Are forests of different successional age equally susceptible to invasion by nonnative invasive plant species (nnis)? We examined the frequency, abundance, and local spatial distribution of nnis in forty deciduous forest stands in SE Ohio. Stands formed a chronosequence ranging from 0-20 to 140-160 years since canopy closure.
Nnis were most frequent and most abundant in stands <40 years old and declined rapidly thereafter, although some species (notably Rosa multiflora, Glechoma hederacea, and Ranunculus abortivus) were also found in stands as old as 140 - 160 years. In young stands (20-40 years) many nnis distributions showed spatial aggregation corresponding to local light availability. In older stands (80-100 years) nnis species were spatially aggregated, but showed little correlation with environmental variables. Species may be separated into two groups: those characteristic of open habitats (probably residual from a pre-forest successional stage) and those with a degree of shade tolerance (which are likely to have arrived after canopy closure). In young stands, spatial distribution appears to reflect heterogeneity of light in the progress of canopy closure, whereas in older stands distribution appears to be caused by stochastic dispersal events. Long-established forest appears to offer less opportunity to nnis than young forest, although species responses are individualistic.