- In 1978, a 22 ha diked pasture in the Salmon River
estuary, Oregon, was restored to tidal influence. The
goal was to re-establish the original salt marsh. The
pasture had been diked for 17 years and was dominated by
upland pasture species. The site had also subsided by 30-
40 cm relative to surrounding, undiked high salt marsh.
This study evaluates the restoration process from 1980 to
1988. Data on species cover and frequency, surface
elevation, soil texture, soil-water salinity, and standing
biomass were collected at 49 permanent plots established
in 1978 by Mitchell (1981)
After dike removal, there was a rapid die-off of
pasture species. Potentilla pacitica and Agrostis alba
remained as residuals at higher tidal elevations but
diminished or disappeared at lower elevations. Newly
barren flats were revegetated by colonizing species that
were mostly absent in 1978, but comprised 31% cover by 1980 and 91% cover by 1988. Ephemeral colonizers
Spergularia marina, Puccinellia purnila and Cotula
coronopifolia never became abundant and did not persist.
Persistent colonizers dominated the restoration site by
1988; of particular importance are Salicornia virqinica,
Distichlis spicata, and especially Carex lyngbyei (67%
The behavior of residuals and colonizers are clearly
expressed in 1988 plant conuiiunities. Mid-transitional
marsh elevations (1.21 - 1.50 m MLLW) support a residual
Potentilla/Agrostis community. Due to surface subsidence,
restoration has been to low rather than high salt marsh.
Two colonizing communities, Salicornia/Distichlis and
Carex, occupy the low-transitional marsh zone (1.01 - 1.35
m MLLW). The widespread Carex community is a nearly
monotypic (98% cover) stand of Carex lyngbyei.
Although the Carex and Salicornia/Distichlis
communities occupy a similar elevational range, the latter
community is situated in closer proximity to the ocean and
sand spit at the mouth of the estuary. Both Salicornia
and Distichlis are positively correlated with substrate
sand (r=0.48, p=0.O01; r=0.56, p=0.000 respectively) and
salinity (r=0.59, p=0.002; r8=O.66, p=0.000). Carex has a
weak negative correlation with both sand (r8= -0.42,
p=0.005) and salinity (r8= -0.423, p=0.003).
In 1988, peak standing biomass of the restored marsh was 1645 g/m2, more than twice that of the 1978 pasture
bioinass (758 g/m2).
Results of this study suggest that the diked pasture
has been restored to a functioning salt marsh system. It
has not, however, been restored to its pre-impact
condition. Lowered marsh surface elevation as a result of
diking has had a major effect on restoration results, and
will continue to exert a strong influence on hydrology and
vegetation. While changes in species composition and
biomass production were most rapid between 1980 and 1984,
significant changes continued to occur between 1984 and
1988, the last year reported in this study.