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  • 1
    Electronic Resource
    Electronic Resource
    Plant competition, abiotic, and long- and short-term effects of large herbivores on demography of opportunistic species in a semiarid grassland (1992)
    Springer
    Oecologia 92 (1992), S. 520-531 
    Details
    ISSN: 1432-1939
    Keywords: Herbivory ; Compensatory growth ; Disturbance ; Establishment ; Landscape topography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The emergence and subsequent survival and growth of five opportunistic “weeds” were monitored after seed additions to long-term grazing treatments with or without current-year grazing, long-term ungrazed treatments, and removal treatments designed to eliminate plant competition from existing perennials while either leaving vegetation and soil structure unaltered or disturbed. The treatments were applied on both uplands and lowlands to assess the relative influence of macroabiotic environment versus plant competition. The long-term effects of large herbivores on the initial emergence of seedlings were greater than the effects of removing competition. Very few individuals emerged on the long-term grazed treatments that were either grazed or ungrazed during the experiment. Numbers of individuals emerging on the long-term ungrazed treatments were greater or equal to those emerging on the no-competition-undisturbed treatments, but numbers were greatest on no-competition-disturbed treatments. None of the seeded individuals on the long-term grazed, currently grazed treatments survived to the end of the growing season. There was a slightly greater end-of-season biomass of seeded species and percentage of the total population reaching reproductive status on the long-term ungrazed compared with grazed-nondefoliated treatments, and very high survival, biomass, and proportions of reproductives on both no-competition treatments. Cover types in the immediate vicinity of seedlings influenced both germination and survival, but the effects differed between species and treatments. Equal compensation to current-year herbivory occurred on long-term heavily grazed treatments even though above-ground production was much greater on long-term protected sites. Productivity varied with topography, but very few topographic main effects or interactions occurred with demographic variables of seeded species, suggesting that macroabiotic effects were of minor importance compared with grazing and plant competition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317844
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Neighborhood interactions in a natural population of the perennial bunchgrassBouteloua gracilis (1993)
    Springer
    Oecologia 94 (1993), S. 595-602 
    Details
    ISSN: 1432-1939
    Keywords: Intraspecific competition ; Space partitioning ; Neighborhood ; Bouteloua gracilis ; Shortgrass steppe
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We analyzed neighborhood interactions in a natural population of the perennial bunchgrass blue grama (Bouteloua gracilis). Space occupation by individual plants was characterized in terms of neighborhood size. Neighborhood size was defined as the area potentially ‘available’ to an individual, which included the basal area of the plant and the bare area closer to the edges of the plant than to any others. Geographic Information Systems (GIS) were used to describe space partitioning. Growing season performance was evaluated as a function of neighborhood area and neighbor size, controlling for focal plant size. The area of the neighborhood was significant in explaining the remaining variation of allometric relationships between basal area and current vegetative and reproductive performance. In contrast, current performance of focal individuals was not related to the average basal area or the sum of basal areas of adjacent neighbors. Growing season performance was apparently affected by plant spacing, suggesting that competition for spatially distributed resources occurs. The presence of relatively small plants in neighborhoods with a high proportion of bare soil is consistent with the view of a community composed of patches undergoing their own successional dynamics. Competition and disturbances seem to play an important role in this semiarid grassland.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566977
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    A comparison of 14C, 86Rb, and total excavation for determination of root distributions of individual plants (1992)
    Springer
    Plant and soil 144 (1992), S. 125-132 
    Details
    ISSN: 1573-5036
    Keywords: isotopes ; monolith excavation ; plant life-forms ; root distributions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Individual grass (Bouteloua gracilis) and shrub (Gutierrezia sarothrae) plants were either excavated as monoliths on nail boards, exposed to 14CO2, or stem-injected with 86Rb to compare the ability of the techniques to determine horizontal and vertical distribution of roots. The vertical distribution or roots directly under plant centers obtained by coring most closely correlated with monolith root length. 14C activity greatly overestimated near-surface roots and underestimated deep roots. 86Rb activity did not follow the pattern of geometric decrease in root biomass with depth. Comparisons of both isotopes with monolith root length, over both horizontal and vertical axes, indicated that 14C activity was consistently concentrated near the soil surface, and 86Rb activity was highly variable and randomly distributed. 14C may better represent root activity than root mass, and stem-injection methods can result in nonuniform labeling of roots. Caution should be exercised when using tracers to infer root biomass distributions. Resource partitioning between shrubs and grasses is discussed in relation to soil water dynamics in this semiarid grassland.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00018853
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    Paper (German National Licenses)
    Fulltext
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