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  • 1
    ISSN: 1573-5052
    Keywords: Bouteloua gracilis ; Disturbance characteristics ; Shortgrass steppe ; Simulation model ; Succession
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We evaluated effects of soil texture and disturbance size on the successional dynamics of a semiarid grassland dominated by the perennial bunchgrass, Bouteloua gracilis (H.B.K.) Lag. ex Griffiths. A spatially-explicit gap dynamics simulation model was used to evaluate recovery patterns. The model simulates establishment, growth, and mortality of individual plants on an array of small plots through time at an annual time step. Each simulated disturbance consisted of a grid of plots of the same soil texture interconnected by processes associated with dispersal of B. gracilis seeds. Soil texture was incorporated into the model as effects on seed germination, seedling establishment, and subsequent growth of B. gracilis. Five soil texture classes and five disturbance sizes were simulated. Soil texture was more important to recovery of B. gracilis than either size of a disturbance or location of plots within a disturbance. Constraints on recruitment of seedlings had a greater effect on recovery than constraints associated with plant growth. Fastest recovery occurred on soils with the largest silt content, the variable that affects seedling establishment. Disturbances with slowest recovery were on soils with low silt contents, and either high or low water-holding capacity, the variable that affects plant growth. Biomass and recovery decreased as disturbance size increased, and as distance from a disturbed plot to the edge of the disturbance increased. In most cases, important interactions between soil texture and disturbance size on recovery were not found.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5052
    Keywords: Bouteloua gracilis ; Cattle grazing ; June beetle larvae ; Root feeders ; Shortgrass steppe ; Succession
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The importance of disturbance intensity and herbivory by cattle and white grubs, or the larvae of June beetles (including Phyllophaga fimbripes), to recovery of shortgrass steppe ecosystems in Colorado, U.S.A. were evaluated over a fourteen year time period. Disturbance intensity was defined by survival of the dominant grass species (Bouteloua gracilis) after an outbreak of root feeding activity by white grubs. Sixteen patches of vegetation consisting of four pairs of adjacent ungrazed-grazed by cattle locations with two replicates that were recently affected by white grubs were selected in 1977. Disturbance intensity was determined in 1977 by the area in each patch that contained live tillers of B. gracilis. Permanent plots were located both within and outside of each patch. Plant basal cover and density by species were estimated at time of peak aboveground biomass in six different years on each plot. Successional dynamics on patches was similar to areas affected by other types of disturbances, however, rate of recovery was faster for patches affected by grubs. Grazing by cattle was infrequently important to plant recovery, a result similar to effects of grazing on other aspects of shortgrass steppe ecosystems. Disturbance intensity was important to recovery of B. gracilis since tiller survival in 1977 was linearly related to cover in each year of sampling. For ungrazed patches, initial conditions were important to recovery of B. gracilis for as many as 14 years. For grazed patches, initial conditions decreased and grazing increased in importance through time. Changes in resource quality and a more uniform distribution of roots due to grazing likely resulted in more complete mortality of plants by grubs under grazed compared to ungrazed conditions. Persistence of shortgrass ecosystems in spite of disturbances with different intensities are determined at least in part by characteristics of disturbances interacting with the ability of plants to respond, and in part by the evolutionary history of the system. Although white grubs affect shortgrass communities infrequently, they have large and important effects on plant community structure through time, and represent an important class of disturbance defined by intensity.
    Type of Medium: Electronic Resource
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