Forestry
Forestry
Forestry and its broader goals
Resource values managed in forestry
Silvicultural systems and management
Forestry is the science of harvesting, planting, and tending trees within the broader context of landscape management. Traditionally, forestry has focused on providing sustainable yields of economically important products, especially wood for the manufacture of lumber or paper, or to generate energy. Increasingly, however, forestry must consider nontraditional goods and services provided by the forested landscape, such as
populations of wildlife, recreational opportunities, aesthetics, and the management of landscapes to maintain clean air and water. Because these values can rarely be accommodated in the same area, there are often conflicts between forestry and other landscape uses. However, integrated management can often allow an acceptable, working accommodation of forestry and other resource values.
Forestry and its broader goals
Forestry is a science, but also something of an art. Forestry’s ultimate objective is to design manage forested landscapes that can yield sustainable flows of a range of goods and services. The most important of these resources are products directly associated with tree biomass, such as lumber, paper, and fuel. However, nonarboreal resource values are also important, and these must be managed in conjunction with traditional industrial products.
In many respects, forestry is analogous to agricultural science, and foresters are akin to farmers. Both deal with the harvest and management of ecological systems, and both seek optimized, sustainable yields of economically important biological commodities. Agriculture, however, deals with a greater diversity of economic species and biological products, a wider range of harvest and management systems (most of which are much more intensive than in forestry), and relatively short (usually annual) harvesting rotations. Still, the goals of forestry and agriculture are conceptually the same.
Another shared feature of forestry and agriculture is that both cause substantial ecological change. Forestry and agriculture are both undertaken in specific sites. However, in aggregate these places are numerous, and therefore entire landscapes are significantly affected. For example, populations of many native species may be reduced or even extirpated, the viability of natural communities may be placed at risk through their extensive conversion to managed ecosystems, erosion is often caused, the environment may become contaminated with pesticides and fertilizers, and aesthetics of the landscape may be degraded. One of the most important challenges to both forestry and agriculture is to achieve their primary goals of sustainable harvests while keeping the associated environmental degradations within acceptable limits.
Resource values managed in forestry
Forested landscapes support a variety of resources. Some are important to society because they can be harvested to yield commodities and profit. Others, however, are important for intrinsic reasons, or because they are important ecological goods and services. (That is, while their importance is not measured economically, they are nevertheless important to society and to ecological integrity.) Often, the different resource values conflict, and choices must be made when designing management systems. In particular, activities associated with the harvest and management of trees for profit may pose risks to other nontimber resources. Sometimes timber values are judged most important, but sometimes not.
The most important resources that modern foresters consider in their management plans are:
(1)Traditional forest products are based on harvested tree biomass. These include large logs that are cut into lumber or manufactured into laminated products such as plywood, as well as other trees that are used to produce pulp and paper or burned to generate energy. All are important forest products that are harvested to sustain employment and profits. Almost always, managing for a sustained yield of these tree-based products is the primary objective in forestry.
(2)Some species of animals are exploited for subsistence and recreation by hunters; maintaining these populations is another prominent management objective in forestry. The most important of the species hunted in forested lands in North America are large mammals such as deer, elk, moose, and bear; smaller mammals such as rabbit and hare; game birds such as grouse, ptarmigan, and quail; and sport fish such as trout and salmon. In some cases, forestry can enhance the abundance of these species, but in other cases it can damage game animal populations, and this conflict must be managed to the degree possible.
(3)Species with commercial value are another common consideration in forestry. These include fur-bearing animals such as marten, fisher, weasel, beaver, bobcat, lynx, wolf, and coyote. Foresters may also be involved in the management and protection of the habitat of river-spawning fish such as salmon.
(4)Nongame species, however, comprise the great majority in forested landscapes. Most are native, occurring in natural communities dispersed across the ecological landscape. Although few are of direct economic importance, all have intrinsic value. Forestry-related activities may threaten many of these species and their communities, creating great controversy and requiring difficult social choices. In North America, for example, there are concerns about the negative effects of forestry on endangered species such as the spotted owl and red-cockaded woodpecker, and on endangered ecosystems such as old-growth forest. These concerns may have to be addressed by declaring ecological reserves of large tracts of natural forest, in which the commercial harvesting of timber is not allowed.
(5)Recreational opportunities are another important resource value of forested landscapes. Examples include wildlife observation (such as bird watching), hiking, cross-country skiing, and driving off-road vehicles. In some cases these activities are made easier by forestry that may, for example, improve access by building roads. In other cases, it may detract from recreational values because of the noise of industrial equipment, dangers associated with logging trucks on narrow roads, and degraded habitat qualities of some managed lands.
(6)Natural beauty is another important consideration in forestry. Compared with natural, mature forests, few people consider clear-cut sites aesthetically pleasing. Foresters, on the other hand, may not share this interpretation. Societal choices must determine the most appropriate management objectives for site or landscape aesthetics in particular regions.
(7)Nonvaluated ecological goods and services are also important considerations in forestry. These include landscape’s ability to prevent erosion, maintain a particular hydrologic regime, to serve as a sink for atmospheric carbon dioxide through the growth of vegetation, and to produce oxygen through photosynthesis. As noted previously, these are all significant resource values, although their importance is not always assessed in monetary terms.
Harvesting and management
Forest harvesting refers to the methods used to cut and remove trees, and they vary greatly in their intensity. Clear-cutting is the most intensive system, harvesting all trees of economic value at the same time. Clear-cuts can range from patch-cuts smaller than a hectare to enormous harvests thousands of hectares in area, sometimes undertaken to salvage timber from areas that have recently been affected by wildfire or an insect epidemic.
Strip-cutting is a system involving a series of long and narrow clear-cuts, with alternating uncut strips of forest left between. A few years after the first strip-cuts are made, tree regeneration should be well established by seeding-in from the uncut strips, which would then be harvested. Shelter-wood cutting is a partial harvest of a stand in which selected large trees are left to favor particular species in the regeneration, and to stimulate the growth of uncut trees to produce high-quality sawlogs at the next harvest, usually one or several decades later. In some respects, the shelter-wood system is a staged clear-cut, because all of the trees are harvested, but in several steps.
The least intensive method of harvesting is the selection-tree system, in which some of the larger individual trees of desired species are harvested every ten years or more, always leaving the physical integrity of the forest essentially intact.
Usually when trees are harvested, they are delimbed where they have fallen, the branches and foliage are left on the site, and the logs taken away for use. However, some harvest systems are more intensive in their removal of tree biomass from the site. A whole-tree harvest, usually used in conjunction with clear-cutting, removes all aboveground biomass. A complete-tree harvest is rare, but would include the attempted additional harvest of root biomass, as is possible on sites with peaty soils. These very intensive harvesting methods may be economically advantageous when trees are harvested for the production of industrial energy, when biomass quality is not an important consideration. However, the whole-and complete-tree methods greatly increase the removal of nutrients from the site compared with stem-only harvests, and this can be a consideration in terms of impairment of fertility of the land.
Forest management refers to those activities associated with establishing new crops of trees on harvested sites, tending the stands as they develop, and protecting them from insects and disease. As with harvesting, the intensity of management activities can vary greatly. The least-intensive management systems rely on natural regeneration of trees and natural stand development. Although relatively natural systems are softer in terms of their environmental impact, the rate of forest productivity is often less than can be accomplished with more intensive management systems.
One natural system of regeneration uses advance regeneration, or the population of small individuals of tree species that occurs in many mature forests and can contribute to development of the next stand after the overstory trees are harvested. Other natural-regeneration systems try to encourage the post-harvest establishment of desired species seedlings after the site is harvested. For some species of trees, the site must be prepared to encourage seedling establishment. This may require slash and surface organic matter to be burned, or mechanical scarification using heavy machines. Depending on the particular nature of the forest and tree species, either of the advance regeneration or seeding-in regeneration systems might be utilized with selective harvesting or with clear-cutting.
If the forester believes that natural regeneration will not be adequate, or that it would involve the wrong tree species, then a more intensive system might be used to establish the next stand. Often young seedlings will be planted to establish an even-aged, usually single-species plantation. The seedlings are started in a greenhouse, and may represent a narrow genetic lineage selected for desirable traits, such as rapid productivity or good growth form.
Once an acceptable regeneration is established, the stand may require tending. Often, undesired plants compete with the trees and interfere with their growth, making them silvicultural “weeds.” They may be dealt with by using a herbicide or by mechanical weeding. Once the growing stand develops a closed canopy of foliage, even the individual trees may start to compete among themselves and reduce the overall growth rate. This problem may be dealt with by thinning the stand, an activity in which the least productive individuals or those with poorer growth form are selectively removed, to favor productivity of the residual trees.
In some cases, the regenerating stand may be threatened by an insect outbreak capable of severely reducing productivity or even killing trees. This may be managed by protecting the stand using an insecticide. In North America, insecticides have most commonly been used to deal with severe defoliation caused by outbreaks of spruce budworm or gypsy moth, or with damage associated with bark beetles.
Silvicultural systems and management
Silvicultural systems are integrated activities designed to establish, tend, protect, and harvest crops of trees using a management plan appropriate to that larger scale. The landscape-scale management plan is typically detailed for the first five years, but it should also contain a 25-year forecast of objectives and activities. The design and implementation of silvicultural systems and management plans are among the most important activities undertaken by modern foresters.
The primary goal of forestry is generally to achieve an optimized, sustainable yield of economically important, tree-derived products from the landscape. In places where forestry focuses on the economic resource of trees, the silvicultural system and management plan will reflect that priority. However, where management of a range of resource values (that is, not just trees) is required, then integrated management will be more prominent in the system and plan.
As with the individual harvesting and management practices, silvicultural systems can be more or less intensive. An intensive system used in North America, beginning with a natural forest composed of a mixture of native species of trees might include: (1) whole-tree clear-cut harvesting of the natural forest, followed by (2) scarification of the site to prepare it for planting, then (3) an evenly spaced planting of young seedlings of a narrow genetic lineage of a single species (usually a conifer), with (4) one or more herbicide applications to release the seedlings from the deleterious effects of competition with weeds, and (5) one or more thinnings of the maturing plantation, to optimize spacing and growth rates of the residual trees. Finally, the stand is (6) harvested by another whole-tree clear-cut, followed by (7) establishment, tending, and harvesting of the next stand using the same silvicultural system. If the only objective is to grow trees as quickly as possible, this system might be used over an entire landscape.
KEY TERMS
Plantation —A tract of land on which economically desired trees have been planted and tended, often as a monoculture.
Rotation —In forestry, this refers to the time period between harvests. A forestry rotation is typically 50-100 years.
Scarification —The mechanical or chemical abrasion of a hard seedcoat in order to stimulate or allow germination to occur.
Silvicultural system —A system designed to establish, tend, protect, and harvest a crop of trees.
Silviculture —The branch of forestry that is concerned with the cultivation of trees.
Weed —Any plant that is growing abundantly in a place where humans do not want it to be.
In contrast, a much softer silvicultural system might involve periodic selection-harvesting of a mixed-species forest, perhaps every decade or two, and with reliance on natural regeneration to ensure renewal of the economic resource. However, even a system as soft as this one might pose a risk for certain nontimber resource values. For example, if certain species dependent on old-growth forest were believed to be at risk, then an appropriate management plan would have to include the establishment of ecological reserves large enough to sustain that old-growth resource value, while the rest of the land is worked to provide direct economic benefits.
Because silvicultural systems can differ so much in their intensity, they also vary in their environmental impact. As is the case with agriculture, intensive systems generally create substantially larger yields. However, intensive systems have much greater environmental impact. The challenge of forestry is to design socially acceptable systems that sustain the economic resource while at the same time accommodating concerns about the health of other resources, such as hunted and nonhunted biodiversity, old-growth forests, and ecologically important but nonvaluated goods and services that are provided by forested landscapes.
See also Deforestation.
Resources
BOOKS
Freedman, B. Environmental Ecology. 2nd ed. San Diego: Academic Press, 1995.
Kimmins, H. Balancing Act. Environmental Issues in Forestry. Vancouver: University of British Columbia Press, 1992.
OTHER
Food and Agriculture Organization of the United Nations. “Forestry” <http://www.fao.org/forestry/index.jsp> (accessed November 24, 2006).
U.S.Department of Agriculture, Forest Service. “USDA Forest Service Strategic Plan for Fiscal Years 2004-2008” <http://www.fs.fed.us/publications/strategic/fs-sp-fy04-08.pdf> (accessed November 24, 2006).
Bill Freedman