Population Dynamics and long-term management of an invasive plant hybrid: a periodical model approach

Background/Question/Methods

: A common goal in invasion ecology as well as in the management of invasive species is finding the most cost-effective control strategies. Demography is a valuable tool to evaluate different management techniques, as the finite population growth rate (lambda) indicates whether a population is increasing or decreasing. Additional analyses such as elasticity and Life Table Response Experiments yield information regarding which stages should be affected for reducing population growth or which treatments work better to decrease lambda.In this study we asked how demography might help us find a long term management strategy for an invasive plant hybrid, Kalanchoe ×houghtonii (Mother of millions, Crassulaceae) by using a matrix model approach to compare three management techniques: mechanical removal (clearance), herbicide and the combination of both, in two different seasons (dry and rainy). The study was conducted in a population located in Central Mexico from 2013 to 2015, where 28 plots (50cm x 50cm) were established and monitored over three years. For long-term projections, we used a periodical model approach considering three different scenarios simulating management every 5, 10 and 15 years.

Results/Conclusions

: A combination of clearance and herbicide use during the rainy season yielded lambdas below 1, indicating a population decrease in the three modelled scenarios. The control plots showed the population was increasing at a 36% yearly rate, thus confirming the invasive potential of this hybrid in arid and semi-arid zones of central Mexico. Transient dynamic metrics such as amplification and attenuation were consistent with those of other successful invasives. Besides using a combination of management methods in a convenient season, we recommend restoration actions such as revegetation with a native species (Pilea Microphylla, Urticaceae) to prevent further invasions of K. ×houghtonii or other invasive plants that threaten the diversity of arid systems, which in Mexico are megadiverse. Periodic models allow the incorporation of cycles in the study of population dynamics with the benefit of not only capturing natural seasonal fluctuation but also for applied purposes as in this study. We hope more demographic studies of invasive species can inform better management decisions in the future