Between the tundra to the north and the deciduous forest to the south lies the vast expanse of the North American boreal forest, second largest forest in the world with only the great Siberian forest exceeding it in size. Although the temperatures there can dip to a low of 40
°
C below zero, the average summer temperature rises to 10
°
C, warm enough to support the growth of trees. The trees that grow there must face long periods of cold and drought, winds, and very poor soils. The soil is not only thin in depth, scraped away by the movements of glaciers, but also very acidic. This acidity comes from the pine needles themselves as they decompose on the forest floor. The acids in the black humus seep down through the layers of soil leaching valuable minerals and nutrients to below the root zone. The absence of earth churning invertebrates, like earthworms, means the soil becomes hard and compacted. The conifers do have an ally however. Certain kinds of fungi live among the root hairs of the trees. The fungi are able to decompose the leaf litter and make the nutrients available to the trees, and the trees contribute carbohydrates in return.
Conifers have several adaptations that make them well suited to their northern environment. Their needles are thin and waxy protecting them from dessication, the deep green color helps them absorb the maximum warmth from the sun. Their branches are flexible and down-drooping to prevent breakage by heavy snowfalls, and because they retain their needles year-round they are ready for food-production (photosynthesizing) as soon as the sunlight is adequate.
The most common evergreens in the taiga are the spruce, balsam fir, and pine. Other types include hemlock, cedar, redwood, and juniper which can be found at varying latitudes. Just as latitude influences species, so also does altitude. In the northern Rocky Mountains the lower slopes may be dominated by ponderosa and sugar pine. At about 4,000 feet Douglas fir and white fir appear, and above 9,000 feet alpine fir and whitebark pine can be found. In the southern Rockies a most unusual pine is found, the bristlecone pine. Some of these gnarled and stunted trees are as much as 4,000 years old and they are generally found above the 10,000 foot mark, where the soil and the climate are very inhospitable to all but the toughest survivors.
Evergreens can survive in areas that are far too cold or dry for deciduous trees due to their effective conservation of moisture. However in some places there is sufficient rainfall for deciduous growth but conifers are able to take over because of another set of adaptations which allow them to not only survive but benefit from the occurrence of fire. Pines have a pulpy bark that does not easily burn and protects the inner layers of the tree from heat. Buds are protected by a cloak of long needles which will burn, but slowly, and with less heat-generation. Other adaptations to fire include cones that only release their seeds when dried and split open by the heat. The needles that the pines shed decay very slowly but are very flammable, so wildfire spreads over the ground quickly killing competing plants, harmful insects and fungi, and releasing the nutrients tied up in the fallen needles to the pinetrees roots. Fire in a forest is not necessarily a bad thing. Fire has been used by nature to clear away shrubby growth, return nutrients to the soil, open clearings in dense forests to allow new growth which provides wildlife with new food sources, and allow heat-sensitive cones and seeds to germinate. In forests that have been allowed to burn periodically the large healthy trees have little damage done to them and most wildlife is able to outrun or burrow in long enough to make it. It is when man over many, many years has “protected” a forest from fire and a great deal of deadwood and low shrub material has accumulated that a forest fire is harmful to the ecosystem. However even a hot devastating fire merely opens up new opportunities for a whole new set of plants and animals to move into.
The vegetative offerings in the coniferous forest are not very palatable to most animals. Pine needles are eaten by very few of the forest’s inhabitants with the exception of certain caterpillars and grubs. The seeds in the cones are more desirable but not easy to extract. One kind of bird, the crossbill, has a specialized beak that allows it to pry the cone open and a type of nutcracker bird has a bill that is large and powerful enough to break the cones open. There are several small mammals; squirrel, voles, and lemmings, that feed on the pine seeds also. They are the mainstay of the taiga food web. Their amazing birthrate keeps their numbers up even as they are heavily preyed upon as long as sufficient food is available to them. Pedators that will feed on the small mammals include owls, wolves, fishers, weasels, and wolverines. The largest predators, grizzlies, lynx, and mountain lions, will feed on the smaller mammals as well as moose or elk when they can pick out a young or weakened individual.
Part of America’s history is tied to the animal inhabitants of the coniferous forest. Early trappers travelled throughout this area hunting for the valuable furred mustelideas; martens, fishers, weasels (ermine), mink, otters, and wolverines. They of course would also take beaver, wolves, and bears. The early settlers depended on moose, elk, and bears for their hides and for the quantity of food they provided for the winter. But the biggest threat to the animals of the coniferous forest has been the increased population and habitat reduction that resulted as America grew and expanded west and northward.
In order for the children to better understand the nature of the forest we will go the two representative areas, the hemlock forest and the deciduous forest in East Rock Park. A variety of activities will be undertaken there, leaf collecting, insect hunts, bird-watching, and soil sampling. These are described in the Activity section.
