Plants

Muir Woods is famous for its old-growth redwoods, but these trees define just one of several plant communities - groups of different plant species that live in the same area.

From shady creeks to windswept ridge tops, different environmental conditions support a wide range of plant life. The flow of water, the coastal fog, the orientation and slope of the hills, and the frequency of disturbances like fire and flood all influence what plants will grow.

Below are the key plant communities of Muir Woods - and the factors that shape them.

 

 

At Muir Woods, the tallest coast redwood reaches 258 feet, while farther north in California some redwoods reach over 380 feet. The average age in Muir Woods is 600-800 years, with some individuals more than 1,000 years old.

NPS/ Jules Cooch

Old-Growth Coast Redwood Forest

Old-growth coast redwoods engineer conditions for all who live under them.

Trees of mixed ages and a multi-layered canopy provide habitat for animals, including fire scars that shelter bats and standing dead trees that offer cavities for birds. The dense redwood canopy filters the sunlight, allowing shade-loving plants like western sword fern and redwood sorrel to grow on the forest floor.

Between early summer and late fall, precipitation is rare in the park. But moisture arrives in another form: coastal fog. Low clouds develop above the Pacific Ocean and are pulled inland. Coast redwoods use foliar uptake to drink fog water directly through their leaves. The fog condenses on the redwoods’ leaves and drips down, providing precious water to the ecosystem below.

In this part of their range, redwoods grow mainly in creek valleys and lower slopes, while reaching higher on shady north-facing hillsides. Companion plants include Douglas-fir (which can also grow to more than 300 feet), tanoak, California bay laurel, and beaked hazelnut. Perenial ferns and redwood sorrel as well as seasonal wildflowers like trillium, Andrew’s Clintonia, and fetid-adder’s tongue dot the forest floor.

 

Wet soil and gaps in the canopy allow different trees to grow by the creek.

Parks Conservancy/ Vivien Kim Thorp

Riparian Forest

The redwoods stand straight and tall, but along Redwood Creek, other trees angle their branches over the water, reaching for sunlight through gaps in the canopy. This riparian – or creek-side — community includes species adapted to life along the water.

Here, red alder lines the creek and stabilizes the soil with its roots. Bigleaf maple, a deciduous tree with dinner plate-sized leaves, glows golden each fall. Farther downstream, arroyo willow lines the creek but does not grow under the redwoods. Along with redwoods and ferns, these trees cool the creek with their shade and benefit the survival of salmon eggs. Common herbaceous plants include Western azalea and scarlet monkeyflower. Elk clover grows seasonally along streambanks, as does the flaming orange leopard lily.

Intense winter rains occasionally disturb the creek. Flooding can be beneficial by increasing diversity of plant life along its banks and releasing nutrients from creek floor sediment.

 

Madrone and California bay laurel are better equipped to grow on drier slopes than the coast redwoods.

NPS/ Jason Bosinoff

Mixed Conifer Forest

Higher up the valley into Mount Tamalpais State Park, the shape and orientation of the hillsides determine who will survive. South-facing slopes receive more sun, helping Douglas-fir to outcompete the moisture-living coast redwoods. Madrone, with its red peeling bark and glossy leaves, is common here too. Farther uphill toward Panoramic Highway grow canyon live oak and coast live oak, their tough evergreen leaves adapted to endure the dry conditions.

Common understory plants include evergreen huckleberry and milkmaids.

 

Where trees can’t survive, shrubs take over. Watch out for poison oak, which is especially prevalent in this plant community.

NPS/ Jason Bosinoff

Coastal Scrub

Closer to the ocean, high winds, salty air, and low-nutrient soil make it too hard for trees to grow. Instead, low shrubs live here, led by coyote brush. Their short stature helps them withstand wind, and their leaves with small surface area reduce the effects of evaporation.

Common plants here include poison oak, California sagebrush, Douglas iris, Western blue-eyed grass, California poppy, and bush lupine.

 

Hard leaves reduce water loss through evaporation, like for this Mount Tamalpais manzanita.

iNaturalist/ emjtca

Chaparral

Higher still on Mount Tamalpais, the exposure, wind, and dryness are too much for most tree species. Here, hardy shrubs dominate in an ecosystem known as chaparral. They prevent water loss with hard, evergreen leaves with low surface area. Coastal fog brings occasional relief by reducing the evaporation rate on otherwise sunny days.

Many chaparral plants are adapted to fire: some have seeds that require fire for germination, while others will resprout from their base following a burn.

Manzanita, chamise, blue blossom ceanothus, golden chinquapin, and sticky monkeyflower are among the common species here.

 

Threats & Changes

Natural forces have long shaped these plant communities. Human behavior will determine the future of these forces - and of the ecosystems themselves.

 

Coastal fog rolls in from the Pacific Ocean

NPS/ Jason Bosinoff

Defining Forces

Fog

Compared to 100 years ago, the Northern California receives about one third less fog as coastal ocean surface temperatures have risen. Redwoods get up to 40% of their water from the fog each year - and share much of the fog water they collect with the rest of the forest - so the changing climate has a profound impact on the trees.

Researchers continue to study how these changes will affect redwoods and other plant communities that depend on them. Visit the following link for more information about fog, redwoods and a changing climate at Muir Woods.

 

California State Park rangers have conducted prescription fires in the Mount Tamalpais watershed near Muir Woods, like this burn on the Deer Park Fire Road & Dipsea Trail in fall 2024.

NPS/ Emily Pellegrini

Fire

Fire has long shaped plant communities of the Mount Tamalpais watershed. Regular fire clears away duff – dead plant material on the forest floor – and encourages certain plants to germinate. Most local plants are adapted to fire; some even require it, with seeds that only germinate after burns.

Without regular burning, invasive species can gain an advantage over fire-adapted natives, and habitats can be lost. For example, without regular burns to maintain shrubland, Douglas-fir encroaches, converting them into forest.

Coast Miwok, who have lived in the area for over 10,000 years, have supported fire’s role in the ecosystem by lighting cultural burns. Research shows that fires historically occurred every 22-27 years at Muir Woods. To protect habitat, the National Park Service partners with the Coast Miwok, organized today as the Federated Indians of Graton Rancheria (FIGR) to restore beneficial burning practices that are supportive to native plants and the local ecosystem.

 

Learn More

Plant Communities Map

Curious where each plant community is found? Marin County and One Tam have created an interactive, high-resolution map that shows dominant vegetation types and plant species. Built from field surveys, LiDAR, and aerial imagery, the map is a great way to connect observations on the trail to the landscape features and topography of Muir Woods and Mount Tamalpais. Click here to explore the map.

iNaturalist Plant Observations

Want to learn what others have noticed, and share your own observations? See what others have observed growing at Muir Woods and in surrounding Mount Tamalpais State Park:
Muir Woods plant observations on iNaturalist
Mount Tamalpais State Park plant observations on iNaturalist

One Tam Health Study

Researchers are monitoring the health of Mount Tamalpais plant communities. View the One Team Peak Health Report and latest findings here.