Our New Native Bioswale: Urban Restoration in Collaboration With the Watershed Stewards Program

Outside of our Urban Forestry Education Center at Martial Cottle Park is a shallow channel that borders our plot. At two points there are drains where run-off and stormwater enter and are directed to the bay. The water that manages to percolate into the soil enters the watershed by way of groundwater. There is a missing piece to this picture.

Impermeable surfaces like the asphalt walking paths next to this channel allow water to quickly run off and enter storm drains, redirecting water that could otherwise be put back into the watershed and restore groundwater levels. However, there are infrastructure solutions that can be easily installed, such as bioswales. For the past few months, we have been planning the installation of a bioswale outside of our Education Center and it will finally become a reality this Spring with help from the California Conservation Corps' Watershed Stewards Program!

What is a bioswale?

A bioswale, also called a bio-retention or biofiltration site, is a vegetated, sloped channel where large amounts of water flow are slowed and directed with purpose. This slowing allows the water to percolate into the soil to be filtered by the vegetation. This filtration removes excess nutrients, such as nitrates and phosphates, which can come from agricultural sources as well as urban fertilizer use. Abundant nutrients may sound like a positive, however excessive levels of nutrients result in a process known as eutrophication. High levels of nutrients result in the uncontrolled growth of plants and microorganisms such as algae. When these plants and microorganisms decay, the amount of bacteria needed to break them down consumes the dissolved oxygen in the water, creating what is often referred to as "dead zones'. These dead zones are stripped of dissolved oxygen which suffocates animals such as fish. Other contaminants such as metals and pesticides are also removed from the water by plants. Green infrastructure like bioswales helps protect and restore watersheds through this process of filtration and percolation.

Example of a California Native bioswale (Image source)

What is a watershed?

A watershed, also known as a drainage basin or catchment, is an area where rainfall and melted snow are channeled into groundwater, creeks, streams, and rivers where they eventually drain into estuaries, bays, and the ocean (NOAA). A watershed connects different ecosystems, including the urban environment, together from the highest mountain tops whose glacial peaks slowly melt down and travel through the landscape to the depths of the ocean. The paths of creeks and rivers are also critical habitat corridors that species such as salmon and terrestrial animals like bobcats and deer need to move their range and complete important points in their life cycle. In Santa Clara County, the Coyote Creek watershed (where our bioswale is located) includes key habitats that connect the Santa Cruz mountains to the Diablo Range. The riparian corridors created by the path of the creek and the habitats that it supports provide safe paths for our wildlife as well as food, water, and shelter.

Watersheds of Santa Clara County. (image source)

The Watershed Stewards Program

As previously mentioned, our Bioswale project is a joint effort between Our City Forest and the Watershed Stewards Program (WSP) with plant donations made by local nurseries such as Grassroots Ecology. WSP is a program run by the California Conservation Corps (CCC) in partnership with Americorps. As stated by the CCC, WSP “is dedicated to improving watershed health by actively engaging in restoration science, civic service, and community education while empowering the next generation of environmental stewards". WSP corps members complete 11-month terms at placement sites such as government agencies, local organizations, and nonprofits to improve watershed health through a variety of methods like water quality monitoring, habitat restoration, and urban restoration projects like our bioswale.

WSP Corpsmembers Kalvin Joe, Katharine Major, and Emily Cox surveying a creek with WSP Mentor Eric Ettlinger. (Image source)

About Our Bioswale

On March 30th and April 6th, we will be installing our bioswale which is composed of over 200 plants across 22 California native species. The selection of these plant species is based on multiple factors. To start, we wanted this bioswale to be composed primarily of grasses and only native species. Unlike the grasses used in traditional lawns, many grasses native to California have vigorous, resilient, and long root systems which make them ideal for stabilizing slopes, preventing erosion, capturing water, and filtering out excess nutrients and pollutants. Many of these grasses are adaptable and can handle California's characteristic climate patterns of drought and flooding. Other factors in the species selection process included what species are resilient enough for the climate and soil at Martial Cottle Park, plants that support pollinators, aesthetics, and the availability of plants at our nursery as well as from the nurseries that have been so generous in their donations. Here is the complete list of species in our design:

• Common Yarrow (Achillea millefolium)

• Saltmarsh baccharis (Baccharis glutinosa)

• Valley Sedge (Carex barbarae)

• Foothill sedge (Carex tumulicola)

• Soap Plant (Chlorogalum pomeridianum)

• Sacred Datura (Datura writii)

• Wild Rye Canyon Prince (Elymus condensatus ‘Canyon Prince’)

• Creeping Wild Rye (Elymus triticoides)

• Western Goldenrod (Euthamia occidentalis)

• California Fescue (Festuca californica)

• Creeping Red Fescue (Festuca rubra 'Pt. Molate')

• Great Valley gumweed (Grindelia camporum)

• Oregon gumweed (Grindelia stricta)

• Common Rush (Juncus patens)

• Deer Grass (Muhlenbergia rigens)

• Marsh fleabane (Pluchea odorata)

• Blue-eyed grass (Sisyrinchium bellum)

• Yellow Eyed Grass (Sisyrinchium californicum)

• Alkali Sacaton (Sporobolus airoides)

• Purple needlegrass (Stipa pulchra)

• California Aster (Symphyotrichum chilense)

• California Grape (Vitis californica)

If you are interested in helping us plant our Native Bioswale, sign up for the first workday on March 30th and/or the second workday on April 6th. If you cannot make these dates don’t worry! Our new bioswale will have plenty of weeding, watering, and educational workdays in the coming future and possibly even an extension along our southern gate! 

Common Yarrow (Achillea millefolium). (Image source)

Deer Grass (Muhlenbergia rigens). (Image source)

Wild Rye Canyon Prince (Elymus condensatus ‘Canyon Prince’). (Image source)

Western Goldenrod (Euthamia occidentalis). (Image source)

Sacred Datura (Datura writii). (Image source)

Plant Communities of Santa Clara County

What is a plant community?

In Ecology, a community is one of the various levels of ecological organization. These levels of ecological systems are used “to better understand the frame of reference in which they are being studied” (MSU). In other words, it helps ecologists define the scope of their studies and observations. These levels start at an individual of a species then climbs upward to species population, community, ecosystem, and biosphere. The community level is composed of multiple species that share a common environment. An ecosystem, on the other hand, includes both living organisms and nonliving features such as minerals and water. A plant community refers more specifically to plant species that grow in shared environments and in relation to each other. However, plant communities, and ecological communities more broadly, are not discrete zones that have definite and defined boundaries. Plants found in one community can be found in others and communities transition into others. Chaparral spills into oak woodlands and oak woodlands blend into redwood forests.

Serpentine Chaparral overlooking San Francisco (Image source)

The California Floristic Province and Mediterranean Climates

Santa Clara County is part of the California Floristic Province, a biodiversity hotspot that ranges from Baja California up to Southern Oregon, including the coastal islands along that range including the Channel Islands. 

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This region of biodiversity is defined by a Mediterranean Climate. This type of climate is considered to be globally rare and found only in 5 regions in the world: California, Central Chile, the Western Cape region of South Africa, South West and Southern Australia, and the Mediterranean basin (which includes North Africa, parts of Europe, Western Asia, and parts of the Middle East). This climate type is characterized by hot, dry summers and wet, cool winters which is reflective of Santa Clara County’s hills, which become a brilliant emerald in winter and golden in the summer. Many non-native, drought-tolerant species of trees and shrubs found in Santa Clara County are native to other Mediterranean climates such as rosemary, lavender, African fern pine, etc. Unfortunately, some of these plants are highly invasive (such as mustard, broom, and eucalyptus) and out-compete native species that our native ecosystems depend on.

(Image Source)

Plant Communities of Santa Clara County

Santa Clara County is highly diverse with many microclimates that allow for certain plants to thrive in specific areas. 

CHAPARRAL

Chaparral is dense shrubland characterized by diverse drought-tolerant, woody shrubs. The California Chaparral Institute lists 13 different types of chaparral in California alone and notes of other international chaparral communities from other Mediterranean climates. Among these California types are Serpentine chaparral, Desert chaparral, Ceanothus chaparral, and Island chaparral.

Species found in Santa Clara County

Chaparral Currant (Ribes malvaceum) is a member of the Gooseberry family. This beautiful shrub with pink, tassel-like flowers and round, pink berries is one of our most popular shrubs that Our City Forest plants in our Lawn Busters program. 

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Hairy Ceanothus (Ceanothus oliganthus var. oliganthus), commonly called California Lilac, is a wildfire resilient shrub. Its dark leaves contrast beautifully with seasonal blooms of periwinkle flowers. Ceanothus is another popular drought-tolerant shrub that we use in our Lawn Busters program and they come in a large variety of species and cultivars.

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GRASSLAND

Serpentine Grasslands at Calero County Park (image source)

Grasslands in Santa Clara County include Serpentine Grasslands, Annual Grasslands, and Non-Native Grasslands. Serpentine Grasslands are perhaps the most interesting. This type is defined by serpentine soil, which is high in serpentinite, a stunning banded green rock. It is also California’s State rock! Because of serpentine soil’s unique balance of calcium and magnesium, non-native plants tend to not survive in these soils, leaving room for native plants to flourish.

Species found in Santa Clara County

Purple needlegrass (Stipa pulchra) is California’s State Grass and most widespread native grass. It is perennial and evergreen and attracts many bird species from the large amount of purple seeds that it produces.

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Ithuriel’s Spear (Triteleia laxa) is an herbaceous perennial wildflower in the Lily family. The name Ithuriel comes from a character in John Milton’s  epic poem, Paradise Lost, who reveals a toad to be Satan’s by pricking him with a spear (USDA).

(image source)

OAK WOODLAND

Oak woodlands at Coyote Lake - Harvey Bear Ranch County Park (image source)

The eastern hills of Santa Clara County are rolling hills bespeckled with the dark green foliage of oak trees. These hills are generally drier than their western counterpart, the Santa Cruz mountains which tower with misty Coast Redwoods. The Oak Woodland plant community is generally dry, especially in the summer, and intermingles with other communities like grasslands and chaparral. 

Species found in Santa Clara County

Coast Live Oak (Quercus agrifolia) is a keystone species, meaning that it supports the survival of hundreds of other species. This species in particular, according to Calscape, supports a total of 270 species. It is also highly fire resistant and old growth trees can survive being scorched.

(image source)

Toyon (Heteromeles arbutifolia) gave Hollywood its name. Settlers who came to California thought it to be a type of holly berry! Toyon is another fire resistant species and commonly likes to grow as a companion to Coast Live Oaks. While Toyon is technically a shrub, it can be pruned into a tree. Birds love their red winter berries which are also edible for humans when cooked.

(image source)

RIPARIAN

Coyote Creek is a critical wildlife corridor in Santa Clara County (image source)

Riparian habitat exists in the transition between terrestrial and aquatic environments. This plant community is dense and rich with shrubs, grasses, and trees. These plants must be adapted to tolerate seasonal floods from California’s winter rain storms whereas plants specifically adapted to drier environments can be very intolerant of excess water. Riparian habitats are important wildlife corridors that allow animals such as bobcats, deer, and coyotes to move across the landscape safely. 

Species found in Santa Clara County

Blue Elderberry (Sambucus cerulea / Sambucus mexicana) is a gorgeous shrub that can also be pruned into a tree. Its delicate parasol-shaped clusters of flowers turn into dusty blue berries that a variety of wildlife depend on. Both the flowers and berries are edible and have medicinal uses. However, the berries are toxic to humans unless they are ripe and cooked. There are four types of Elder in California (and more internationally), but only Blue Elderberry grows naturally in Santa Clara County.

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California Mugwort (Artemisia douglasiana) is an edible, aromatic, and medicinal herb often found along creek sides. Some California Indigenous tribes, such as the Chumash and Paiute, used mugwort to nurture sacred dreams. If you come across this towering herb, gently rub a leaf between your fingers to release its medicinal aroma.

(Image source)

CONIFEROUS FOREST

Mt. Madonna County Park (image source)

Conifer trees are cone-bearing trees such as redwoods, firs, and pines. Santa Clara County is bordered from the South and South-West by the Santa Cruz mountains that maintain their deep forest-green foliage year-round. Many plant species live in the shady Redwood understory including other coniferous species. The Santa Cruz mountains are the primary place in Santa Clara County where Redwoods naturally occur. Throughout San Jose and bordering towns, Redwoods have been planted at lower elevations in an urban setting. However, these Redwoods tend to live stressed lives from that lack of fog that they have evolved to live with.

Species found in Santa Clara County

Coast Redwood (Sequoia sempervirens) is the tallest tree species. The tallest known living tree is a Coast Redwood named Hyperion, standing 379 ft tall. This tree’s exact location is undisclosed but lived approximately in Northern California close to Oregon. Hyperion is estimated to be 600-800 years old, but Coast Redwoods can live up to 2,200 years old.

(Image source)

The Pacific Madrone (Arbutus menziesii) is an evergreen tree that lives in the understory of Coat Redwoods but can also be found in oak woodlands. Like its cousins the manzanitas, the Pacific Madrone has reddish orange bark that peels away as it ages. Its flowers are shaped like clusters of delicate, white bells that flower in the spring.

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WETLAND

The EPA defines wetlands as “areas where water covers the soil, or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season”. This broad definition means that wetlands are incredibly biodiverse! The National Oceanic and Atmospheric Administration (NOAA) divides wetlands into 5 types: marine (ocean), estuarine (estuary), riverine (river), lacustrine (lake), and palustrine (marsh). These categories include both saltwater and freshwater environments, as well as brackish (a mix between freshwater and saltwater found in areas like estuaries where the salinity levels fluctuate). Read more about Wetlands in our World Wetlands Day 2024 blog post!

Species found in Santa Clara County
Tule or Hardstem Bulrush (Schoenoplectus acutus) is a large freshwater grass that grows throughout California wetlands. Indigenous groups across California use tule to make houses, clothing, mats, baskets, and tools.

(image source)

Saltmarsh Baccharis (Baccharis glutinosa) is a flowering perennial herb that grows in saltwater marshes. This plant grows through rhizomes, a specialized stem that grows underground (not a root!). These rhizomes spread underground where new stems and leaves can pop up away from the original plant.

(image source)

Trees and Wetlands- World Wetlands Day 2024

Wetlands and the Diablo Mountain Range (source)

Today, February 2nd, is World Wetlands Day! This celebration of wetlands was created in 2021 by the UN General Assembly in order to raise awareness about the importance of wetlands and the dangers this critical habitat faces. For 2024, the World Wetlands Day theme “Wetlands and human wellbeing” strives to educate the public on how human health and wellbeing is tied to the health of wetland ecosystems. While Our City Forest does not work directly with wetland habitats, growing the urban forest has positive impacts for many ecosystems, including wetlands. In honor of World Wetlands Day, this article will give a brief overview of wetlands and how they are connected to trees and the urban forest.

What is a Wetland?

The EPA defines wetlands as “areas where water covers the soil, or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season”. This broad definition means that wetlands are incredibly biodiverse! The National Oceanic and Atmospheric Administration (NOAA) divides wetlands into 5 types: marine (ocean), estuarine (estuary), riverine (river), lacustrine (lake), and palustrine (marsh). These categories include both saltwater and freshwater environments, as well as brackish (a mix between freshwater and saltwater found in areas like estuaries where the salinity levels fluctuate). The prolonged presence of water has resulted in plants adapting to these wet conditions. These plants are called “hydrophytes”. For example, the freshwater marsh community in the San Francisco Bay includes hydrophytes such as cattails, rushes, sedges, willows, ferns, and tules (nps.gov).

Tule (Schoenoplectus acutus var. occidentalis) (source)

Why are wetlands important?

Wetlands are biodiversity hotspots that have many critical ecosystem roles and provide food for over 1 billion people. Wetlands filter water of excess nutrients and pollutants, provide flood and erosion control, and provide food and shelter for both migrating and permanent wildlife. According to the UN, wetlands, while only covering approximately 6 percent of the Earth’s land surface, “40 percent of all plant and animal species live or breed in wetlands”. Wetlands are also “carbon sinks”, meaning that they capture more carbon from the atmosphere than they release. In fact, they capture more atmospheric carbon dioxide than any other ecosystem on earth.

Threats to Wetlands

In the US, 60,000 acres of wetlands are lost per year. This loss is due to many different causes such as being drained for agricultural use and development for industry, habitat fragmentation, pollution from run-off, eutrophication from agricultural run-off and commercial fertilizer, competition from invasive species, and changes in water level and quality. Unfortunately, California has lost 95% of its historic wetlands. In the post-gold rush era, wetlands were seen as unproductive, wasted land. Many wetlands were intentionally drained for agricultural use. In San Jose during the early 20th century, Laguna Seca, a 1,000+ acre freshwater wetland located at the present intersection of Santa Teresa and Bailey Avenues, was drained and burned for agricultural purposes. The Peninsula Open Space Trust (POST) describes Laguna Seca as a place where “water slowed and fanned out across the landscape, creating a mosaic of wet meadows and ponds, providing habitat for a variety of wildlife and percolating into a groundwater basin that now supplies San Jose with drinking water”.

Laguna Seca (source)

How are trees and wetlands connected?

Trees and forests, including the urban forest,  play a critical role in protecting wetlands and other parts of the watershed by regulating water flow, providing water filtration, and preventing erosion. When the tree canopy is removed and replaced by impermeable surface such as roads, parking lots, concrete, etc., there is an immediate impact on the watershed (PSU). Water runs off of the many impermeable surfaces found in urban landscapes rather than being slowed by the tree canopy and absorbed into the soil. These large amounts of water are often carried directly to streams, lakes, or rivers without first being naturally filtered by trees and other plant species. This large amount of water increases erosion and deposits large amounts of sediment, both of which can destroy important habitats and breeding grounds. The canopy is first to slow incoming rainfall which then drips down into the soil where it is absorbed and gradually released into the watershed, including important groundwater stores. According to Penn State University, 

“Average interception of rainfall by a forest canopy ranges from 10-40% depending on species, time of year, and precipitation rates per storm event. In urban and suburban settings a single deciduous tree can intercept from 500 to 760 gallons per year; and a mature evergreen can intercept more than 4,000 gallons per year”.

(source)

This water is then filtered by trees and other plants before entering the watershed. Excess nutrients, such as nitrates and phosphates, come from agricultural sources as well as urban fertilizer use (such as for lawns). While abundant nutrients may sound like a good thing, high levels cause a detrimental effect called eutrophication. Excessive nutrients result in unbridled growth of plants and microorganisms such as algae. When these plants and microorganisms decay, the amount of bacteria needed to break them down consumes the dissolved oxygen in the water, creating what is often referred to as “dead zones'. These dead zones, stripped of oxygen, suffocate animals such as fish which have a key role in the food web . Furthermore, other contaminants such as metals and pesticides are also removed from the water by plants, particularly woody plants like trees and shrubs. While wetlands can filter pollutants and nutrients, the accumulation of too many nutrients can outweigh the ecosystem’s filtering capacity.

Eutrophic water with algal bloom (source)

Where do wetlands fit into this picture? Without trees and other plants that make up wild and urban forests, these excessive flows of water, nutrients, and pollutants enter straight into the watershed and into down-stream wetland systems. Eutrophication of a wetland can change the water quality and chemical composition and completely destroy the plant and animal life.

How can I help?

While Laguna Seca was mostly drained, it is not completely gone! It remains as San Jose’s largest freshwater wetland and is located in the critical Coyote Valley habitat corridor. You can volunteer with Santa Clara Open Space Authority to help save and restore this important habitat. Grassroots Ecology, based out of Palo Alto, also does restoration work in San Jose’s Alviso wetlands where the Guadalupe river meets the San Francisco Bay. You can also plant trees or convert your lawn to help capture more stormwater and filter it before the water drains into the watershed.