This is an opportunity for you to
test your tree knowledge!

What's wrong with the tree in this picture? (Click somewhere to find out.)

See if you can answer some of these common questions about trees:

     What is the largest tree in the world?

     What is the tallest tree in the world?

     What is the oldest tree in the world?

     How do trees grow?

     What do trees eat (or do they actually "eat" at all)?

     Can trees feel pain?

     Are there male and female trees?

     Why are trees important to us?

     If a tree fell in the forest, and nobody was there to hear it, would it make a sound?

The World's Largest Tree

The largest tree in the world (by volume and weight), and the biggest, most massive organism alive today, is called General Sherman, and is a giant sequoia (Sequoiadendron giganteum).  It stands in Sequoia National Monument, in the western Sierra Nevada Mountains, California.  This tree is 274.9 ft. tall (83.8 meters), has a diameter of 36.5 ft. at the base (11.1 meters), and is estimated to have a volume of 52,500 cubic ft. (1,486.6 cubic meters).   In lumberman's terms, this one tree probably contains 630,000 board feet of lumber.  (A board foot is 12 in. x 1 in. plank that is one foot long.)  Luckily, since this tree is protected, it will never be cut down and we will never know for sure how much wood could be cut from it.  It is approximately 2,200 years old, and is apparently still growing vigorously.

Trees of this species are also known as sierra redwood, or simply Big Tree, and are called Wellingtonia in Europe, where it was introduced over 150 years ago.  Several specimens in England are already over 100 ft. (30.5 meters) tall.  The Morris Arboretum has a few specimens which are only around fifty years old but are already at least 60 ft. (18.3 meters) tall.

In their native California, they are a high sierra tree, growing at mountain elevations between 4,500 and 8,000 feet (1,370 to 2,440 meters) above sea level.  The average specimen reaches about 250 ft. (76 meters) at maturity, with a diameter at the base of around 15 ft. (4.6 meters).  Although the growth rings are extremely close together, meaning the tree expands only slightly in girth each growing season, adult trees of this species are thought to grow faster than any other tree in the world:  In just one year, the average giant sequoia tree gains enough wood to make a sixty-foot tall, three-foot diameter oak tree!  The maximum lifespan of this species is thought to be about 3,000 years; that's a LOT of wood.  This tree once grew in dense forests, which covered millions of acres.  Now only about 2% of these forest stands are left; all the rest have been cut down for their lumber, and all of this logging occurred in the last 150 years.

For photos and more information about the world's largest tree, you can visit the National Park Service's General Sherman Tree web site.  There is also a Gymnosperm Database page with lots of botanical information on giant sequoias, and a page on the Yosemite Associations's web site that discusses how the age of the General Sherman Tree was estimated.  (Following these links will take you off of the Morris Arboretum's web site.)

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The World's Tallest Tree

The tallest tree in the world is the Mendocino Redwood, which is a coast redwood (Sequoia sempervirens).  It is 367.5 feet tall (112 meters), and it stands at the Montgomery Woods State Reserve near Ukiah, California.  Even though the General Sherman tree is the largest tree on Earth, there are plenty of trees that are taller than it.  The coast redwoods, which grow near the Pacific Coast in California and Oregon, commonly grow to heights of over 300 feet (91 meters)!  This species grows taller than the giant sequoia, but they are more slender and not as massive.  The Mendocino Redwood is estimated to be ten centuries old, and the height was measured using a laser in 1998; at this time it had a diameter of 10 feet, 4 inches (3.14 meters).

Coast redwood forests once occupied millions of acres along the Pacific coast between southern Oregon and southern California, but sadly they were heavily logged, and now only about 5% of the original trees are left.

It is worth mentioning that the Mendocino Redwood was not always the tallest tree on earth.  In Australia, the mountain ash, a.k.a. Australian eucalyptus (Eucalyptus regnans) commonly reaches heights of 260 feet (80 meters), and is the tallest hardwood (broadleaf) tree in the world.  A specimen at Watts River, Victoria, Australia, was originally 492 ft. (150 meters) tall, and is the tallest tree ever measured.  It is thought that this species once grew even taller, perhaps up to 500 feet (152 meters) tall!

For photos and more information about the world's tallest tree, you can visit the Sempervirens Fund's facts page on coast redwoods.  You can also read a great article about visiting the Mendocino Redwood. (Following these links will take you off of the Morris Arboretum's web site.)

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image from the National Park
Service's Great Basin On Line web site

The World's Oldest Tree

The oldest tree in the world is the called the Methuselah Tree and it is a Great Basin bristlecone pine (Pinus aristata var. longaeva, also called simply Pinus longaeva).  This wind-blasted, gnarled tree is 4,767 years old, and is located in California's White Mountains.  Careful study of growth rings from a core sample yielded the tree's age.  There are dozens of other trees in the same general area which are almost as old.  There are several trees in Patriarch Grove at the Ancient Bristlecone Pine Forest, but scientists have not actually publicized the exact identity of Methuselah, in an effort to protect it.  Most of the bristlecone pine trees of this high-altitude grove, which is over 8,000 feet above sea level, are actually quite small and stunted, and appear to be just barely alive.

For photos and more information about the world's oldest tree, you can visit an excellent web site devoted to the bristlecone pines.  There is also a PBS web site about Methuselah, and a National Park Service page on the tree.  (Following these links will take you off of the Morris Arboretum's web site.)

How Trees Grow

Trees grow upwards and outwards, adding new wood each year, expanding in volume.  They add new tissue at the tips of their branches, which is called primary, or extension growth.  They also expand outwards, adding another annual ring to the entire outer layer of the tree, which is called secondary, or annual growth.  Once a branch appears somewhere, let's say ten feet above the ground, it stays there; it does not get carried up the tree as the tree grows, because that is not how trees grow (this is a popular misconception).

The typical tree starts as a seed, then devotes all of its energy to growing larger each year and protecting itself from its natural enemies.  Some trees in a forest setting have to try to grow as tall as possible, as quickly as possible, because they must compete with other trees for valuable sunlight (see "Do trees eat?").   When a tree reaches maturity, it starts flowering and producing seeds or fruit.  A mature tree is not necessarily a full-sized tree, and different species of tree mature at different rates, in different conditions.  Some trees, such as oaks, take several decades to mature, while others, such as some of the maples, can mature in only a few years.  Similarly, some trees grow extremely slowly and live for a long time (centuries, even millenia), while others grow extremely rapidly and die after only a few decades.  Plants are modular organisms, which makes them different from most of the animals.  They can suffer extreme injury and still survive by adding new tissue (see "Do trees feel pain?").  If a tree is split in half or has its top chopped off, it can survive; most animals can not keep living after such an extreme injury.  The rate at which a tree can grow also depends strongly on the conditions it experiences, such as the quality of the soil it grows in, the amount of sunlight and water it gets, and the temperature and altitude.

Trees can reproduce in a few other ways, besides simply sprouting from a seed.  Some trees create clones of themselves by growing new stems from their roots.  In this manner, one original tree can form a whole forest of trees; all of them are genetically identical clones, since they originated from one seed.  Other trees can resprout after they fall over or after they have been cut down, because the roots store enough energy to grow new leaves.  Still others can reproduce by layering, which is when a plant grows roots down from where a branch contacts the ground; if the part of the tree connecting the original roots to then new roots is severed or dies, there are two independent trees where before there was one!  By cloning, resprouting, or layering, a tree could be potentially immortal!

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Trees Eat...  Sort Of

Trees do not "eat" in the same sense that animals do.  Although you can buy "plant food" and often people "feed" a tree's roots, there are not little hungry mouths underground, gulping down food for the tree.  (There are some truly carnivorous plants, but they are a different story, and thankfully none of those is even close to tree-sized anyway, so we won't discuss them here...)  Instead of chewing and swallowing food like we do, a tree absorbs the nutrients and water that it needs from the soil, though its roots.  Then, using carbon dioxide from the air, and the raw materials it has drawn from the soil, it harnesses the energy of sunlight to create food for itself in its leaves!  The process of making food by using sunlight is called photosynthesis, and all trees, as well as all other green plants, do it.

Trees Don't Feel Pain...  But they Do React To their Surroundings

When you "wound" a tree, it does not feel pain.  An injured or sick tree is not suffering in the sense that we would suffer.  You can not hurt a tree, if by "hurting it" you mean "causing it pain".  Unlike most of the animals, plants do not have a central nervous system, and therefore cannot sense their surroundings in the same way that animals can.

However, trees can be harmed or injured; when the tree's outer layer of living tissue, which is just under the corky bark, is damaged, it is considered an injury.  A typical injury that trees suffer occurs when something crashes into the bark, such as another falling tree (in the forest), or an automobile (in the city); either way, the tree's protective bark is not strong enough to prevent injury, and the living tissue underneath is crushed, cut, or physically damaged in some other fashion.  Often the bark is completely removed when the injury is inflicted, exposing the living wood of the tree.  Lots of organisms feed on trees, which is one reason trees have bark in the first place:  To protect them!  A healthy tree will actually react to such an injury in order to prevent the tissue from becoming infected by bacteria or fungi, and to prevent insects and other animals from exploiting the breach in the tree's defenses.   The reaction is extremely slow, so you can't see it, but it is certainly happening.

Depending on the season and the type of tree, a tree will respond to an injury by forming "wound wood", which gradually grows over the injury and covers it.  Eventually the wound wood seals off the injury and the bark is once again complete, only this time a "scar" is visible.  Sometimes the process is complete within a year, but if the wound is large, it can take years or even decades for a wound to close.  Tissue that is damaged in a plant cannot be repaired in the same way that tissue can heal in animals; instead, the plant allows the injured area to die, and it builds "walls" around it to prevent decay from spreading into uninjured tissue.

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Some Trees Have Gender, Some Don't

Before you can understand gender in trees, you have to understand that flowers are the reproductive parts of trees.  When a flower on a tree is pollinated, it can produce a fertile seed, which can later germinate and grow into another tree.

There are some tree species in which an individual tree can be called "male" or "female"; these trees are referred to as dioecious ("dye-EE-shus").   Female trees have only female flowers, and therefore are the only ones that can produce seeds or fruit.  Male trees have only male flowers, and therefore are the only ones that can produce pollen; they produce the pollen that pollinates female flowers, but they cannot produce seeds themselves, so you will never see a single fruit or seed on a male tree!  Examples of dioecious trees include American holly (Ilex americana), boxelder (Acer negundo), poplar (Populus spp.) and white ash (Fraxinus americana).  [Yews (Taxus spp.) and the ginkgo tree (Ginkgo biloba) occur as male or female individuals as well, but they are not actually flowering plants, and as such, they can not be truly considered dioecious.]

There are other tree species in which all individuals are both male and female; either their flowers are perfect, meaning that they have male and female reproductive parts in each flower, or they have separate female and male flowers on the same tree.  Trees that have two different kinds of flowers on the same tree are called monoecious ("mon-EE-shus"); trees that have only perfect flowers are called bisexual.  Examples of some monoecious trees include sugar maple (Acer saccharum), red oak (Quercus rubra), black walnut (Juglans nigra) and American sycamore (Platanus occidentalis).  Some trees which are bisexual are magnolia (Magnolia spp.), flowering dogwood (Cornus florida), tuiliptree (Liriodendron tulipifera) and wild black cherry (Prunus serotina).

There are even a few trees that are normally dioecious, but are sometimes observed to be monoecious; these are referred to as polygamodioecious ("pol-IG-a-moe-dye-EE-shus").  An example of a polygamodioecious tree is the sassafras (Sassafras albidum).

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Trees Are Important To Us For All Sorts Of Reasons

Outside of residential communities, trees are used by people in many different ways; they are cut and used as a source of lumber or fuel, their fruits or nuts are used for food and oil, and their flowers are used for decoration.  Within residential areas, we use living trees as sources of shade and as landscape accents.  Everywhere they grow, trees provide shelter, food and habitat to birds and other wildlife.

In addition, trees help the environment.  Trees (and all other green plants) consume carbon dioxide and produce oxygen; both of these things are good for humans because we need oxygen to breathe, and too much carbon dioxide is thought to contribute to the Greenhouse Effect.  Trees also play a key role in the cycling of water from the ground into the atmosphere; in tropical rainforests, they function as "rain machines", and if the forest is cut down, there is actually less rain.