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

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 similar to 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.

Automated summary

Understanding the dispersal and establishment patterns of invasive plant species, such as sea spurge, is crucial for controlling and eradicating their populations. The study on E. paralias populations in New Zealand revealed that one adult plant led to the establishment of a considerable number of healthy plants at different incursion sites, indicating the species' ability to form large populations and pose a threat to coastal environments. However, the study also found that the populations were concentrated around the adult plant in the early stages of invasion, providing opportunities for seed bank removal. Early detection and removal of new populations will be essential for successful eradication programs.