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Mt. Washington| Cathedral Grove

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Coastal Forest Ecosystems
by Terry Taylor

A forest is much more than an industrial or recreational resource. It is a dynamic ecosystem, with trees being only one of many life forms in that system. The trees may be the dominant and most obvious components, dictating conditions of shade, humidity, acidity, and nutrient availability to which other living things must adapt, but they are still only a small part of these complex communities.
Many people are familiar with the more common understory shrubs and herbs, as well as the most frequently encountered birds and larger vertebrates. But there are thousands of small life forms which are important components of coastal forests. Some of these are known to specialists, but the vast majority have not been discovered. Included in this assemblage are invertebrates, mosses, lichens, fungi, algae, protozoa, and soil bacteria.

Photo Credit: Carol Fuegi

Studies in the old growth canopies of the Carmanah Valley have identified many insects previously unknown to science. The interactions taking place within this insect community probably lessen the potential for pest species to reach epidemic proportions. One reason for the success of these insects is the dense growth of mosses on the large branches of ancient forest trees. Large, old-growth Douglas firs possess massive branches, densely covered with thick cushions of moss, especially hanging moss (Antitrichia curtipendula) which is seldom well-developed in second growth forests. On the branch surface beneath the moss carpet is a soil layer. This layer of moss and soil supports a rich population of insects, mites, fungi, and bacteria. But that layer of soil is unusual. It is in the canopy high above the forest floor.
In old-growth western hemlock forests there are also thick branches supporting dynamic micro-ecosystems, but these are formed in a different way. They are the result of hemlock dwarf mistletoe (Arceuthobium campylopodum), a parasitic flowering plant that distorts the growth of hemlock branches. These large, distorted branches are important as marbled murrelet nesting sites. Because dwarf mistletoe causes significant economic losses, and the wood debris resulting from its activities increases the possibility of forest fires, it is usually viewed in a negative way. Although the economic impacts cannot be disputed, dwarf mistletoe is, nevertheless, a very important component of coastal western hemlock forests. Hemlock forests allow very little sunlight to reach the forest floor, and the death of trees from mistletoe infections results in openings within the forest where light can penetrate, supporting the growth of herbs and shrubs, increasing biodiversity.

The canopies of old trees are home to a number of different lichens. A lichen can be thought of as a fungus which farms an alga - a microscopic green plant - within its tissues. The photosynthesizing alga supplies the "food" requirements for the fungal component and the fungus in turn is thought to give the alga protection from desiccation and mechanical injury. Most lichens cannot tolerate continuous shade and humidity, and are usually not present on rapidly growing young trees, where they are shaded out before they can become established. The upper branches of old trees, however, receive more sunlight, promoting much more rapid cycles of wetting and drying. These conditions favour lichen success. The branches of old growth trees often have large amounts of a lettuce-looking lichen, the Oregon lungwort (Lobaria oregana). This species also contains bacteria that remove nitrogen from the atmosphere, making it available to other forest organisms. In such old forests lungwort is often an important source of nitrogen, which in turn is an indispensable building block for the proteins needed by all living things. In forests less than 100 years old it is very rare. Much of the nitrogen in young forests is supplied by red alder or, more correctly, by nitrogen-fixing bacteria contained in the roots of the alder.

If you look at the trunk of a tree, you are not seeing just a tree trunk, but a complex association of different organisms. In some cases the growth of lichens and mosses is so dense that the actual trunk itself is not visible. The age, species of tree, type of bark, position of branches, and shading all have an effect upon the life forms occurring upon the trunk, and where they are located on that trunk. Where it is shaded and moist, mosses predominate, and where it is dry and sunny the lichens flourish. Mosses do tend to grow better on the north side, but this is a generality. The other factors involved are often more important than the direction. Most trees are not perfectly vertical, but possess a slight lean. The underside of this lean is protected from rain, and it normally has a sparse population of lichens. On overhangs that remain dry, even during rainstorms, there grows a group of lichens known as "dust lichen" (Lepraria sp.). These species form continuous, dusty, gray coatings, and depend entirely on water vapour for their physiological needs. As most other plants require liquid water they cannot invade the micro-deserts where the dust lichen thrives. The microscopic dust particles of this lichen are easily blown or transported from place to place, and are capable of regenerating the lichen should they reach an appropriate location.

On the upward directed surface of the trunk, or on the upper surface of branches, there is ample water supply from rainfall, and here there is often a dense layer of mosses of several different species, as well as some members of a related group of plants, the liverworts. Water runs down the branches, and is then channelled down the trunk. Even in dry weather it is possible to see where that flow takes place, as the mosses occupy the moist areas. In humid regions, long festoons of cat-tail moss (Isothecium myosuroides) hang from the hemlock trees. This growth form allows the moss to collect water droplets from the air. If you are hiking through the woods and see a tree trunk that is entirely sheathed in a green layer of mosses it is probably a big leaf maple. This tree supports a complex ecosystem of many different moss species. The alkaline bark is nutrient rich, and is home to a much richer micro-community than any of our other trees.
The wood within the trunk and branches creates another area of biodiversity. Many of the nutrients in the forest are tied up in wood, and there are many organisms which utilize this food source. A number of insects live in wood, and their tunnels permit the entry of wood decay fungi. Most of the fungi in deciduous trees differ from those of coniferous ones, and different fungi use different components of the tree. The outer living wood is called sapwood, and is more nutrient-rich than the inner core of dead heartwood. Those fungi that live on sapwood require a rich food source, and are only active in a log or snag for a few years. Once this food is exhausted the species which live in the nutrient-poor heartwood replace them. Wood is predominantly composed of cellulose, and many of these fungi feed on that substance, which consists of long chains of sugar molecules. The big brackets of the red belt fungus (Fomitopsis pinicola), which are so conspicuous on coniferous tree trunks, are produced by a fungus which breaks down cellulose. After many years of devouring this compound the food supply is exhausted, and the red belt dies from starvation. Many of the rusty-brown rotten stumps in our forests are a result of the activities of this organism. The reddish color is that of lignin, which functions as the cement holding the cellulose fibres together. Lignin is a complex chemical, extremely resistant to decay, but there are a few fungi that can break it down and return it to the soil.

Decay fungi certainly cause considerable economic loss, but they are also indispensable. Without them old wood could not be recycled into new growth. In the oldest forests the oldest trees are over 1,000 years in age. When such a tree dies it can remain as a snag, and later, a log for about 500 years. After the original shape of the log has vanished, the resistant lignin can remain in the soil for another 500 years, before being completely broken down. This is a total cycle of 2,000 years, and none of our forest management practices take into account time spans of this duration.

It is within the soil, however, that the greatest degree of biodiversity is found - a degree of biodiversity so complex that it can be only dimly perceived at the present time. A hint of some of this hidden wonder becomes apparent in the autumn, when many different mushrooms appear. They seem to burst forth without any signal, but this sudden appearance is a deception. A mushroom is a visible manifestation of a microscopic organism. Fungal threads which are essentially invisible grow through the soil, rotten wood, decaying needles, or other substrate, gathering nutrients and supplying them to tiny buds which eventually develop into the mushrooms which are such a conspicuous part of the autumn woods. A considerable amount of fungal investment goes into producing these bodies, which are reproductive organs for producing spores - dust-like particles that function as microscopic seeds. On a fall day the air is full of millions of these spores.

Many of the larger mushrooms are produced by mycorrhizal fungi. There would be no forests without these types of fungi as trees and mycorrhizal fungi are dependent on each other for survival. In seasons other than the autumn the mushroom fungi are still there, hidden in the forest soil, but not producing mushrooms. These fungi grow in intimate association with the roots of plants. They collect water and minerals and channel them back to the plant's roots. In exchange the fungi take some of the sugar produced by the plant's leaves and use it for their own growth. However, by far the largest number of fungi are entirely microscopic, requiring careful research to even reveal their existence.

But the greatest diversity within the forest soil is on a smaller scale yet again. This diversity is represented by the bacteria, of which the numbers of species are probably greater than that of all the other organisms combined. Recent molecular biological research indicates there may be as many as 10,000 different species of bacteria in a handful of soil. This is four times greater than all the higher plant species in the entire province of British Columbia. With present day technology it is not possible to do more than speculate about the dynamics that are taking place in these complex micro-ecosystems. It is generally believed that 99% of bacteria cannot be grown on a Petrie dish, and it is the ones that can be cultured that have been named and studied. Almost all of these hordes of species are completely unknown. We don't know what they are doing, what metabolites they are producing, or what ecological communities they are forming. There is every reason, however, to believe that some of them are producing medically valuable compounds.

In this short article it has only been possible to touch briefly on some of the life forms that grow in our forests. There are many complex inter-relationships taking place here that amply reward the efforts required to study them, and greatly add to the enjoyment of a hike in the woods.
 

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Douglas Fir Tree (Pseudotsuga menziesii)
 
This is the largest tree found in Cathedral Grove. It measures 76 metres (250 feet), 3 metres (9.5 feet) through the middle, and 9 metres (30 feet) around.

Douglas Fir trees presently dominate this old-growth forest at cathedral Grove making up most of the canopy while shading the ground cover. Older Douglas Firs, like the ones found in Cathedral Grove have a long, branch-free trunk and a short cylindrical crown with a flattened top.

There are two varieties of the Douglas Fir, coastal and Interior. The Coastal variety is the one you will see in Cathedral Grove. Both varieties of Douglas Fir grow in very different ecosystems. The Interior variety grows in a variety of habitats. In Cathedral Grove the Douglas Fir grows with Western Red Cedar, Western Hemlock, Broadleaf Maple, Balsam Fir, along with ferns, salmon berries, and devil's club.
 
There are many animals that eat Douglas Fir seeds. These include squirrels, chipmunks, mice, and shrews. Bears will also scrape off the bark of a young tree and eat the sap layer beneath.

A young Douglas Fir has smooth, grey -brown bark. As the tree ages, the bark becomes very thick and deeply grooved, with dark reddish-brown ridges.

The cones on a Douglas Fir are 5 to 11 centimetres long, turning from green to grey as they mature.

The needles of a Douglas Fir are flat with a pointed tip. The needles appear to stand out around the twig.

Another tree species found in Cathedral Grove is the Western Hemlock. The Western Hemlock grows between 30 to 50 metres tall. It has down-sweeping branches and delicate feathery foliage. It has a shallow root system, which makes it susceptible to being blown over by wind as well as being damaged by fire. It also provides an important source of food for deer and elk.

Also found in Cathedral Grove is the Western Red Cedar tree. The Western Red Cedar is a large tree that measures up to 60 metres tall when mature. It has drooping branches and a trunk that often spreads out widely at the base.
 
The Western Red Cedar grows best in moist to wet soils, with lots of nutrients. They can live up to 1,000 years.
 

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