TESTS FOR NONEQUILIBRIUM, INSTABILITY, AND STABILIZING PROCESSES IN SEMIARID PLANT COMMUNITIES

TESTS FOR NONEQUILIBRIUM, INSTABILITY, AND STABILIZING PROCESSES IN SEMIARID PLANT COMMUNITIES Models of semiarid vegetation dynamics incorporating concepts of equilibrium and stability have been largely replaced by nonequilibrium models in recent years. However, neither equilibrium nor disequilibrium and neither stability nor instability have been formally demonstrated. Most records of semiarid vegetation are inadequate for conclusive tests. We tested for equilibrium at seven study sites in six locations and vegetation types, in grazed semiarid grassland in central Otago, New Zealand, using data collected twice annually over 5––13 yr. Some sites showed overall directional change in composition over time, but others appeared to fluctuate about an average equilibrium state. At one site, an instantaneous perturbation experiment was used to test formally for stability, and to seek evidence for intrinsic stabilizing processes. In this experiment, three herbicide treatments removed or decreased different components of the community, and recovery and convergence with the untreated control was monitored over time. Although all exotic species increased or rapidly re-invaded the treated plots, many native species failed to re-invade, and treatments had not recovered by 194 wk after perturbation. We conclude that the vegetation is not stable, but that some stabilizing processes are evident. Contrary to some nonequilibrium theory, we observed strong competitive interactions between species. We suggest that New Zealand semiarid vegetation exists on a continuum between equilibrium and nonequilibrium dynamics. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Ecology Ecological Society of America

TESTS FOR NONEQUILIBRIUM, INSTABILITY, AND STABILIZING PROCESSES IN SEMIARID PLANT COMMUNITIES

Ecology, Volume 83 (3) – Mar 1, 2002

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Publisher
Ecological Society of America
Copyright
Copyright © 2002 by the Ecological Society of America
Subject
Regular Article
ISSN
0012-9658
DOI
10.1890/0012-9658%282002%29083%5B0809:TFNIAS%5D2.0.CO%3B2
Publisher site
See Article on Publisher Site

Abstract

Models of semiarid vegetation dynamics incorporating concepts of equilibrium and stability have been largely replaced by nonequilibrium models in recent years. However, neither equilibrium nor disequilibrium and neither stability nor instability have been formally demonstrated. Most records of semiarid vegetation are inadequate for conclusive tests. We tested for equilibrium at seven study sites in six locations and vegetation types, in grazed semiarid grassland in central Otago, New Zealand, using data collected twice annually over 5––13 yr. Some sites showed overall directional change in composition over time, but others appeared to fluctuate about an average equilibrium state. At one site, an instantaneous perturbation experiment was used to test formally for stability, and to seek evidence for intrinsic stabilizing processes. In this experiment, three herbicide treatments removed or decreased different components of the community, and recovery and convergence with the untreated control was monitored over time. Although all exotic species increased or rapidly re-invaded the treated plots, many native species failed to re-invade, and treatments had not recovered by 194 wk after perturbation. We conclude that the vegetation is not stable, but that some stabilizing processes are evident. Contrary to some nonequilibrium theory, we observed strong competitive interactions between species. We suggest that New Zealand semiarid vegetation exists on a continuum between equilibrium and nonequilibrium dynamics.

Journal

EcologyEcological Society of America

Published: Mar 1, 2002

Keywords: competitive interactions ; equilibrium ; fluctuation ; nonequilibrium ; recovery from perturbation ; selective species removal ; semiarid grassland ; New Zealand ; stability ; theoretical model

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