How the forest grows...
How the forest grows
On a warm summer day the leaves of a large tree can suck up from its roots as much as two or three hundred gallons of water. This intense activity underneath the placid surface of a tree is one of the basic activities of growth in the forests.
Trees, for all their great bulk and strength, can be up to 90% water. Leaves draw in carbon and oxygen from the atmosphere. Roots get potassium, nitrogen and other minerals from the soil. Water and sap pass upward and downward in the stem and branches of the tree through bundles of tubes that are like tiny chambered straws. They distribute nutrients where they are needed, and thus the forest grows.
Water is the essential element here. The biggest trees in Canada grow on the west coast where there is abundant rainfall and mild temperatures. In the interior of the continent, where there is less rainfall and where severe winters freeze the water in the soil so that it is not available to trees over long periods, trees are smaller in size.
Man and nature w'ork together to promote forest growth. Natural re-seeding is given every encouragement in forests managed by MacMillan Bloedel as this form of regeneration is a natural and efficient means of bringing in a new forest crop. However, where nature is slow to re-stock, seedlings are planted by hand — many millions of them since the programme started in 1938.
This concentration on growing trees is based on man’s need for more and more products created from trees and their fibres. Some materials, such as certain plastics, are by-products of petroleum or natural gas and as those fossil fuels are exhausted they can never be replaced. Base metals will also become scarce in the years ahead because there is no way to create new ones. But as long as we
have water, soil and light we can grow trees to satisfy our needs for wood and wood fibres, for building materials, paper, packaging, forest chemicals and scores of other products. And those growing forests, well-tended and in vigorous health, are available for recreation and as wildlife habitats through their long growth cycle. They will help hold and conserve the lakes and water courses on wffiich both man and wildlife depend.
The study of trees is a major science in itself and every day botanists, tree physiologists, silviculturists and other scientists are learning new things about the growth and function of trees, the conditions that make them healthy or sick, how they age and finally die. At MacMillan Bloedel we feel that one of the most important parts of our role as forest managers is the improved growth of forests entrusted to our care. Because all Canadians share the benefits of the forests. we believe you will be interested in this report on the way the coniferous forests grow and flourish on the west coast.
So the forest grows
The story of forest growth begins with the soil which has been accumulating over the centuries through the action of plants and weather. In pre-history, primitive plant forms such as lichens fastened themselves to rock surfaces and slowly broke them down to small particles. Then mosses and ferns developed and when they died they added humus to the earth’s crust. The weather played its part. The action of ice. rain, heat and cold created more soil particles from solid rock. When larger plants evolved, their roots pierced cracks and crevices and continued the age-old process of breaking up rocks and turning them to soil. Then, if water was present, and light, giant plants such as our northern conifers grewand established vast for-
ests that are a living community of interdependent life forms, animal and vegetable. Trees create thick masses of humus that are an essential part of the forest’s growth. Leaves, bark, branches, cones and dead trees fall to the ground and decay into organic matter that returns minerals to the soil. Like a great sponge, this humus retains moisture, even in the heat of summer.
Trees such as we know them today did not exist until about 300 million years ago. About that time the vascular cambium evolved and made possible the strong timber plants we call trees. Before that, plants grew to about 2 metres in height and they were flabby, soft, shortlived and weak.
The vascular cambium is a thin film, just one cell thick, inside the bark of a tree. On its outer side it develops green bark cells. These newly formed cells carry food from the leaves to the rest of the tree. Outside the green bark, or phloem, new bark cells are produced by a cork cambium to form a protective sheath. On the vascular cambium’s inner side the sapwood is developed that transports w'ater and sap to the leaves for the manufacture of food. Each year the cambium develops a new layer of sapwood on the outside of the previous year’s layer. The results are the familiar rings we see in the cross-section of a tree, a graphic record of each year’s growth.
Old sapwood dies and becomes heartwood. Therefore, most of the tree is dead and only its outer layers are alive. Still, the dead cells of old wood retain their structural strength and trees can. in many cases, stand for centuries in the face of great stress from wind and weather. It is this quality of strength that has made wood one of man’s most important building materials.
A tree with its cambium layer intact but with its green or inner bark removed in a ring around its trunk will eventually die. Water, coming down from the leaves
and horsetails, but no trees. All these plants repoduce by spores and they lack a vascular cambium.
coastal rain forests and they are one of the signs foresters read when assessing the biological, geological and climatic conditions of a forest locality. This particular moss (Isothecium stoloniferum, sometimes called “Old Man’s Beard”) indicates abundant rainfall.
with its store of carbohydrates created by the process of photosynthesis, won’t get through the break in the circulation system caused by the removal of the ring of inner bark. The roots, without these carbohydrates, lose their ability to grow and in time the tree will die from lack of minerals and nitrogen from the soil.
A cross section of a tree trunk provides an excellent illustration of the movement of water within the plant’s structure. The early wood, made by the tree in spring, reveals wood tube cells that are much larger than those made in summer. This is because they must carry more water in spring for developing leaves, shoots and flowers than they do in summer. The lighter and darker shadings of annual growth rings results from the difference in cell size.
much as a foot thick. This outer being produced continually by the cork cambium. The inner bark or phloem (2) is a spongy layer which stores food manufactured in the leaves and transports it to the other parts of the tree. The vascular cambium layer (3), if it could be detached from the bark and the wood.
would be almost invisible because it is only one cell thick. It is vital to the tree’s survival as it continually produces wood or xylem cells on its inner face and phloem cells on its outer side.
Sapwood (4) is the wood which carries water and dissolved mineral sap up the tree.
The heartwood (5), while dead, gives the tree its strength and rigidity. If air reaches it, it soon decays and leaves the tree hollow. As long as it is sealed off from the air by living tissue on the outside it gives the tree its firm backbone.
ture. Just under the surface is the layer of green chlorophyll which captures the energy of the sun and uses it to create food.
The amazing ability of the vascular cambium to build the structure of the tree depends on a steady supply of food during the growing season. The twin sources of food — roots and leaves — work in delicately balanced co-ordination to collect various forms of nourishment from the soil and from the air and combine these elements into sugars and starches that feed the vascular cambium.
Roots draw in water, the principal component of a tree’s bulk, and soil minerals. To make minerals soluble for transport up through the wood as sap, root tips secrete droplets of acid which dissolve mineral elements before they are drawn into the tree’s system.
While this is going on, the leaves, the other half of this remarkable food factory, are at work.
The needles of a conifer tree are its leaves and they function in the same way as the broad, flat leaves of deciduous trees. Through the miracle of photosynthesis (putting together with light), leaves, with energy from the sun, take carbon dioxide from the air and combine it with water and minerals from the roots to make sugar and starches which supply the tree with food. An important byproduct of this process, for man, is oxygen.
The flowers of forest trees, as in other plants, are their reproductive organs. Flowers produce and exchange genes with those of nearby trees of the same species and the fruits which result from pollination and fertilization contain the seed for new trees.
Most trees have separate flowers for each sex — some for pollen, others for ovules. The yew and the juniper have separate trees with all-male or all-female flowers but the others generally have both types of flowers on every tree. However, genes are predominantly exchanged between male and female flowers of different trees.
When speaking of conifers, it is not strictly correct to speak of flowers. Their male and female organs are more appropriately called strobili. The female strobili are usually on the upper or outer branches of the tree and stand upright during pollination. Male strobili or cones hang downward from the branch when pollen is released.
Eventually, the female strobilus of the majority of B.C. conifers develops and hardens into a cone, and that is the distinguishing feature of most conifers.
Some conifers, yews for example, have fleshy strobili called “berries”.
In the coniferous forest, wind is the primary instrument of pollination rather than bees or other insects. The male strobili produce a copious amount of pollen of which only a portion reaches the receptive female strobili.
It is a fact that plants make their greatest effort to reproduce when their life is
in danger through old age or lack of nutrition. After a summer when nutrients are in short supply, flower and fruit crops tend to be large. In conifers, such bumper seed production has been called stress crops. They may arise from a number of causes such as root diseases, extreme drought, or damage to a tree’s translocation system which moves necessary elements to various parts of the plant.
The fruit of a tree bears the seed. On the broadleaf tree it is the female part of the flower, the ovary with the ovule inside, fertilized and grown to ripeness. The ovule becomes the seed, the ovary its covering. For example, in a peach, the shell of the stone is the ovary; the kernel the ovule. The fleshy covering around it is a development of the stem just below it.
Conifers are different. The fruit of the conifer is usually a woody cone but may be fleshy as in the juniper or yew.
Conifers are known as gymnosperms (from the Greek “gymno” meaning naked and “sperm” meaning seed). The naked seeds develop on the base of the scales of the cone and. at maturity, the cones open and shed their seeds to be scattered in the wind. Some pine cones require heat to open.
The reproductive cycle — from bud, strobilus, pollination, and cone formation to the release of the seed — takes varying lengths of time depending on species and growing conditions. Studies in British Columbia have shown that the entire reproduction cycle of the Douglas fir extends over 17 months, starting with buds visible in April. The vegetative buds develop into shoots during the following ten weeks. Early in that period the function of new buds is determined as vegetative or male or female strobili. Pollination of the female strobili doesn’t occur until the following April and the mature seeds are shed in the fall of the same year. Some conifers, the pines for example, require an additional year for the seed to mature.
The fruit of a tree — whether plum, peach, berry or wood cone — has a single purpose: to carry the seed away from the parent tree to a site where it can take root and start a new tree.
Birds, animals and the elements cooperate in nature’s seed dispersal process. Thousands of broadleaf species have their seeds distributed by birds which feed on the trees’ berries. Conifers get help from the wind. Most seeds of the Douglas fir fall within 1,000 feet of the parent tree but some have been carried by the wind for a mile or more. Squirrels, field mice and other animals hoard seed for the winter and inevitably lose some of them so that they are in effect planted.
Most forest seed ripens in the autumn The conifer seed is dormant during the winter. Then it will germinate after the winter cold has activated it and broken its dormancy.
sap for the vigorous development of the leader. If the tip is broken off, or eaten by deer, its strength is inherited by the next bud down the stem which becomes the new leader.
In a forest untended by man, crowded conditions and nature’s competition frequently bring slower growth in trees which must fight for space, sunlight and nutrients. A cross-section of a tree from such a stand will show annual rings becoming smaller and smaller as the tree gets older, especially when the tree passes its prime which, in the case of conifers in British Columbia may range anywhere from 80 to 200 years. MacMillan Bloedel has found that its managed forests show more consistent annual growth rates.
Under modern technology, trees are cropped with the same regularity as food crops, though the cycle is much longer. For example, a Douglas fir at 5 years of age is the equivalent in maturity to a corn crop 5 days after germination. The forester who sows a new crop is not likely to be around at harvest time, while the grain farmer will take off many crops from the same land in a lifetime. A Douglas fir will mature in about 80 years. You can harvest ears of corn in about 80 days after seed germination.
A 50 year-old Douglas fir in its prime, having reached 100 feet in height, can add .8 cubic feet of wood in a single growing season, 2 feet in height and Vi inch in diameter 4l/i feet above ground level.
belt forests marked by a predominance of Douglas fir interspersed with arbutus and other species which require more light but less rainfall.
strobili with pollen collected from other superior trees. The resulting seeds should produce a new crop of superior trees.
the forest floor is often covered to a depth of several feet with fallen logs. These victims of storms, fires or old age constitute rich sources of decaying humus in which seeds can germinate and grow. Later the upper roots of the young trees, such as those shown here, embrace the nurse tree and then seek out the soil below. In some cases when the nurse tree has rotted away completely, the surviving tree stands on its upper roots as though on stilts.
right has been thinned by MB’s forestry crews. Each tree has put on optimum growth because it has been assured ideal food and light conditions.
Improved strains of trees are being developed by selecting the best trees and using them as parents in controlled breeding. There is an agency known as the Tree Improvement Board, started in 1958 as an association of government and industry foresters. MacMillan Bloedel foresters play an active part in this organization which has selected more than 600 Douglas fir “plus” trees — trees which appear to be superior to their neighbours in growth and form.
In an area near Nanaimo, a “bank” of trees of known origin has been established by means of rooted or grafted cuttings. The resulting plants are genetically the same as their parents and represent “clones”.
In some special experiments, clones are fertilized with pollen from one other selected plus tree. First, all male cones are picked off to eliminate any possibility of self-fertilization and a paper bag with a polyfilm observation window is fastened over the plant. Pollen is injected with a hypodermic needle and the needle hole is plugged so the bag excludes the entry of airborne pollen from any other source.
MacMillan Bloedel is a Canadian company with operations in many parts of the world. Its principal products are building materials, pulp and paper products, and packaging products. It also offers worldwide shipping services through its transportation subsidiaries. It is the largest company of its kind in Canada, employing almost 19,000 people in this country and 5,600 in other parts of the world.
MB is a company harvesting a renewable resource as illustrated in this booklet. The trees it cuts in managed forests are replaced so that the resource is not diminished. yet the products manufactured in the Company’s plants are sold at home and abroad to earn millions of dollars in payrolls for its employees, further millions in taxes and other charges for all levels of government, and foreign exchange that benefits the entire Canadian economy. The Company’s sales last year were well over a billion dollars and about 80% of
that represented income brought into Canada from sales outside the country.
Since it was founded more than 60 years ago in British Columbia, the Company has pioneered many of today’s methods of harvesting trees, getting the logs to converting plants, and shipping the end products to markets. In 1973 we spent more than $86 million adding to our plants, equipment and property.
Investments of that size have a spin-off effect on dozens of other companies that supply the forest industry with goods and services. They represent thousands of additional jobs. Therefore, it is in the interest of all Canadians to assure that their forest industry is taxed and regulated on a scale no greater than that in other wood-producing countries. If the costs of making our products are raised beyond those of our competitors, we will be in no position to supply the new jobs a growing Canadian labour force will need. Indeed,
we will be hardpressed to maintain employment at present levels.
Canadians have the technology to grow and harvest the finest forests in the world. For itself, MB hopes to expand the contribution it makes to the economies of British Columbia and of Canada, but this will depend, to a large extent, on the cost of getting the raw materials out of the forests, converting them and getting them into the hands of our customers. If governments and industry can work together to keep those costs under control, we can continue to compete with the best.
Copyright 1975, MacMillan Bloedel Limited.
1075 W. Georgia, Vancouver. B.C V6E 3R9