Semiarid ecosystem development as a function of resource processing and allocation
Date
1985
Authors
Redente, E. F., author
Cook, C. W., author
Stark, J. M., author
Simmons, C. L., author
Department of Range Science, Colorado State University, publisher
Journal Title
Journal ISSN
Volume Title
Abstract
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.
Description
Prepared for the U.S. Department of Energy.
Submitted February 1985.
Submitted February 1985.
Rights Access
Subject
Biotic communities
Shale oils -- Refining