Energy and nutrients move through trophic levels in the forest ecosystem. Students should understand the concepts of trophic levels, food chains and food webs. Point out the importance of decomposers as well as the more obvious producer and consumer levels.

As you discuss each organism with your group of students, ask them to describe its distribution in the forest. Ask the group to suggest biotic or abiotic factors that may affect the distribution of the organism (e.g. light intensity, associations with other organisms, availability of moisture, type of substrate, etc. Make sure that you discuss this for at least one member of the plant, animal and fungal kingdoms.

To start your walk head across campus to the Shell station. Walk carefully across the road (watch for traffic!) and stop just beside the Shell station. A number of features are described below, but feel free to point out any other features of interest.

  1. The first stop is the alder grove to the right of the Shell station. Alder represents an early stage in forest succession, the predictable sequence of replacement of the plants and other organisms that make up a forest community. Discuss succession (primary versus secondary) with your group, and explain why alder are a successful pioneer species. Alder plants grow fast, quickly moving into and growing in newly opened areas, such as logged areas. These trees are almost 30 years old, the same age as SFU. The university gave them a start when they cleared the old growth from the mountain top. Red alder seedlings are intolerant of shade. The seedlings grow only in full sunlight. Nodules on alder roots are packed with mutualistic bacteria. These bacteria fix nitrogen into a form that is usable by the trees.

    Walk down the trail that angles down from the Shell station and look at the shrubs beside the trail.

  2. Indian plum is the first tree to come into leaf and flower in the spring. Why does Indian plum flower so early? Southern B.C. represents the northern limit to the distribution of this species, which is common in Oregon and Washington. Indian plum is rarely found in exposed areas this far north. The larger trees create a protected microclimate that offers protection from frost.

  3. On your left is salmonberry. This plant is clonal. Above ground runners produce new upright plants, allowing a rapid spread of this plant over a large area by asexual reproduction. Many of the shrubs we see in the forest are clonal, including trailing blackberry and most of the other berries. Discuss with your students the possible benefits of clonal growth. How do we define an individual plant? Is it one upright salmonberry plant or the whole clone? Salmonberry, with its showy flowers of mauvey-red, flowers quite early in the spring. Chickadees feed on the nectaries at the base of the flower, pulling off one petal to feed on insects that visit the nectary and serve as pollinators.

    Point out the cedars to the students. The cedars and alders probably got started together. The fast growing alder is taller now, but the cedar will eventually tower over it and shade it out. Cedar is important in continuing forest succession, replacing alder as the next successional stage.

  4. The broken alder trunks are testament to the massive blowdown that took place in the Fall of 1994. Use this dramatic pile of alder trunks to discuss the costs and benefits of deciduous vs evergreen habit in trees. Deciduous trees of the northern temperate zone lose their leaves in the winter. Their broad, flat leaves lose water readily through their stomata. In the winter, there is insufficient light to warrant the cost of maintaining these leaves. Natural selection has favored the habit of disposing of the leaves when the costs of maintaining the leaves and supplying them with water become greater than the benefits of the photosynthesis they carry out. The tree extracts everything possible from the leaves before they are shed. The blowdown illustrates a further cost to a tree of retaining its leaves too long. In the Fall of 1994, wet snow fell on the mountain early, when many alders still had their leaves. Wet snow and high winds combined to tear off the top halves of many alder trees. During this episode of selection, alder that had already shed their leaves were undamaged. They would have greater reproductive success in the future than the heavily damaged alders.

    Conifers are evergreen. Why do they not pay the same costs as the alder for retaining their leaves? Conifers have features of leaf design which reduce water loss - sunken stomata and heavy cuticle. Point out the way the branches and needles are arranged, and how snow is less likely to accumulate on these trees. Turn right at the Y in the trail and stop.

  5. You are standing under a grove of Western hemlock. If you look up in the canopy, the large growths that you see in the hemlock branches are dwarf mistletoe, a parasitic species of plant. Sticky seeds of the parasite land on the hemlock. Specialized structures called haustoria grow into the branches of the host and obtain nutrients for mistletoe. The mistletoe resembles a fungus, structurally with its haustoria and nutritionally with its absorptive nutrition. This is a good example of convergent evolution. The growth of the mistletoe weakens the apical dominance of the hemlock branch and results in the haphazard, sprawling branch growth you can see above. The parasitized trees have reduced vigor. They are prone to secondary infections and often suffer from root and trunk rot. You can see why they are not suitable for logging.

    Go on a little further to the large hemlock on your left.

  6. This large hemlock will not be alive much longer. Note the large canker at the base from some long ago wound. Within the canker are fungi which are helping to break down the tree tissue. These fungi probably infected the weakened tree. Look over the trunk, noting the woodpecker holes. This tree will soon be a snag. Although dead, the trunk will be a good wildlife refuge with cavities and a decaying core. Small mammals such as squirrels and rodents and later racoons will find a home in this tree.

  7. Look to the left and you will see a grove of vine maple. Look closely at the branches. The dichotomous branching you see is diagnostic of this tree and can be seen very clearly in the flagged vine maple seedling a couple of paces down the trail. Vine maples require a fair amount of light to flower and fruit. Note that the gap in the canopy at this point in the trail, allowing the vine maple to flourish.

  8. Review with your group the life cycle of a fern. The sword fern is large and very abundant in this forest. Remind them that they are looking at sporophytes. Show them sori on the underside of the leaves. Meiosis in the sori produces haploid spores (homosporous), which are shed and develop into multicellular, photosynthetic, sexual gametophytes.

    Point out to your group that quite different groups of plants have evolved similar solutions to the common problem of seed dispersal. Hemlocks, alders and maple trees all have winged seeds. Thus, gymnosperms and angiosperms have independently evolved the same basic mechanism to solve a common problem. This is an excellent example of convergent evolution. Salmonberry, elderberry and Indian plum - all lower level shrubs - have tasty, showy fruits. These species rely on small birds to eat their fruit and disperse the indigestible seeds. Ground plants have hooked or barbed seeds which attach to fur (or socks) for dispersal.

  9. A few steps further, young hemlocks are growing on the snag to your left. Such stumps or logs are called nurse logs, as their decomposition provides nutrients which nourish the growth of young seedlings. Consider how essential fungi are as decomposers in the forest. The nutrients released to the soil by the decomposition of leaves, twigs and fallen trees (like this nurse log) are essential to the new growth of plants each year. Remind students that fungi have absorptive nutrition. They secrete digestive enzymes and then absorb the released nutrients. Also explain to students that energy does not cycle in ecosystems but inorganic nutrients do.

    Look at the huckleberry growing on the old nurse log as you walk a little further down the trail.

  10. Look up at the forest canopy. Only the upper branches of the trees have leaves. The lower branches are dead. The canopy leaves intercept the light. Not enough light penetrates to the lower levels to warrant the cost of having leaves on the lower branches.

    The reduced light under the forest canopy is an important factor leading to succession. The alders that grow so well in brightly lit clearings cannot germinate or grow in the shade and hence they are succeeded by those who can, primarily the conifers such as the Western Red Cedar, the Western Hemlock and Douglas Fir. These trees are able to grow in the shade of the faster growing alder but eventually the conifers outgrow the alder and form the new upper canopy. The shaded red alder will eventually die off, leading to the old growth forest.

  11. Huckleberry is another clonal plant. It is also interesting because it is partially deciduous. The lower branches retain their leaves throughout the winter, while the upper branches lose theirs. Discuss with your students the advantages of such a dual strategy.

  12. The size and age of the hemlocks which can be seen growing on this nurse log is testament to the length of time it takes for nurse logs to decompose. Some may persist for over 100 years. Look at the nurse log and see how many different types of organisms you can find on it. Mosses and fungi will probably be the most common, but look also for lichens and small insects.

    As you walk along, look and listen for birds. You could talk about some of the forest birds to the students, even if you don't see any. Kinglets are common birds and may be seen flitting through the canopy. These tiny birds may weigh less than 10 grams. Like chickadees, they are permanent residents who do not migrate for the winter. They feed continuously in the branches of the canopy, eating small insects, tiny spiders and insect eggs. They must eat something every few seconds through the daylight hours just to stay alive.

    Emphasize why we don't see many higher level consumers in the forest. Only about 10% of the available energy at each trophic level is captured as biomass in the next higher trophic level. Thus it takes a lot of autotrophs to supply energy to secondary and tertiary consumers.

  13. Look for bracket fungi on tree trunks and point out to your students that this reproductive structure is just a small part of the total mycelium of the fungus.

    Keep your eye out for Douglas squirrel in this area. These squirrels have relatively small territories of less than 5 hectares. Discuss with the students why squirrels chatter at intruders, expending energy in defending a territory.

  14. Look for snags with woodpecker and sapsucker holes. Both birds feed on insects under the bark and the holes they drill serve as entry points for decomposing fungi. Go on a few steps and look to your right. In the large snag, you can see a chink. A platform was placed in this chink for loggers to stand on while sawing down the tree. This reflects the old style logging practices of 80 years ago.

  15. Walk on again until you see a steep bank on your right. As you walk along the bank, consider how the obvious stratification you see here developed. As you can see, the sediments have been sorted by size. Consider how a stream might transport sediments downstream and how small pebbles and fine silt might become separated.

  16. Look for mosses and liverworts on the bank or in the area moistened by the stream. These are seedless non-vascular plants that they saw earlier in the course. Remind them that the green plant they see is the haploid gametophyte. Look among the moss plants for a 2n sporophyte growing on the gametophytes.

  17. Head up the hill and walk along for a few minutes until you see the flag on your right. In this area you can see a dense growth of sword ferns. This dense growth is due partly to the reduced amount of canopy cover in this area. Note also the large maple trees. Light is very important in the distribution of plants. Soil nutrients are also important and the abundance of sword ferns indicates a productive area. This productivity and abundance of plants also results in an increased abundance of insects and small mammals.

    Head along the trail and turn right at the Y intersection. Take a deep breath and head up this trail known as Cardiac hill (Note: students not fit enough to make it up this hill may retrace their steps back to the Shell station). If you want a breather, turn and look back at the view below, assuming it's clear. Turn right at the Y at the top of the trail and as you come out onto the Ring Road head right and cross through C lot towards Strand Hall.