CALIFORNIA ACADEMY OF SCIENCES
Hotspot: California on the Edge
Mature coast redwood trees, Muir Woods National Monument
Redwood Forests
Survivors Of An Ancient Time

They are the largest and among the oldest living things on Earth and stood as silent witnesses to millions of years of change.  Redwoods’ long history dates back over 200 million years to when the dinosaurs lived. The climate then was warmer and more humid and redwoods were more widely distributed across the northern hemisphere.  As the Earth’s climate became cooler and drier, redwoods gradually retreated to areas where abundant rainfall and stable temperatures provided refuge. Several species that did not adapt became extinct and only three species now remain.  Today, redwoods are found in only a few places. The coast redwood, Sequoia sempervirens, grows in California’s cool, moist coastal valleys and canyons from Big Sur to just north of the Oregon border.  
The giant sequoia, Sequoiadendron giganteum, is only found in 75 isolated groves in the Sierra Nevada.  Natural populations of their close relative, the dawn redwood, Metasequoia glyptostroboides, went extinct in California. Today, they only occur naturally in the central Chinese provinces of Sichuan and Hubei.

Marbled Murrelet
Learn more about the Marbled Murrelet >

Explore a Coast Redwood Forest
View the Coast Redwood Forest >
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Redwood snag
Can remain upright for hundreds of years and offer lookout perches and nesting sites for animals.

Nurse log
Rotting logs provide shelter for salamanders and other animals.

Understory
Sword ferns, rhododendrons, Douglas fir and tanbark oak grow where shafts of sunlight reach the forest floor.

Bark
12 inch (30 cm) thick bark
and tannins make redwoods resistant to fire, disease,
insects and decay.

Goose pen
Hollows in live trees caused by recurring fires were once used by early settlers to hold poultry.

Canopy
The world’s tallest trees, coast redwoods add 2 to 6 feet (61 cm - 1.8 m) in height and 1 inch (2.54 cm) in
diameter each year.

Burl
Knobby growths contain dormant buds that can sprout when the main tree falls or dies.

Leaf litter
Dense ground cover prevents many seeds from reaching the soil to germinate.

Banana slug
These mollusks help recycle dead plant material and animal droppings into soil.

Fairy ring
Young trees sprouting from the roots of a dying parent tree form a circle.

REDWOOD ROUND
The Key to the Past

Dendrochronology is the study of tree rings to date past events. By analyzing a tree’s growth rings, we can determine its age, fire history and the climate. Each year, a tree adds a new layer of wood to its diameter. When moisture is plentiful in the spring, the new cells are large. In the drier summer, cell size decreases until growth stops in the fall.
The seasonal difference in cell size creates a distinct ring.

redwood growth rings

Other factors can also affect the appearance of tree rings including sun, wind, soil properties and temperature. sDendrochronology can help unravel mysteries about what the environment was like in the past. Climatic changes or the effects of pollution can be interpreted by the study of old living trees.

Turning Wood into Stone
About 3 million years ago, coast redwoods in the mountains west of present-day Calistoga were leveled by a powerful volcanic eruption. The knocked-down trees were buried in layers of hot ash and sediment.

Over centuries, groundwater dissolved the silica in the volcanic ash and saturated the trees’ tissues. One by one, molecules of wood were gradually replaced by molecules
of silica, eventually turning the entire tree into solid rock. 

Fossilized coast redwoods, like this one from Arizona, are evidence that this species once had a much wider distribution than today. Unlike petrified trees from other areas, these are light-colored due to the sandy, white ash that covered them.

A Nursery for Young Trees
When a tree falls, it creates favorable conditions for redwoods to germinate. It leaves a gap in the canopy so more sunlight reaches the forest floor to stimulate seedling growth.
Fallen trees also retain moisture and nutrients that aid in new plant growth. Often called nurse logs or mother stumps, rotting logs and the root wads of toppled trees are good sites for re-generation of seedling redwoods. 

Many young trees may sprout from a single nurse log. Once the seedling germinates, it sends roots down into the nurse log reaching the moisture and nutrients of the decaying log. Dead logs also serve as ground cover which lessens erosion of the soil.

Dead Trees Are Vital to the Forest Ecosystem
Dead trees provide habitat to many animals and play an important role in maintaining the forest. Standing dead trees, or snags, can remain upright for 200 years and offer lookout perches and nesting sites for birds and other animals. The main trunk and large upper branches also provide shelter to cavity-nesting woodpeckers and owls.

Birds are not the only animals to benefit.  Fallen trees scattered throughout a redwood forest provide refuge for small mammals, amphibians, reptiles and invertebrates. Salamanders rely on the security and dampness of soil found beneath a rotting log. Spiders, beetles, worms, and microbes move and feed within the damp rotting log.
Decay happens little by little aided by moss, lichens and fungi that grow on the surface of logs. They break down organic matter to release important nutrients back into the forest ecosystem.

The Importance of Being Slimey
Banana slugs produce mucus, or slime, which has many functions. Slime keeps banana slug skin moist, and is necessary for the slug to be able to breathe. On damp days, slime pulls moisture out of the air and on dry days slime wicks water out of the soil.

Slime protects banana slugs from being eaten as most animals cannot tolerate the texture. The mucus also contains a numbing anesthetic that makes them even more unpalatable. A thin cushion of slime helps the slug move over rough ground more easily and protects it from injury.

banana slugs

Banana slugs are hermaphrodites, which means they contain both male and female reproductive organs. They cannot fertilize their own eggs, however, and must exchange sperm. A special slime signals when a slug is ready to mate and is an attractant to other slugs.  After mating, up to 20 translucent eggs are laid under a log or in leaves.
Mating and egg-laying occur several times throughout the year.

Banana slugs
Ariolimax sp.

These soft-bodied mollusks live on moist forest floors where they recycle leaf litter, animal droppings and dead plant material. In the process, they also spread seeds and fungal spores. They are the largest slug in North America and can grow to be 10 inches (25 cm) long.

Nurse Logs
Fallen trees scattered throughout a redwood forest provide refuge for small mammals, amphibians, reptiles and invertebrates. Salamanders rely on the security and dampness of soil found beneath a rotting log. Spiders, beetles, worms, and microbes move and feed within the damp rotting log.

Mordant scorpion
Uroctonus mordax
The most common scorpion in the Bay Area lives in woodlands, including redwood forests of the Coast Range. It burrows in the ground and is active at night. Females give birth to about 32 live immature scorpions that pile onto her back until they are big enough to go off on their own. While their sting can be painful, the venom is not known to be dangerous to humans.

Snail-eater (in tank)
Scaphinotus interruptus
These beetles are widely distributed in forest habitats of California, from the Pacific Coast to the Cascade Range and Sierra Nevada. Active almost exclusively at night, both adults and larvae feed mainly on snails and slugs, but occasionally supplement their diets with berries and other wild fruits. 

CONCERNS
Habitat Loss

Over the last 150 years, intensive logging significantly reduced stands of coast redwoods. Less than 5% of remaining forests are protected. Sustainable management is needed to protect remaining old-growth forests.

Fire Suppression
Without a cycle of natural fires, the build-up of dense understory vegetation increases the risk of fire. While redwoods are naturally resistant to fire, current fuel loads could feed a crown fire so hot that it could destroy the forest.

Conservation
In 1900, the Academy advocated preserving Big Basin redwoods. In 1902, through efforts by the Sempervirens Club, Big Basin became California’s first state park.

In 1918, Save-the-Redwoods League was organized in response to widespread destruction of redwood forests.

In spite of these conservation efforts the trees may still be in peril. Sudden oak death syndrome, caused by an introduced parasitic mold, affects 36 California plants including coast redwood seedlings. It is unknown if mature redwoods are susceptible, but tan oak, a common understory tree in redwood forests, is highly susceptible. 

What You Can Do

  • Experience California’s redwoods. Visit Muir Woods National Monument. Big Basin State Park, and Humboldt Redwoods State Park.
  • Join Save-the-Redwood League and/or the Sempervirens Fund:
    www.savetheredwoods.org
    www.sempervirens.org
  • Learn how to prevent the spread of sudden oak death syndrome on the Big Basin Redwoods State Park website: www.bigbasin.org.
 

Above: Mature coast redwood trees, Muir Woods National Monument

Marbled Murrelet

Redwood Round - key to the past

redwood growth rings

Explore a Coast Redwood Forest

A nursery for young trees

Dead Trees Are Vital to the Forest Ecosystem

Banana Slug

banana slugs

Concerns

Habitat Loss

Fire Suppression

Conservation

What you Can Do