Forest management

Spruce saplings, in the foreground, are grown for 10 years in the European mountains, then are cut for pulpwood. Spruce wood is thought to make some of the best paper pulp. These trees grow faster and on poorer soils than do broadleaved species.

Given good management, trees are a renewable natural resource that provide many products including fuel, lumber, wood pulp, fiber, and food for human and animal consumption in the form of fruits, bark, and leaves. Forests are also ecologically valuable because they recycle nutrients, fix energy, retain soil and water, and keep the soil fertile. They may also influence rainfall and climate generally.

The problem is that pressure from the need for space for cash crops and felling for lumber has led to large-scale destruction, particularly of tropical rain forests, which are a major source of hardwood timber for the world. In the early 1990’s, tropical forests were being destroyed at the rate of about 100 acres (40 hectares) a minute.

Forests are delicate systems which, if disturbed, can be permanently destroyed, as has been the case with many tropical forests. It is, therefore, in our own interests to extend, conserve, and manage the forests of the world rather than simply exploit them for short-term gain. Proper scientific management of forests (silviculture) includes the establishment, development, and reproduction of trees to provide salable lumber in the shortest possible time, to control erosion, protect watersheds, provide recreation and enhance the landscape, to protect animals, and to make provision for agriculture.

Limbing, the removal of the lower branches of trees when they are about 10 years old, serves to reduce the number of knots in the mature timber. The removed young wood is then used for pulp.

Forest establishment

Afforestation is the primary establishment of forests in previously unforested areas or those that have long been deforested. To begin, the ground needs to be broken up and drained and, if sloping, may also be terraced to prevent runoff of water. Soil and fertilizers, such as phosphate, are then applied in the planting holes. The soil, climate, quality, and type of timber expected are considered, but the trees chosen are not always indigenous; more importantly they need to be fast-growing and hardy: for example, Sitka spruce (Picea sitc-henis), which is used in Britain; Monterey pine (Pinus radiata), which is widely grown in warm temperate climates, most extensively in New Zealand; and Caribbean pine (Pinus caribaea), which is planted throughout the seasonal tropics and subtropics. The fast-growing pines are used for pulp. Other fast-growing trees make veneer logs, such as Gme/ina arborea, which is grown in Brazil. With good management, trees take up to 50 years to mature; to attain saw log size, a mature forest ecosystem may take twice as long to reestablish.

Seedlings are first raised in a nursery where they may have been bred for hardiness, fast growth, or dense or soft wood. They are usually planted out when one to four years old, during their dormant period. They can be planted at other times provided they are guaranteed water to prevent them from drying out before the roots establish themselves—during a tropical rainy season, for example. After planting, the trees are weeded for the first few years until they are tall enough to overtop and suppress any weeds.

The number of trees planted in a given area depends on the species and the planting site.

In temperate areas, hardwoods such as ash (Fraxinus sp.), beech (Fagus sp.), and oak (Quer-cus sp.) are usually planted 5 feet (1.5 meters) apart. Conifers such as larch (Larix sp.) and pines (Pinus spp.) are usually planted 5 to 6.5 feet (1.5 to 2 meters) apart, whereas poplars [Popuius spp.) are usually planted 16.5 to 19 feet (5 to 5.8 meters) apart.

When the developing trees are about 8 to 10 years old the forest floor is generally cleared of bushes and woody climbers. The low branches of the trees are removed, which helps to reduce the number of knots in the mature timber. The trees are thinned out about 12 to 15 years after planting, the thin

nings providing the first lumber crop. Their removal allows the final crop to achieve its maximum potential. Diseased and unsatisfactory trees are also removed at the same time.

In caring for forests, such factors as frost, snow, lightning, sunlight, water, and wind need to be considered. Measures taken to reduce the damage done by these elements include proper drainage, adequate provision of water, and shading seedlings. Fires are often the major hazard, causing damage that varies from slight bark scorching to complete destruction. Surface fires, if not too intense, may be beneficial. Such fires are deliberately started in mature eucalyptus (Eucalyptus sp.) forests in Australia and in pine forests in the Southeastern United States, for example, where they prevent the build-up of a deep flammable litter layer so that the intensity of fires is kept low. Many species of gum need fires to trigger germination. To prevent fires from spreading, fire lines 33 feet (10 meters) or more across are created and kept clear of vegetation.

The growth rates of forest trees vary depending on the species. Of the softwoods, Monterey pine can be one of the fastest growers, sometimes shooting up as much as 18 feet (5.5 meters) in one year. Redwood grows more steadily, slowing down as it reaches 100 feet (30 meters). Among the hardwoods, ash grows fast, often reaching 100 feet (30 meters) well before it is 100 years old. It achieves a mature height of about 150 feet (45 meters). In contrast, beech grows very slowly to begin with but later spurts up to reach about 85 feet (26 meters).

Monocultures versus mixed forests

Natural forests usually contain a mixture of tree species. Flowever, many forestry practices have favored single species, for these forests take less time to plant, require less skill to thin, yield more uniform timber, and are more economical to harvest. Ecologically mixed forests are more desirable than monocultures because different species have different requirements for growing conditions and are less susceptible to drought and disease.

Mixed forests are created either by natural succession or by planting several species during reforestation, in Europe, ash (Fraxinus) and beach (Fagus) may be planted with one or more coniferous species. In the Northwestern United States, red alder (Alnus rubra) often establishes along with Douglas fir (Pseudo-tsuga menziesii) and western hemlock (Tsuga heterophylla). The alder and hemlock do not live as long as the Douglas fir, nor is their wood as valuable.

Pests and diseases are a problem, especially with monocultures, among which they spread quicker than in mixed forests. Aphids and sawflies, for example, create galls, and mites, moth larvae, scale insects, and some fungi can cause defoliation. Other fungi damage the wood, fruits, and roots, and eventually kill the trees. The application of insecticides, such as nicotine and malathion, fungicides, tar-oil washes, copper compounds, and burning are effective in reducing disease. However, these measures can at the same time damage the trees and kill off other animal life. Natural control of these pests is, therefore, preferred—insect-eating birds and other animals can provide some measure of control. Animal life is, however, more abundant in natural mixed forests than in monospecific plantations.

The management of a pine forest grown for timber starts when the saplings, of between two and four years old, are planted. From four to seven years old they are weeded and then, at about eight to ten years, the lower branches are cut off for pulp. Two * years later they are thinned, the wood also being used for pulp. They are felled all at once when mature, and soon after the ground is replanted.

Lumber extraction

In the planted forest everything is organized to extract lumber as economically as possible, which is usually by removing all the trees and then replanting the whole area. This method is known as clear-felling or clear-cutting. The area to be felled is calculated by dividing the total area of forest by its rotation time (the time a species needs to grow before it can be cut). If, for instance, a total forest is 500 acres (200 hectares) with a rotation of 100 years, then the area cut and replanted each year is 5 acres (2 hectares). The rotation times vary depending on the species; oak requires 100 to 150 years, and poplar, 40 to 45 years. For a fast-growing tropical tree grown for pulp, less than 40 years may suffice.

The advantages of clear-felling are that it is the simplest system to manage, no seedling trees are damaged during felling, and replanting is more dependable than natural regeneration (even if it is more expensive). If, however, planting is not started soon after felling, weedy species may establish. In addition, the absence of mature trees to provide cover for young seedlings may slow down their establishment.

A mature natural forest presents a slightly different problem in lumber extraction. A selective system may be operated, in which trees are felled singly, in twos and threes, or in small areas of up to one-third of an acre (in a temperate forest). The trees are felled when mature or when commercially valuable.

The advantages of this system over clear-felling are numerous: natural regeneration is the norm after selective felling and is supplemented by planting only where necessary; the soil is not exposed, so there are no problems of erosion or landslip; and seedlings are protected by the surrounding trees. Moreover, the financial returns are immediate because the trees are already mature. The disadvantages of selective felling are the difficulties and extra cost of extraction and the damage that may be done to the young regenerating trees.

Forests can be felled in strips instead of a block, which simplifies the problems of extraction. Cut at right angles to the prevailing wind in the lee of the wood, the strip is sheltered and can be seeded from the standing trees. When regeneration is underway the next strip can be cut. This is repeated until the whole mature forest is cleared.

Another variant of selective felling is the polycyclic system in which selected mature trees are felled to open up the canopy, which allows previously shaded seedlings to grow and develop. A second felling thins out the canopy further to allow the regeneration process to continue. The final felling removes all the mature trees. The advantages and disadvantages are similar to those of single group and strip-felling.

Fires are often deliberately caused in Australian eucalyptus forests to limit the undergrowth and initiate seed germination. If the understory were allowed to become too dense and were set alight, the fires would be less controllable, becoming crown rather than ground fires.

Coppicing techniques

Coppicing systems have been used in Europe for hundreds of years and provide a mixture of large and small hardwood timber. Because it relies on regrowth from a cut stump, however, this method cannot be used for conifers, which do not normally regenerate from a stump.

A coppice wood is composed of a number of stumps in various stages of regeneration that are managed on a short rotation, dependent on the species. For ash the rotation time can be as little as 5 years, for alder (Alnus sp.) it can be 25 years. Initially a mature tree is felled to leave a stump, or stool, 1.5 feet (46 centimeters) high. This is allowed to regener

ate, and the new shoots grow until they reach the correct cutting size. The shoots grow quickly, nourished by the mature root system. The coppice is generally cut in strips or blocks, the area to be cut being calculated by dividing the size of the coppice by its rotation time.

A number of species are suitable for this treatment and include hazel (Corylus sp.), sweet chestnut (Castanea sp.), hornbeam (Car-pinus sp.), and birch (Betula sp.). The life of the stools varies depending on the species—for oak it is more than 100 years.

If the coppice is combined with tall trees, the system is known as coppice-with-standard. The stools are mixed with “standard” trees which are typically oak. The standards are normally felled on a rotation that is, for convenience, a multiple of the stools’ rotation; they may themselves be regenerated by selecting and retaining one shoot from a coppice stool, rather than grown as “maidens” from seedlings.

Abundant, vertical slim branches are the distinctive mark of coppiced trees. The low thick stump, or stool, in the foreground regenerates new shoots every time the old ones are cut for timber.

Other factors of management

Considerations of erosion and watershed management are important in forestry. Large-scale clear-cutting can cause erosion, waterway and reservoir silting, damage to fisheries, and loss of drinkable or usable water. Additionally, with clear-cutting there is an increase in floods in regions with high precipitation, such as the Pacific Northwest. Good forest management by the regular opening up of the forest canopy increases the diversity of forest structure and consequently that of the flora and fauna.

Population pressures and increasing demands for space for crop cultivation have led in some places to a need to devise management programs that allow the production of food and wood from the same land. Mixed cropping and grazing have also been implemented in forestry plantations.

The potential of forestry as a source of rural development, rehabilitation of degraded land, water catchment, and provision of shelter and recreation is now being appreciated. So too is the need to safeguard the diversity of the species-rich natural forest ecosystems—not simply for the sake of diversity, but for the sake of life on earth.

The effects of acid rain-caused by sulfurous pollution in the atmosphere—are evident in the dying foliage of these conifers growing in the Black Forest of Germany. Gradually the trees will die, destroying the habitats of birds and other animals that live in the forest.