Competition and Facilitation in the Recruitment of Seedlings in Patagonian Steppe

Aguiar, Martı́n R.; Soriano, A.; Sala, Osvaldo E.

doi:10.2307/2389772

Cited by 141 publications

(144 citation statements)

References 15 publications

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“…In the mature phase, as completeness becomes high enough, shrub facilitation fails to show its effects because grasses already established exert a strong competition for soil water (Soriano & Sala 1986;Aguiar et al 1992). The major role of grass competition was emphasized by a manipulative experiment which demonstrated that adult shrubs compete minimally with adult grasses in the Patagonian steppe (Sala etal.…”

Section: Discussionmentioning

confidence: 99%

Patch structure and dynamics in a Patagonian arid steppe

1994

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Two patch types were recognized in the Occidental District of the Patagonian arid steppe: i) shrubs encircled by a ring of tussock grasses, and ii) tracts of scattered tussocks. Completeness of the ring of grasses around the three dominant shrubs was a function of shrub size. Average completeness was 62, 71 and 83 ~o, respectively for the three dominant shrubs (Senecio filaginoides, Mulinum spinosum and Adesmia campestris). A model for the cyclic dynamics of the two patch types was proposed. It includes a building phase (grass ring construction), a mature phase (maximum ring completeness) and a degenerate phase. In this last phase, triggered by shrub death, completeness of the ring progressively decreases until remnant grasses become undistinguishable from the scattered tussocks patch type. Ring formation occurred independently of shrub species. Grass species were differentially associated to the two patch types and to rings of different shrub species. Cyclical patch dynamics influenced the pattern of resource utilization, since the shrub-ring patch, with a share of only 18 ~o of cover, contributed 44~o of the total primary productivity.Abbreviations." Shrub-ring patch (ST), M = asymptote, maximum completeness, D = parameter related to the initial lag, B = rate of increase in ring completeness, z = shape parameter, r = radius.Nomenclature: The taxa names are given according to Correa, M.N., 1971Correa, M.N., -1984. Flora Patag6nica. Colecci6n Cientifica del I.N.T.A.

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Section: Discussionmentioning

confidence: 99%

Patch structure and dynamics in a Patagonian arid steppe

1994

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“…Before transplanting, we dug a hole 0.20 m in diameter by 0.30 m deep, and the extracted soil was sieved to remove any roots and stones. Reduced competition treatment was achieved with a fine mesh cloth that was fitted before replacing the sieved soil in the pits, which functioned as a barrier to growth of roots of neighbour plants under Poa target plants (Aguiar, Soriano & Sala 1992;Graff, Aguiar & Chaneton 2007). Transplants with competition had no mesh around the soil core.…”

Section: F I E L D E X P E R I M E N T : S E X -R E L a T E D I N T Ementioning

confidence: 99%

Changes in sex ratios of a dioecious grass with grazing intensity: the interplay between gender traits, neighbour interactions and spatial patterns

2013

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Summary1. Dioecious plants frequently face sex-related resource allocation trade-offs. Differential traits of male and female plants can have important consequences that influence their direct and indirect interactions with neighbours and herbivores. 2. Gender differences in traits have been considered to be inherently linked to sex-biased ratios along environmental stress gradients. However, the mechanisms behind the variation in sex ratios with increasing biotic stress remain elusive. 3. We linked the results of process-based field experiments with fine-scale spatial patterns of naturally established plants (both sexes) at different grazing intensities. We demonstrated that slowgrowing females were better defended against insects and small mammals but were more susceptible than males to competition from neighbours. 4. In large-herbivore exclosures, we found that sex-biased spatial patterns at the microsite scale can be predicted from gender-specific traits, with females more segregated from competitors (unpalatable grasses) than males. Traits related to growth/defence trade-off in females, coupled with their higher competition costs than males, suggest that gender dimorphism in traits can directly influence species interactions and spatial organization. 5. In the presence of large herbivores, female individuals were preferentially browsed despite their larger investment in antiherbivore compounds. The greater distance of females from unpalatable competitors was the main determinant of female-biased consumption by domestic herbivores. Females growing close to neighbours successfully eluded browsing but also faced competition. Scaling up to a population level, population sex ratios drift from female-to male-bias with increasing domestic grazing intensity. 6. Synthesis: The sexual dimorphism in traits of a dioecious bunchgrass results in differential herbivory by natural enemies, differential competitive ability and differential spatial distribution of sexes. Domestic grazers disrupt this balance by shifting species interactions and their spatial organization. Changes in dioecious plant populations towards male-biased sex ratios with grazing intensity could not be predicted solely by gender-specific traits.

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“…Although shrubs may deplete grass production through competition, they may favour soil, litter and seed accumulation (Aguiar et al, 1992;Castelli et al, 1993). In some overgrazed areas, good forage species are only found under the protection of shrubs and they may be the seed source for eventual recovery.…”

Section: Introductionmentioning

confidence: 99%