Competition and Abiotic Stress Among Trees and Shrubs in Northwest Colorado

Welden, Charles W.; Slauson, William L.; Ward, Richard T.

doi:10.2307/1941654

Cited by 42 publications

(51 citation statements)

References 39 publications

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“…Wilson and Keddy 1986;Campbell and Grime 1992;Turkington et al 1993;Bonser and Reader 1995;Gaudet and Keddy 1995;Kadmon 1995) or to have no relation to productivity (e.g. Welden et al 1988;Di Tomasso and Aarssen 1991;Wilson and Shay 1990;Wilson and Tilman 1993;Cahill 1999). Our results show a clear relationship between community above-ground phytomass and competition intensity when the latter is calculated using population-level measures, such as number of shoots.…”

Section: Resultscontrasting

confidence: 43%

“…Weiner 1980;Fowler 1982;Berendse 1983;Johansson and Keddy 1991). The third study addressing the importance of competition (Welden et al 1988) established no relationship either between competition intensity and water stress, or between importance of competition and water stress for shrubs in northwestern Colorado. The effect of productivity on interactions between species was not studied directly in any of these papers, although water stress may be related to productivity.…”

Section: Discussionmentioning

confidence: 99%

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Competition intensity and its importance: results of field experiments with Anthoxanthum odoratum

et al. 2000

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The effect of community productivity on competition was studied in 82 permanent plots using two removal experiments with the rhizomatous perennial grass Anthoxanthum odoratum. The removal of neighbouring plants had a positive effect on the number of shoots and total above-ground biomass of Anthoxanthum but no significant effect on mean shoot biomass. The relative competition intensity coefficient (RCI) calculated from these data showed that competition intensity increased with increasing community productivity. Similarly, the importance of competition and the difference between local maximum and local average population density increased with increasing community productivity. We concluded that for Anthoxanthum the impact of competition is greater in high-productivity areas and that competition reduces population density. No evidence was found supporting the importance of positive interactions between plants in tundra areas.

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Section: Resultscontrasting

confidence: 43%

Section: Discussionmentioning

confidence: 99%

Competition intensity and its importance: results of field experiments with Anthoxanthum odoratum

et al. 2000

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“…In a comparison of three plant species C imp decreased with fertility but it was suggested that competitive importance was dependent on the ability of the species to tolerate low resource availability (Gaucherand et al 2006). Sammul et al (2000), using a different calculation of competitive importance, reported a correlation between both C int and C imp when competition was calculated using the number of shoots rather than biomass, and Welden et al (1988) detected no relationship between importance or intensity and a water stress gradient for desert shrubs. We observed a reduction in competitive importance due to clipping under the high resource conditions for F. campestris, which further supports arguments that competition in CSR theory is best measured with this index because the measure of competition declines when additional processes are in place.…”

Section: Competitive Intensity and Competitive Importancementioning

confidence: 99%

Using three pairs of competitive indices to test for changes in plant competition under different resource and disturbance levels

Carlyle¹,

Fraser²,

Turkington³

2010

Journal of Vegetation Science

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Questions: How do different resource and disturbance levels interact to affect competition? How do different indices of competition change the interpretation of how competition changes under different resource and disturbance conditions? Location: Greenhouse, Thompson Rivers University, Kamloops, British Columbia, Canada. Methods: Three pairs of indices that have been used to differentiate the predictions of Grime (CSR) and Tilman's (R Ã ) theories were used to assess competition on two species of temperate bunchgrass, (Pseudorogeneria spicata and Festuca campestris) grown in a greenhouse on stress and disturbance gradients. Stress was created by manipulating the amount of water (high, low) and concentration of nutrient solution (high, low) added to pots, while disturbance was created by clipping (clipped, unclipped) in a fully factorial design. Plants were grown individually or with a single neighbour. The three pairs of indices were: (1) absolute and relative competition; (2) competitive effect and response; and, (3) competitive importance and intensity. Results: Absolute competition and competitive importance were the only indices responsive to the resource gradient, which supports CSR theory, and also the only ones to record an effect of disturbance on the strength of competition -under high resource conditions. The other indices showed few responses along the gradients, which supports R Ã theory. Measures of competitive effect and response did not differentiate the two theories. Conclusion: We show that some indices of competition show a decline with increased stress and disturbance, while other indices do not. Therefore, it is necessary to choose a competition index appropriate to the question being asked. Competitive importance and absolute competition were responsive to changes in stress and disturbance, while the other indices were not.Keywords: Absolute and relative competition; Clipping; Competitive effect and response; CSR strategy theory; Drought; Festuca campestris; Importance and intensity of competition; Nutrient availability; Pseudoroegneria spicata; R Ã theory. Nomenclature: Douglas et al. (1994).Abbreviations: C ab 5 absolute competition; C int 5 competitive intensity; C imp 5 competitive importance; C e 5 competitive effect; C r 5 competitive response.

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“…However, recent meta-analysis suggests that some results will be unexpected and largely inconsistent with this hypothesis (Goldberg et al 1999;Maestre et al 2005). The effects of competition in arid plant communities can be inferred from the study of the relationship between distance and size of neighbouring plants (Pielou 1962;Fowler 1986;Welden et al 1988;Wilson 1991;Briones et al 1996). The hypothesis is that competition between neighbours results in density-dependent growth and mortality; thus, closely spaced plants will be small and have low survivorship (Pielou 1962;Fowler 1986).…”

Section: Introductionmentioning

confidence: 99%

Spatial Associations, Size–Distance Relationships and Population Structure of Two Dominant Life Forms in a Semiarid Enclave of the Venezuelan Andes

Larrea-Alcázar

Soriano

2006

Plant Ecol

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The role of three thorny legume species as nurse plants and competitive relationships with columnar cacti were evaluated in a semiarid enclave of the Venezuelan Andes. Abundance and size of three columnar cacti species (Stenocereus griseus, Cereus repandus and Pilosocereus tillianus) under isolated shrubs of three thorny legumes species (Prosopis juliflora, Acacia farnesiana and A. macracantha) were recorded and compared with open areas. Using size -distance data we inferred the intensity of intra-and interspecific competition between both life forms in a ''cardonal'' (xeric zone) and ''espinar'' (mesic zone) of the enclave. Sixty-one columnar cacti were found beneath the three thorny legume species (92%), while only 5 cactus individuals were found in open areas (8%). Comparison of observed and expected number of cactus individuals shows that S. griseus and C. repandus are significantly associated with isolated shrubs of A. farnesiana and A. macracantha. Although P. juliflora contributed more than 40% of the total legume plant cover, the number of columnar cacti under its isolated shrubs was significantly lower than would be expected by chance. In all, 19 of 21 possible plant -plant combinations between and within columnar cacti and legume shrubs were recorded (espinar: 18, cardonal: 13, common combinations: 12). In both zones, intra-and interspecific combinations among columnar cacti species were relatively high (positive correlation between the sum of neighbour plant sizes and the distances separating them). Our results strongly suggest, at least for case of S. griseus and C. repandus, that these columnar cacti species require nurse plants for their establishment. The results on interference need still support from further research. We discuss the effects of plant -plant positive interactions on natural regeneration of these columnar cacti.

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Competition and Abiotic Stress Among Trees and Shrubs in Northwest Colorado

Cited by 42 publications

References 39 publications

Competition intensity and its importance: results of field experiments with Anthoxanthum odoratum

Competition intensity and its importance: results of field experiments with Anthoxanthum odoratum

Using three pairs of competitive indices to test for changes in plant competition under different resource and disturbance levels

Spatial Associations, Size–Distance Relationships and Population Structure of Two Dominant Life Forms in a Semiarid Enclave of the Venezuelan Andes

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