|dc.description.abstract||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.