Invasion resistance and persistence: established plants win,even with disturbance and high propagule pressure |
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Authors: | Email author" target="_blank">Christopher?M?McGloneEmail author Carolyn?Hull?Sieg Thomas?E?Kolb |
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Institution: | (1) Ecological Restoration Institute, Northern Arizona University, Box 15017, Flagstaff, AZ 86011, USA;(2) School of Forestry, Northern Arizona University, Box 15018, Flagstaff, AZ 86011, USA;(3) USDA Forest Service, Rocky Mountain Research Station, 2500 S Pine Knoll Dr, Flagstaff, AZ 86001, USA |
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Abstract: | Disturbances and propagule pressure are key mechanisms in plant community resistance to invasion, as well as persistence of
invasions. Few studies, however, have experimentally tested the interaction of these two mechanisms. We initiated a study
in a southwestern ponderosa pine (Pinus ponderosa Laws.)/bunch grass system to determine the susceptibility of remnant native plant communities to cheatgrass (Bromus tectorum L.) invasion, and persistence of cheatgrass in invaded areas. We used a 2 × 2 factorial design consisting of two levels of
aboveground biomass removal and two levels of reciprocal seeding. We seeded cheatgrass seeds in native plots and a native
seed mixture in cheatgrass plots. Two biomass removal disturbances and sowing seeds over 3 years did not reverse cheatgrass
dominance in invaded plots or native grass dominance in non-invaded native plots. Our results suggest that two factors dictated
the persistence of the resident communities. First, bottlebrush squirreltail (Elymus elymoides (Raf.) Swezey) was the dominant native herbaceous species on the study site. This species is typically a poor competitor
with cheatgrass as a seedling, but is a strong competitor when mature. Second, differences in pretreatment levels of plant-available
soil nitrogen and phosphorus may have favored the dominant species in each community. Annual species typically require higher
levels of plant-available soil nutrients than perennial plants. This trend was observed in the annual cheatgrass community
and perennial native community. Our study shows that established plants and soil properties can buffer the influences of disturbance
and elevated propagule pressure on cheatgrass invasion. |
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