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Forestry Definitions

Annual ring. Trees in climates where growth stops or slows during a portion of the year will form annual rings which can be read to determine tree age and rate of growth. The science of dendrochronology studies tree rings to infer knowledge about past climatic conditions, based on the fact that trees will form wider annual rings during seasons when growing conditions are favorable and narrow rings when not.

Annual rings are highly visible in tree species that form less dense wood during favorable growing conditions early in the season and denser wood during less favorable conditions later in the year. In some tree species this differentiation does not occur and annuals rings are difficult to see. In tropical species, growth never, or seldom, ceases and annual rings may not be apparent.

Bark. The outer layer of the stems, limbs and twigs of woody plants. Often bark is characteristic of the species and can be used for identification.

Basal area. The cross sectional area of the base of any object. In forestry it means the cross sectional area of a tree at a point 4.5 feet above the ground line expressed in square feet. The sum of all the basal areas of all the trees on an acre is a measure of the density of the population of trees growing on the acre and is useful for making forest management decisions.

A helpful way to think of basal area is to imagine all the trees on an acre cut off with 4.5 foot stumps. Basal area on the acre could then be measured by measuring and totaling the cross sectional area of all the stumps. Fortunately, it is not necessary to cut trees to measure basal area. It can be calculated from tree diameter or can be easily measured with an angle gauge when certain relationships are known.

Basal area will commonly range from 20 to 70 square feet per acre for poorly stocked stands to more than 200 square feet per acre for dense stands of conifers.

Board foot. A unit of measure of wood 1" thick, and 1 foot on each side. Equals 1/12 cubic foot of wood. In practice, a board foot seldom contains 1/12th of a cubic foot due to loss from surfacing such as planing and sanding. For example, a 8 foot 2 x 4 would be said to have 5 and 1/3 board feet, but would actually be more like 4.08 board feet after losses from surfacing.

Bole. The stem or trunk of a tree, usually thought of as being that part without limbs, the merchantable part of the stem, the bottom part of the stem.

Canker. An imperfection on the trunk, limb or twig of a tree caused by an organism that kills a part of the tree's tissue. Canker causing organisms sometimes exist in some sort of a balance with the host, never killing enough tissue to cause death. Cankers tend to weaken trees at the points where they are growing causing the tree to eventually break.

Clearcut. A method of regenerating a forest in which all trees on a given area are cut. Clearcutting results in conditions which allow the greatest amount of sunlight to reach the forest floor, a desirable condition for the regrowth of certain valuable tree species which need a lot of sunlight to grow, such as oaks and walnut. Clearcutting also confers certain benefits for many wildlife species.

Cord. A unit of measure of wood that is equivalent to a pile of round wood 4 feet wide, 8 feet long and 4 feet high. Contains 128 cubic feet of wood and space. May contain approximately 80 to 90 cubic feet of solid wood. A common, but fairly meaningless conversion is 500 board feet per cord. See face cord.

Crop tree release. Natural stands of trees start out with thousands of trees per acre. Planted stands may contain 500 to 1500 trees per acre. At maturity, due to constraints of space, nutrient availability and the increased size of individual trees, there can be only 50 to 70 trees per acre. Crop tree release is the practice of selecting the individual trees that are to remain in the stand until maturity and then removing the trees competing with them.

Crop trees could be selected on the basis of any of the values associated with trees such as aesthetics or wildlife values, but are almost always selected on an economic basis. In Iowa selected trees would most likely consist of walnut and red and white oak. Selected trees would be straight with long, clear boles and would be the trees bringing the best dollar return upon maturity.

Crown. Refers to that part of the tree consisting of limbs, branches, twigs and leaves. In other words, the top of the tree.

Cull. Refers to a tree having no commercial value, usually from having rot, holes, large knots or from being crooked rather than from being too small or of an unmerchantable species. It is important to note that a cull, though having no commercial value may have wildlife, aesthetic or other value.

D.B.H. stands for diameter breast high. Always taken as 4.5 feet above the ground, that being a convenient height at which to measure a tree's diameter. For trees on slopes, d.b.h. is taken at 4.5 feet from the ground on one of the two sides of the tree that is at right angles to the direction of slope.

Defect. An imperfection in a tree making it less desirable for some purpose. The term is commonly used to refer to some imperfection that will reduce the value of a tree or log for a product, resulting in reduced monetary value.

Den tree. A tree that has a hole in its stem that can be used as shelter by wildlife such as birds and small mammals.

D.i.b. Diameter inside bark. When calculating the volume of a log, the average diameter, inside bark at the small end of the log is one of the factors used. In practice, it is measured with a scaled stick, and since logs are not perfectly round, it is measured at the diameter guessed to be the average, or the greatest and smallest diameters are averaged.

Diameter tape. Usually a steel or cloth tape graduated with numerals that are 3.1416 inches apart. When placed around a tree at d.b.h., the tree's diameter can be read directly in inches. Same result could be obtained by using a standard measuring tape and dividing the reading by 3.1416.

Extractives. Chemicals within the cells of wood that can be gotten out by some form of treatment, often soaking in water. Walnut is an example of a wood that contains extractives. Often walnut logs or lumber are steamed or soaked so that extractives will move from heartwood, which contains the extractive which gives walnut its rich color, to sapwood which is normally white. The process makes the white sapwood as valuable as the dark heartwood, thus increasing the value of the lumber or logs.

Two other species that contain water soluble extractives are Osage orange and sumac.

Face Cord. A unit of measure of wood that is equivalent to a pile of round wood 8 feet long and 4 feet high and of variable width, commonly the width of the finished product. For example, if the face cord was firewood, its width might be 12, 16, 18 or 24 inches. Interestingly, face cords are never wider than a standard cord of 4 feet. A face cord is sometimes a device to make people think they are receiving a cord of wood when actually they are not. A face cord contains an undeterminable amount wood and air space and may contain approximately 60 to 70 percent of its volume in solid wood.

Forest. A forest is an ecosystem, an association of plants and animals. Trees are its dominant feature. They provide many of the benefits of forests like habitat, quality water, recreation, climatic amelioration and wood products. The plants and animals that make up a forest are inter-dependent and often essential to its integrity.

Hardwood. Hardwood as opposed to softwood is a relative term. Hardwoods are generally defined as the woods of deciduous trees, i.e., trees which shed their leaves in the winter. However, some hardwoods don't. Moreover, some hardwoods are softer than some softwoods. To confound the situation, the group is divided into hard hardwoods; oak, ash, hickory are examples, and soft hardwoods such as elm, cottonwood, willow, soft maple and so forth. As long as you confine your universe to Iowa or the midwest United States, hardwoods are those species which loose their leaves on an annual basis and softwoods are evergreens.

Heartwood. Wood found at the center of a tree and distinguished from sapwood by being darker in color due to the extractives it contains.

Increment borer. A T shaped tool consisting of a bit, a handle and an extractor that is used to measure the age or growth rate of a tree. The bit is hollow and when turned into the tree, cuts a pencil shaped piece of wood showing the growth rings. By counting the number of rings in the inch of wood closest to the bark, a statement can be made about the increase in tree diameter in the last "x" years. By drilling into the center of the tree, its age can be determined by counting annual rings.

Mast tree. Mast = nut. A mast tree is a nut bearing tree such as oak, walnut, beech, etc.

Plantation. A planted stand of trees.

Pole or poletimber. A young tree or stand of young trees between 3.5 inches and 12.9 inches in diameter at a point 4.5 feet above the ground. In referring to a stand of trees the upper limit holds, however, when referring to processed roundwood, pieces larger than 12.9 inches in diameter could be correctly referred to as poles.

Pruning. The practice of removing tree limbs so that a straight, bole, free of limbs, will develop. Several years after pruning, the resulting wound will have grown over and the wood that grows over the site of the former branch will be clear, that is, knot free. Pruning is a component of T.S.I.

Roundwood. Wood products that are used in their original form, only being cut to length. Includes firewood, posts, poles, pulpwood and similar products.

Sapling. A young tree that has grown beyond the seedling stage. When a tree has grown to a diameter of 3.5 inches in diameter at a point 4.5 feet above the ground it is no longer a sapling, having become a small pole.

Sapwood. That wood found closest to the bark or outside of the bole and usually distinguished from heartwood by being lighter in color.

Seedling. A baby plant. In forestry the term usually used to refer to young trees that have grown beyond the stage where they have just emerged from the soil up to the point that they become saplings. See sapling.

Seedtree. A method of regenerating a forest whereby all trees on an area are cut except for several per acre which are left to provide seed to reseed the harvested area. Usually 5 or 6 tree per acre are left. After the new stand is well established, the residual trees are harvested. The method is used to regenerate species not tolerant of shading.

Selection harvest. A method of harvesting whereby individual trees are selected for harvest. A characteristic is that the form and appearance of the forest is maintained and the site is not exposed to sunlight and weathering. This scheme favors tree species which tolerate shading such as maple and basswood. It also benefits certain wildlife species.

Shelterwood. A method of regenerating a forest whereby a portion of the stand is harvested and the rest of the stand, evenly distributed over the area, is left to protect the site and provide seed to reseed the area. After the new stand is well established, the residual trees are harvested. The method is used to regenerate species not tolerant of shading.

Silviculture. Stands for forest (silva) + culture = forest culture. Defined by Webster as the art of producing and caring for a forest.

Site index. A measure of the productive quality of an area where trees grow. Site index is based on the height of dominant and co-dominant trees at age 50. That is to say, if the average height of dominant and co-dominant trees on a site was 70 feet at age 50, 70 would be the site index. Graphs are developed to enable determination of site index over a range of tree ages.

Snag. A snag is a dead tree, commonly a tall, limbless tree left after a logging operation. Though of little or no commercial value, they can be very valuable wildlife resources.

Softwood. Generally considered to be the wood of conifers, although the wood of some conifers is harder than that of some hardwoods. See the definition of hardwood for a further explaination.

Springwood. That part of an annual ring formed early in the growing season, a period of more rapid growth. Walls of wood cells are thin and wood formed is less dense.

Stand. A group of standing trees is referred to as a stand. One stand will usually have characteristics that will distinguish it from other stands. Differences could be species, average diameter, density and location.

Stumpage. According to Webster, the value of standing timber. Also, the timber itself or the right to cut it.

Summerwood. That part of an annual ring formed during the summer when growth has slowed. It is more dense than spring wood, having thicker cell walls.

T.S.I. stands for timber stand improvement. It is any cultural practice carried out on a tree or group of trees that is designed to improve them for any purpose. The term is commonly used to refer to practices designed to help trees grow faster and develop more valuable products than if left alone.

Volume. Refers to the amount of wood in a tree or log. Expressed as board feet, cubic feet, cords or other measure.