Demographic evaluation of a herbivory-sensitive perennial bunchgrass: does it possess an Achilles heel? Academic Article uri icon

abstract

  • Plant and tiller demography of a C4 perennial bunchgrass, Eriochloa sericea, were evaluated to define specific traits that contribute to its sensitivity to herbivory by domestic grazers. We tested three hypotheses: (1) defoliation adversely impacts tiller recruitment to a greater extent than mortality, (2) tiller recruitment and/or mortality are particularly sensitive to defoliation at the time of culm elongation, and (3) synchronous tiller recruitment contributes to a meristematic limitation which constrains growth following defoliation. Demographic variables were monitored on permanently marked plants and tillers that were defoliated at various frequencies and stages of phenological development for two successive years. Hypotheses one and three were rejected because defoliation adversely impacted per capita tiller mortality to a greater extent than per capita tiller recruitment and tiller recruitment occurred throughout the spring and summer, rather than synchronously. Apical meristem elevation in vegetative tillers did not extend beyond 5 mm above the soil surface and the proportion of reproductive tillers did not exceed 10% of the total number of tillers. Low values for both morphological attributes indicate that they did not contribute to a meristematic limitation constraining leaf growth. Hypothesis two was not rejected because cumulative, but not per capita, tiller recruitment was reduced to a greater extent by defoliation during culm elongation than during the pre-culm or post-culm stage. Plants that received multiple defoliations exhibited the greatest decline in basal area and tiller number compared to undefoliated plants, and only the undefoliated plants and plants defoliated during the pre-culm stage recruited a sufficient number of tillers to offset tiller mortality. In spite of the adverse effects of two of the four defoliation regimes, we were unable to identify a specific trait (i.e., Achilles heel) within this species that contributed to a meristematic limitation and herbivory-sensitivity. An alternative interpretation of herbivory-sensitivity is proposed which emphasizes the involvement of more subtle extrinsic mechanisms, including herbivore-mediated competitive interactions and drought-herbivory interactions. Assessment of herbivory resistance based on the 'specific trait approach' fails to recognize and address the importance of extrinsic mechanisms associated with herbivore-induced processes at higher ecological scales.

published proceedings

  • OIKOS

author list (cited authors)

  • Hendon, B. C., & Briske, D. D.

citation count

  • 8

complete list of authors

  • Hendon, BC||Briske, DD

publication date

  • October 1997

publisher

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