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.

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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).

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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.

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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.

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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.

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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.

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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.

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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.

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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”.

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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.

More Than Trees: Creating Habitat for the Urban Environment

What do you see when you think of a forest? Do you see oaks or redwoods? Look below the canopy, between and below the trees. There are mosses and lichens hanging and climbing amongst branches, trunks, and rocks. The creeks and rivers are full of fish and aquatic insects. Below the soil, fungi connect the forest in a mycelial network that orchestrates communication and nutrient exchanges. Just like wild* forests, urban forests are composed of much more than just trees. Urban forests are ecosystems that integrate humans and our built environments with cultivated and wild plants, wild and domesticated animals, fungi, microorganisms, bodies of water, soil, minerals, and organic matter. Our City Forest is dedicated to planting not just trees, but also understory plants that create habitat and save water.

*For lack of a better term, I use the word “wild”. The reason this word can be problematic is that the word wild implies a place where nature lives outside of human society. It brings up images of pristine places untouched by humans. However, the myth of the pristine wilderness is highly inaccurate, especially in North America where we know that forests and other ecosystems  were tended to for thousands of years by Indigenous peoples and continue to be tended to this day.

The Urban Environment

Integrating the built environment with urban forests often requires innovation to solve problems. Ideally, the built environment (which consists of buildings, infrastructure, agricultural lands, etc.) would mesh with the rest of the environment with no conflict. However, many of the systems in urban and suburban environments make the built environment difficult to survive in and even uninhabitable in some situations. For example, the Urban Heat Island Effect describes how surfaces common in urban settings, such as glass, concrete, and asphalt, absorb and retain heat, causing higher temperatures. These higher temperatures put more physical stress on trees, animals, and other organisms in the urban forest while also evaporating more water.

Worldwide urban development has also caused habitat loss and habitat fragmentation, which are both tied to one another. Habitat loss is the reduction in total land while habitat fragmentation is the isolation of habitat islands from others. Generally, habitat loss leads to fragmentation, making it difficult and dangerous for animals to migrate, establish new ranges, escape wildlifes, and adapt to climate changes. However, it doesn’t need to be this way. Creating and maintaining habitat corridors, safe road crossing (under or over), green roofs, lawn conversions, and more can help solve the conflict between the environment and urban development and lead to integration. Our City Forest has a role in this integration not by just planting trees but also by converting lawns into drought-tolerant landscapes.

Lawns

One of the biggest issues regarding the urban environment across the United States is the lawn. In the United States, there are over 40 million acres of lawn, roughly the same size as the state of Florida! Lawns, including artificial grass, pose many negative consequences. Grass lawns consume up to 31 gallons per square foot, per week. The average residential lawn in the U.S. is 10,871 square feet (in California the average is 5,575 square feet). That’s up to 337,001 gallons of water per week to water the average U.S. lawn and up to 172,825 gallons per week in California! To put these numbers into context, the average shower is 17 gallons of water. The upper limit of water used to water the average U.S. lawn is equal to 639 showers! Alternatively, many drought-tolerant native plants usually do not need any watering once they have become established. 

Besides the issue of water use and waste, lawns and artificial grass have no ecological value. They are desolate places for most plants and wildlife. They do not provide food, shade, or shelter for animals. Many grasses used for lawns are invasive, spread easily, and can be difficult to remove or kill, such as Bermuda Grass which is common in warmer climates and is used  in San Jose. Grass like this pushes out native plants that animals and other organisms have evolved to depend on.

Non-native grass lawns are also not able to capture as much water as native grasses and other native plants. The image below demonstrates the difference in root systems between lawns and prairie plants. To the far left, you can see that the root system of typical lawn grass is only 3-4 inches, whereas the native plants to the right have root systems up to 12 feet long! Longer root systems help to stabilize the soil and prevent erosion, capture more stormwater, filter pollutants in the water before it ends up in the ocean, and help to restore groundwater.

Lawn Busters

The Lawn Busters Team at Our City Forest is dedicated to converting lawns into drought-tolerant landscapes that save water and create habitat in a county that has suffered much habitat loss and fragmentation. We plant a wide variety of native and drought-tolerant plants from California Lilacs, Penstemon, succulents, native grasses like Creeping Red Fescue and California Fescue, tree-like shrubs such as Toyon and Elderberry, various Mediterranean species, and more! In some cases we also include trees in a landscape design, but overall we focus on grasses and shrubs. While trees are important to the urban forest, shrubs are just as important and provide food, shade, and habitat for non-arboreal species.

Recently, the Lawn Busters Team sent out a wildlife reporting survey to homeowners who had their lawns converted by Our City Forest. The majority of respondents reported an increased presence of wildlife in their new landscape, especially pollinators such as bees, butterflies, and hummingbirds as well as lizards, hawks and other bird species, and even opossums!

In addition to transforming lawns, we also teach the community how they can transform their lawns by themselves through workshops held at our Urban Forestry Education Center. Many of the plants we use in lawn conversions can be seen in our various gardens at our Education Center and more gardens are being added, such as a bioswale, a native wildflower meadow, and a Lawn Buster’s demonstration garden.

If you would like to continue learning about the urban forests and the projects Our City Forest works on to increase San Jose’s canopy and understory, consider volunteering with us! As a volunteer, you can learn how to plant trees and shrubs, learn gardening skills, learn about native and drought-tolerant plants, climate change, community science, and more!