Forestry: The Living Tree: Tree Germination and Growth

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Germination
Growth

Germination

A tree starts life as a tiny seed. Given the right conditions, the seed will start to germinate. The tree embryo absorbs water and splits the seed coat. First a tiny root grows and bends downward into the soil under the influence of gravity. Finally. the stem and leaves emerge from the seed coat and push their way through the soil toward the sunlight. The seedling then begins to manufacture its own food. Eventually, it grows into a larger tree called a sapling.

Each year, the tree adds a new layer of wood and bark and the trunk and branches grow thicker. Once the tree has reached maturity, it produces seed for the next generation. As the tree passes maturity and declines in vigour, it becomes more susceptible to insects and disease. A tree may also be destroyed by fire. Once the tree is dead, it eventually falls to the ground and decays. The burned or decayed remains of a tree add nutrients to the soil in which new seedlings thrive.

Tree Growth Requirements

The growth rate and the ultimate height and shape of a tree are governed partly by the growing conditions of its environment, but also by its genes. In optimal conditions of sunlight and moisture, different species reach different maximum heights. The tallest species of trees are the coastal redwoods, which grow on the west coast of California and Oregon and reach heights up to 112 m. A tree can continue to grow for as long as it lives, so its ultimate height depends on its growth rate and its longevity. Height can however be adversely affected by environmental factors such as long periods of cold summers and insect attacks.

The rate of photosynthesis and hence tree growth is affected by the quality, intensity and duration of light, amount of water a tree receives, the temperature of the surrounding environment and the type of chlorophyll found in the leaves of the plant.

A tree's need for light varies depending on the species. Some trees, such as the jack pine, require full sunlight in order to grow. Others, such as white spruce, will tolerate partial shade. In general, trees can be classified into two main groups: the intolerants (requiring full sunlight) and the tolerants (which do not require full sunlight).

Trees also require nutrients from the soil. Again, different tree species require different types of soils. The jack pine, for example, usually grows well in dry, sandy soils, whereas the tamarack prefers moist or wet, peaty soils. Trees actually help to make soil by scattering leaves over the forest floor. These leaves decay along with other forest litter to form humus.

Water forms 80 to 90 per cent of the tree's bulk. It is essential for transporting minerals and nutrients from the roots to the leaves. It is also an important raw material used in photosynthesis.