Measuring the effective dispersal of an emerging coastal weed, Euphorbia paralias (sea spurge), to help inform its eradication

Abstract

Understanding dispersal and establishment patterns of invasive plant species is critical information to help control and eradicate their populations. Euphorbia paralias, sea spurge, is a highly invasive weed that can be a serious threat to coastal environments. Two recent incursions of E. paralias on New Zealand’s coastline consisted of one reproductive adult surrounded by several hundred juveniles, providing the opportunity to gather effective dispersal distance data for this species. Using these two separate populations effective dispersal distances curves were created for E. paralias. It was found one adult led to the establishment of 213 healthy plants at NZ’s southern-most incursion and 484 healthy plants at the northern-most incursion. All plants were subsequently removed from the site. The maximum effective dispersal distance of 15.8 m on land for E. paralias was larger than would be predicted by the majority of trait-based dispersal distance models and the estimate of ~ 2 m in the literature. These results show that E. paralias can establish large healthy populations, making it a considerable threat to coastal environments. However, populations around an adult plant are fairly concentrated at the very early stages of invasion (90% of offspring < 5.5 m from the adult) providing opportunities to remove the seed bank at incursion sites. Early detection of E. paralias populations using comprehensive surveillance and removal of any new populations (seed and establishing plants) will be essential components for the success in any eradication programme for sea spurge.