the Coast Redwood
This online review is updated and revised continuously, as soon as results
of new scientific research become available. It therefore presents
state-of-the-art information on the topic it covers.
Coast Redwood (Sequoia sempervirens) grows naturally along the
Pacific Coast of North America from central
California north to southern Oregon.
Its distribution is correlated with that of the thickest part of the
"California fog belt" where, each day during the summer, cool fog moves
off the ocean and onto land. See
relatively little rain falls in summer, so during this period redwoods are
especially dependent upon fog for moisture to grow and survive. Studies show that fog supplies
13-45% of the total water used annually by redwoods (Dawson 1998), and
that redwood leaves can even absorb some water directly from
the fog (Burgess and Dawson 2004).
In addition, fog blocks the evaporating rays of direct sunlight, reducing the amount of water that redwoods lose by
transpiration (Byers 1953; Azevedo and Morgan 1974; Burgess and Dawson
When fog comes into contact with redwood trees, it
condenses into liquid water and drips off the foliage onto the ground.
In this way, redwoods and other giant trees "strip water"
from the fog and drip it onto the ground, where it is used not only by the
redwoods but by other plants as well.
During summer in
California, Dawson (1998) found that two-thirds of the water used by plants
growing in the understory of a redwood forest came from fog that had
condensed on redwood foliage and then dripped into the soil." When
redwood trees are cut down for timber, plants growing under them
receive less water and even the flow of water in nearby streams is
decreased, because the redwoods are no longer present to "strip water"
from the fog and put it in the ground (Ingwerson 1985).
The Coast Redwood is the tallest
tree in the world, growing to heights of
over 110 meters and to a very great
age (Koch et al. 2004). One Coast Redwood is confirmed to be at
least 2,200 years old, but it is suspected that many other individual
redwoods are much older (Sawyer et al. 2000). Thus, some of the
redwoods living today began their lives before the time of Christ.
The Redwood Canopy
According to Sillett and
Bailey (2003), large redwood trees are among the "most structurally
complex trees on earth," with individual crowns composed of "multiple,
reiterated trunks rising from other trunks and
branches...indistinguishable from free-standing trees except for their
origins within the crown of a larger tree" (see also Sillett 1999).
For example, Sillet and Van
Pelt (2000) studied a single old-growth redwood tree in Redwood National
Park and found that its crown had "148 resprouted trunks arising from the
main trunk, other trunks, or branches." Five of the resprouted
trunks had a basal diameter of over one meter, and the largest resprouted
trunk was over 40 meters tall. These researchers concluded that the
crown of this redwood could itself be considered a forest.
Each year, redwoods shed their
foliage. While some foliage falls to the ground, other foliage
accumulates on large branches of the redwood and decomposes there into an
organic soil called "canopy soil" Seeds of plants and spores of
fungi colonize this soil, creating a plant community high in the canopy of
redwood trees (Sawyer et al. 2000).
that grow on trees rather than on
the ground are called epiphytes. Redwood trees often support
sizable communities of epiphytes because their large size,
great height and complex architecture make them excellent structures for
soil and plants to colonize. In addition, the great age of redwoods
increases the probability of colonization by epiphytes since
so much time is available.
The number of epiphyte species growing in redwood
canopies is quite large. For example, Williams & Sillet (2007)
sampled the canopies of nine large redwood trees and found a total of 282
plant species growing there, including "183 lichens, 50 bryophytes and 49
vascular plants...Compared to Douglas-Fir and Sitka Spruce, redwood
consistently supported more epiphyte richness, except for cyanolichens."