In 2010, I initiated a long-term study that investigated the effort required to eradicate the invasive biennial, garlic mustard (Alliaria petiolata). The population was confined to a 17 ha area within a broader forest landscape, with no known other populations within 5 km. Individual plants were counted, staged, weighed, and removed each year for 8 years. I developed a stochastic matrix population model with harvesting to determine the minimum effort that would likely result in sustained population decline. In year 7 of the study, a microburst resulted in significant blowdown of canopy trees in half of the study area.
Results/Conclusions
The harvest model revealed with moderate year-to-year variation in vital rates, a sustained population decline could likely be maintained with 90% harvest of adult plants prior to seed production. Between 2010-2016, the number of individual garlic mustard plants declined from ~8000 to 536. The detection of newly-established satellite patches of plants decreased from over 100% per year to 2%. Wet weight biomass of harvested plants declined from 9.1 kg to 1.3 kg. However, these gains were eliminated after the microburst. In 2017, we detected and removed over 14,000 individuals weighing 212 kg. No stochastic model runs produced the results observed in 2017. In the death match between an incorrectly estimated stochastic matrix population model and a stochastic disturbance event, the stochastic event emerged victorious.