Using population matrix models to reduce the spread of wild carrot

Wild carrot was most likely introduced to North America from Europe as a weed. It has since spread to every state in the USA and has been declared invasive. Wild carrot can easily hybridize with cultivated carrots leading to the potential transfer of genes from the crop to wild carrot. Hybridization could become an issue if the genes transferred to wild carrot conferred a selective advantage and increased its competitiveness or invasiveness. A better understanding of the demography of wild carrot would permit the identification of the life history stages that most affect its population growth. Such knowledge would facilitate the design of management practices to best control its spread. In this study, we used data collected from wild carrot populations on reproduction, germination rate, overwinter survival and flowering rate to parameterize a stage structure model for a biennial lifecycle with a non-reproductive and a reproductive stage. Carrot populations were predicted to increase in size (λ>1), with growth rate (λ) of 1.9 when germination was low and 6.1 with high germination. Overwinter survival and flowering rate were the life history parameters that most affected population growth. Therefore, milder winter temperatures resulting from global warming could increase overwinter survival and the potential for spread of wild carrots. Effective management methods to control the spread of wild carrot and of the genes introduced into wild carrot populations should focus on lowering flowering rate and overwinter survival. For example, mowing should occur before flowering because our models predict that a single plant setting seeds could increase the population to 382 individuals within 3 years.