Professional tree services and tree surgeons in the United States

Tree injuries caused by ice, strong winds, lightning, fire, or disease require major repair by a tree surgeon. If left uncorrected, such damage can result in the death of the tree. Common tree surgery procedures include the removal of broken, dead, or diseased branches; cutting back limbs that interfere with traffic, impede power and telephone lines, obstruct views, or mar the shape of a tree; thinning to permit air circulation and secure more light; removal of branches that rub against others to prevent wounding and possible future decay; judicious cutting to compensate for root loss and promote formation of blossoms; and heading back to revitalize an aged tree. The origin of modern tree surgery is attributed to John Davey of Kent, Ohio, who established a landscaping business there in 1880.

A tree differs from a shrub in that it usually produces a single main stem, or trunk, and from an herb in that the stem is composed almost entirely of woody tissue. The largest trees may reach higher than 112 m (367 ft), with trunks that have a diameter of more than 6 m (20 ft).

Trees are generally grouped as either evergreens or deciduous trees. Evergreens are those that bear foliage throughout each year. Two evergreen leaf types are common: the needle leaf, typified by the narrow leaves of most conifers; and the broadleaf angiosperms, or flowering plants. Deciduous trees are broad-leaved and lose their foliage each year, usually at the approach of the coldest and darkest season.

All trees are seed-bearing plants: either gymnosperms, mostly cone-bearing plants commonly called softwoods, or angiosperms, the trees of which are commonly called hardwoods. Angiosperms are further divided into monocots and dicots, depending on seed structure. Of the 60,000 to 70,000 species of trees, all are dicotyledonous except a few hundred monocotyledonous species and less than 1000 gymnospermous species. The most important gymnosperm orders are the Pinales and Taxales, which make up the conifers.

Trees grow wherever adequate groundwater is available for the major portion of the year. They do not grow profusely in desert areas or in areas in which the groundwater table is sufficient only for grassland vegetation. Under optimum conditions, however, trees grow in large aggregations called forests. The climatic and soil requirements of trees are different for each species. Most tree species grow over large areas, of which only a small proportion permits optimum growth of the plant.

The growth of trees requires the successive addition of many layers of woody tissue to the stem. The root and stem, together called the axis, of a tree seedling is divided into three main layers: a protective outermost layer called the epidermis; a middle layer called the cortex; and an innermost layer, or stele, which is composed of layers of tough pericyclic cells, a multicellular layer of vascular phloem cells, a multicellular layer of xylem, or wood, cells, and an inner core that is called pith.

Early in the development of the plant a layer of cells, called the cambium, develops between the phloem and xylem. The cambium alternately produces additional phloem and xylem cells by constant division. The constant divisions of the cambium gradually increase the circumference of the axis. A new cambium, called the cork cambium, develops outside the phloem and produces successive layers of cork cells. In a mature tree the layers of xylem usually constitute more than 95 percent of the diameter of the stem. The xylem layers are called wood and the layers outside the cambium are called bark.

The growth of wood for each year appears as a distinct ring called an annual, or growth, ring. The width of each ring is affected by climate and other variables, and archaeologists have studied tree rings to determine the climatic conditions and variations in environment of former times. Xylem carries water and dissolved mineral nutrients upward from the soil to the leaves. Water is used in the leaves in a process of food manufacture called photosynthesis. Food is transported downward to the roots by the phloem.

Trees add to our enjoyment of the outdoors and contribute to the value of our property. However, trees also have liabilities associated with them.. With age or disease weakening a tree, it can cause injury to property and individuals, interfere with power and telephone lines, crack sidewalks or even the foundation of a home. A professional tree service company (tree surgeons) can recognize when a tree becomes hazardous and take actions to correct these hazards.