Gorchov, David L. .
Plant invasion in systems characterized by discrete distrubance: alternative hypotheses.
Many invasions of exotic plant species are associated with disturbance, supporting the ‘disturbance hypothesis’ for community invasibility. For systems characterized by discrete disturbances (e.g., treefall gaps) as opposed to stand-wide disturbances, I identify two mechanisms (hypotheses) for how disturbance can promote invasion. Under ‘disturbed site invasion,’ disturbance creates sites where individuals colonize, but the invader does not expand throughout the stand. This should occur where both establishment and survival to reproductive age require conditions associated with disturbance. If seeds disperse and persist in the seed bank, new recruits will appear in new disturbances elsewhere in the stand, but the invader will remain an ephemeral ‘gap species.’ Under the second alternative, ‘disturbance-mediated stand invasion,’ disturbance enables the invader to pervade the entire stand, although this may require several generations. This is predicted in systems where either establishment or survival (but not both) are limited to disturbed sites. If individuals require new disturbance to establish, but survive post-disturbance conditions, the population will spread as new disturbances are colonized by propagules. If disturbance is not required for establishment, but is required for survival to reproduction, then disturbance enables population growth to exceed that due to propagule pressure. If neither establishment nor survival is limited to disturbances, then invasion is not disturbance-dependent. Understanding which mechanism is operative has important management implications. For example, disturbance-mediated stand invasion implies that invasions can be halted by inspecting recent disturbances and removing colonists. I outline a research protocol to efficiently test these hypotheses. For several invaders of eastern North America deciduous forest, available data permit some inference. Establishment of Rubus phoenicolasius and Lonicera maackii is limited to disturbed sites, but established individuals survive undisturbed conditions, supporting disturbance-mediated stand invasion. In contrast, both Alliaria petiolata and Acer platanoides are not dependent on disturbance for either establishment or survival.
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1 - Miami University, Department of Botany, Oxford, Ohio, 45056, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Council Chambers/SUB
Date: Monday, July 28th, 2008
Time: 8:00 AM