Graduation date: 1992

Thesis (M.S.)--Oregon State University, 1989. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Several models exist for investigating the effects of plant competition within and among species, i.e. intra- and inter-specific competition. The models for interspecific competition are based upon additive and replacement (de Wit) series experiments. Each approach has previously been used almost exclusively to study the effects of binary mixtures, and each has been used to derive various indices of competitiveness among species. Studies were undertaken in 1980 and 1981 to compare and evaluate the different models, and to investigate the relative performance of species in ternary combinations. Monoculture (density), additive and replacement series experiments involving binary mixtures of barnyard grass (Echinochloa crusgalli), redroot pigweed (Amaranthus retroflexus ) and green foxtail (Setaria viridis) were undertaken in both years; monoculture (density) and replacement series involving binary and ternary mixtures of rapeseed (Brassica napus) with pigweed and foxtail were also investigated in both years; in 1981, the rapeseed-pigweed-foxtail experiments also included additive series mixtures, the experimental design for which permitted the investigation of binary replacement series at different total densities. Monoculture experiments showed that yield of all four species was related to the density according to de Wit's spacing formula. Additive series experiments involving barnyard grass or rapeseed with the other two species showed that the yield of the indicator species followed the Dew's relationship between yield and the square root of the density of the associated species. The present studies have shown that the yield of the latter (in the presence of the indicator species) can also be described by the spacing formula. In binary replacement series experiments, de Wit's relative crowding coefficients (k) were calculated. Estimates of yield obtained from the k-values were usually found to agree well with observed yields. Dew's Index of Competition (CI) was calculated from additive series data for each combination of species tested. Relative crowding coefficients (k), Willey and Rao's Competition Ratio (CR) and McGilchrist's Aggressivity (A) were calculated from binary replacement series data. Both k- and CR- values contain components which relate to intra- and inter-specific competition. The actual relative contributions of intraspecific and interspecific competition were calculated by comparing the effect on a given species of adding equal densities of its own kind or of a second species, to the same total density; the ratio of the former to the latter is a new parameter, termed the Interference Ratio (IR), and is related to the relative crowding coefficient. Intercomparisons of the various measures of competitiveness showed that in both years k-values were highly correlated with A and CR, and in 1980 were also correlated with CI. However, there was only a weak correlation between k and IR. In general, CR-, k- and A-values suggested that barnyard grass and rapeseed were the most competitive species. However, IR-values indicated that the greatest competitiveness was exhibited by pigweed against foxtail. Pigweed was much more sensitive to its own kind than to foxtail. Estimates of k-values for untested combinations based upon either the use of de Wit's spacing formula or upon k-values determined for binary mixtures involving each of the untested pair with a common third species were found to be unreliable. In several mixtures, k was found to be density dependent. In ternary mixtures, the effects on the yield of a given species could not be predicted from its behaviour in the presence of either of its competitors in binary combinations. For example, pigweed and foxtail behaved synergistically against high density rapeseed, but tended to act antagonistically at low rapeseed densities. Although foxtail was consistently the weakest competitor in any binary mixture, it had the greatest effect of any species in determining the competitive interaction between the other species. In order to estimate yield losses, e.g. in crop-weed systems, only additive series data are shown to be of general applicability. / Land and Food Systems, Faculty of / Graduate

The effects of fertiliser application, recultivation type and site age on chemical and microbiological soil properties were examined on a short-term (1year) experimental trial situated on spoil heaps in Sokolov mining district, Czech Republic. Treatments at the site included fertilisation by inorganic form of nitrogen, concretely calcic saltpetre (N) and fertilisation by inorganic form of phosphorus, namely superphosphate (P). Plots were either fertilised in the beginning of growing season or unfertilised. Microbial biomass-C increased as a consequence of both N and P addition while comparing with control. There was a significant effect of fertilisation on non-fumigated C representing labile source of carbon. With N,P application non-fumigated C significantly decreased. Specific respiration rate calculated as basal microbial respiration to microbial biomass-C was significantly increased by fertiliser application. In contrary, no significant treatment effect on the other parameters include water extractable carbon, total C, total N, available P, soil pH and basal respiration was recorded. The results indicate that short-term fertilisation is not able maintain soil condition. Therefore, site age or recultivation treatment had significant effect on mostly investigated parameters (WEC, total C) rather...

"June 2002" / Bibliography: leaves 172-198. / viii, 198 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Proposes that the overall outcome of plant interactions along a temporal gradient of resource availability changes from positive during interpulses to negative during pulses. Examines negative interactions between 4 co-dominant chenopod scrubs in arid Acacia papyrocarpa woodlands. Negative interactions were more intense when conditions were least productive. Positive interactions between seedlings also changed over time, depending on the facilitation mechanism. Plant interactions seem to be most intense at the beginning of interpulses when plants are competing for diminishing water, or survivorship is enhanced in the favorable microsites provided by other plants. Later in the interpulse, interactions become less intense as conditions become more stressful and therefore survivorship and growth are affected more by abiotic conditions than plant interactions. / Thesis (Ph.D.)--University of Adelaide, Dept. of Environmental Biology, 2002

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references. Also available on the World Wide Web.

In this study I assessed the potentials of selected, established perennial grasses to maintain site occupancy in the foothills ecosystem of the Rogue River Valley of southwest Oregon which is currently dominated by a variety of annual plants. The first evaluation compared growth curves of the perennial grasses and contrasted them to growth patterns of residual annual plants. Periods of growth varied among the perennial grasses studied. Of the perennial grasses, Idaho fescue (Festuca idahoensis), a native, and Berber orchardgrass (Dactylis glomerata var. 'Berber'), introduced, most closely emulated the growth patterns of the majority of the annual plants. Relative to the other perenial grasses tested, they initiated growth earlier, continued some growth through the winter and matured earlier. Once established, they should be able to effectively compete with the resident annuals for resources and maintain their populatiOhs. To assess the potential for competition for available moisture, the second evaluation considered timing and extent of soil moisture extraction by the perennial grasses and the resident annual community through the periods of active growth. This verified growth analysis results. Idaho fescue and Berber orchardgrass extracted moisture earlier than the other perennial grasses. Perennial grass plots and plots dominated by yellow starthistle (Centaurea solstitialis) end of season residual soil moisture levels were similar. Resident annual grasses left considerably more soil moisture. In years with an early summer drought, the earlier growing perennial grasses should be able to satisfy growth requirements and persist. An assessment was also made of the abilities of several selected established perennial grasses to resist reinvasion by resident annual plants. Earlier growing perennial grasses such as Berber orchardgrass and Idaho fescue suppressed the annuals more effectively than the later growing perennial grasses. Of the perennial grasses studied, those emulating the growth patterns of the annuals have been the Most competitive and have maintained the most vigorous stands. / Graduation date: 1990

Thesis (M.S.)--Oregon State University, 2003. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (doctoral)--Oulun yliopisto, 2002. / Includes bibliographical references. Also available in electronic format.