Introduction, establishment and spread ofSpartina patens on Cox Island, siuslaw Estuary, Oregon

Abstract

We employed sequential aerial photographs from 1939 to 1981 to document establishment and exponential spread ofSpartina patens on Cox Island the only recorded Oregon locality for this east coast species.Spartina patens, growing in distinctive circular patches, now occupies more than 3000 m2 with no diminished expansion rate. Eight marsh communities are aggregated into four generalized marsh types: Low Marsh, Middle Marsh, High Marsh, and Transition Marsh.Spartina patens invades theDeschampsia caespitosa-Scirpus maritimus community, the most open (7.7 percent “bare ground”) of the Middle Marsh communities.Spartina patch elevation ranges from 1.83 to 2.05 m above MLLW comparable to its indigenous east coast tidal position. Proximate expansion of individual circular patches is by clonal growth. The role of seed and vegetative propagule dispersal in establishment of new colonies has not been determined. Once established,S. patens in Oregon performs comparably to its performance in Delaware and New England as shown by its general growth form, average above-ground live biomass of 329 gdw m2, above-ground dead biomass of 411 gdw m2, and a below-ground to above-ground biomass ratio of 4.80.