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Amazing
Redwood Trees Ask the Redwood Doctor by Will Russell, Ph.D. |
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 Will Russell, Ph.D., is an Assistant Professor at San Jose State University in the Department
of Environmental studies. In addition to teaching Natural Resources
and Sustainable
Forest Management, he conducts research on the
preservation and restoration of coast redwood forests.
Dr. Russell's question and answer column appears in every issue of The Mountain Echo, the quarterly redwood newsletter for Sempervirens Fund members. Note that archived column excerpts and associated essays include many penned by Redwood Doc Emeritus Chris Brinegar. Dr. Russell welcomes questions about the biology and ecology of the indigenous redwood forest. He regrets that he cannot answer queries about redwoods grown as ornamentals, or in non-native habitats. He advises that questions about disease, pruning or structural damage from redwood roots should be directed to a professional arborist in your localality. E-mail your questions to Dr. Russell. |
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The life history of a tree can also play an important role in determining what its growth trajectory will be. This is particularly true when it comes to coast redwood trees as they reproduce primarily through clonal sprouting. A single mature redwood, when felled, can produce hundreds of sprouts that compete with each other to become the main stem. Over time, the more vigorous stems grow larger while other stems grow very little and eventually die off. Forest managers who are in the business of growing big trees as quickly as possible often thin some of the sprouts to "release" the rest. This increases the growth of individual sprouts in the short run, but makes very little difference in the long run as it is essentially mimicking a natural process. Kevin O'Hara at the University of California, Berkeley, developed a practical model for redwood growth under optimal conditions. He predicts a maximum 24-inch diameter by age 50, and a 44-inch diameter at age 100. If you are a math buff you can try his formulas for maximum and average diameter yourself: Maximum diameter = (0.35) x (age) + 8.07; Mean diameter = (0.28) x (age) + 1.37 .Spring 2009 |
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 Wildfires are a serious concern in California. Should people who live in and around the redwood forest be worried about potential forest fire hazards?  Anybody living in the urban-wildland interface should practice basic fire safety by clearing defensible space around structures. As vegetation types go, however, the coast redwood forest is remarkably fire resistant. Individual trees survive fire due to thick fire resistant bark. A lack of flammable resins makes the bark difficult to ignite, and air pockets act as insulation protecting the living tissue below. The height of the coast redwood also provides protection from fire. With the lowest branches far from the forest floor it is difficult for fire to travel up to the crown. During the most severe fires when significant foliage is destroyed it quickly sprouts back, and only the youngest and smallest redwood trees are lost. Generally speaking, the older and larger trees are the most fire resistant. The coast redwood forest community, as a whole, also tends to be less susceptible to fire than many other vegetation types due to high moisture content in both live and dead fuels. For more information on defensible space check the Cal Fire website at www.fire.ca.gov.
Winter 2009 | |
 It occurred to me that since Redwoods live so long they are the ideal plant based carbon sink. Where most trees and plants might lock up carbon for 50-100 years redwoods could lock it up for hundreds even thousands of years. On average how much carbon is stored in one mature redwood tree? Since I can't find a reference that estimates the amount of carbon sequestered in a mature redwood, I've done my own calculation based on the following set of facts:
Summer 2007 |
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| Do you know when redwood trees stop growing? Do they ever completely stop growing after a certain number of years? Redwood trees grow until they die. Even the older redwoods, which exceed 2,200 years, are still growing. However, once they get to be a few hundred years old, their growth slows down significantly and most of the growth is in radial expansion of the trunk. Also, the crowns of old trees are prone to wind and lightning damage, so sometimes the growing tip is knocked off, which further slows vertical growth.
Measuring the age of large standing redwoods is not an easy task, since standard increment borers—devices used to obtain trunk cores for counting annual rings—are not long enough to penetrate to the center of the trunk.
Due to different environmental and growing conditions, you cannot estimate age accurately by measuring height or diameter. Unfortunately, for the biggest trees we have to count the rings after they have fallen over or have been cut down.
Summer 2006 |
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| What is the evolutionary history of Sequoia? The early history of conifers, including the ancestors of modern Sequoia, parallels the evolution of dinosaurs. Their origins and major diversification was during the Mesozoic Era (Triassic, Jurassic and Cretaceous Periods) about 250-65 million years ago. Fossils of extinct genera indicate that a recognizable ancestral form of Sequoia had been established by at least100 million years ago. Species of the genus Sequoia reached their widest global distribution around 50 million years ago (when the middle and higher latitudes of the Northern Hemisphere were warmer than today), with fossils of that age found in North America, Europe, Asia nd even as far north as the Arctic Circle! A cooling and drying trend in global climate led to the loss of Sequoia forests except on the U.S. Pacific coast, where the uplifting of the coastal mountain ranges (about 5 million years ago) created a moist, temperate climate for modern Sequoia sempervirens.
Spring 2006 |
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| How
can I collect seeds from redwood cones?
Mature
redwood cones slowly turn from green to brown as they begin to dry out
in the Fall. Once they are dry enough, the cone scales separate
and release the seeds. The timing of this dispersal can be quite
variable, but most seeds are shed between November and February as the
winter storms blow through. To guarantee that you'll get the seeds
before they drop out of the cone, pick one before it opens (around December
or January) then allow it to desiccate for a few weeks or more in a dry
environment until the scales separate enough for you to shake the seeds
free. But if you try to germinate and plant them, please use seeds
from local stock in order to grow redwoods that are adapted to this region. Fall 2005 |
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| I've
just learned that there are several varieties of Sequoia sempervirens. How many are there and how are they used in reforestation efforts?
There is quite a bit of natural variation in needle color, branch angle,
crown shape and growth rate in redwoods. When propagated for commercial
use, these natural varieties are called cultivars. Well over 20 such
cultivars are available in nurseries. One of the most popular ornamental
types is "Aptos Blue", which has deep blue-green foliage
and rapid growth. Others, such as Prostrata, are selected
for their short mature height. Most reforestation, however, is done
using seedlings grown from a seed pool obtained from healthy trees
in the same region. This ensures that the new redwoods will be adapted
to the local climate and elevation. Spring 2005 |
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| In the Giant Sequoia grove near Wawona in Yosemite, our guide told
the group that as redwoods age (in late maturity) they lose some of
their height and become wider. Lots of giggles from the group of mostly
seniors. Is this indeed true, or was he just putting us on?
Plants
display indeterminate growth (which means they don't stop
growing until they die), and giant sequoias and coast redwoods are no
exceptions. However, once these trees get past a few hundred years of
age, their upward growth slows down considerably and most of their
increase in mass is due to an increase in trunk diameter via annual
rings. Neither giant sequoias nor redwoods actually "shrink" like
humans when they age, but the growing tips of very tall trees are
sometimes broken by wind or lightning so they can lose some of their
height. In a way, your Wawona guide was telling the truth, although he
left out a few illuminating facts! Winter 2005 |
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| Is it true redwood trees lose about 1/3 of their foliage each
year?
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| I
know that high levels of tannins help the coast redwoods resist both
disease and decay. Yet tan oak trees in the redwood forest – which
also have high levels of tannins -- are often loaded with parasites,
and they decompose readily. What is it besides tannins that explains
this difference?
High
tannin content can impart disease resistance, but bark thickness also
plays a role. Tan oak bark can be relatively thick in places
but it is deeply furrowed and has a tendency to split as the tree ages,
leaving the wood exposed or only minimally covered. The bark of
a redwood, although furrowed, can be a foot thick in older trees
and completely covers the wood. Therefore, tan oaks offer more
infection sites for fungi and entry points for wood-boring insects that
do not occur so readily in redwoods. There are probably many other
unknown genetic factors that account for their differences in disease
and insect resistance. Summer 2004 |
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| How
many cones and seeds does a coast redwood tree produce each year?
Cone and seed production
in coast redwoods can be extremely variable. Some trees can
generate tremendous numbers of seeds while others may not even
develop cones in a given year. My research group in the Conservation
Genetics Laboratory at San Jose State University is currently
conducting a reproductive study on a 70-year-old, 3-foot diameter,
140-foot tall coast redwood in the Soquel Demonstration State Forest
which produced over 5,000 female cones this year. We estimate that
it produced more than 400,000 seeds. (Mature redwoods have the potential
to produce well over 1 million seeds!) Of course, not all redwood
seeds are viable and very few, if any, from an individual tree will successfully germinate and grow into mature trees. Winter 2004 |
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| I recently
found an albino (white) redwood tree in the forest. How common is it? Albino redwoods are
not very common. But in my own hikes through the Santa Cruz Mountains,
I've run across a dozen or so of them. Most likely, the albinism is
caused by a mutation in one of the genes involved in the production
of chlorophyll. The failure to synthesize chlorophyll sometimes results
in an off-white, slightly yellowish tissue. In other cases, the tissue
is snow white. As far as I know, there are no other conifers that have
this albino trait. With your discovery, you are now a trusted member
of the "albino redwood club," which means you need to keep
the location of the tree a secret. I'm always afraid that someone will
want to chop one down for a Christmas tree!
Fall 2003 |
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| I recently encountered a large redwood tree with a huge bark-covered
bulge at the base of the tree. What causes this? The growth
you describe is almost certainly a "burl" or,
technically, a "lignotuber." A burl forms at the base of the tree and
provides a reservoir of dormant buds that can sprout in the event of
major structural damage to the trunk. The burl tissue provides a source
of carbohydrates to its growing sprouts and can also generate roots. In
California, it's not uncommon to find redwood burl for sale.
Unfortunately, most burl is harvested illegally from parks and
conservation land causing damage and disfigurement to the trees. Burl
is best left in its natural state where it can serve its important role
in redwood regeneration. [Editor: Read Dr. Brinegar's essay: About
Redwood Burl for more detail.] Summer 2003 |
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| I live
in (pick any city, state or country). The redwood tree I planted in
my yard appears to be dying. Can I do anything to save it? I have lost count of the number of e-mails I have received on this topic! After seeing groves of majestic coast redwoods and giant sequoias in California's state and national parks, it comes as no surprise that people would want to plant their own. Unfortunately, many
attempt to cultivate these trees in climates that are far too extreme.
Several inquiries from Oregon and Washington bemoan the browning of the
growing tips of their ornamental coast redwoods (too cold). One reader
described the poor condition of a giant sequoia she found planted in
Kansas (too dry). Californians try to grow coast redwoods too far
inland, even in the Central Valley (too hot). Against all odds, one
intrepid redwood-lover has managed to grow a relatively healthy tree in
his backyard garden in Warsaw, Poland! However, he was only able to do
this by warming the root system in the winter. There are a few regions
of the world that are hospitable to redwoods, such as parts of New
Zealand and Spain because they mimic the temperate, moist, foggy
conditions of coastal northern California. But there is no other region
in the United States where coast redwoods will grow nearly as well as on
the California coast. [Editor: For more on this topic, see Dr. Brinegar's essay: Growing Redwoods in Non-Native Habitats.] Spring 2003 |
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| Is
there an easy way to tell the difference between a Sequoia sempervirens and a Sequoia gigantea, except for location? Yes, it is very easy
to tell the difference between a coast redwood and a giant sequoia.
The leaves on a coast redwood are flat needles (about 1 inch
long) arranged in flat "sprays" on the branchlets,
whereas the leaves of a giant sequoia are very tiny, overlapping
and "
awl-shaped" similar to a cypress or juniper. Also the cone of a
giant sequoia is about the size of an egg while the coast redwood's
cone is only one quarter as big. In mature trees, the giant
sequoia's crown is more obviously rounded than the crown of a coast redwood. Winter 2003 |
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| I
have seen a grove of redwoods that had all their foliage
burned. Now it appears dormant buds have generated new
growth. Is this normal?
The
quick answer is yes -- it is quite common to see a
redwood tree "refoliate" after burning. If the fire burns
the foliage but leaves the trunk intact (that is, only
scorches the bark), then the vascular cambium (inner bark)
survives and is able to provide nutrients to regenerate new
branches and needles. In the beginning stages of regrowth,
the trees look a bit funny because the new foliage tends to
make the trunk look "furry" for awhile. In cases of major
fire damage where the parent tree's bark is girdled or the
tree is burned down to the stump, new shoots will arise from
dormant buds in the tree's burl (or lignotuber) at the base
of the trunk. This results in a "fairy ring" of new trees
circling the original stump. Fall 2002 |
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| While
hiking in Big Basin I saw numerous fire scarred redwood
trees and stumps. What is the recent fire history of the
park? The most
recent wildfires in Big Basin occurred in 1980 and 1984 in
the southern and southeastern sections of the park. In
addition to these, there have been a series of intentional
"prescribed burns" in the northern and northeastern parts of
the park since 1978. Such low intensity fires are designed
to lessen the fuel load on the forest floor to prevent
future fires from spreading into the upper canopy. The
ultimate goal, according to State Parks ecologist George
Gray, is to mimic a natural 40-year fire return
interval. Summer 2002 |
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| Earlier this year there were reports that redwoods might
be susceptible to Sudden Oak Death. How much of a threat
does this disease pose to redwoods?
According to the California Oak Mortality Task Force
(COMTF), redwood is not a confirmed host of Sudden Oak Death
(SOD). The earlier media reports were based on
circumstantial evidence which is currently being
investigated by researchers at UC-Davis and UC-Berkeley.
They hope to have a definitive answer soon.
UPDATE (September 2003): According to the California Oak Mortality Task Force (COMTF), there are more than three dozen species of plants in California known to host P. ramorum. This now includes Sequoia sempervirens. However, according to Dave Rizzo (plant pathologist at UC-Davis), there is still no evidence that mature redwoods are harmed by the pathogen. For a complete list of host plants and future updates, please refer to the COMTF web site (see below). Phytophthora ramorum, the pathogen that causes SOD, is a parasitic water mold with a broad host range among native California plants. Symptoms range from bleeding trunk cankers (coast live oak, California black oak, and tan oak), leaf spotting (rhododendron and buckeye), and leaf tip die back (bay and madrone). SOD can be fatal to some species, especially the oaks, but not necessarily to others such as rhododendron, buckeye, and bay. P. ramorum has never been proven to be the cause of disease in any conifer. Even if redwood seedlings and sprouts are affected, it is very possible that mature redwoods could show resistance to infection. If further research indicates that redwoods are not significantly affected by SOD, the disease still poses a major threat to the redwood forest ecosystem. Tan oak, the most susceptible species, is one of the most common understory trees in the southern range of redwood forests. Many animals rely on tan oak acorns for food; birds and arboreal mammals use tan oaks for nesting. Dead tan oaks will not only jeopardize forest wildlife through loss of food and habitat, but could also lead to an increase in the fuel load resulting in more intense fires that could kill the larger redwoods and Douglas firs. Although the eradication of SOD will not come soon, there is hope for the future. More funding has become available for SOD research, monitoring, management and education from private, state, and federal sources. The Gordon and Betty Moore Foundation has recently contributed $1 million to UC research efforts. The USDA is considering an allocation of $3.5 million in emergency funds. Senator Barbara Boxer has sponsored a rider to the current farm bill that would make $70 million available to study and fight this disease. Sempervirens Fund will continue to support these efforts through member-education and careful monitoring of its forest property. Internet sources: www.suddenoakdeath.org; www.parks.ca.gov; www.ucmp.berkeley.edu/chromista/oomycota.html
Spring 2002 |
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| What
is the major ecological benefit of adding more land to local
redwood parks?
If the
addition of land is done strategically, then the major
ecological benefit to a park is an increase in its
"connectivity"-- the degree to which individual parcels of
land contribute to a continuous forest uninterrupted by
roads, urbanization or timber harvesting. The larger blocks
of forest are more buffered from physical damage by wind or
erosion and suffer less habitat disturbance caused by
changes in canopy structure or invasion by non-native
species. [Editor: For more on this theme, see our essay Protecting the Regional
Ecosystem.] Winter 2002 |
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| How
long does it take for a coast redwood to mature into a tree
that produces seeds?
Redwoods
that grow from seed can be anywhere from 5-15 years old
before they start producing seeds themselves. No one knows
exactly why there's such a wide range, but environmental and
genetic factors probably control the production of
seed-bearing cones. Fall 2001 |
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| What
are the primary uses of redwood lumber? Are alternatives
available? The vast
majority of redwood lumber is used for fences and decks.
Cedar, with decay resistance similar to redwood, is a good
natural alternative. Pine and fir can also be used if
treated with weather-proofing coatings or stains. New
"synthetic" lumber made from recycled wood and plastics
(Trextm and Timbertectm) is an
attractive and forest-friendly alternative. [Editor: For
sources of alternatives, see our Synthetic
Decking Materials page.] Summer 2001 |
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| Which
is the bigger threat to redwood forests, logging or
development? In the
sparsely populated counties of the northern redwood region
(Mendocino, Humboldt and Del Norte) clear-cut logging is by
far the bigger threat to redwood forest ecosystems. But in
the Santa Cruz Mountains where more selective logging
methods are used, the recent boom in housing and commercial
development poses an equally great threat to redwood
lands. Spring 2001 |