PNW 98 Session - Full AbstractsPNW 98 Session - Full AbstractsThe purpose of this research was to compare growth (height increase) and
survival of four hand-planted wetland species (Carex stipata, Juncus
ensifolius, Scirpus acutus, and Sparganium emersum ) among three different
soil types along a hydrologic gradient at the King County Pilot Wetland
Mitigation Bank Site. These soil types are a salvaged peat, commercial
topsoil, and existing soil on project site (fill material).Seven 3 x 3 m
plots were established in each soil type along a hydrologic gradient.
Sixteen individuals of each species were hand-planted in each plot.
Regression equations were constructed to analyze differences among the
three soil types. Growth in the topsoil and fill had a linear relationship
with water levels while growth in the salvage peat showed a unimodal
response curve indicating a different treatment affect than the other soil
types. Predicted levels of growth were highest in the salvage peat at
medium (-5 cm) and low (-20 cm) water levels and lowest at high (10 cm)
water levels for all species except Juncus ensifolius. Growth in the
fill was higher at all water levels than the topsoil for Juncus ensifolius.
Although not significant, predicted levels of growth were highest under
high water levels in the topsoil for Scirpus acutus and Carex stipata
and were significant for Sparganium emersum than the other soil types.
Percent survival in the salvage peat had a unimodal response curve for
Scirpus acutus and Sparganium emersum . Under high water levels, the fill
exhibited the highest survival rates while the topsoil showed the lowest
(except Sparganium emersum ) for all species.
Species response is highly variable, however the results suggest that the
salvage peat would be most effective under saturated or intermittently
flooded conditions, where plant growth was shown to be highest for all
species. Under permanently flooded conditions survival was best in the
fill, suggesting that a very fine dense substrate be used in areas of
permanent inundation. Under these same conditions, the topsoil showed the
lowest levels of survival for most species but had higher growth rates
(not always significant) for the plants that did survive. Thus, if survival
could be increased, the results suggest that the topsoil would be most
beneficial under flooded conditions. The topsoil exhibited the strongest
relationship between survival and hydrology suggesting that this soil has
less water holding capacity than the other soil types and may be susceptible
to stress under drought conditions. Therefore the use of topsoil may be
limited to areas where hydrology is highly predictable.