Restoration Ecology Laboratory

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This digital collection includes reports from the Piceance Intensive Study conducted by the Restoration Ecology Laboratory.

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Open Access
Ecological studies of natural and established ecosystems on energy related disturbances in Colorado
(Colorado State University. Libraries, 1984) Redente, Edward F., author; Cook, C. Wayne, author; Department of Range Science, Colorado State University, publisher
During this research period studies have concentrated on soil, plant, and microbial interactions to gain a better understanding of plant community changes over time on perturbed systems. These studies have shown that disturbance and revegetation practices influence vegetation structure and succession primarily in two ways: (1) by modifying chemical, physical, and biological properties of the soil and (2) by influencing the initial floristic composition of the plant community. Both the intensity and the type of disturbance, through their effect on soil chemical and physical properties have been shown to influence aboveground vegetation structure and succession. These studies show that types of disturbances which create highly productive soil conditions result in low plant diversity, while disturbances which create less productive soil conditions result in high diversity. In addition, very intense disturbances which increase the rockiness of the surface soil have been shown to not only alter the rate of succession but also the direction of succession. Similarly, the nature of the disturbance can have major effects on soil biological properties. Disturbed and revegetated soils continue to have markedly higher microbial activity and organic matter contents than undisturbed native soils. Where topsoil has been stockpiled, however, microbial activity is generally reduced. Stockpiling affects various microbial populations differently, depending on the length of the stockpiling period and whether or not the stockpile is vegetated. When the stockpile is vegetated, there is a relative increase in bacteria 1 and fungal populations while when a stockpile is not vegetated actinomycetes show greater relative abundance. When topsoil is stored for a period of four years, significant and predictable declines in Mycorrhiza Inoculum Potential (MIP) of the soil occur. However, the MI P of the upper level s (< 90 cm) of topsoil can be preserved and enhanced by seeding with plant species that host YAM fungi. Certain reclamation practices may temporarily influence soil chemical and physical characteristics and thus affect biological structure and succession in the above- and below ground compartments. Fertilization, for example, continues to have a positive influence on plant production in some studies. Its influence on plant species diversity, however, has been negative. The effect of fertilizer on the belowground compartment is most apparent with fungal populations. In general, fertilization causes reduced fungal hyphal lengths and a reduction in MIP values. When disturbance results in a material such as retorted oil shale being used as a growth medium, the chemical, physical, and biological properties are drastically altered. Few plant species have been shown to perform we 11 on this material and as a result, plant communities established on Paraho retorted shale are low in diversity and canopy cover. In the belowground compartment, retorted shale has a negative effect on phosphatase activity and nitrogen fixation and seems to prevent mycorrhizal formation. Mixing retorted shale with topsoil ameliorates these effects somewhat. Mycorrhizal formation is not inhibited until the amount of added shale exceeds 50%. The negative effects of retorted shale are primarily due to its high salt content and its high pH which results in a high availability of toxic elements and poor nutrient availability. The chemical equilibria involved in producing the high pH in oi 1 shale have been studied. During the processing of oil shale at high temperatures, carbonate minerals are often destroyed and silicate minerals such as CaSiO3 (pseudowallastonite) and MgSiO3 (clinoenstatite) are formed. These minerals buffer the pH of spent shale near 12. When processed Lurgi shale is recarbonated by bubbling CO2 through suspensions of spent shale, the pH is decreased from 11.6 to 7.9. The result is a disappearance of the silicate minerals and formation of CaCO3 (calcite) and MgCO3 (magnesite). In addition to modifying soil properties, these studies show that the second major way that disturbances and revegetation practices affect vegetation structure and succession is by influencing the initial floristic composition of the plant community. By initially seeding grasses and forbs alone, shrubs can be prevented from invading the stand in spite of the fact that shrubs are well adapted to the site and there is a ready seed source. Including adapted shrub species in the initial seed mixture on the same sites, however, can result in greater total biomass without significant reductions in grass and forb biomass. Since results of another study on competition among woody plants offer no support for the hypothesis that intensity of competition between shrubs is correlated with the abiotic environment, planting densities for the shrubs studied may be selected without consideration of shrub competition. Once the initial floristic composition of the community is determined, changes in species composition may occur due to competitive interactions. The competitive interactions among four native grass species occurring on the site have been studied. Competitive relationships among species are discussed in terms of the effect of fertilizer, soil depth, and phenologic stage on biomass and gross energy content of competing pairs. Identification of adapted species for use in revegetation is often difficult since ecotypes of the same species can be quite variable. Therefore, the ecogenic variation within eight native species (five shrubs, one forb, and two grasses) has been studied and adaptive advantages of the genetic differences are discussed.
Open Access
Long-term plant community development on topsoil treatments overlying a phytotoxic growth medium
(Colorado State University. Libraries, 2002) Sydnor, Russell S., author; Redente, Edward F., author; Colorado State University. Colorado Water Resources Research Institute, publisher
The application of topsoil over phytotoxic mine waste materials is often the most effective method of establishing and maintaining plant communities during reclamation. However, long-term data on the effectiveness of topsoil cover treatments, as well as on treatments used to enhance vegetation establishment on soil covers, are lacking. Therefore, we evaluated long-term plant community development on study plots in which 60 cm of Paraho retorted oil shale was covered by various depths of topsoil. Each plot was drill seeded with one of three seed mixtures (native, introduced, and combination of native and introduced species), and fertilized with one of three rates of nitrogen (N) and phosphorus (P) fertilizer following plot construction in 1977. Data collected in 1997 showed that native species were as productive as introduced species on deeper topsoil depths and on the control. Also, relative plant species composition and plant species richness continued to be greatly influenced by seed mixture treatments. Plots seeded with a particular seed mixture were still dominated by those species originally seeded, and native seed mixture plots were more species rich than introduced seed mixture plots. Finally, the onetime application of N and P was no longer influencing aboveground biomass.
Open Access
Reclamation studies on oil shale lands in northwestern Colorado
(Colorado State University. Libraries, 1980) Cook, C. Wayne, author; Redente, Edward F., author; Department of Range Science, Colorado State University, publisher
The overall objective of this project is to study the effects of various reclamation practices on above- and belowground ecosystem development associated with disturbed oil shale lands in northwestern Colorado. Plant growth media that are being used in field test plots include retorted shale, soil over retorted shale, subsoil materials, and surface disturbed topsoils, The project was initiated in June 1976 and is presently reporting on fourth-year data from both field and laboratory studies. The majority of research reported on within this report is being conducted on a 20-ha Intensive Study Site located near the focal points of oil shale activity in the Piceance Basin. The site is at an elevation of 2,042 m, receives approximately 30 to 35 cm of annual precipitation, and encompasses the plant communities most typical of the Piceance Basin. Some of the more significant results that are reported herein are (1) a soil cover of at least 61 cm in conjunction with a capillary barrier provided the best combination of treatments for the establishment of vegetation and a functional microbial community, (2) aboveground production values for native and introduced species mixtures are comparable after three growing seasons, (3) cover values for native species mixtures are generally greater than for introduced species mixtures, (4) native seed mixtures, in general, allow greater invasion to occur than introduced mixtures, (5) sewage sludge at relatively low rates appears to provide the most beneficial overall effect on plant growth of any fertilizer treatment tested, (6) cultural practices, such as irrigation, mulching, and fertilizing, have significant effects on both above- and belowground ecosystem development, (7) topsoil storage after 1.5 years does not appear to significantly affect general microbial activities but does reduce the mycorrhizal infection potential of the soil at shallow depths, (8) populations of mycorrhizal fungi are decreased on severely disturbed soils if a cover of vegetation is not established, (9) significant biological differences among ecotypes of important shrub species have been identified and will assist in selecting appropriate plant materials for reclamation, (10) a vegetation model is outlined which upon completion will enable the reclamation specialist to predict the plant species combinations best adapted to specific reclamation sites, and (11) synthetic strains of two important grass species are close to development which will provide superior plant materials for reclamation in the West.
Open Access
Rehabilitation potential and practices of Colorado oil shale lands: progress report for period June 1, 1978 - May 31, 1979
(Colorado State University. Libraries, 1979) Cook, C. Wayne, author; Colorado State University, publisher
The following document is a third-year progress report to the original contract [Contract No. EY-76-S-02-4018] for the period June 1, 1978 to May 31, 1979. The overall objective of the project is to study the effects of seeding techniques, species mixtures, fertilizer, ecotypes, improved plant materials, mycorrhizal fungi, and soil microorganisms on the initial and final stages of reclamation obtained through seeding and subsequent succession on disturbed oil shale lands. Plant growth medias that are being used in field-established test plots include retorted shale, soil over retorted shale, subsoil materials, and surface disturbed topsoils. Because of the long-term nature of successional and ecologically oriented studies the project is just beginning to generate significant publications. Several of the studies associated with the project have some phases being conducted principally in the laboratories and greenhouses at Colorado State University. The majority of the research, however, is being conducted on a 20 hectare Intensive Study Site located near the focal points of oil shale activity in the Piceance Basin. The site is at an elevation of 2,042 m, receives approximately 30 to 55 cm of precipitation annually, and encompasses the plant communities most typical of the Piceance Basin. Most of the information contained in this report originated from the monitoring and sampling of research plots established in either the fall of 1976 or 1977. Therefore, data that have been obtained from the Intensive Study Site represent only first- or second-year results. However, many trends have been identified in the successional process and the soil microorganisms and mycorrhizal studies continue to contribute significant information to the overall results. The phytosociological study has progressed to a point where field sampling is complete and the application and publication of this material will be forth coming in 1979. The plant selection and ecotype studies have made substantial progress, but because of the nature of the research publishable information is not yet available.
Open Access
Revegetation research on oil shale lands in the Piceance Basin
(Colorado State University. Libraries, 1981) Redente, Edward F., author; Cook, C. Wayne, author; Department of Range Science, Colorado State University, publisher
The overall objective of this project is to study the effects of various reclamation practices on above- and belowground ecosystem development associated with disturbed oil shale lands in northwestern Colorado. Plant growth media that are being used in field test plots include retorted shale, soil over retorted shale, subsoil materials, and surface disturbed topsoils. This project was initiated in June 1975 and is presently reporting on fifth-year data. Satisfactory stands of vegetation failed to establish on unleached retorted shale during two successive years of seeding (1977 and 1979). Only salt-tolerant species produced any measureab1e biomass during the second year's planting (1979), and these produced less than 200 kg/ha. Straw mulch and additions of nitrogen and phosphorus had little effect upon establishing vegetation on retorted shale. Coverings of topsoil over retorted oil shale (30 cm, 61 cm, and 91 cm) showed increased herbage production from seeded species, both native and introduced, with increased depth of soil covering. All seedings with soil over retorted shale were judged to be successful at the end of three growing seasons, but deep-rooted shrubs that depend upon subsoil moisture may have their growth hampered by the retorted shale substrate. Natural revegetation on areas with various degrees of disturbance shows that natural invasion and succession was slow at best, but invading species and biomass production was greatest on the least disturbed and least on the most severely disturbed soils. Plants that are nonmycorrhiza1 appear to be the first invaders on severely disturbed areas. Yearly environmental fluctuations and severity of disturbance appear to be the primary factors in determining rates of natural invasion and succession on disturbed native rangelands. Invasion of species on disturbed topsoil plots showed that after three years introduced seed mixtures were more effective than native mixtures in occupying space and closing the community to invading species. Fertilizer appears to encourage the invasion of annual plants even after the third year following application. Long-term storage of topsoil without vegetation significantly decreases the mycorrhizal infection potential and, therefore, decreases the relative success of aboveground vegetation and subsequent succession. Severe disturbance of soils, use of fertilizer, and soil stockpiling can all adversely affect the microbial processes essential for establishment of plant communities in mined land reclamation. In general, treatments that increase the production of organic matter in the soil increase microbial activity. Microbiological activity in retorted oil shale is minimal and shows a direct negative effect when mixed with topsoil. Ecotypic differentiation related to growth and competitive ability, moisture stress tolerance, and reproductive potential have been found in five native shrub species. From this work it is possible to predict the appropriate species combinations or ecotypes that are best suited for different landscape reclamation. Germp1asm sources of two grasses and two legumes, that have shown promise as revegetation species, have been collected and evaluated for the production of test seed. Suitable breeding procedures are being used to develop improved strains which will eventually increase the availability of native plant materials for disturbed land reclamation. The use of fertilizer in the reclamation of disturbed soils remains questionable. Fertilizer (nitrogen) when added to the soil at the time of planting may encourage competition from annual weeds to the detriment of seeded species. Likewise, fertilizers may promote grass growth to the extent that it decreases the growth of other life forms. Heavy applications of nitrogen are lost from the soil and are, therefore, not as suitable as smaller annual applications following seedling establishment.
Open Access
Revegetation studies on oil shale related disturbances in Colorado
(Colorado State University. Libraries, 1982) Redente, Edward F., author; Cook, C. Wayne, author; Department of Range Science, Colorado State University, publisher
An interdisciplinary research project was initiated in 1976 to provide both basic and applied information that would aid in the reestablishment of natural functioning ecosystems on land disturbances associated with energy development. The approach included field, laboratory, and greenhouse experiments designed to provide both structural and functional information about disturbed ecological systems in the semiarid west. This report presents results from the sixth year of the study. The degree of soil disturbance substantially influences the rate of natural plant success ion. Mixing soil horizons reduces the probability that perennial species would contribute significantly to rapid invasion and increases the probability that annual weeds would be the more prominent invader. In general, introduced and native seed mixtures produce similar amounts of aboveground biomass. However, introduced species were slightly more resistant to invasion by volunteer species. Fertilizer is effective in increasing seeded grass and shrub production, and the effect may still be evident five years following initial application. The use of 90 cm of topsoil and 60 cm of topsoil over a capillary barrier proved to be the best treatments for supporting plant species over Paraho retorted shale after four years. The manipulation of topsoil depth and the use of a capillary barrier may ultimately prove useful as a management tool in modifying the ultimate plant community structure. Soil disturbance may have a long-lasting effect on belowground processes; with better maintenance of the surface soil and decomposer subsystems such effects can be minimized. Monitoring of the nitrogen cycle has shown that a single fertilizer treatment at the beginning of reclamation of a disturbed soil can have long-lasting effects. The results of nitrification and ammonium volatilization trials also suggest that only a minor pan of the added N will be lost due to volatilization. As reestablished plant communities mature, it appears that there is a major shift in biogeochemical cycling with the reallocation of nitrogen and phosphorus to less available pools and subsequent decreases in the cycling of these components. Storing topsoil may have negative effects upon populations of viable mycorrhizal fungi. Topsoil storage for three years clearly indicates significant decreases in the mycorrhizal inoculum potential (MIP) of the topsoil when the soil is left unplanted. However, when the topsoil is planted with mycorrhizal plant species, the MIP values are maintained in the upper 90 cm of the storage pi le. Functional mycorrhizae do not form in Paraho and Union decarbonized shales after several growing seasons, but there does not appear to be any adverse effect in terms of MIP of the soil that retorted shale exerts on soil placed over these shales. TOSCO II spent shale, when leached and amended with fertilizer, allowed mycorrhiza formation in the upper 30 cm of the growth media profile but inhibited mycorrhiza formation at deeper depths. In the study of ecogenetic variability in native shrubs, it has been found that ecotypic differentiation is not strongly evidenced for the populations studied of mountain mahogany, ante lope bitterbrush, and fourwing saltbush. It appears, at this time that range of source materials comparable to the collections in the study could be used interchangeably for a variety of reclamation situations. Ecotypic differentiation with respect to competitive ability, moisture, and short growing season stress has been documented for snowberry, serviceberry, and winterfat. The maintenance of fertility levels (especially nitrogen) on disturbed lands depends upon adequate and timely supplies of nitrogen either as fertilizer or through enhanced activity of natural elements of the ecosystems. Biological and chemical pathways have been studied as to their contribution of nitrogen to disturbed plant-soil systems.
Open Access
Secondary succession patterns in a disturbed sagebrush community in northwest Colorado
(Colorado State University. Libraries, 1996) Biondini, Mario E., author; Redente, Edward F., author; Colorado State University. Water Resources Research Institute, publisher
The relationship between secondary succession, soil disturbance, and soil biological activity were studied on a sagebrush community in the Piceance Basin of northwest Colorado. Four levels of soil disturbance were imposed following vegetation removal: (1) topsoil left in place; (2) topsoil ripped to a depth of 30 cm; (3) topsoil and subsoil were removed to a depth of 1 m, mixed and rep 1aced; and (4) topsoil and subsoil were removed to a depth of 2 m and replaced in a reverse order. Plant species composition, dehydrogenase and phosphatase enzymatic activity, mycorrhizal inoculum potential (MIP), and percent organic matter were the variables measured. Treatment 4 drastically altered the pattern of vegetation succession. Treatments 2, 3, and 4 started with Russian thistle (Salsola iberica) as the dominant species but six years later, Treatments 3, and to lesser extent 2, were similar to the species composition of Treatment 1, dominated by perennia1 grasses and perennia1 forbs. Treatment 4 developed a shrub-dominated community. Both dehydrogenase enzymatic activity and MIP increased with the change from Russian thistle to a vegetation dominated by either perennial grasses and forbs or shrubs. The intensity of disturbance 228 in Treatments 2s 3s and 4 resulted in drastic reductions of dehydrogenase activity and MIPs but in six years they recovered to levels comparable to Treatment 1. Phosphatase enzyme activity and organ i c matter were unre1ated to species composition but related to treatment and time elapsed. In both cases a significant decrease was observed throughout the six-year period.
Open Access
Semiarid ecosystem development as a function of resource processing and allocation
(Colorado State University. Libraries, 1985) Redente, E. F., author; Cook, C. W., author; Stark, J. M., author; Simmons, C. L., author; Department of Range Science, Colorado State University, publisher
The objective of the research contained in this report is to study the structural and functional changes occurring within and among ecosystem compartments during secondary succession. The report is divided into two major sections. The first part, Ecosystem Development section, presents first year data from a study funded for the first time in 1984. The second part, Restoration of Natural Functioning Ecosystems section, presents results from on-going long-term experiments dealing with ecosystem recovery and restoration following disturbance related to energy development. Accomplishments during the first year of the new study consisted of construction of the Ecosystem Development Plot and collection of baseline data before and after plot establishment. Baseline sampling of the vegetation prior to plot construction has shown that the plant community was essentially a shrub-grass community with big sagebrush (Artemisia tridentata tridentata) being the dominant woody species. The majority of the organic material (87%) and total N (98%) occurred in the belowground system. Approximately 97% of the soil N occurred in relatively resistant organic compounds while 2.2% occurred in mineralizable organic compounds and <1% occurred as mineral ions. Preliminary results also have been obtained for the new study regarding the effects of certain treatments on belowground processes. Fumigation with methyl bromide is being used as an experimental treatment to study the role that the microbial compartment plays in regulating succession. Initial analyses of structural and functional attributes of the belowground microbial compartment indicated that the major effect of fumigation was on the fungal rather than the bacterial component of the system. In addition, there were distinct effects on dehydrogenase activity and N fixation. Studies of mycorrhizal inoculum potential have indicated that fumigation almost completely eliminates VA mycorrhizal propagules. It is not known how rapidly recolonization will take place. Results from on-going long-term studies of ecosystem recovery and restoration are extensive and range from the effects of weathering on retorted shale chemical properties and how this affects the structure of vascular plant and microbial communities, to the influence of competition on the structure of natural and disturbed plant communities. Studies dealing with the effects of growth medium, seed mixture, and fertilizer on plant community structure are still showing significant results. For example, use of retorted oil shale as a plant growth medium results in plant communities that are productive but low in canopy cover and diversity. The use of topsoil over retorted shale moderates the physical, chemical and biological properties of the shale and provides a more favorable plant growth medium. Seed mixtures containing introduced grasses and forbs produce the greatest aboveground biomass during moist years; while mixtures of native grasses, forbs and shrubs are more productive in drier years. The effects of fertilization with N and P on aboveground biomass are no longer visible after seven years. However, the effects of fertilization on species composition is still apparent. The negative effects of retorted shale on plant growth are primarily due to high salt content and high pH that results in high availability of toxic elements and poor nutrient availability. When oil shales are processed, carbonate minerals are destroyed and CO2 (g) is driven off. The pH of such material approaches 12.0 and the solubility relationships of Ca and Mg minerals are markedly altered. Experiments have shown that processing oil shales at high temperatures destroys carbonate minerals and forms silicate minerals such as wollastonite, clinoenstatite, or diopside depending upon the chemical composition of the raw oil shale. These minerals buffer pH above 11.0 and control Ca2+ and Mg2+ activities in solution. Further, these results suggest that oxides or hydroxides produced from the processing of oi 1 shale may not persist very long but dissolve and precipitate as more stable minerals. The concentration of certain trace elements (from retorted shale) in aboveground plant parts and possible toxicity effects on plants and animals have been studied. Increased topsoil thickness over retorted shale reduces trace element concentrations in plants. In general, legumes have the highest concentrations of trace elements with shrubs being intermediate and grasses lowest. In addition, transportation of trace elements to the soil surface by plants was greatest when plants were growing in shallow layers of topsoil over retorted shale. Belowground microbiological studies have shown that chemical stress associated with having retorted shale in the plant growth medium can lead to increased physiological diversity in the rhizosphere. Plants growing in a stressed environment also have higher microbial populations in the rhizosphere than plants growing under non -stressed conditions. Diversity among vascular plants is also higher when plant communities are established in a stressed environment than when the same species are established under favorable growing conditions. Continuing studies on woody plant competition resulted in several conclusions. In two pinyon-juniper communities the spacing pattern of trees changes with time. The youngest trees are aggregated, saplings tend to be randomly distributed, and large trees are either random or uniform in spacing. This change in spatial pattern results from competition. Interspecific competition between pairs of three shrub species has been detected; however, there is no evidence to indicate that competition is related to the amount of stress offered by the competition environment. The study of mycorrhizal dependency of Utah juniper (Juniperus osteosperma) has been completed. This species characterizes "climax" communities in northwest Colorado and may be classified as a stress-tolerator. Experiments indicate that Utah juniper is obligately mycorrhizal and thus requires VAM fungi for competitive growth and survival under natural conditions. Winterfat, (Ceratoides lanata), western wheatgrass (Agropyron smithii), and bluebunch wheatgrass (A. inerme) were tested for their responses to -inter- and intraspecific competition when found in adjacent combinations with one another in the field. The three species represented three different seasonal patterns of carbon allocation to leaves. Winterfat began allocation of carbon to leaves in late May or early June and continued to produce leaves throughout the growing season. Western wheatgrass developed maximum leaf biomass early in the season and maintained more or less the same amount throughout the growing season. This species had the largest leaves of the three species studied. Bluebunch wheatgrass, which is more sensitive to dry soil conditions than are western wheatgrass and winterfat, had the largest amount of leaf biomass early in the season when water from spring rains and snow melt was abundant. As the dry summer progressed, carbon was allocated to green stems which may have been more efficient structures for conserving water.
Open Access
Structural and functional changes in early successional stages of a semiarid ecosystem
(Colorado State University. Libraries, 1986) Redente, Edward F., author; Cook, C. Wayne, author; Department of Range Science, Colorado State University, publisher
The objective of our research is to study structural and functional changes that occur within and between ecosystem compartments during secondary succession in disturbed semiarid environments. This information not only will assist in better understanding fundamental aspects of these processes, but should lead to more effective management of these disturbed semiarid environments. First year data clearly showed an increase in resource abundance after disturbance which produced not only alteration of the soil surface but a decrease in available organic matter. In addition, marked increases in NO3- and soil water potentials were evident at all depths in the disturbed sites as compared to the undisturbed community. Potential N mineralization rates, a measure of plant-available N, primarily from microbial biomass did not differ, but actual mineral N levels were higher because of higher soil moisture. Water use efficiency also varied with the early successional species being more efficient than late successional species. However, the late successional species were able to effectively use water under lower soil water potentials. These results are consistent with available information showing that "climax" species are less efficient in producing biomass at high levels of resource availability but able to sustain growth under conditions of nutrient (including water) stress. Soil disturbance as well as manipulation of the microflora compartment by fumigation had a significant impact on microflora structure and function, and could have a long term impact on resource availability which will be important in understanding microbial contributions to the early development of plant-soil systems. Soil enzymatic activity, phosphatase, dehydrogenase and especially N fixation, ammonium and nitrite oxidation were still markedly reduced by disturbance and fumigation. This reduction of nutrient cycling, together with the elimination of plants, resulted in a sharp decline in fungal species diversity, with the saprobic community being dominated by pioneering species like Penicillium, Phoma, and Cladosporium. The mycorrhizal population was also drastically reduced by disturbance and fumigation. With plant community development, the level of mycorrhizal inoculum potential (MIP) was lower with ruderal (R) and competitive-ruderal (C-R) plants while higher MIP values occurred when the plant community was dominated by stress tolerant plants (S). MIP was also inversely correlated with the level of non-rhizosphere microbial activity. A preliminary study of rhizosphere vs. non-rhizosphere microbial development was conducted in the field in this first growing season where cheatgrass (Bromus tectorum) and western wheatgrass (Agropyron smithii) responses, with and without fertilization, were evaluated. The rhizosphere of both plants had consistently higher microbial populations, enzymatic activity, and fungal diversity than the non-rhizosphere. The rhizosphere of cheatgrass showed higher microbial population and enzymatic activities and lower diversity than the rhizosphere of western wheatgrass. These preliminary studies conducted with an annual versus a perennial plant will be examined in greater detail in comparison with other perennial plant responses in the corning year. The floristic composition of the primary producers on the disturbed site was highly correlated. With the propagule supply, with composition of the seed bank being the main driving force. Resource competition was not important at this stage in determining species composition because plant density was low and N, P, and water resources were abundant. Total aboveground net primary production (NPP) was similar in undisturbed and disturbed plots but the structure of primary producers was significantly different. The disturbed sites were dominated by plants with an R and CR strategy while the undisturbed sites were dominated by plants with an S strategy, indicating strong relationships between plant composition and soil resource abundance. Competition studies between bluebunch wheatgrass (Agropyron inerme), western wheatgrass, big sagebrush (Artemisia tridentata), and winterfat (Ceratoides lanata) showed that these four species were able to coexist under a wide range of water availability conditions. This appeared to be related to differences in carbon allocation to shoots t roots, and sterns and an ability to control water losses among these plants. The grasses showed a faster rate of growth and root expansion than shrubs during the establishment phase and as a result, competition between grasses was more intense than between shrubs or grasses and shrubs, leading to a decline in biomass production. Competitive relationships of mature species in the natural community were in some instances different than those found in greenhouse experiments. For instance, winterfat competed better with western wheatgrass than with another winterfat because winterfat could use water deeper in the profile, which was not available to the grass. Under field conditions, the water status of all plants was more favorable on deeply disturbed soils, than on shallowly disturbed soils and varied carbon allocation patterns, stomatal conductance, and transpiration rates were also evident. The final phase of an experiment designed to determine the effects of retorted shale recarbonation on plant uptake of toxic trace elements was completed. Plants grown on recarbonated retorted shale had significantly lower concentration of B, Ba, and Sr and higher Mo levels than plants grown in non-recarbonated shales. In contrast, As, Cr, F, and Ni uptake was below toxic levels with and without recarbonation. The Cu:Mo ratio in plants was not influenced by recarbonation, being below the recommended levels for utilization by ruminants. This represents a potential source of toxicity which will not be influenced by the recarbonation process. These initial studies, in summary, indicate that both plant community characteristics and the presence of a functioning belowground community will be important in secondary succession processes which occur in disturbed semiarid environments. Rhizosphere and nonrhizosphere microflora structure and dynamics as well as plant competition strategies, as influenced by nutrient resource availability, will be critical factors influencing the successional process.
Open Access
Summary of reclamation research in northwest Colorado from 1976-1986
(Colorado State University. Libraries, 1986) Redente, Edward F., author; Cook, C. Wayne, author; Department of Range Science, Colorado State University, publisher

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