Sunday, July 29, 2018

The Carpeted Dunes of Oregon's Central Coast: The Principle of Unintended Consequences

So how about this plush carpeting on a sand dune? What? It doesn't look like a sand dune? Some people are such skeptics....let's find a trail...
There's the sand, with three or four feet of grassroots on either side.

We are at the north end of Oregon Dunes National Recreation Area near the estuary of the Siuslaw River in Florence. The grass growing on and covering these dunes is European Beachgrass (Ammophila arenaria), an invasive plant that was introduced in the 1920s. It was an excellent example of the principle of unintended consequences. The apparent solution of one problem resulted in a number of others.
There are some very specific problems associated with living along the Oregon coast between Florence and Coos Bay. The forty-mile stretch of sandy beaches and dunes ranges up to three miles inland and any roads or towns built there must contend with the instability of windblown sand and dune migration. The introduction of the European Beachgrass was seen as a way of stabilizing the dunes. In a sense, the grass did the job too well.
The grass has deep roots and spreads rapidly, overwhelming and replacing the native plant species. By anchoring the sand just above the shoreline, new sand blowing in from the beach is trapped in the grasses, causing the foredunes to grow higher and higher. Little of the new sand on the beach gets past the foredune system, and a form of stability is achieved.
Deflation basin in the south jetty area of the Siuslaw River

Without the infusion of new sand, the area inland of the foredune system becomes starved of sediment. The wind blows just as much and carries what sand there is farther inland, sometimes burying the forests growing there. What had been a dune complex with occasional islands of trees and vegetation becomes a deflation basin, a place where sand is removed to the local groundwater level. The wet ground and ponds found there become a stable surface where a thick forest can start growing. The dunes are stabilized to an extent, but much of the dune environment with all the native plants and animals is lost (see the comparison below).

Another problem with many invasive species is that they don't tend to stay where they are supposed to. The desired level of control was achieved in some places, but the grass continued to spread far beyond, invading areas like the Oregon Dunes where open dune environments were still desired. The beach grass is now found on coasts from Southern California to British Columbia. And it is extremely difficult to control or remove.

The grass can be pulled manually (by volunteers most of the time) but roots are always left deep in the sand and the grass soon sprouts again. The shoots have to be pulled seven or eight times before the grass is truly gone. It's hard work. Bulldozers and other mechanical means can be used, but the expenses are high. Some herbicides can be used as well, but the disruptions to the native species can be profound. All in all it is a sticky problem.
The coastal sand dune environment is a fascinating place to visit, and there are many recreational opportunities, but there are also opportunities to volunteer and help achieve a return to the natural conditions that existed before humans tried to mold the landscape to their liking. One place to start is the Oregon Dunes Restoration Collaborative which works to preserve and rehabilitate the dune system.

No comments: