Abstract
Nutrient pulses can facilitate species establishment and spread in new habitats, particularly when one species more effectively uses that nutrient pulse. Biological differences in nutrient acquisition between native and exotic species may facilitate invasions into a variety of habitats including deciduous forest understories. Alliaria petiolata (Bieb.) Cavara & Grande is an important invader of deciduous forest understories throughout much of North America. These understory communities contain many species which perform the majority of their growth and reproduction before canopy closure in spring. Because A. petiolata is a wintergreen biennial that can be active during autumn and winter, it may utilize nutrients released from decaying leaf litter before its competitors. To investigate this we manipulated the timing of leaf litter addition (fall or spring) and experimentally simulated the nutrient pulse from decaying leaves using artificial fertilizer. To determine whether A. petiolata affected the abundance of understory competitors, we also removed A. petiolata from one treatment. A. petiolata that received early nutrients exhibited greater growth. Treatments receiving fall leaf litter or artificial nutrients had greater A. petiolata adult biomass than plots receiving spring nutrient additions (leaf litter or artificial nutrients). However, fall leaf litter addition had no effect on the richness of competitor species. Thus, wintergreen phenology may contribute to the spread of A. petiolata through deciduous forest understories, but may not explain community-level impacts of A. petiolata in deciduous forests.
Highlights
Invasive species pose a serious threat to biodiversity worldwide and have large economic and environmental costs (Mack et al, 2000; Pimentel, Zuniga & Morrison, 2005)
Above-ground biomass There was a highly significant difference among treatments in total above-ground biomass of A. petiolata at senescence in June 2007 (Table 2A) when initial density was included as a covariate (P < 0.001)
Total A. petiolata density was not significantly different among treatments (Table 3A) when plots were harvested in June (P = 0.39)
Summary
Invasive species pose a serious threat to biodiversity worldwide and have large economic and environmental costs (Mack et al, 2000; Pimentel, Zuniga & Morrison, 2005).
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