Faculty Publications

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Open Access
The Colorado climate change markets act: executive summary report: report to the Colorado Legislature, March 15th, 2007
(Colorado State University. Libraries, 2007) Conant, Rich, author; Ojima, Dennis, author; Paustian, Keith, author; Doran, Kevin, author; Guruswamy, Lakshman, author; Keating, Rob, author; Vilsack, Doug, author; Nummedal, Dag, author; Deardoff, Jason, author; Young, Genevieve, author; Natural Resource Ecology Laboratory, Colorado State University, publisher
Open Access
Effects of population growth on wildlife habitat in Colorado: a briefing paper for the Colorado Division of Wildlife commissioners, June 1998
(Colorado State University. Libraries, 1998) Hobbs, N. Thompson, author; Theobald, David M., author; Natural Resource Ecology Laboratory, Colorado State University, publisher
Wildlife and people need habitat in Colorado. Wildlife need forest and range and wetlands. People need places to live, places to work, roads to travel on, and schools to educate their children. Meeting the "habitat" needs of an expanding human population causes fundamental changes in the way land is used in Colorado. Changes in land-use, in turn, can cause marked shifts in habitat available for Colorado's wildlife. There is widespread consensus among professional biologists and wildlife managers that habitat loss to development is the foremost threat to the diversity, abundance, and distribution of Colorado's wildlife. However, this broad agreement is based largely on local experience and is not founded on a comprehensive, statewide analysis of habitat loss in the state. Here, we offer data on the history of habitat loss to development in Colorado and provide projections of the kinds of losses that can be reasonably expected in the future.
Open Access
An assessment of imperiled habitat in Colorado
(Colorado State University. Libraries, 1998) Theobald, David, author; Hobbs, Tom, author; Schrupp, Don, author; O'Brien, Lee, author; Natural Resource Ecology Laboratory, Colorado State University, publisher
Wildlife habitat is threatened by rapid conversion of agricultural to residential land use throughout the Rocky Mountain West. As a result of these changes, citizens, planners and decision makers need to identify areas of land that offer the greatest risk of harm from encroaching development. We combine statewide maps of historical, current, and projected development patterns with maps of habitat quality to set priorities for habitat protection. We use land cover data from the Colorado Gap Analysis project to develop modeled habitat and indices of species richness and patch value. Patch quality is estimated on the number of sensitive species that could potentially inhabit the patch, the size of the patch, and the relative contribution of the patch to al suitable habitat available to the species. Development (housing density) patterns are derived from US Census Bureau block-group and block-level data. Our analyses reveal that mid-elevation habitat types in mountain valleys as well as riparian and foothills areas on the Front Range are high priorities for conservation.
Open Access
Mapping native and non-native riparian vegetation in the Colorado River Watershed
(Colorado State University. Libraries, 2018-10-24) Evangelista, Paul, author; Young, Nicholas, author; Vorster, Tony, author; West, Amanda, author; Hatcher, Emma, author; Woodward, Brian, author; Anderson, Ryan, author; Girma, Rebecca, author
Using remote sensing to map riparian vegetation, particularly single species such as tamarisk and Russian olive, requires georeferenced occurrence locations with estimations of foliar cover to train remote sensing-based models. This report details on the data, resources, methods and results to developing riparian vegetation, tamarisk and Russian olive distribution models along the Colorado River and its’ main tributaries. Change in riparian vegetation for Colorado River Basin was analyzed, finding an overall increase in riparian vegetation between 2006 and 2016. Also, an evaluation of the change map in known regions of tamarisk management showed that our models did identify a substantial decrease in tamarisk. The results of this study are a promising next step for project partners to utilize remote sensing to monitor the efficacy of management efforts throughout the Colorado River Basin and inform future management strategies.
Open Access
Relationships between groundwater use, water table, and recovery of willow on Yellowstone's northern range
(Colorado State University. Libraries, 2011) Johnston, Danielle B., author; Cooper, David J., author; Hobbs, N. Thompson, author; Ecological Society of America, publisher
Excessive levels of herbivory, incision of stream channels, and climate warming are believed to be responsible for the decline of woody deciduous plants in riparian zones in western North America, declines that are likely to be associated with diminished biological diversity. In the northern elk wintering range of Yellowstone National Park, USA, over browsing by elk (Cervus elaphus), lowered water tables resulting from stream incision, and loss of activity by beaver (Castor canadensis) have been implicated in the decline of willow (Salix sp.) communities. Reducing elk browsing appears sufficient for willow recovery in some areas, but where water table changes have been dramatic, recovery may be slow or absent. The importance of water table changes is disputed because experimental results demonstrate water table limitations, but water table depth has failed to explain variation in willow height at landscape scales. One explanation for this apparent discrepancy is that willows that have survived intensive browsing by elk have maintained access to groundwater despite declining water tables. Using stable isotopes of water, we examined the relationships between groundwater use, water table depth, and height of heavily browsed Salix geyeriana. Salix geyeriana groundwater use varied from 30% to 80%, and was higher later in the growing season, when soil water was less available and shoot water potentials were lower. Late season groundwater use explained 26% of the variation in total height of willows (P = 0.002), with taller plants using more groundwater. Water table depth explained only 8% of the variability in total height (P=0.051), with shorter willows having deeper water table depths. Groundwater use and water table depth were uncorrelated. Height recovery following a winter of heavy browsing was related to groundwater use, but not groundwater depth. We suggest that access to deeper water sources alleviates late season water stress, allowing for more rapid height recovery and higher total plant height. Variability in groundwater access may account for variability in height recovery at landscape scales.
Open Access
Hydrologic regime and herbivory stabilize an alternative state in Yellowstone National Park
(Colorado State University. Libraries, 2007) Wolf, Evan C., author; Cooper, David J., author; Hobbs, N. Thompson, author; Ecological Society of America, publisher
A decline in the stature and abundance of willows during the 20th century occurred throughout the northern range of Yellowstone National Park, where riparian woody-plant communities are key components in multiple-trophic-level interactions. The potential causes of willow decline include climate change, increased elk browsing coincident with the loss of an apex predator, the gray wolf, and an absence of habitat engineering by beavers. The goal of this study was to determine the spatial and temporal patterns of willow establishment through the 20th century and to identify causal processes. Sampled willows established from 1917 to 1999 and contained far fewer young individuals than was predicted from a modeled stable willow population, indicating reduced establishment during recent decades. Two hydrologically distinct willow establishment environments were identified: fine grained beaver pond sediments and coarse-grained alluvium. Willows established on beaver pond sediment earlier in time, higher on floodplain surfaces, and farther from the current stream channel than did willows on alluvial sediment. Significant linear declines from the 1940s to the 1990s in alluvial willow establishment elevation and lateral distance from the stream channel resulted in a much reduced area of alluvial willow establishment. Willow establishment was not well correlated with climate-driven hydrologic variables, but the trends were consistent with the effects of stream channel incision initiated in ca. 1950, 20-30 years after beaver dam abandonment. Radiocarbon dates and floodplain stratigraphy indicate that stream incision of the present magnitude may be unprecedented in the past two millennia. We propose that hydrologic changes, stemming from competitive exclusion of beaver by elk over browsing, caused the landscape to transition from a historical beaver-pond and willow mosaic state to its current alternative stable state where active beaver dams and many willow stands are absent. Because of hydrologic changes in streams, a rapid return to the historical state may not occur by reduction of elk browsing alone. Management intervention to restore the historical hydrologic regime may be necessary to recover willows and beavers across the landscape.
Open Access
Water tables constrain height recovery of willow on Yellowstone's northern range
(Colorado State University. Libraries, 2008) Bilyeu, Danielle M., author; Cooper, David J., author; Hobbs, N. Thompson, author; Ecological Society of America, publisher
Excessive levels of herbivory may disturb ecosystems in ways that persist even when herbivory is moderated. These persistent changes may complicate efforts to restore ecosystems affected by herbivores. Willow (Salix spp.) communities within the northern range in Yellowstone National Park have been eliminated or degraded in many riparian areas by excessive elk (Cervus elaphus L.) browsing. Elk browsing of riparian willows appears to have diminished following the reintroduction of wolves (Canis lupis L.), but it remains uncertain whether reduced herbivory will restore willow communities. The direct effects of elk browsing on willows have been accompanied by indirect effects from the loss of beaver (Castorcanadensis Kuhl) activity, including incision of stream channels, erosion of fine sediments, and lower water tables near streams historically dammed by beaver. In areas where these changes have occurred, lowered water tables may suppress willow height even in the absence of elk browsing. We conducted a factorial field experiment to understand willow responses to browsing and to height of water tables. After four years of protection from elk browsing, willows with ambient water tables averaged only 106 cm in height, with negligible height gain in two of three study species during the last year of the experiment. Willows that were protected from browsing and had artificially elevated water tables averaged 147 cm in height and gained 19 cm in the last year of the experiment. In browsed plots, elevated water tables doubled height gain during a period of slightly reduced browsing pressure. We conclude that water availability mediates the rate of willow height gain and may determine whether willows grow tall enough to escape the browse zone of elk and gain resistance to future elk browsing. Consequently, in areas where long-term beaver absence has resulted in incised stream channels and low water tables, a reduction in elk browsing alone may not be sufficient for recovery of tall willow stands. Because tall willow stems are important elements of habitat for beaver, mitigating water table decline may be necessary in these areas to promote recovery of historical willow–beaver mutualisms.
Open Access
Local knowledge production, transmission, and the importance of village leaders in a network of Tibetan pastoralists coping with environmental change
(Colorado State University. Libraries, 2016) Hopping, Kelly A., author; Yangzong, Ciren, author; Klein, Julia A., author; Resilience Alliance, publisher
Changing climate, social institutions, and natural resource management policies are reshaping the dynamics of social-ecological systems globally, with subsistence-based communities likely to be among the most vulnerable to the impacts of global change. These communities’ local ecological knowledge is increasingly recognized as a source of adaptive capacity for them as well as a crucial source of information to be incorporated into scientific understanding and policy making. We interviewed Tibetan pastoralists about their observations of environmental changes, their interpretations of the causes of these changes, and the ways in which they acquire and transmit this knowledge. We found that community members tended to agree that changing climate is driving undesirable trends in grassland and livestock health, and some also viewed changing management practices as compounding the impacts of climate change. However, those nominated by their peers as experts on traditional, pastoral knowledge observed fewer changes than did a more heterogeneous group of people who reported more ways in which the environment is changing. Herders mostly discussed these changes among themselves and particularly with village leaders, yet people who discussed environmental changes together did not necessarily hold the same knowledge of them. These results indicate that members of the community are transferring knowledge of environmental change primarily as a means for seeking adaptive solutions to it, rather than for learning from others, and that local leaders can serve as critical brokers of knowledge transfer within and beyond their communities. This highlights not only the interconnectedness of knowledge, practice, and power, but also points toward the important role that local governance can have in helping communities cope with the impacts of global change.
Open Access
Agriculture's role in greenhouse gas mitigation
(Colorado State University. Libraries, 2006-09) Paul, Eldor A., author; Sheehan, John, author; Antle, John M., author; Paustian, Keith, author; Pew Center on Global Climate Change, publisher
This report describes opportunities for U.S. agriculture to contribute to reducing net greenhouse gas emissions. The Pew Center on Global Climate Change was established by the Pew Charitable Trusts to bring a new cooperative approach and critical scientific, economic, and technological expertise to the global climate change debate.
Open Access
Biological and molecular structure analyses of the controls on soil organic matter dynamics
(Colorado State University. Libraries, 2008-09) Magrini, K., author; Follett, R. F., author; Conant, R., author; Paul, Eldor A., author; Morris, S. J., author; Lomonosov Moscow State University, Department of Chemistry, publisher
The dynamics of soil organic carbon (SOC) are controlled by the interaction of biological, physical, and chemical parameters. These are best measured by a combination of techniques such as long-term field sites with a C3↔C4 plant switch. Acid hydrolysis and 14C- dating measure the mean residence time (MRT) of the resistant fraction. Long-term incubation allows the in situ biota to identify and decompose the labile SOC components. Statistical analysis (curve fitting) of the CO2 release curves, determines the pool size and of the two labile fractions (1). The effect of chemical structure is measured with pyrolysismolecular beam mass spectrometry (py-MBMS). The dynamics of charcoal, clay and silt are measured with both 13C and 14C.
Open Access
Analytical determination of concentric carbon gradients within stable soil aggregates = Détermination analytique de gradients concentriques de carbone au sein d’agrégats stables de sol
(Colorado State University. Libraries, 1998-08) Paul, Eldor A., author; Smucker, Alvin J. M., author; [ISSS-AISS-IBG-SICS], publisher
Soil aggregation dynamics directly control agricultural production and reduce environmental contamination by convection-dispersion sequestrations of most ions. Greater containment and longer residence times of most plant nutrients, pesticides, and water would better sustain most agricultural production systems without polluting nearby groundwater supplies. In short, the large surface areas associated with the plethora of porosities within each natural soil aggregate provide dynamically interactive areas for chemical sequestration. Once known, it is these active/inactive centers which can be modified to improve plant productivity and water quality.
Open Access
Analytical determination of soil C dynamics = Détermination analytique de la dynamique du carbone du sol
(Colorado State University. Libraries, 1998-08) Haile-Mariam, Shawel, author; Collins, Harold P., author; Paul, Eldor A., author; [ISSS-AISS-IBG-SICS], publisher
The significance and possible management of soil organic C (SOC) in ecosystem functioning, global change and sustainable agriculture is best determined through a knowledge of its dynamics. This requires analytically determined measurements of SOC pool sizes and flux rates. The amount and quality of plant residues inputs, biotic activity, site characteristics and management are reflected in the size of the pools and their turnover rates. Some constituents are decomposed during periods of weeks; some persist for centuries and millenia. Fractionation of the soil and the use of tracers such as 14C and 13C makes possible the determination of the dynamics of the pools involved such that more meaningful estimates of the role of SOC in the many functions in which it plays a role can be calculated.
Open Access
The extraction and measurement of adenosine triphosphate from marine sediment
(Colorado State University. Libraries, 1976-05) Paul, E. A., author; Bancroft, K., author; Wiebe, W. J., author; American Society of Limnology and Oceanography, publisher
A technique has been developed, using boiling sodium bicarbonate buffer, to extract adenosine triphosphate (ATP) from marine sediments and has been tested on a variety of sediments, including those with high organic content, clay, and carbonate. Recovery of ATP, as measured by the addition of bacteria of known ATP content to sediment, varied from 64-100%. The technique also was as effective as the conventional Tris buffer for extraction of ATP from both pure cultures of bacteria grown in broth and natural seawater samples.
Open Access
Greenhouse gases in intensive agriculture: contributions of individual gases to the radiative forcing of the atmosphere
(Colorado State University. Libraries, 2000-09-15) Harwood, Richard R., author; Paul, Eldor A., author; Robertson, G. Philip, author; American Association for the Advancement of Science, publisher
Agriculture plays a major role in the global fluxes of the greenhouse gases carbon dioxide, nitrous oxide, and methane. From 1991 to 1999, we measured gas fluxes and other sources of global warming potential (GWP) in cropped and nearby unmanaged ecosystems. Net GWP (grams of carbon dioxide equivalents per square meter per year) ranged from 110 in our conventional tillage systems to -211 in early successional communities. None of the annual cropping systems provided net mitigation, although soil carbon accumulation in no-till systems came closest to mitigating all other sources of GWP. In all but one ecosystem, nitrous oxide production was the single greatest source of GWP. In the late successional system, GWP was neutral because of significant methane oxidation. These results suggest additional opportunities for lessening the GWP of agronomic systems.
Open Access
Automated analysis of 15N and 14C in biological samples
(Colorado State University. Libraries, 1989) Paul, Eldor A., author; Harris, D., author; Marcel Dekker, Inc., publisher
An automated method for the simultaneous analysis of total N, total C, 15N and 14C in small plant and soil samples is described. A commercial C-N analyser - continuous flow isotope ratio mass spectrometer (ANCA-MS) has been extended to also measure CO2 and collect 14CO2 produced by sample combustion. Samples containing 20 - 200 μg N and up to 5 mg C can be analysed directly with no sample preparation other than drying and fine grinding. The precision of total elemental analysis is comparable to that by conventional methods. The average standard deviation of 15N analyses of plant material at natural abundance was ±1 ‰. This is accurate enough for all 15N studies except those using natural abundance and possibly long term studies of soil organic matter. Recovery of 14C in test samples was 100%. The instrument can be operated by graduate students under supervision and operating costs are primarily for sample cups, combustion catalyst and quartz tubes.
Open Access
Carbon flow in plant microbial associations
(Colorado State University. Libraries, 1981-07-24) Kucey, R. M. N., author; Paul, Eldor A., author; American Association for the Advancement of Science, publisher
Measurement of the distribution of the photosynthesis product in the symbiotic association of a legume, a mycorrhizal fungus, and nitrogen-fixing bacteria showed that the fungus incorporated 1 percent of the photosynthesis product and respired 3 percent. The nodules of a 5-week-old plant utilized 7 to 12 percent of the photosynthesis product. The legume compensated in part for the needs of its microbial partners through increased rates of photosynthesis.
Open Access
Continuous flow isotope ratio mass spectrometry of carbon dioxide trapped as strontium carbonate
(Colorado State University. Libraries, 1997) Paul, Eldor A., author; Porter, L. K., author; Harris, D., author; Marcel Dekker, Inc., publisher
The isotopic signal provided by differential discrimination against atmospheric carbon dioxide (13CO2) by C3 and C4 plant photosynthetic pathways is being widely used to study the processes of carbon (C) fixation, soil organic matter formation, and mineralization in nature. These studies have been facilitated by the availability of automated C and nitrogen (N) combustion analyzers (ANCA) combined with continuous flow isotope ratio mass spectrometers (CFIRMS). Analysis of 13CO2 in these instruments requires consistent sample mass for best precision, a requirement that is easily satisfied for soil and tissue samples by adjusting sample weight. Consistent CO2 sample size is much more difficult to achieve using gas handling systems for samples of headspace gases when CO2 concentrations vary widely. Long storage of gaseous samples also is difficult. Extended respiration studies are most easily conducted by trapping CO2 in alkali and conversion to an insoluble carbonate. Thermal decomposition of the carbonate in an on-line ANCA allows consistent and optimal CO2 sample mass to be obtained. The use of precipitated carbonates also facilitates storage of samples and enables full automation of sample analysis using an ANCA interfaced to a CFIRMS. Calcium (Ca), strontium (Sr), and barium (Ba) carbonates were tested. Strontium carbonate (SrCO3) with the addition of vanadium pentoxide (V2O5) as a combustion catalyst was found most suitable.
Open Access
Carbon dynamics and estimates of primary production by harvest, 14C dilution, and 14C turnover
(Colorado State University. Libraries, 1992-04) Lauenroth, W. K., author; Milchunas, D. G., author; Ecological Society of America, publisher
Large plots of native shortgrass steppe were labeled with 14C to assess short-term patterns of carbon allocation and the long-term process of herbivory, death, and decomposition, and to compare estimates of net aboveground, crown, and root primary production using 14C dilution, 14C turnover, and traditional harvest methods. Stabilization of labile 14C via translocation, incorporation into structural tissue, and respiration and exudation required one growing season. Exudation was 17% of plant 14C after stabilization. Estimates of turnover time for leaves, crowns, and roots by 14C turnover were 3, 5, and 8 yr, respectively, yielding estimates of belowground production that were much lower than previously thought. Estimates of aboveground production by 14C turnover were close to those obtained by harvest of peak-standing crop, but lower than reported values obtained by harvest maxima-minima. Estimates of root production by harvest maxima-minima were zero in 2 of 4 yr. 14C turnover appeared to provide reliable estimates of aboveground, crown, and root production. In contrast to reliable estimates by 14C turnover, 14C dilution estimates of root production were anomalous. The anomalous estimates were attributed to a nonuniform labeling of tissue age classes resulting in differential decomposition/herbivory of 14C:12C through time, as well as movement and loss of labile 14C through the first growing season. Isotope-dilution methodologies may be unreliable for any estimate of pool turnover when the labeling period is not as long as pool-turnover time. Problems and biases associated with traditional harvest maxima-minima methods of estimating aboveground primary production are well known, but are greatly exacerbated when the method is used to estimate root production. Estimates of root production by 14C dilution were unrealistic. 14C turnover methodology provided reliable estimates of production in this community.
Open Access
Soil bacterial community composition altered by increased nutrient availability in Arctic tundra soils
(Colorado State University. Libraries, 2014-10-02) Koyama, Akihiro, author; Wallenstein, Matthew D., author; Simpson, Rodney T., author; Moore, John C., author; Frontiers Research Foundation, publisher
The pool of soil organic carbon (SOC) in the Arctic is disproportionally large compared to those in other biomes. This large quantity of SOC accumulated over millennia due to slow rates of decomposition relative to net primary productivity. Decomposition is constrained by low temperatures and nutrient concentrations, which limit soil microbial activity. We investigated how nutrients limit bacterial and fungal biomass and community composition in organic and mineral soils within moist acidic tussock tundra ecosystems. We sampled two experimental arrays of moist acidic tussock tundra that included fertilized and non-fertilized control plots. One array included plots that had been fertilized annually since 1989 and the other since 2006. Fertilization significantly altered overall bacterial community composition and reduced evenness, to a greater degree in organic than mineral soils, and in the 1989 compared to the 2006 site. The relative abundance of copiotrophic α-Proteobacteria and β-Proteobacteria was higher in fertilized than control soils, and oligotrophic Acidobacteria were less abundant in fertilized than control soils at the 1989 site. Fungal community composition was less sensitive to increased nutrient availability, and fungal responses to fertilization were not consistent between soil horizons and sites. We detected two ectomycorrhizal genera, Russula and Cortinarius spp., associated with shrubs. Their relative abundance was not affected by fertilization despite increased dominance of their host plants in the fertilized plots. Our results indicate that fertilization, which has been commonly used to simulate warming in Arctic tundra, has limited applicability for investigating fungal dynamics under warming.
Open Access
Comparisons between P-fertilized and mycorrhizal plants
(Colorado State University. Libraries, 1986-01) Paul, Eldor A., author; Bethlenfalvay, G. J., author; Pacovsky, R. S., author; Crop Science Society of America, publisher
In experimentation with vesicular-arbuscular mycorrhizal (VAM) fungi, the availability of non-VAM control plants of equal size to VAM plants is a fundamental requirement. The purpose of this work was to determine nutrient regimes needed to achieve growth equivalence between VAM and non-VAM plants. Soybean [Glycine max (L.)Merr.] cv. Amsoy 71 and sorghum [Sorghum bicolor (L.) Moench] cv. Bok 8 plants were grown under controlled conditions in a soil (Josephine silty clay loam, mesic Typic Haploxerult) low in plant-available P. Soybeans were inoculated with one of four species and sorghum with one of two species of VAM fungi. Non-inoculated control plants received nutrient solutions that contained 0.0, 0.2, 0.4, or 1.0 mM P. while the growth of P-supplemented controls may be equivalent to VAM plants, an important question remains: Are these plants also equivalent in terms of such functional parameters as leaf development, dry matter partitioning, and nutrient assimilation? The objective of this experiment was to answer these questions. The response to VAM colonization was similar in both hosts, although less extensive colonization was observed in sorghum. Dry weight, leaf area, and P content increased exponentially with nutrient solution P level. Plants colonized with VAM fungi grew 3 to 6 times larger than the P-free controls but attained only 35 to 65% of maximum growth possible with high fertilizer P input. Host response to VAM colonization was equivalent to that of plants receiving between 0.12 and 0.22 mM P for phytomass, leaf area, and N content. Mycorrhizal plants contained less P, Mn, and root Fe but more Zn and Cu than comparable plants fertilized with P. It was concluded that P-treated, non-VAM plants differed physiologically and anatomically from VAM plants of equivalent size grown under P stress. It may therefore be necessary to establish the comparability of VAM plants and of "VAM-equivalent controls" separately for each plant parameter of interest. Even then, differential growth responses in VAM-host associations may prevent complete comparability between VAM and P-fertilized plants.