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  • 1
    Electronic Resource
    Electronic Resource
    Relationships between the effects of insect herbivory and sheep grazing on seasonal changes in an early successional plant community (1987)
    Springer
    Oecologia 71 (1987), S. 245-253 
    Details
    ISSN: 1432-1939
    Keywords: Calcicolous grassland ; Herbivory ; Insects ; Plant succession ; Sheep
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The effects of spring grazing by sheep and of natural levels of insect herbivory were studied in 1985 on a limestone field abandoned from arable land for four years. A split-plot design was adopted in which paddocks, arranged in Latin squares, were either left ungrazed or heavily grazed by sheep for ten days in April. Within each paddock plots were either sprayed regularly with Malathion-60 or untreated. Natural levels of insect herbivory, compared to the reduced levels in insecticide-treated plots, had effects of similar magnitude to those from the short burst of spring grazing. Many attributes of the grazed/insecticide-treated sward were either increased or decreased by a factor of two within a season. Both types of herbivore caused changes in the direction of plant succession as well as in its rate. Effects on early successional species were large and similar when caused by either type of herbivore. Effects on later successional species were often smaller, but also showed differences in the action of the two herbivore types, as did effects on sward height, species richness and total cover. The effects of sheep and insect herbivory were not always additive or in the same direction. The results suggest that manipulations of both mammal and insect herbivores may be powerful tools for directing changes in plant community composition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377291
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  • 2
    Electronic Resource
    Electronic Resource
    The effects of sheep grazing on seedling establishment and survival in grassland (1988)
    Springer
    Plant ecology 78 (1988), S. 91-98 
    Details
    ISSN: 1573-5052
    Keywords: Gap size ; Grazing ; Insect herbivory ; Seedling ; Sheep
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This paper examines the effects of sheep and insect grazing on the generation of natural gaps in turf and the establishment of seedlings therein. The site is on an old field on limestone. There were five sheep grazing treatments: ungrazed, and grazed briefly in spring, briefly in autumn, in autumn or in summer and autumn. The first three of these treatments also contained plots in which insecticide was applied regularly during the growing season. Pins of increasing size (1.6 mm–12.8 mm diameter) were lowered at grid intersections in permanent quadrats to record gap type and the occurrence of seedlings on seven dates over 15 months. Heavily-grazed plots had more bare ground in spring and more herb seedlings established in them. Seedlings of annual species of Bromus were able to establish in gaps (bare ground and litter) of smaller size than was required by herb seedlings (which had much smaller seeds). The use of an insecticide increased seedling establishment in October in ungrazed and in spring-grazed paddocks but decreased it in autumn-grazed paddocks. This may indicate the greater importance of insect herbivory in making gaps in the matted sward of autumn-grazed plots. Seedlings which established in October 1986 and March 1987 were more likely to die than those establishing earlier in 1986. This may be because of winter-kill and especially vigorous spring vegetation growth respectively. Seedling mortality was not affected by gap size or grazing treatment (unless such effects operated before we detected the seedlings).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00045643
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  • 3
    Electronic Resource
    Electronic Resource
    Transition matrix models and succession after release from grazing on Aldabra atoll (1983)
    Springer
    Plant ecology 52 (1983), S. 151-159 
    Details
    ISSN: 1573-5052
    Keywords: Aldabra ; Atoll ; Markovian model ; Succession ; Tortolse grazing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The process of succession after release from grazing by giant tortoises was investigated in three different vegetation types on Aldabra atoll. After four years there was very little change in two vegetation types: a tall mixed scrubland and an open single-species grassland. Probably in the former case grazing had no effect and in the latter case soil nutrients were limiting sward growth and establishment. In the third vegetation type, a patchwork of scrub and low vegetation, analysis of transition matrices showed that the succession was non-independent, non-stationary and depended on more than one past state (high order). This succession was extrapolated by simulation. The results suggested that other vegetation types studied were discrete associations, not merely different stages in the same grazing-mediated sere. The transition matrix approach proved useful in helping to generate initial hypotheses, but became too cumbersome for a realistic model of this succession. An experimental approach will be better for dealing with problems identified from the transition models. We are extremely grateful to the staff of the Seychelles Islands Foundation and of their Aldabra Research Station for permission to work on the island and for their assistance in the field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00044990
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  • 4
    Electronic Resource
    Electronic Resource
    Spring grazing by sheep: effects on seasonal changes during early old field succession (1987)
    Springer
    Plant ecology 70 (1987), S. 33-43 
    Details
    ISSN: 1573-5052
    Keywords: Early secondary succession ; Grazing ; Restoration ; Sheep
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This paper describes early secondary succession on an old field on limestone released from cultivation four years previously. Seasonal changes in plant composition after spring grazing by sheep are compared with those in ungrazed controls. Grazed and ungrazed paddocks were laid out in Latin squares. Plants were sampled before and several times after grazing in April, at several spatial scales. Major changes in plant abundance and sward characters such as height and density persisted throughout the growing season. Annual herbs increased after grazing, but annual grasses declined, as did short-lived perennial herbs. Effects on perennial herbs were weak; perennial grasses usually increased but this depended on the species. This pattern confirms that sheep grazing affects the direction, as well as the rate of succession. Some effects, such as increases in biennial herbs and in species richness, were only evident at large scales of sampling, suggesting that they arose from changes in rare and widely dispersed species. Other species were affected at different spatial scales, and no one sampling method detected the full range of effects. These results indicate the potential power of manipulating grazing early in secondary succession for directing the course of community change, for conservation or other purposes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00040756
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