Looking at Canada's forest industry, three things are evident:

• it is becoming necessary to grow timber rather than find it

• silviculture needs to be intensified

• it is necessary to learn how to accommodate the demands for different uses made of the forest.

Silviculture addresses these concerns and consists of actions taken at the level of individual stands to renew and enhance the forest crop to meet stand management objectives for timber, wildlife, recreation, landscape design, preservation, and water yield. Silvicultural practices in Canada have developed in response to local or regional needs and as a result, are constantly changing and evolving.

Historical Development

• From 1910 to 1950, Canadian silviculture was primarily concerned with planting trees on prairie farms and abandoned farmland in eastern Canada. Unassisted natural regeneration was relied on in the logging of public forests.

• During the 1950-1970 period, much effort was put into ways to assist the natural regeneration process by cut modification, scarification, and preparation of ecologically based natural regeneration prescriptions. Some planting and tree-improvement programs were started in this period.

• Between 1970 and 1980 emphasis was placed on quality planting and dealing with unsatisfactorily restocked (NSR) lands, including expanded use of herbicides.

• The period 1980-1990 saw further expansion of planting programs to cover over 25% of the approximately 900 000 ha of annual cutover.

Initially, most silvicultural programs were implemented by government agencies. During the 1980s, the silvicultural contracting industry expanded rapidly as government programs were privatized. Increasing emphasis was placed on customizing and designing silvicultural and forest management programs to forest age-class structures to ensure continuity of wood flows. By 1990, most surplus allowable cut in the provinces had been taken up by new industrial expansion. Although most logging operations are still cutting, and will continue to cut old-growth virgin timber, the end of this supply is now approaching.

The emphasis of silvicultural practices has shifted from almost total concern over successful regeneration to a more balanced and designed program of regeneration and stand-tending actions, based on pre-harvest silvicultural prescriptions. This shift in emphasis has focused attention to pre-commercial thinning, pruning, tree improvement, commercial thinning, and fertilizing to produce quality stands in the time frame imposed by declining old-growth reserves.

As public concern about the appearance and environmental effects of clearcutting (the dominant harvesting practice) mount, increasingly attempts are made in silvicultural prescriptions to use appropriate alternative harvesting systems that meet multiple land-use constraints imposed by public demands, the concerns of wildlife, recreation, and watershed managers, and the mandatory requirement for successful regeneration.

Basic Silvicultural Practices

Basic silvicultural practices are regarded as the minimal performance needed on public lands to ensure that the new crop of trees will be as good as or exceed the productivity of the original stand. Provincial forest service policies seek to assign to each Canadian generation a limited equity in forest resource property and to pass it undamaged from generation to generation. Basic silvicultural practices are seen to satisfy this ethical responsibility.

Ecological Classification

Following early unsuccessful attempts with large-scale applications of modified harvesting systems, it became evident that the biological guidance for successful regeneration must be based on more detailed study of forest ecology. The approach used has been biophysical classification, that is, the classification of forest land on the basis of ground vegetation in relation to a nutrient and moisture regime matrix. These regimes range from dry to wet and from poor to rich.

The ecosystems are recognized as operational silvicultural groups in the nutrient-moisture matrix. The matrices are set up for large ecoregions or biogeoclimatic zones representing a recognizable regional relationship between forest cover, climate, and landform. The units recognized are described in terms of typical forest types and associated soil-profile characteristics. Management interpretations, limiting factors, and successional information are also provided; thus, a biological-classification framework, based on natural forest conditions, is the basis for silvicultural practices. Around the classifications are accumulated knowledge and experience on silvicultural successes and failures and forest-productivity information. This knowledge base is thus called site-specific. It has been found to be an essential framework for silvicultural practice.

Silvicultural Systems used in Canada

The planned program of silvicultural treatments during the life of a stand is a silvicultural system. The following silvicultural systems are used in Canada.

• clearcutting systems, involving the removal of all trees

• shelterwood systems, involving the retention of an overstory of mature trees while an understory of regeneration becomes established; such an understory is called advance growth and often occurs naturally in old forests

• seed-tree systems, involving the leaving of a selected number of individual or groups of trees of superior form together with a receptive seedbed

• selection systems, involving the maintenance of an uneven-aged and uneven-sized stand structure that is self-regenerating and periodically harvested to remove a portion of the growing stock from trees of all size classes

• coppice systems, involving clearcutting but relying on the vegetative propagation of a new crop of trees from stump sprouts or root suckers

Each tree and plant species has particular reproduction and growth strategies and characteristics, and this body of knowledge is known as the silvics of the tree species.

It is not biologically possible to secure both rapid and abundant natural regeneration in many Canadian forest associations, even when silvicultural systems are carefully prescribed. We continue to harvest large areas of very old over-mature forest that are often composed of climax species, ill-adapted to rapid establishment and growth on open cutovers. The extreme age and high incidence of decay and disease in old forests often mandate clearcutting. Clearcuts are initially not beautiful and are subject to much public criticism. Planting such areas is usually required for prompt regeneration. Large areas of poorly stocked cutovers of this type have accumulated in the absence of planting. They are known as backlog and are given high priority for artificial regeneration treatments. The mechanical preparation of improved seedbeds, primarily designed to expose mineral soil and remove vegetative competition, is called scarification. Scarification treatment is a common component of natural regeneration prescriptions.

Securing Natural Regeneration

All of Canada's forests originally developed from natural regeneration without human intervention. Fire, blowdown, and insect attack are the usual agencies for mortality of old timber. The tree species are adapted to regenerate after these disturbances. Harvesting of timber results in some critical changes to seedbed conditions and seed supply that have no natural precedent.

Observed conditions for natural regeneration are the basis for silvicultural prescriptions.

These prescriptions are designed to provide appropriate seed supply, seedbed, and moisture and vegetative conditions that favor desired tree species. For example, knowing how a forest stand can be made to increase its timber yield is part of a silvicultural prescription. This increase can be achieved by

• changing the stand density and structure.

• increasing the net balance of photosynthesis to respiration by crop trees and the forest stand as a whole.

• making genetic improvement in the tree species grown.

• using new or different species, strains, or races of trees on particular areas to give greater total wood production or improved quality and stem form.

Ways of changing forest site productivity to increase wood yields can also be part of a prescription for the forest. These include

• restoring lost productivity of abused sites by protection from fire, grazing, and abnormal erosion and by the use of species adapted to the soil and climate.

• improving the productivity of the site by cultivation, fertilizing, or irrigation.

• eliminating forest-floor vegetation that competes with trees and thus detracts from wood production.

These ways of increasing wood yield are stand-level actions, that is, actions taken to change the structure and dynamics of individual forest stands. Forests are composed of many individual stands, usually grouped into a forest management unit for planning purposes. Forest management involves actions at the level of the whole forest management unit Û protection; forest renewal and stand tending; determining the size, location, and scheduling of harvests; and multiple-use planning.

Use of Artificial Regeneration

The decision to use artificial means to regenerate forests is taken where

• natural regeneration cannot be reliably secured or is excessively dense, of poor quality, diseased, or the wrong species.

• prompt regeneration is needed with simultaneous control of species and density.

• the benefits of tree breeding and tree improvement are available in improved nursery stock.

• matching species to site and/or planting an exotic species will result in significant gains in production.

Since such circumstances are common, artificial regeneration has expanded greatly in the 1960-1990 period. Approximately one-third of current cutovers are planted.

Use of artificial regeneration requires the following:

1. Seed supply - Seed collections must be made either from natural untreated stands, selected natural stands dedicated to seed production (seed production areas), or plantations of families of selected trees planted in orchards and subject to irrigation and fertilizing to induce flower production (first generation seed orchards). Following cross-pollination between families and progeny, test seed orchards are rogued to leave orchards composed of trees of proven genetically superior performance (second generation seed orchards).

Tree species vary in their seed production patterns and seed storage and germination requirements. Forest tree seed is usually labeled by seed zones and location and there are generally rules controlling the use of seed outside its zone or elevation range.

Forest tree seed is usually stored in large central seed banks under refrigeration, with enough storage to provide many years of demand for each species. Some species and seed zones are in short supply. Large amounts of first-generation seed-orchard seed will not generally be available until at least the year 2000.

Some species, notably black spruce and jack pine, produce large quantities of seed in cones stored on trees for many years. Collection of their cones is easy, and this leads to large reserves of inexpensive seed in storage. This seed is used in direct seeding, from aircraft or ground (for example, snowmobiles, all-terrain vehicles), usually on scarified cutovers. Direct seeding relies on large quantities of tree seed, and thus on inexpensive tree seed. For this reason direct seeding is mainly limited to these two species. Cone collections are often made from trees felled in logging operations. Access to cones in standing trees is gained through tree climbing, ladders, and lifting devices.

Seed collected from different parts of the range of a tree species is tested for suitability at different locations in provenance trials. Seed from certain provenances is in short supply. Some provenances of British Columbia seed, notably Douglas-fir, Sitka spruce, grand fir, and lodgepole pine, are famous or infamous in Europe for their superior or inferior characteristics. Historical lack of control over seed supply and subsequent poor plantation performance gave rise to the current tight restrictions and government control on seed collection and storage and allocation on Crown lands in Canada.

2. Nursery practices - Seedlots of species selected as suitable for specific forested sites are sent to forest nurseries for the production of planting stock. Originally, most planting stock was produced in bare-root nurseries, where the seed was sown on raised beds, covered with protective grit or sand, grown for one or two years, and then either outplanted in the forest, or transplanted in the nursery for a year or two to grow bigger before outplanting.

Currently, most nursery stock is raised in containers in greenhouses under more controlled temperature and moisture conditions and is irrigated with standardized nutrient solutions. Container seedlings grow faster, are more uniform, and are often cheaper to produce; however, they are often less able to compete after outplanting than bare-root stock. The stock type is usually ordered and custom grown one to three years in advance of outplanting. Current Canadian production is approaching one billion seedlings per year, grown in government and private nurseries. Much planting stock is held in cold storage following lifting, then trucked various distances to planting sites. Over 95% of the production is conifer, two-thirds pine and spruce species. There is a limited production of poplar raised from cuttings.

3. Site preparation - Physical disturbance of the forest floor to create improved seedbeds for natural regeneration is called scarification. Site preparation practices are used to make the task of planting easier and to aid plantation survival and growth.

The practices consist of

• the mechanical actions of ploughing, discing, trenching, crushing, and slash piling;

• the use of chemicals, usually herbicides, to kill or suppress competing vegetation; and

• prescribed burns to remove slash and woody debris, set back competing vegetation, provide ash as fertilizer, and increase nutrient mobilization and availability through increased soil temperatures.

Such site preparation techniques are often essential for plantation establishment on richer sites, that is, very fertile soils prone to rapid brush and grass invasion. There has been rapid development of a wide variety of mechanized site-preparation equipment, aided by the availability and development of specialized prime movers for logging (wheeled skidders, specialized tracked tractors, and new types of forwarders and backhoes).

The use of prescribed burning has expanded rapidly following the development of fire ignition systems from helicopters and the scientific calculation of burning indices, slash loadings, and rates of fire spread. Site-preparation practices are a particular necessity in Canadian conifer silviculture because of the many unusable small trees, rotten trees, and non-commercial trees in the virgin old-growth forests that are being cut today; the need to improve soil temperatures in northern forests with thick humus layers; vegetative competition on clearcut areas; and the large volumes of slash.

4. Planting methods - Of all the silvicultural practices, the task of planting approximately a billion trees per year is the least mechanized. Careful planting on the appropriate microsite is very important; this can really only be done well by hand, in spite of many expensive attempts to develop mechanized planting machines. Over a million person days of work per year are required. Manual planting is a major source of annual income to the reforestation contracting industry.

Not only must seedlot and species be custom selected for each planting site, but so must the planting-stock type, that is, its age, size, and whether it is bare-root or container, and if container, of what container size and type and whether the type is compatible with the treatment used.

Planting is usually done in early spring following snowmelt and is subject to rigorous quality checks and inspections. Payment is usually on a piecework basis. The work is physically demanding and is usually carried out by young people using tools such as planting mattocks or shovels for bare-root stock or planting tubes for container stock.

5. Vegetation management practices - Experience has shown that planting must be followed by tending practices to ensure free-growing trees, that is, trees free enough of competition and with adequate supply of moisture and nutrients to ensure continued survival and height growth. Achievement of free-to-grow status is a mandatory basic silvicultural requirement for licensees on Crown lands in some provinces. The objective of free-to-grow status is to ensure a new forest crop of reliable and predictable stand development, low in risk and with calculable dimensions, product values, and yields.

Vegetation management practices include those of site preparation before and after planting and also following natural regeneration germination. Release of trees from competing vegetation (weeds) uses:

• chemical methods (usually selective herbicides with and without fertilizers),

• manual methods (hand slashing, pulling, and thinning with chain and brush saws), and

• biological methods (cattle, sheep, goat, and deer grazing).