Disturbance governs dominance of an invasive forb in a temporary wetland |
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Authors: | J N Price P J Berney D Ryder R D B Whalley C L Gross |
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Institution: | (1) Ecosystem Management, University of New England, Armidale, NSW, 2351, Australia;(2) Department of Botany, University of New England, Armidale, NSW, 2351, Australia;(3) Present address: Institute of Ecology and Earth Sciences, University of Tartu, Tartu, 51005, Estonia |
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Abstract: | Dominance of invasive species is often assumed to be due to a superior ability to acquire resources. However, dominance in
plant communities can arise through multiple interacting mechanisms, including disturbance. Inter-specific competition can
be strongly affected by abiotic conditions, which can determine the outcome of competitive interactions. We evaluated competition
and disturbance as mechanisms governing dominance of Phyla canescens (hereafter lippia), an invasive perennial forb from South America, in Paspalum distichum (perennial grass, hereafter water couch) meadows in floodplain wetlands of eastern Australia. Water couch meadows (in the
study area) are listed under the Ramsar Convention due to their significance as habitat for migratory waterbirds. In the field,
we monitored patterns of vegetation boundaries between the two species in response to flooding. Under controlled glasshouse
conditions, we explored competitive interactions between the native water couch and lippia subject to different soil moisture/inundation
regimes. We did this using a pairwise factorial glasshouse experiment that manipulated neighbor density (9 treatments) and
soil moisture/inundation (4 treatments). In the field trial, inundation increased the cover of water couch. Under more controlled
conditions, the invader had a competitive effect on the native species only under dry soil conditions, and was strongly inhibited
by inundation. This suggests that dry conditions favor the growth of the invader and wetter (more historical) conditions favor
the native grass. In this system, invader dominance is governed by altered disturbance regimes which give the invader a competitive
advantage over the native species. |
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