Trees are an important part of our world. They provide wood for building and pulp for making paper. They
provide habitats (homes) for all sorts of insects, birds and other animals. Many types of fruits and nuts come from trees -- including
apples, oranges, walnuts, pears and peaches. Even the sap of trees is useful as food for insects and for making maple syrup -- yum!
Trees also help to keep our air clean and our ecosystems healthy. We breathe in oxygen and breathe out carbon dioxide. Trees breathe in carbon dioxide and breathe out oxygen. We're perfect partners!
Trees do lots for us, our environment and other plants and animals in nature but we don't just love trees for practical reasons. Trees can also be very beautiful -- tall enough they seem to touch the sky and so big around you can't even hug them. Thousands of artists, professional and amateur alike have painted pictures of trees and thousands of poems, songs and stories have been written about them. I would guess that just about everyone on earth has at some point in their life stopped to enjoy the beauty of a tree.
There are two main types of trees: deciduous and evergreen. Deciduous trees lose all of their leaves for part of
the year. In cold climates, this happens during the autumn so that the trees are bare throughout the winter. In
hot and dry climates, deciduous trees usually lose their leaves during the dry season.
Evergreen trees don't lose all of their leaves at the same time -- they always have some foliage. They do lose their leaves a little at a time with new ones growing in to replace the old but a healthy evergreen tree is never completely without leaves.
The roots are the part of the tree that grows underground. Trees have a lot of roots -- the size of the root system is usually as big as the part of the tree above the ground. This is necessary because the roots help support the tree. It takes a lot of roots to hold up a 100 foot tree!
Besides keeping the tree from tipping over, the main job of the roots is to collect water and nutrients from the soil and to store them for times when there isn't as much available.
The crown is made up of the leaves and branches at the top of a tree. The crown shades the roots, collects energy from the sun (photosynthesis) and allows the tree to remove extra water to keep it cool (transpiration -- similar to sweating in animals). The crowns of trees come in many shapes and sizes!
Leaves are the part of the crown of a tree. They are the part of the tree that converts energy into food (sugar). Leaves are the food factories of a tree. They contain a very special substance called chlorophyll -- it is chlorophyll that gives leaves their green colour. Chlorophyll is an extremely important biomolecule, used in photosynthesis -- leaves use the sun’s energy to convert carbon dioxide from the atmosphere and water from the soil into sugar and oxygen. The sugar, which is the tree’s food, is either used or stored in the branches, trunk and roots. The oxygen is released back into the atmosphere.
The branches provide the support to distribute the leaves efficiently for the type of tree and the environment. They also serve as conduits for water and nutrients and as storage for extra sugar.
The trunk of the tree
provides its shape and support and holds up the crown. The
trunk transports water and nutrients from the soil and sugar
from the leaves.
Inside the trunk of a tree are a number of rings. Each year of the tree's life a new ring is added so many people refer to them as the annual rings. The rings are actually made up of different parts:
The outside layer of the trunk, branches and twigs of trees. The bark serves as a protective layer for the more delicate inside wood of the tree. Trees actually have inner bark and outer bark -- the inner layer of bark is made up of living cells and the outer layer is made of dead cells, sort of like our fingernails.
The scientific name for the inner layer of bark is Phloem. The main job of this inner layer is to carry sap full of sugar from the leaves to the rest of the tree.
A number of handy things are made from bark including latex, cinnamon and some kinds of poisons. Because bark is a protective layer for the tree, keeping it safe from insects and animals, it isn't surprising the strong flavours, scents and toxins can often be found in the bark of different types of trees.
The thin layer of living cells just inside the bark is called cambium. It is the part of the tree that makes new cells allowing the tree to grow wider each year.
The scientific name for sapwood is xylem. It is made up of a network of living cells that bring water and nutrients up from the roots to the branches, twigs and leaves. It is the youngest wood of the tree -- over the years, the inner layers of sapwood die and become heartwood.
The heartwood is dead sapwood in the center of the trunk. It is the hardest wood of the tree giving it support and strength. It is usually darker in colour than the sapwood.
Pith is the tiny dark spot of spongy living
cells right in the center of the tree trunk. Essential
nutrients are carried up through the pith. It's placement
right in the center means it is the most protected from damage
by insects, the wind or animals.