South Bay School Wetlands
South Bay Wetlands Learning Center
South Bay Wetlands Learning Center Restoration and Monitoring Plan
Prepared by Andrea Picart for South Bay Union School District, May 1998
COASTAL PRAIRIE/SCRUB RESTORATION
INTRODUCTION
The South Bay wetland is located north of South Bay Elementary School on Humboldt Bay in Eureka, California (Fig. 1). The freshwater wetland lies within an 8.5-acre triangle of land circumscribed by the South Bay school parking lot, South Broadway, and Purdue St. The Humane Society is located adjacent to the wetland in the southwest corner of the site, and a garage is situated in the northern corner of the triangle. The majority of the site consists of freshwater marsh dominated by soft rush (Juncus effusus) and sedge (Carex obnupta) with interspersed willow (Salix hookeriana) swamp. To the south, adjacent to the South Bay parking lot, is a disturbed area covered with a near monoculture of introduced, invasive Spanish heath (Erica lusitanica), and an upland meadow dominated by the introduced perennial sweet vernal grass (Anthoxanthum odoratum). Approximately 5.5 acres of wetland (with about .6 acres of interspersed upland) in the southern portion of the triangle are owned by Humboldt Area Foundation (HAF), who have agreed to allow South Bay School District use of the wetland for educational purposes. The Foundation plans to transfer title of the wetland to a non-profit entity to be created by the School District.
Although the South Bay wetland is a fragmented portion of a larger marsh system, it represents a relatively rare wetland type in this area and provides important ecological functions. The wetland is currently degraded by the presence of Spanish heath and other exotic plant species. The proposed project will enhance the current ecological values of the marsh by removing exotic heath, replacing it with an area of open water and/or freshwater marsh, and restoring the upland area to native coastal prairie/scrub.
Figure 1: Location of South Bay wetland, Humboldt County.
PHYSICAL CHARACTERISTICS
Humboldt Bay is located 30 miles from the junction of the Gorda, Pacific, and North American crustal plates, marking a highly active tectonic region with a number of northwest-southeast trending faults. Rocks formed from marine sediments have been uplifted and folded to form marine terraces (Barnhart et al. 1992). The Bay is divided into three subunits, Arcata Bay, South Bay, and Entrance Bay. The South Bay wetland is part of a system of marshes that at one time was connected with King Salmon Slough which has its outlet in South Bay. Historic maps from the 1850s show that this slough had associated salt and probably brackish marshes that extended some distance inland. The South Bay wetland is near the boundary of what is shown as marsh on the 1858 map (Fig. 2). Based on the location of old gulches to the east and south of the site, it appears that the site was on a slightly elevated terrace and at least at its southern end may have been out of tidal influence and possibly not even wetland. At least some of the site, to the north, is underlain by the Bayside silty clay loam, which is a very poorly-drained fine-textured soils typical of reclaimed salt marshes in the Humboldt Bay region (McLaughlin and Harradine 1965).
Figure 2: 1858 map with the approximate location of South Bay wetland.
By 1886 dikes had been constructed along the King Salmon slough (Fig. 3), eliminating salt water influence. The area was converted to agricultural use. A 1948 air photo shows the area cleared and grazed (Fig. 4). The construction of the freeway in 1963 may have further altered the hydrology of the area, possibly causing impoundment and increasing the amount of surface ponding and groundwater saturation. South Bay Elementary School was built in 1952, and the large parking area probably increased surface water runoff into the wetland.
Figure 3: 1886 map showing diked wetlands along King Salmon Slough.
Figure 4: 1948 air photo with approximate location of South Bay wetland.
WETLAND ECOLOGY
The South Bay wetland is classified by the National Wetland Inventory (NWI) as Palustrine Persistent Emergent Wetland. "Palustrine" wetlands are freshwater and non-tidal (Cowardin et al. 1979). The NWI mapping was done at a small scale that precluded subdividing the wetland further. The complex actually contains several different classes and subclasses of palustrine wetlands that are mapped at a larger scale in Fig. 5.
1. Palustrine Emergent Wetland (freshwater marsh).
Emergent wetlands are dominated by erect herbaceous vegetation. In our climatic zone most emergent marshes are of the subclass "persistent", i.e. the vegetation persists throughout winter months. There are three different plant associations present in the South Bay freshwater marsh. The driest areas, which rarely have surface water present, are dominated by soft rush (Juncus effusus), a tussock-forming species. In some places, aster (Aster chilensis), a horticultural species that is sometimes invasive, has become dominant. Slightly wetter areas are dominated by slough sedge (Carex obnupta). In the northern and eastern portion of the site are the wettest areas, which are inundated during the rainy season. These areas are dominated by water parsley (Oenanthe sarmentosa) and introduced buttercup (Ranunculus repens).
2. Palustrine Scrub-shrub Wetland (freshwater swamp).
a) Broad-leaved deciduous. In the northeast and southeast corners are stands of Hooker's willow (Salix hookeriana), which are not tall enough to qualify as forested wetland. In other areas, this wetland type is dominated by California blackberry (Rubus ursinus). Occasional cascara (Rhamnus purshiana), red alder (Alnus rubra), wax myrtle (Myrica californica), and Sitka spruce (Picea sitchensis) occur throughout the site. In a few places, introduced Himalaya berry (Rubus discolor) has taken hold, and an infestation of introduced English ivy (Hedera helix) has become established in the willows near the parking lot.
b) Needle-leaved evergreen. A .6-acre area adjacent to the school parking lot is dominated by the highly invasive Spanish heath (Erica lusitanica). The term "heather" is often used for this species, but technically refers to other genera. Spanish heath aggressively outcompetes native species, spreading by epicormic shoots and creating a dense litter layer of fallen needles that acidifies the soil.
3. Upland meadow.
In the southwest corner of the site is a .6-acre upland meadow dominated by introduced sweet vernal grass (Anthoxanthum odoratum). Invasive bull thistle (Cirsium vulgare) is also present. Upland species occurring on the meadow and interspersed on higher areas throughout the complex include Douglas-fir (Pseudotsuga menziesii), black huckleberry (Vaccinium ovatum), yarrow (Achillea millefolium), sword fern (Polystichum munitum), and introduced Monterey pine (Pinus radiata).
ECOLOGICAL VALUES
The wetlands around Humboldt Bay underwent a drastic conversion beginning in 1901 with the completion of the Northwestern Pacific Railroad. The railroad served to dike the tidal marshes surrounding the bay, and tidegates were placed at the entrances of sloughs. Most of the tidal salt marshes were converted to seasonal agricultural wetlands, and others were filled or drained (Barnhart et al. 1992). The actual extent of the bay has been reduced from 27,000 to 18,000 acres, and 90% of salt marshes have been lost through conversion and filling (Shapiro and Associates 1980). In a 1984 inventory of wetland types around Humboldt Bay, it was estimated that only 243 acres of freshwater (non-agricultural) marsh remain in the region (Humboldt Bay Working Group 1984). Given the scarcity of this wetland type, the South Bay wetland can be considered a rare and valuable natural resource. Wetlands, once treated as "wastelands" and valued only for their potential conversion to upland, have been recognized as having many inherent values (Mitsch and Gosselink1986). In addition to providing excellent habitat for wildlife including mammals, birds, reptiles, amphibians, fish, and invertebrates, freshwater wetlands provide flood protection by storing surface water, and improve water quality by absorbing organic and inorganic nutrients and toxic materials. On a more subjective level, wetlands provide important aesthetic and recreational values and open space. The South Bay wetland, while already of high natural value, can be further enhanced by restoration of natural values and enhancement of educational opportunities.
RESTORATION PLAN
The following plan calls for the removal of exotic species (including the infestation of Spanish heath), the creation of a freshwater pond and/or marsh (with seasonal to permanent inundation), and the planting of additional willows, alders, and spruce on the wetland's perimeter. The goal of the restoration project is to enhance the natural values of the South Bay wetland, especially wildlife values, natural diversity, and educational values. The wetland already has high inherent values and is utilized by a rich diversity of wildlife including raptors, migrating song birds, mammals, and amphibians. The addition of a seasonal or permanent freshwater pond will enhance the wetlands use by waterfowl and other aquatic wildlife. The addition of this new wetland type and its associated plants, along with increased wildlife use, will improve the biological diversity of the site. Plant diversity will be improved and maintained by the removal of exotic species including Spanish heath. The accessibility of this site to students of South Bay Union School District makes it an ideal site for education. Tree planting on the perimeter will serve to reduce noise impacts and improve aesthetics by screening the site from nearby roadways. The District also intends to construct educational improvements and safety measures such as fencing, but these improvements are not covered by this plan.
POND/MARSH EXCAVATION
Spanish heath (Erica lusitanica) is native to damp heaths of southwestern Europe from Portugal to Southwestern France (Tutin et al. 1972). In California it is cultivated as an ornamental, and has become naturalized and invasive in coastal Humboldt County (Hickman 1993). The stand of Spanish heath in the South Bay wetland may have dispersed from ornamental plantings that are present on the school grounds or along the highway. Although this particular species of heath has not received much study in the U.S., it has been observed to sprout from shallow roots after a disturbance such as cutting, a common regeneration strategy among Mediterranean shrubs (Montserrat 1997). The ability to resprout, in combination with a well-developed root system and extremely abundant seed production make this species very difficult to control. Other species in the genus require a low pH and a moist organic layer in order for seedlings to develop (Sansen and Koedam 1996). Although no studies have been done in this country, it is hypothesized that the deep litter layer caused by leaf drop of this species acidifies the soil, discouraging the establishment of other species. At the South Bay wetland Erica occurs as a dense monotype with a springy layer of bare, poorly decomposed peat beneath a near closed canopy.
Because of the regenerative ability of heath, and its abundant seed shed, cutting is not sufficient as a method of removal. The California Department of Parks and Recreation has been controlling a population of this species at Elk Head and is still removing plants after four years. At Elk Head, the population was relatively new and had not yet displaced native plants or formed a peat layer. At South Bay wetland, the plants have been present long enough to develop a layer of acidic peat that will be detrimental to the establishment of native marsh plants. As a method of eliminating Erica while simultaneously improving the habitat values of the wetland, conversion of the Erica stand to freshwater pond and/or marsh is proposed (Figure 6). The desired outcome is to lower the surface elevation sufficiently to cause year-round ponding in the center of the excavated area, with a fringing area of seasonal marsh. Until groundwater testing can be conducted this summer, we will be uncertain as to whether the summer water table is high enough to cause permanent ponding. If not, the entire excavated are will function as a seasonal marsh, with ponding occurring during winter months. The excavation will result in the removal of acidic peat and any plant parts that could otherwise regenerate. Because the soil will contain seed and root fragments, it will be disposed of at the city landfill. Excavation work will be done by the National Guard in August 1998 as a training exercise. The heath will be removed by the California Conservation Corps prior to excavation to help dry the site and make it easier for the National Guard to see the boundaries of the excavation. The Corps will also remove any other heath growing on the school grounds. Pending the outcome of summer water table testing, the proposed maximum depth of excavation will be 6 feet below surface level. The pond's maximum dimensions are roughly 325 ft. x 150 ft . The sloped area will extend approximately 50 feet from the perimeter of the excavation, resulting in a slope of 12%.
POND/MARSH PLANTING
Planting will be carried out in September-October 1998. Planting will not be initiated until the rainy season has become established in order to promote survival of transplanted materials. Because it not yet known what the hydrology of the site will be, planting plans may be modified to reflect the hydrology. Assuming that the center of the pond remains inundated year round, native aquatic plants collected from nearby wetland sites will be introduced (Fig. 6). Species will be selected from the following: duckweed (Lemna spp.), pondweed (Potamogeton foliusus), water starwort (Callitriche heterohylla), and mosquito-fern (Azolla filiculoides). Both duckweed and mosquito fern are floating plants that can simply be placed on the surface. Water startwort and pondweed will be planted towards the center of the pond when depth is at a seasonal minimum. The peripheral areas will not be inundated at the start of the growing season, and will be planted with rushes, sedges, and wetland forbs that are already characteristic of the wetland. These will include water parsely (Oenanthe sarmentosa) in deeper/wetter areas, slough sedge (Carex obnupta) in intermediate areas, and soft rush (Juncus leseurii) in drier areas. All three species are rhizomatous and can be collected as divisions with rhizomes attached. Collection will be from the existing marsh, with harvesting done such that impacts are minimized and dispersed. A total of approximately .3 acres (of the total excavated area of .6 acres) will be planted, at a density of 1 plug per 4ft2 (24-inch centers), requiring a total of 1,256 plugs. Plants will be collected as larger plugs (6 in x 6 in) that can be subdivided into 9 individual planting plugs. This will necessitate the collection of 46 6-inch plugs of each species, yielding 419 plugs per species to plant. When collected, leaves willl be trimmed to reduce transplant stress. Plants will be collected and transplanted the same day.
If it is determined during water table testing that the excavated area will receive only seasonal ponding, then the planting area will be increased to the entire .6 acres, with plants zoned from rushes in drier areas to water parsely in lower areas). If permanent water is present, mosquito fish will be introduced to the pond to help control mosquitos.
ENGLISH IVY ERADICATION
English ivy (Hedera helix), a member of the Ginseng family (Araliaceae), is a woody, evergreen vine native to Europe but widely cultivated in California and other mild-winter regions. Juvenile plants are climbing, and have lobed leaves. Plants will not reproduce as a groundcover, but once the plant has climbed, flowering individuals become more shrub-like with unlobed leaves. Berries and leaves are toxic when eaten (Hickman 1993) and in rare cases may cause contact dermatitis. English ivy usually becomes established in disturbed areas of forest. It is an aggressive invader that may kill the trees it climbs, and smothers understory plants. English ivy will be eradicated in summer 1998 by hand pulling and cutting, with care taken to avoid allergenic reactions. On the ground, the plant is shallow-rooted and easily pulled up by hand or with pliers (Freshwater 1991). Pulled plants will be piled off of the wetland on school grounds and will be burned after material has dried. Climbing plants can be killed by cutting the vine at waist height. Follow up checks will be done every six months until plants are extirpated.
MONTEREY PINE REMOVAL
Monterey pine (Pinus radiata), a popular landscaping tree in the Humboldt Bay area, is a closed-cone pine native to the central coast of California. Although not native to the site, the presence of coniferous trees adds structural diversity, of value to wildlife, to the South Bay wetlands. To retain this benefit, these pines will be replaced by the native conifer Sitka spruce (Picea sitchensis), which historically grew on moist bottomlands around Humboldt Bay. Young trees will be purchased from a nursery or collected from a nearby site in places where trees are dense and thinning is desirable. If purchased from a nursery trees should be of local derivation. The introduction of non-local genes can cause trees to be poorly adapted to local conditions, and/or can introduce genetic contamination to local populations.
PERIMETER PLANTINGS
Those portions of the perimeter of the wetland that are within the ownership of Humboldt Area Foundation and do not already support woody vegetation will be planted with a mixture of willow (Salix hookeriana), alder (Alnus rubra), and Sitka spruce (Picea sitchensis) (Fig. 6). This will serve the purposes of enhancing habitat for migratory songbirds, creating a visual and noise screen from surrounding roadways, and reducing the likelihood of unauthorized use of the wetland. Planting will be done in Fall 1998 after the rainy season has become established. Willow and alders will be harvested from existing trees on the site after autumn leaf drop. Cuttings should be at least 3 ft in length, with basal cuts made at a 45 degree angle. Cuttings will be spaced 3 feet apart. An estimated 300 ft. of perimeter will be planted, requiring 100 cuttings (50 willow and 50 alder). Spruce will be obtained as in the manner described above, and will be planted every 10 feet in intervals between the willlow and alder, requiring 30 trees. The spruce are shade tolerant and will eventually grow above the alder and willow, creating year-round screening.
COASTAL PRAIRIE/SCRUB RESTORATION
Native coastal prairies are rare, due to the preponderance of non-native annual and perennial grasses in California. Grasslands are maintained naturally by fire or grazing, and in managed areas mowing is sometimes substituted. A combination of native grasses and coastal scrub species will be planted in the upland area, which due to its small size is not suitable for strict maintenance as a coastal prairie. First, invasive non-native bull thistle (Cirsium vulgare) and Himalayaberry (Rubus discolor) will be removed from the site in Summer 1998 (before seed set of thistles). Thistles can be cut at the base of the rosette and do not need to be pulled up by the roots, but the Himalayaberry must be grubbed out. Non-native grasses will be mowed with a weed-eater in May 1998 prior to this summer's seed set. In the fall the upland will be plowed under using a rototiller. Native shrubs will be retained. Large clumps of grass will be removed, piled, and burned. The site will be left until the following spring, to encourage germination of non-natives from the seedbank. In summer of 1999 non-natives will be removed again, and native grasses and forbs will be planted. Tufted hairgrass (Deschampsia cespitosa), California brome (Bromus carinatus), red fescue (Festuca rubra), and seathrift (Armeria maritima), will be collected locally as divisions (including roots/rhizomes) or seed or, if purchased, stock will be from the Humboldt Bay region. If collected as seed, plants will be grown in flats and planted when they have at least 5 true leaves. Grasses will be planted on 2 ft. centers (1 per 4 ft2) over an area of approximately .3 acres (Fig. 6), requiring approximately 3,200 seedlings or plugs. IA total of 355 divisions will be collected and subdivided into 9 plugs each, consisting of at least 2 culms. The 355 divisions will be equally distributed among the species collected, and species will be planted in a clustered pattern (i.e. clusters of same species). Native shrubs of evergreen huckleberry (Vaccinium ovatum), salal (Gaultheria shallon), twinberry (Lonicera involucrata), and cascara (Rhamnus purshiana) will be planted as transplants. Shrubs will be planted over a .3-acre area (Fig. 6) on 3 ft. centers, requiring a total of approximately 1,500 transplants or cuttings. These will be collected locally, with appropriate permits and under the guidance of a qualified botanist, or will be purchased as local stock. Shrubs will be planted in Fall 1999, and remedial planting will be done in Fall 2000 to compensate for mortality.
In this and all planting areas fertilizer will not be used as it will encourage weedy plants. Watering may be used to help promote survival of transplants if weather conditions dictate. Weeding of non-native grasses will be continued on an annual basis for at least five years, and remedial planting will be done if survival if less than 60% overall, or less than 80% in any localized area. Weeding will be done annually for at least 5 years.
MONITORING PLAN
Monitoring will be conducted to determine the success of restoration efforts and as a basis for ongoing adaptive management. Two vegetation macroplots will be established in representative areas of the excavated freshwater marsh area and the restored coastal prairie/scrub area. Each macroplots will consist of a 100 permanent baseline marked with rebar. Thirty 50-meter transects will extend perpendicular to the baseline at randomly selected intervals. The location of these transects will vary from year to year. Along each transect, one-meter plots will be spaced every 5 meters. Each plot will consist of quantitative vegetation data on cover collected as point data (i.e. a gridded quadrat will be used and the species occuring at each intersection recorded). This will enable the estimation of cover values by species within each macroplot.
Permanent photo points will also be established at marked intervals along the existing chain link fence along the south boundary of the marsh. Points will be photographed quarterly for the first year, using a 50 mm lens. In the second through fifth year, points will be photographed annually in summer. To evaluate the utility of the wetland to wildlife, students at Humboldt State University and College of the Redwoods will be solicited to carry out senior projects.
OTHER CONSIDERATIONS
This plan covers the ecological restoration aspects of the proposed South Bay wetland restoration. The District is also proposing to establish educational use of the wetland through a boardwalk interpretive trail, and to fence those boundaries of the site that are within their ownership and not already fenced. The combination of fencing and boardwalks will enhance the safety of the site for student use. The boardwalk will reduce the potential contact with ticks, and the fence and locked gate will prevent trespass and reduce the likelihood of accidents. Approval for these improvements is being sought through a coastal development permit and conditional use permit through the County Planning Department.
REFERENCES CITED
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Freshwater, V. 1991. Control of English ivy (Hedera helix) in Sherbrooke forest-a practical experience. Plant Protection Quarterly 6:127.
Hickman, J.C. 1993. Editor. The Jepson manual: higher plans of California. U.C. Press, Berkeley, California.
Humboldt Bay Working Group. 1984. Humboldt Bay wetland mitigation needs and restoration goals study. Humboldt County Public Works Department, Eureka, California.
McLaughlin, J. and F. Harradine. 1965. Soils of western Humboldt County. Department of Soils and Plant Nutrition, University of California, Davis.
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Sawyer, J.O. and T. Keeler-Wolf. 1995. A manual of California vegetation. California Native Plant Society, Sacramento.
Shapiro and Associates. 1980. Humboldt Bay wetlands review and baylands analysis. U.S. Army Corps of Engineers, San Francisco District.
Tutin, T.G., V.H. Heywood, N.A. Burges, D.M. Moore, D.H. Valentine, S.M. Walters, and D.A. Webb. Editors. Flora Europaea, Volume 3: Diapensiaceae to Myoporaceae. Cambridge University Press.
U.S. Fish and Wildlife Service. 1987. National Wetland Inventory map for Fields Landing Quadrangle. Portland, Oregon.