Arrival order among native plant functional groups does not affect invasibility of constructed dune communities.

Abstract

Different arrival order scenarios of native functional groups to a site may influence both resource use during development and final community structure. Arrival order may then indirectly influence community resistance to invasion. We present a mesocosm experiment of constructed coastal dune communities that monitored biotic and abiotic responses to different arrival orders of native functional groups. Constructed communities were compared with unplanted mesocosms. We then simulated a single invasion event by bitou (Chrysanthemoides monilifera ssp. rotundata), a dominant exotic shrub of coastal communities. We evaluated the hypothesis that plantings with simultaneous representation of grass, herb and shrub functional groups at the beginning of the experiment would more completely sequester resources and limit invasion than staggered plantings. Staggered plantings in turn would offer greater resource use and invasion resistance than unplanted mesocosms. Contrary to our expectations, there were few effects of arrival order on abiotic variables for the duration of the experiment and arrival order was unimportant in final community invasibility. All planted mesocosms supported significantly more invader germinants and significantly less invader abundance than unplanted mesocosms. Native functional group plantings may have a nurse effect during the invader germination and establishment phase and a competitive function during the invader juvenile and adult phase. Arrival order per se did not affect resource use and community invasibility in our mesocosm experiment. While grass, herb and shrub functional group plantings will not prevent invasion success in restored communities, they may limit final invader biomass.