D., author; Stapp, Paul, author; SGS-LTER, Colorado State University, publisher
Arthropods play important roles in the ecology of shortgrass steppe as consumers, prey and detritivores. Here we describe past, ongoing, and future studies of arthropods conducted as part of the Shortgrass Steppe (SGS) LTER project in north-central Colorado. Our goals are to increase awareness of our arthropod research and existing datasets, and to identify opportunities for collaboration and cross-site comparisons with LTER researchers. Arthropods have been the focus of much short-term comparative and experimental research on the site, but we know of only two long-term studies. Since 1995, insects and spiders have been sampled monthly during summer (May- September) in live pitfall traps along a 1-km transect spanning a representative topographical gradient (catena). This project continues research conducted by other SGS-LTER scientists from 1990-1994 to investigate spatial dynamics of darkling beetle (Tenebrionidae) populations. A second project initiated in 1998 involves monthly summer sampling of macroarthropods in small pitfall grids in grassland and saltbush vegetation. This study was implemented to track changes in relative abundance of arthropod prey, and grids are located on trapping webs used for rodent population studies. In addition, we maintain on-site a small but growing reference collection of representative arthropods, which is mostly used to train field assistants and support other research projects. Poster presented at the Ecological Society of America Annual Meeting held in Snowbird, Utah.
Open Access
Dynamics of exotic species and their establishment in the Pawnee National Grasslands
(Colorado State University. Libraries, 2000) Lauenroth, William K., author; Betz, Dani-Ella, author; SGS-LTER, Colorado State University, publisher
We investigated the distribution of plant species in the shortgrass steppe to determine if the roadsides were acting as corridors, increasing the susceptibility of the open steppe to exotic species establishment. We surveyed 45 paired roadside and open steppe sites and found few exotic species in the the open steppe (.36/m2), whereas the roadsides contained significantly more (5.42/m2). We examined the soil seed bank along a transect from roadsides to 25 meters into the open steppe to investigate the range of seed dispersal and abundance of roadside exotic seeds. We found that a significantly greater number of exotic seeds in the roadsides (873 seeds per m2) versus the open steppe (109 seeds per m2). To investigate the dynamics of exotic species establishment we planted two exotic species, downy brome (Bromus tectorum) and Dalmation toadflax (Linaria dalmatica), into the open steppe. A matrix of 5 treatments was applied and after one field season Bromus tectorum germinated and established in many plots. The nitrogen and nitrogen plus water treatments were the most successful in promoting the growth of Bromus. Linaria dalmatica did not establish in any of the research plots. The open steppe has few exotic species and we found that few exotic seeds exist in the seed bank. Furthermore, our work indicates that even if exotic species seeds were numerous, they may have difficulty germinating and establishing in the native communities.
Open Access
Black-tailed prairie dog mounds: do they contribute to plant species diversity and nitrogen cycling?
(Colorado State University. Libraries, 2001) Detling, J. K., author; Farrar, J. P., author; SGS-LTER, Colorado State University, publisher
Soil mounds around burrows are natural disturbances in plant communities where prairie dogs (Cynomys spp.) occur. We hypothesized that one or more sub-dominant plant species are more abundant on black-tailed prairie dog (C. ludovicianus) mounds than on inter-mound areas or off-prairie-dog-town areas, and that soil mixing results in enhanced N-mineralization which increases N-content of plants growing on mounds. During summer 2000, we measured plant cover and biomass by species in on-mound, inter-mound, and off-town plots on three active prairie dog towns in each Texas, Colorado, and Montana. In Montana and Colorado, Solanum triflorum was found only on mounds, and Sphaeralcea coccinea was more frequent on prairie dog mounds than on inter-mound and off-town areas. In Texas, Achillea millefolium and Amaranthus blitoides was found only on prairie dog mounds, and Hoffmanseggia glauca was more frequent on mounds than on inter-mound and off-town areas. Biomass of grasses increased from on-mound to off-town sites while biomass of most forbs decreased. Plant nitrogen concentration showed a general decline from mounds to off-town areas. These findings support the hypothesis that soil disturbance caused by C. ludovicianus during construction and maintenance of their mounds contributes to plant species diversity and enhanced N-mineralization in grasslands.
Open Access
Recreational shooting: how are sites selected and what are the implications for Burrowing Owl (Athene cunicularia) reproduction?
(Colorado State University. Libraries, 2001) Van Horne, Beatrice, author; Woodard, Jason D., author; SGS-LTER, Colorado State University, publisher
Declines in burrowing owl populations are inextricably linked to human activity and associated disturbances. Habitat loss and rodent control programs are the primary cause of observed declines (Butts 1973). Recreational shooting, harassment, and other human disturbances may exacerbate this decline by promoting mortality and nest failure in local populations. The extent and magnitude of these effects, however, remain unknown (Haug et al. 1993, Holroyd 1998).
Open Access
The influence of prey use and habitat on burrowing owl (Athene cunicularia) reproduction
(Colorado State University. Libraries, 2001) Van Horne, Beatrice, author; Woodard, Jason D., author; SGS-LTER, Colorado State University, publisher
Food, competition, and predation dictate habitat use (Schmutz et al. 1991) and ultimately reproduction. Avian reproduction is frequently food-limited (Wellicome 2000), and predation is the primary cause of nest failure (Martin 1993). Selection of prey and habitat features which minimize these effects should therefore enhance reproduction. We examined this issue using the Burrowing Owl, a declining species of the Great Plains.
Open Access
Livestock exclusion increases the spatial heterogeneity of vegetation in the Shortgrass Steppe
(Colorado State University. Libraries, 2001) Adler, Peter, author; SGS-LTER, Colorado State University, publisher
Ecologists have collected extensive information on how various factors affect the MEAN values of key response variables, but typically ignore how spatial distribution is affected. Describing spatial heterogeneity is important because 1) pattern may affect process and 2) the identification of previously unrecognized patterns generates new hypotheses.
Open Access
Database tools for ecological data integration and synthesis
(Colorado State University. Libraries, 2003) Cushing, Judy, author; Vanderbilt, Kristin, author; Ramsey, Ken, author; Nadkarni, Nalini, author; Kaplan, Nicole, author; Finch, Michael, author; Fiala, Anne, author; Melendez-Colom, Eda, author; SGS-LTER, Colorado State University, publisher
The challenge: 1. To synthesize across research sites syntactically disparate, but thematically similar, data. 2. To efficiently perform cross-site synthesis, using new informatics tools that exploit database component technology. 3. To aid analysis of ecological data through visualization tools that take advantage of informatics-processed data.
Open Access
Plague outbreaks in prairie-dog colonies associated with El Niño climatic events
(Colorado State University. Libraries, 2003) Stapp, Paul, author; Antolin, Michael F., author; Ball, Mark, author; SGS-LTER, Colorado State University, publisher
Plague (Yersinia pestis) was introduced to the western U.S. in the mid-20th century and is a significant threat to the persistence of black-tailed prairie dog (Cynomys ludovicianus) populations. The social, colonial habits of prairie dogs make them particularly susceptible to plague, and many flea species, including known carriers of plague, are associated with prairie dogs or their extensive burrow systems. Mortality during plague epizootics, or outbreaks, is nearly 100% (Cully and Williams 2001; J. Mammal. 82:894), resulting in the extinction of entire colonies. In northern Colorado, prairie dogs exist in metapopulations (Roach et al. 2001, J. Mammal. 82:946), in which colonies naturally isolated by topography, soils and vegetation are connected by dispersal. Dispersal of either infected prairie dogs or plague-resistant reservoir species is hypothesized to spread plague among colonies. Plague outbreaks therefore may disrupt the dynamics of prairie-dog metapopulations and affect regional persistence. In the context of a century of past eradication efforts that have drastically reduced prairie-dog numbers, and increasing agricultural and urban development, plague represents a relatively new and unique threat to prairie dogs and the species that are closely associated with them. Poster presented at the 6th SGS Symposium held on 1/10/03.
Open Access
Mediation of spatial organization in the swift fox, Vulpes velox
(Colorado State University. Libraries, 2005) Dabelsteen, Torben, author; Darden, Safi K., author; SGS-LTER, Colorado State University, publisher
Animals communicate in a network of individuals. Acoustic, chemical, and visual signals can operate in this network to convey information about a signaller's identity, behaviour, physiological state and location. Poster presented at the 7th Shortgrass Steppe Symposium held in Fort Collins, Colorado on 1/14/05.
Open Access
Phosphorus fractionation chemistry across the Great Plains
(Colorado State University. Libraries, 2005) Kelly, E. F., author; Blecker, S. W., author; Ippolito, J. A., author; Freeman, C. L., author; SGS-LTER, Colorado State University, publisher
Phosphorus is one of the three important plant nutrients found in soils and has been used with great success as an index for soil and ecosystem development (Aguilar et al., 1988; Honeycutt et al., 1990; Vitousek et al., 2004). In general, phosphorus is has minimal solubility in soil because it participates in a number of secondary reactions after release from primary minerals as a result of weathering. Studies of the biogeochemical cycling of P in humid ecosystems has led to important insights about soil and ecosystem development. Arid and semi-arid ecosystems have largely been ignored under the assumption that chemical transformations are minimal. We conducted research on the biogeochemistry of P along a bioclimatic gradient in grassland ecosystems of the Great Plains. The overall goal of our research is to use a systematic approach to characterize and further quantify the P transformations in biogeographically diverse grassland ecosystems. Identifying P quantities originally contained in central Great Plains soil will allow us to assess 1) the relative importance of P in the biogeochemical behavior of grassland soils, 2) help us quantify the degree of chemical weathering in semi-arid-humid grassland ecosystems, and 3) elucidate cultural use and potential productivity of these ecosystems prior to use of commercial fertilizers. We sampled soils along a bioclimatic gradient that represent three grassland ecosystems, namely, the shortgrass steppe, the mixed-grass prairie, and the tallgrass prairie in eastern Kansas. The soils were collected from sites studied within the Long-Term Ecological Research Program in areas that had not been used for agricultural practices other than grazing. We conducted a sequential extraction procedure to identify the following P fractions: soluble, Al-bound, Fe-bound, occluded, and Ca-bound. Our results suggest that soluble P is generally below detection limits at these sites, illustrating the high turnover rate of available P in these undisturbed systems. The Al-bound fraction was variable across all sites. The Fe-bound P contributed to the total P fraction only from the mixed grass and tall grass prairies. The occluded P fraction was greatest in the shortgrass steppe, decreased dramatically as mean annual and primary production increase from west to east.
Open Access
Shortgrass Steppe Long Term Ecological Research
(Colorado State University. Libraries, 2005) Moore, J. C., author; Lauenroth, W. K., author; Stapp, P. A., author; Burke, I. C., author; Kelly, E. F., author; Antolin, M. F., author; Pielke, R. A., author; Paustian, K. H., author; Parton, W. J., author; Mosier, A. R., author; Milchunas, D. G., author; Detling, J. K., author; Morgan, J. A., author; SGS-LTER, Colorado State University, publisher
The shortgrass steppe (SGS) Long Term Ecological Research (LTER) site is part of a network of long-term research sites supported by the National Science Foundation. The network consists of 26 sites representing diverse ecosystems and research emphases, yet maintaining a common mission and sharing expertise and data. We assert that the ecological structure and function of the shortgrass steppe is governed by climate, human use, natural disturbance, biota and physiography. Our conceptual framework, right, depicts the relationship between these factors and our core research areas. Poster presented at the 7th Shortgrass Steppe Symposium held in Fort Collins, Colorado on 1/14/05.
Open Access
Ecosystem carbon & nitrogen cycling across a precipitation gradient of the central Great Plains
(Colorado State University. Libraries, 2005) Knapp, A. K., author; Lauenroth, W. K., author; Burke, I. C., author; McCulley, R. L., author; SGS-LTER, Colorado State University, publisher
Regional analyses have shown that ecosystem pools of carbon (C) and nitrogen (N) increase as precipitation increases from the semi-arid shortgrass steppe to the tallgrass prairie of the Central Great Plains. Models based on our functional understanding of biogeochemical processes predict that ecosystem C and N fluxes also increase across this community gradient; however, few field flux data exist to evaluate these predictions. We measured decomposition rates, soil respiration, and in situ net nitrogen mineralization at five sites across a precipitation gradient in the Great Plains region. Soil respiration (SResp) and the decomposition constant, k, for common substrate litter bags were significantly higher in the sub-humid mixed and tallgrass prairie (growing season average mid-day SResp = 7.20 μmol CO2 m-2 sec-1, k = 0.66 yr-1) than the semi-arid shortgrass steppe (SResp = 4.55 μmol CO2 m-2 sec-1, k = 0.32 yr-1). In contrast, in situ net nitrogen mineralization was not significantly different across sites. The C flux data concur with predictions from current biogeochemical models; however, the in situ net nitrogen mineralization results do not. We hypothesize that this discrepancy results from the difficulties associated with measuring in situ net nitrogen mineralization in soils with vastly different immobilization potentials.
Open Access
GIS data and tools available at SGS-LTER
(Colorado State University. Libraries, 2005) Kaplan, N. E., author; Flynn, R. L., author; SGS-LTER, Colorado State University, publisher
Poster presented at the 7th Shortgrass Steppe Symposium held in Fort Collins, Colorado on 1/14/05.
Open Access
LTER: long term ecological research network
(Colorado State University. Libraries, 2005) Yonker, C. M., author; Kaplan, N. E., author; Kelly, E. F., author; SGS-LTER, Colorado State University, publisher
The Long Term Ecological Research (LTER) Network is a collaborative effort involving more than 1800 scientists and students investigating ecological processes over long temporal and broad spatial scales. Each LTER site encompasses unique ecosystems and research approaches, investigators, students and management systems. Each of the 26 sites works as part of the Network sharing expertise, data and a common mission. Poster presented at the 7th Shortgrass Steppe Symposium held in Fort Collins, Colorado on 1/14/05.
Open Access
Colorado Front Range GK12 connecting kids and ecology — teachers and researchers
(Colorado State University. Libraries, 2005) Seemueller, Carol, author; Quirk, Meghan H., author; Moore, John C., author; Hartley, Laurel M., author; SGS-LTER, Colorado State University, publisher
The Colorado Front Range GK12 project is a collaborative effort of Colorado State University, the University of Northern Colorado, Weld County School District 6, and Poudre School District.
Open Access
Arthropod diversity and abundance on a suburban remnant of the Shortgrass Steppe
(Colorado State University. Libraries, 2005) Hartley, Laurel, author; SGS-LTER, Colorado State University, publisher
Arthropod censuses are recorded on the Shortgrass Steppe Long Term Ecological Research site and Pawnee National Grasslands as a part of long term ecological monitoring. As the front range becomes developed, remnants of the shortgrass steppe become surrounded by human habitation. Subsequently there are increased efforts to control "pest" insect species, an increase in water availability, changes in insect food sources, and changes in predator species. These environmental changes are likely to affect arthropod communities. Long term monitoring of arthropod communities on a remnant shortgrass steppe enclosed by development may provide baseline data useful for local agencies creating management plans for natural areas along the front range.
Open Access
Plant community changes associated with prairie dog usage of a suburban remnant of the Shortgrass Steppe
(Colorado State University. Libraries, 2005) Hartley, Laurel, author; SGS-LTER, Colorado State University, publisher
Dr. Detling and others have documented changes in plant communities in the mixed grass prairie caused by the herbivory of the Black-tailed prairie dog, Cynomys ludovicianus. Canopy height, litter cover, and graminoid cover relative to forbs decrease, while species diversity, nitrogen mineralization, and plant shoot protein increase. The shortgrass steppe is significantly different from the mixed grass prairie: precipitation is lower, the grasses are dominated by the drought resistant (hence grazing resistant) grass blue grama, and prairie dog colonies are killed off periodically by plague. Additionally, in the suburban setting, large herbivores are excluded, habitat is fragmented, human interaction is increased, and there is an increased presence of non-native species. Currently, SGS-LTER graduate students are researching changes in plant communities in response to prairie dog herbivory on the shortgrass steppe at the SGS-LTER site and Pawnee National Grasslands in order to compare to the results from the mixed grass prairie. In this study, we are tracking changes in the plant community in response to prairie dog herbivory on a suburban shortgrass steppe remnant which we hope to compare to the results from the SGS-LTER/PNG and the mixed grass prairie. We hope to provide useful data for local agencies creating management plans for natural areas along the Front Range.