Murren, C.J.; Purvis, K.G.; Glasgow, D.; Messervy, J.; Penrod, M., and Strand, A.E., 2014. Investigating lag phase and invasion potential of Vitex rotundifolia: a coastal dune exotic.
After initial establishment in nonnative environments, exotic species are often found in low numbers for long periods of time. After a lag phase, a transition to an exponential growth phase is characteristic. A broad question remains: Can we identify factors that contribute to the lag phase or assess the potential for additional invasion? Our approach employed a case study of V. rotundifolia (beach vitex), a nonnative dune plant introduced in the late 1980s to North and South Carolina. We performed manipulative and observational experiments on the sexual and asexual reproductive ecology, mating system, seed ecology, and pollination ecology to assess the possibility of additional invasion potential and to gain an understanding of potential among population variation and among site ecological variation that could contribute to a transition from lag to exponential spread phases. We found that vegetative reproduction, sexual reproduction, and viable seed set rates are high, and there is future potential for spread through vegetative reproduction as not all the ovules set seed. Pollinator activity varied by year and was consistent with increased fruit and seed set, indicating a likely mechanism contributing to current sexual reproductive success. Germination rate was low, but given the high numbers of seeds produced per square meter, we estimate an average of 13 new germinants m−2 y−1. On the basis of our observations, we found the potential for increased reproductive success and increased invasion potential. Management practices that minimize vegetative expansion from nearby sites and through seed dispersal are the highest priority.