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Site Assessment

Site Description
The wetland area being restored is a small seasonal pond, which was formed by the subsidence of the landfill and the shallow water table on the clay cap. The pond lies south of our prairie and shrub plots, adjacent to 2001 shrub plots 1 and 2. Each group is responsible for restoring a pie-shaped wedge equal to one seventh of this pond. Our group is responsible for restoring a wedge on the east side of this pond, the measurements of which are presented in the site plan (see Wetland Plan).

Hydrology
In the center of the pond the water depth was measured to be 28 cm on March 5, 2001. Rain seems to be the only source of water for the pond; therefore water levels should correlate to precipitation levels in this area. Since precipitation has been lower than average this year, the pond is probably smaller and shallower than it would be during a wet year. As the Table 2 and Figure 1 demonstrate, average Seattle precipitation is highest in the winter and lowest in the summer months. It is unknown how well the pond can retain water during the summer months. It has been reported to dry up completely by the end of the summer (Ewing 2001).

Soils
Like the rest of the Natural Area, the soils in this area consist of layers of compacted clay, sand, and gravel soils. The impervious clay layers prevent drainage of water from the pond in the winter months.

Existing Vegetation
Before we started our restoration plantings the vegetation in the pond consisted almost entirely of a single, low-growing rhizomatous grass species. We believe that the species may be Agrostis tenuis, but are uncertain about its identification. The grass extends all the way to the middle of the pond, providing strong evidence that the wetland dries out substantially during the summer. A small willow plant, that appeared to have been trimmed low by a mower was also found near the middle of the pond.

Restoration Goals and Rationale

The eventual goal of this project is to establish a functional, self-sustaining native wetland community on the site. We have begun working towards this lofty goal that will take several years to achieve. In order to reach this larger goal, we have developed a few specific goals to guide this year's class project:
1) Increase native plant diversity.
2) Increase wildlife habitat
3) Test the effects of water depth on plant growth and survival.

We have chosen other seasonal wetlands at the Union Bay Natural Area to serve as reference site for this project. Native vegetation has been established in Shoveler's Pond and other wetlands in the Natural Area both through natural recruitment and restoration activities (Ewing 2001). These wetlands have elements that resemble the Scirpus acutus, Cornus stolonifera-Salix spp.-Spiraea douglassi, and Salix spp. community types described by Linda Kunze (1994) in a DNR publication on wetland classification. The borders of the wetlands are ringed with woody vegetation, such as cottonwoods, willows, Oregon ashes, and red twig dogwoods. The deeper center of Shoveler's Pond is vegetated with emergent herbaceous vegetation, including bulrush and spikerush.

Increase native plant diversity
Our initial site assessment revealed only one native plant (a willow) growing in the wetland. By planting native wetland species on the site, we can accelerate the establishment of a native wetland community on the site.

Increase wildlife habitat
Wetland plants provide food and homes for a variety of bird, insect, mammal, and fish species. The willow, for example, has buds that are eaten by grouse and grosbeak, cavities in snags that are nested in by black-capped chickadees, and flowers that provide early spring nectar for honey bees (DOE 1993).

Test effects of water depth
So little is known about the hydrologic nature and other characteristics of our site, this year's goal is simply to run experiments on the capability of the site to support specific wetland species rather than to create a wetland habitat. Different plant species vary in their tolerance of flooding and drought. In particular, we are looking at the effect of depth on plant growth and survival. By assessing the results of our experiment, future groups will be better informed about how to go about successfully restoring the wetland site.

New Plantings and Experiments

We are testing the effect of depth or water availability on three woody wetland species: black cottonwood (Populus trichocarpa), Pacific willow (Salix lasiandra), and red twig dogwood (Cornus sericea). Two herbaceous species, bulrush (Scirpus acutus) and spikerush (Eleocharis palustris), are also being planted on the site to increase species diversity. These plants were chosen based on availability, potential for success, and wildlife and ecological value (DOE 1993). All species are suited to wetlands with mineral soils (DOE 1993), although there is some variation in depth requirements as is shown in Table 3.

We chose to use only woody species in our experiment, because these species will be easier to find and measure next year. The herbaceous species are dormant in the winter, and it would be difficult for next year's group to assess their survival. Black cottonwood, Pacific willow, and red twig dogwood are easily rooted from cuttings (DOE 1993), thus 36 whips of each woody species were cut from trees found within the Union Bay Natural Area. Plants obtained from local sites adapt with greater success (DOE 1993). Cuttings were at least 3/8 inches in diameter and were over the minimum height requirement of 18 inches. The tips and side branches were removed from the cuttings, as recommended in a plant propagation textbook (Hartmann, et al. 1990). Where possible, longer cuttings were obtained, as taller whips fair better through fluctuating water availability (DOE 1993).

The plantings were laid out along 3 rows parallel to the shore of the wetland. We planted four clusters of woody cuttings along each row (see Wetland Plan). Each cluster included nine cuttings with three cuttings of each of the three species (photo). Since we had a few leftover cuttings, 1 dogwood, 2 willows, and 5 cottonwoods were planted in a cluster at the center of the wetland. The remaining herbaceous species have been planted between the clusters in the deeper parts of the pond, not as part of the experiment, but simply to introduce the species to the wetland.

The depth of each cluster was measured on March 11, 200l. The depths measured from north to south along each row were:

Center: 21.0 cm
Row 1 (deep): 15.0, 14.5, 16.0, 14.7
Row 2 (medium): 8.7, 4.3, 8.3, 8.8
Row 3 (shallow): Saturated at surface throughout.

Due to the uneven surface of sediments in the wetland, the depths across each row vary slightly. This will be important in next year's assessments. These measurements will change over the seasons as the water level fluctuates.

Management Prescriptions

As was previously mentioned, the purpose of this experiment is not to establish a working wetland ecosystem, but to test the effect of water availability on specific species. Next year's assessment should measure survival and increment growth of the three species planted on our site. To assist with the interpretation of the survival data, we recommend using a Chi square Test of homogeneity to test the null hypothesis.

HO: There is no difference in survival between species planted at different water depths.
HA: Survival is different between species planted at different
water depths.

Increment growth should be tested for each depth by using a Kolmogorov-Smirnoff Test.

HO: increment growth is uniform across water depths
HA: increment growth is not uniform across water depths

Comparisons of increment growth between species should be compared using
a univariate anova with depth as a treatment.

HO: there is no difference in increment growth between species grown at different water depths.
HA: increment growth between species is not equal across all water depths.

If clear results can be determined, next year's group should either run tests on other species or begin to create a wetland habitat that mimics those found in nature. In order to have enough replicates in our treatments, our group has planted the cuttings very closely together. If many plants in each cluster start to grow, they will need to be thinned. If the results of this experiment are not clear, further tests on these species should be attempted. Perhaps the effect of distance between plants should be examined. It would also be beneficial to look at the water levels over the summer, but as this class will not be in session at that time, it is not guaranteed to happen.