ANATOMY OF A TREE
Leaves are the light harvesting structures of trees. They take the energy from sunlight to fuel photosynthesis, a process that uses carbon dioxide from the air to make plant matter. At the same time, oxygen is released into the atmosphere. Interestingly, the narrow needles of a Douglas fir can expose as much as three acres of chlorophyll surface to the sun.
Typically, leaves are broad, flat and thin. This maximizes the surface area directly exposed to light and enabling the light to penetrate and reach the chloroplasts, where photosynthesis takes place. Leaves are arranged on the plant so as to expose their surfaces to light as efficiently as possible. The flat shape of a leaf also maximizes contact with the air, thereby promoting cooling.
Many conifers have thin needle-like or scale-like leaves that can be advantageous in cold climates with frequent snow and frost. These needles have a thick, waxy coating that retains more water than a regular leaf. Needles can survive ice and very low temperatures. Needles have lower wind resistance than large, flat leaves, so they’re less likely to make the tree fall over during a big storm.
The trunk of a typical tree is made up of five different layers. The outer bark is the tree's protection from the outside world. Continually renewed from within, it helps keep out moisture in the rain and prevents the lost of moisture when the air is dry. It insulates against cold and heat and wards off insect pests.
The inner bark, or phloem, is the pipeline through which food and water is passed to the rest of the tree. Wood also contains xylem that, along with phloem, are the two types of transport tissues in trees.
Evapotranspiration is the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere. In very tall trees this force drive water up against gravity over distances of hundreds of feet!
The cambium cell layer is the growing part of the trunk. It produces new bark and new wood annually.
Sapwood is the tree's pipeline for water moving up to the leaves. Sapwood is new wood. As newer rings of sapwood are laid down, inner cells lose their vitality and turn to heartwood.
Heartwood is the central, supporting pillar of the tree. Although dead, it will not decay or lose strength while the outer layers are intact. A composite of hollow, needlelike cellulose fibers bound together by a biological “glue”, it is in many ways as strong as steel.
Every year, trees grow two annual rings. In the spring, a wider and thinner-walled layer is laid-down. In the summer, a thicker-walled layer develops. Annual rings are typical in temperate forest trees and by counting the number of rings, the age of a tree can be accurately measured.
The tree crown is the top part of the tree, which features branches that grow out from the main trunk and support the leaves. While all trees feature a crown, several types of crowns adorn different types of trees. Thus, tree crowns are adapted to fit the conditions of their environment.
Contrary to popular belief, tree roots are typically found in the top three feet of the soil. They also expand well beyond the drip-line, often occupying an area two to four times the size of the tree crown.
A tree’s root system absorbs water and minerals from the soil, anchor the tree to the ground, and store food reserves for the winter. The root system is made up of two parts – large perennial roots and smaller, short-lived feeder roots.
Plants have evolved different reproductive strategies. Vegetative reproduction is considered any process that results in new plant “individuals” without production of seeds, and is natural for a number of species. Common forms of vegetative propagation are grafting, cutting, layering, tuber, bulb or stolon formation, suckering and tissue culture.
Trees have the means and corresponding structures for reproducing sexually. For angiosperms, the basic function of a flower is to produce seeds via pollination and sexual reproduction. Seeds are the next generation, serving as the primary method by which individuals of the species are dispersed across the landscape.
The female cones of conifers are larger than the male cones and are positioned towards the top of the tree; the small, male cones are located in the lower region of the tree. Because the pollen is shed and blown by the wind, this arrangement makes it difficult for these trees to self-pollinate. A pollen tube forms in the scales of the female cone allowing pollen to migrate to the ovum for fertilization.
Flowers are the structures in angiosperms where pollen fertilizes the ovum. A seed is produced that can, or not necessarily, be contained in a fleshy fruit.
Tree growth occurs at the tips of twigs, the tips of roots and at the cambium in the truck. The latter is known as secondary growth that occurs after the first season and results in increase in thickness. Palm trees do not produce cambium. In fact, palms are incapable of the ring-shaped secondary growth seen in other trees. Consequently, there are no growth rings inside of palm trunks. Most palms do not form branches above ground making the main trunk columnar.