Removal of the Invasive Marine Grass Spartina denisflora
Restoring Denman’s sea asparagus – seashore saltgrass – dune grass shoreline ecosystem involves the removal of a South American import, Dense flower cordgrass Spartina densiflora. This species of Spartina grows high on the foreshore, often right at the seaweed line. On Denman, Spartina occupies the same shallow flat, sand, gravel or shale-shelf habitat as many existing native plant and animal species. Spartina identification and removal in Baynes Sound has been active since at least 2008 and members of the BC Spartina Working Group and the Coastal Invasive Plant Committee have been visiting Denman.
The manual removal of Spartina from some of the known Spartina-areas on Denman’s shoreline commenced mid-September of 2013. That year seven Denman islanders worked to remove two huge dumpster loads of this invasive marine grass and completed the mapping of plant locations on the remaining shoreline. Further plant removal work was done in 2014. Members of the Spartina Working Group put on a workshop in January 2014 organized by the Denman Conservancy Association.
As with any invasive species assessment, a rational review of the new species’ impacts, the feasibility and acceptability of any restoration action and the potential to remain free to the species in the future is important. The following are some of the reasons pro and con around Spartina removal.
Reasons for Spartina Removal
- Grows over sea asparagus, saltgrass and other existing foreshore plants, killing them.
- Tall and very dense colony of stems, eliminates home habitat of marine animals that lived in former plants and prevents others such as native shore birds from foraging, forage fish from laying eggs etc.
- Hydrology of shoreline is altered, can affect geomorphology of lower foreshore and sub-tidal area e.g. negatively affecting eel grass beds.
- Has ability to completely cover high foreshore, creating thick dense saltmarsh ~1m high, restricting marine access, as well as changing shoreline appearance.
- There is a strong long-term commitment to removal by governments and marine stewardship groups from California to BC.
- Denman has a relatively small amount of this grass so manual removal and future shoreline monitoring is realistic. Plants manually removed by upland owners on Denman over 3 years ago have not re-grown.
- Creates a new ecosystem of nearly Spartina monoculture
- Creates a new type of habitat, already spiders make webs among the tall stems, sparrows and juncos feed on seeds and perch on stems, other wildlife use is currently un-studied.
- Spartina may assist in damping incoming waves and protecting the high tide-line.
- Tall tough stately plants have attractive seed plumes.
Reports of recent work are available (pdf) Report Spartina 2016