Here is a definition I like: "A tree is a woody plant with a single erect perennial trunk at least 3 inches in diameter at breast height (DBH). Most trees have definitely formed crowns of foliage and attains heights in excess of 13 feet. In contrast, a shrub is a small, low growing woody plant with multiple stems. A vine is a woody plant that depends on an erect substrate to grow on."
Just knowing a plant is a tree, as opposed to a vine or a shrub, is the first step toward it's identification.
Even cultivated trees in the landscape have boundaries or zones for optimum growth. These boundaries are called Plant and Tree Hardiness Zones and maps of these zones are dependable predictors of where a tree will or will not thrive.
Hardwoods and conifers can live together comfortably under certain conditions but often enjoy separate ecosystems or biomes. Knowing your native tree lives in either the Great American Hardwood or Coniferous Forest ecosystems can give you just a bit more information about a tree.
Probably the first and easiest separation of tree genera are the decidious (hardwoods with leaves) and evergreen (conifers with needles) species. These very different tree classifications provide you with the first division for identification. I have listed the 60 most common hardwood trees and the 40 most common coniferous trees you will find in North America (with detailed information).
The size and shape of a tree can be highly variable and better used to identify the broadest of tree groups or genera. Your best information comes from twigs and leaves which usually have specific botanical patterns and shapes. You have a better chance using these markers to identify the exact species.
I have created a quiz that tests your recognition of many common trees and the shapes of their leaves. Take these Match the Leaf with the Tree quizzes and learn from those leaves with which you are not familiar. This is an excellent way to practice tree leaf identification using a broad number of common trees.
A tree leaf or twig key is simply a list of a series of questions that ultimately directs you through the process of identifying a tree. Find a tree, collect a leaf or needle and answer the questions. At the end of the "interview" you should be able to identify the tree.
My online Tree Leaf Key is one of the most popular resources on About Forestry. It will easily get you a tree name, at least to the genus level. I am confident you can identify most species with the extra information available.
A fantastic collection of tiled imprints of Eastern hardwood leaves is for all to see on Cheaha Mountain, Alabama. I was inspired to photograph each individual tile and they are extremely detailed and helpful in tree identification.
Please considered viewing my most popular tree and forest picture galleries. You will see trees in their most unique settings. These galleries take you from natural forests to beautiful botanical tree displays.
Become familiar with a twig's botanical parts. A twig's bud, leaf and bud scars, pith and arrangement on a stem can be extremely important in winter tree identification.
Determining opposite and alternate arrangements is the primary first separation of the most common tree species. You can eliminate major blocks of trees just by observing its leaf and twig arrangement.