The importance of soil seed banks to invasive plant species

The ability of an invasive plant species to overcome barriers to spread into new environments and traits that allow them to persist in these environments are the keys to invasion success. The capacity of introduced species to form soil seed banks can contribute to their invasiveness and expansion, yet few studies have addressed the role of seed banks in the long-term persistence of naturalized populations.

Seed banks can be considered transient if seed viability is shorter than one year or persistent if seeds remain viable for longer periods. The viability of seeds in seed banks is determined by environmental factors affecting seed germination and dormancy such as radiation level, temperature, and water availability. Increased knowledge of seed persistence in soil seed banks will improve modelling efforts to predict the risk of invasive species spread.

In their new study published in AoBP, Abbas et al. provide new empirical data from field research on spatial and temporal variation in characteristics of soil seed bank composition and size for invasive plant species. The plant species used in their study was the invasive cordgrass Spartina densiflora in invaded estuaries on two continents: on the Pacific Coast of California, USA and on the Atlantic Coast of Andalusia, Spain. It is native to southern South America but is now considered a noxious weed in North America and Europe.

On the Iberian Peninsula, S. densiflora formed transient seed banks, with germination rates reduced considerably within 1 year. In the Californian marshes, viable seeds persisted for at least 4 years though the germination percentage fell abruptly after the first year from 29 % to less than 5 % of remaining viable seeds. Total soil seed bank density increased with above-ground cover in both estuaries, pointing to the transient component of the seed bank as a critical component of vegetation dynamics during S. densiflora invasion. The study of Abbas et al. highlights the importance of evaluating seed banks when making invasive species management decision. Seed bank persistence may vary among invaded sites and can affect the timing and duration for desired management outcomes.