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Site Assessment

Site Description
Our group assessed the restoration of prairie plot 1 and took actions to maintain and enhance the fledgling prairie community established here.   Prairie plot 1 measures 40 ft x 100 ft and is the northernmost of the prairie research plots (see Prairie Plan).  Wahkiakum Lane borders the north side of the site and Parking Lot E5 borders the west side.  The entire site is slightly sloped with a southwest-facing aspect.  The lower west side of the site is inundated with water.  The prairie plots have been the subject of Restoration Ecology student group projects for the last 3 consecutive years.  Previous groups have established mounds on the site and planted species native to the South Puget Sound prairies.

Soil
For over 30 years, the site of the prairie restoration plots was a gravel parking lot.  In order to keep the lot level as the landfill subsided, gravel was continually being added to the site (Ewing 2001).  In 1997 the eastern 40% of the lot was deep ripped to prepare the site for a restoration ecology class project (Brown et al. 1998).  The soil in this area now consists of an unknown depth of gravel overlying the soil landfill cap.  A shallow water table keeps the soil very wet in the winter, but during the warm summer months, the gravel becomes very dry.  The 1998 class group created mounds by raking up the gravel in order to provide a drier, more stressful growing environment where native prairie species might be more competitive (Brown et al. 1998).  They covered half the mounds with a thin layer of topsoil to test the effect of topsoil vs. gravel on native and invasive plant growth.

Existing Vegetation
Before 1998, the site had no vegetation, because it was a parking lot.  The gravel soils of this former parking lot share common characteristics with gravelly glacial outwash soils of the South Puget Sound prairies.  The similarity of soils and the management of maintaining open vegetation in the Natural Area led to the decision to try to recreate a prairie community on these plots.  Extensive descriptions of the prairie community and  a more detailed rationale for creating the prairie community on this site can be found in previous UHF 473 group project reports.

The 1998 UHF 473 class group initiated planting several native prairie species on the site.  Further plantings were performed by the 1999 and 2000 groups.  Several non-native invasive species have also invaded the site since the reclamation.  Since the prairie restoration plots were surrounded to the east and north by weedy pasture grasses, Himalayan blackberry, and Scotch broom, these invasions are not surprising.

Analysis of Previous Years' Projects

An extensive analysis of last years project may be found in the Appendix.  The main conclusions of this analysis are summarized below.  Activities on the prairie plots have focused on two main goals: increasing native plant cover and diversity and reducing weed cover.

Analysis of Experiments
When the success of plants on gravel mounds was compared to the success of plants on mounds covered with topsoil, no conclusive patterns were seen.  Mulching with straw from pasture grasses was found to increase weed colonization on the mounds.  In a controlled experiment where treatments included hand weeding and the selective use of Round-up herbicide, the control mounds had the highest native cover and lowest weed cover.

Last year's experiment included four treatments to control weeds on the mounds: mowing, mowing and herbicide, herbicide, and a control.  A statistical analysis of the results of this study yielded no significant effect.  However, herbicide use was found to decrease native cover and weed cover.  Mowing had little effect on either native or weed cover.  Mowing and herbicide decreased native cover, but had a lower effect on weed cover.  None of these treatments yielded the desired result of decreasing weed cover without impacting native cover.  The use of a broad spectrum herbicide (Round-up) rather than a selective herbicide (such as Poast) is part of the problem.

Survival of Plantings
Idaho fescue (Festuca idahoensis), strawberry (Fragaria virginiana), and cinquefoil (Potentilla gracilis) have all survived and expanded on our prairie plots.  All other species have decreased in numbers.  The success of broadcast seeding of fescue is uncertain, because mature, seed-producing plants could also be contributing to seedling establishment.

Herbivory
We were unable to determine how important herbivory is at our site.  Out of all of our work days on the site, we only observed a goose in our plot once.  Goose droppings are not common on our site, indicating that herbivory is probably low.

Restoration Goals and Rationale

Like groups past, our main goals for the prairie plot are to:
1) Increase the percent cover of native species on the mounds.
2) Increase native species diversity.
3) Decrease the percent cover of weeds.
Our main focus in the prairie plots was on maintaining and enhancing the prairie community on this site.  Rather than starting a new experiment on this site we felt it would be wiser to differentially ameliorate the plantings and target specific weeds for removal.

Increase cover of natives
Jeanette Dorner (1999) found that a healthy Idaho fescue-dominated community in the South Sound prairies will have 82% cover of native plants, 64% cover of invasives, and 5% bare ground.  (The sum of these numbers exceeds 100% because of overlapping foliage).  The percent cover of native plants on the mounds currently ranges from 30 to 54%.  Increasing the cover of native plants should decrease spaces available for weeds to invade.

Increase native species diversity
Dorner found 21 forbs growing in the Idaho fescue-dominated community of the South Sound prairies.  Our restoration plots have a much lower diversity, with only 7 forb species present.  In addition, only two of these forb species (cinquefoil and strawberry) have established successfully and not decreased in numbers on the mounds.  In order to increase species diversity it will be necessary to increase in numbers the less successful species and add new species.

Decrease the percent cover of weeds
Non-native invasive plants compete with prairie plants for light water and nutrients.  Woody weeds, such as Himalayan blackberry (Rubus discolor) and Scotch broom (Cytisus scoparius), have the potential to fundamentally alter prairie systems by shading out herbaceous prairie plants and, in the case of Scotch broom, by altering soil nitrogen levels.  Colonial bentgrass (Agrostis tenuis), a rhizomatous grass disrupts prairie systems by filling in the spaces between fescue bunches and squeezing out native forbs.

We noticed several weeds on the site that were present in small numbers.  These species may be newly invading the site and could have the potential to expand their populations.  Eliminating new weeds before they multiply and establish is an important part of preventative weed management (William et al. 2000).

Alterations to Previous Year's Project

Last year's group established four different weed control treatments on the mounds.  After thoroughly analyzing changes in percent cover of weeds and natives on the mounds, our group concluded that none of the treatments were preferable over the control.  By weeding the mounds this year and adding new plants, our group is preventing any analysis of the long term effects of last year's weed treatments in the future.  We decided that the long term effects of the weed control treatments would probably be negligible.
       
Weed Removal
Woody weed species that threaten to shade out native vegetation such as Scotch broom and Himalayan blackberry were removed from each mound.  Weeds present in low numbers were removed to prevent their future expansion.

Mulching
Applying mulch is a commonly used cultural technique to minimize the impact of weeds (Williams et al. 2000).  In order to effectively suppress weed growth within the site, mulch was distributed to the intermound areas and along the path on the north side of the site (photo). Unfortunately, by doing this, some native plants that had begun to spread throughout the inner mounds were also covered with mulch. However, the total percent cover of native vegetation versus invading weed species within these areas was quite low. Larger fescues and cinquefoils in the intermound areas were transplanted to neighboring mounds. 

The Alpha Group initiated mulching in the intermound areas of plot 1 last year, but the mulch was not thick enough to suppress many weeds.  This year, we had an overwhelming excess of mulch on our shrub restoration plot, so we had plenty to spread thickly in the intermound areas.  Mulching may not help return the site to a prairie community, but it will hold the intermound areas in a relatively weed free state so they don't serve as a source of weed propagules.  Once the native prairie populations on the mounds become better established, we recommend that more attention be focused on restoring the prairie community to the intermound areas.

New Plantings

New plantings were installed on the site to serve two purposes: increasing native cover and increasing native diversity.  See table below for specific planting information.

Increasing native cover
Idaho fescue and cinqefoil were strategically planted on the mounds with fewer plants in order to increase native plant cover.  These species have a history of successfully establishing and expanding their populations on the mounds.

Increasing native plant diversity
Several species have only sporadically survived on the mounds.  Our group reasoned that the surviving individuals are growing in favorable microhabitats for that species.  For the species that have not succeeded as well on the mounds, such as Aster curtus, Eriophyllum lanatum, Prunella vulgaris, and Ranunculus occidentalis, we targeted new plantings around existing survivors.  We are hoping that by bolstering their populations in favorable microhabitats, we may get better survival rates (see Table 1).

We also planted new species that have not been planted on this site before to each of the mounds to increase species diversity.  In addition, we planted two bare root shrub species to the wet, western portion of our site (Rosa pisocarpa and Physocarpus capitatus).

Management Prescriptions

Maintain boundaries
Keeping in mind the objectives and goals for the pre-existing prairie site, certain management prescriptions are necessary. Disturbances from outside sources, such as people and animals wandering onto the site, will be detrimental to native vegetation establishing itself within the site. Some of the plants are difficult to recognize as viable plants especially during the dormant season. This is why it is important that people realize that this is a restoration site in progress. In order to prevent outside disturbances, interpretive signs are posted and the Wahkiakum Lane side of the site has been roped off. 

Continue weed control
Even in the native prairies in the South Puget Sound, weed invasions are a major problem.  Weed management may always need to be necessary to maintain the prairie plant community on this site.  A thick layer of mulch should be maintained in the intermound areas until this area can be a focus for restoration.  Monitoring the arrival of new weeds is another important element of weed management.

The selective grass herbicide Poast has shown promise in the South Sound Prairies for controlling colonial bentgrass.  It is not effective to spray Poast during the winter dormant season; the plant must be actively growing to be affected.  We recommend that the mounds with bentgrass infestations on the west side of our site be sprayed with Poast this spring.

Continue adding native species
The mounds on our site still don't approach the plant diversity of the native South Sound prairies.  Inplanting will need to be continued in order to increase diversity.