Timber Supply Analysis in British Columbia

Introduction

In British Columbia, approximately 90% of commercial timber production is carried out on Crown land.

The Ministry of Forests regularly reviews the rate of timber harvesting to ensure that it is consistent with current timber management, environmental, and social objectives.

Factors that determine timber supply

What do we mean by timber supply?

Timber supply is the rate at which timber is made available for harvesting. It is a measure of the potential flow of logs out of the forest. Timber supply is not the same as the inventory, or amount, of timber in the forest.

The size and productivity of the area available for commercial timber production (timber harvesting land base) determine the amount of timber that can be produced over time. Economic, environmental and social factors shape the manner and rate at which this timber may be harvested.

Economic values, such as prices for wood products, influence the species and location of timber that can be harvested profitably. Environmental values, such as riparian buffers, and social values, such as visual quality, affect where and when harvesting can take place.

Therefore, the flow of available timber out of British Columbia's forests can be thought of as the response to consumer demand for wood products, but moderated by public policy, which determines the rate and distribution of harvesting.

Public policy and timber supply

Four statutes form the legal framework for forest management on Crown lands in British Columbia: the Forest Act, the Forest Practices Code of British Columbia Act, the Ministry of the Forests Act, and the Range Act. Numerous other provincial and federal acts have implications for forestry, as well a multitude of regulations, guidelines and policies apply to all aspects of forestry on Crown lands.

Policies are dynamic. Forest policies are developed based on the social, environmental and economic values of the time, including:

• how British Columbians value their forest resources-not only timber, but also resources such as wildlife habitat, water quality and recreation
• how much of those resources society chooses to consume now, versus in the future.

Timber harvesting is regulated to meet current management objectives and to ensure a flow of timber at a level that can be sustained over time. This long-term harvest level is based on management regimes and forest practices specific to each forest area.

The Forest Act requires a formal allowable annual cut determination for each management unit in the province, every five years. This process ensures that estimates of timber supply are based on current information, land-use designations, and forest policies.

Classification of land on British Columbia timber supply areas, 1996

Why are harvest levels decreasing?

Current harvesting in British Columbia takes place primarily in older forests that have accumulated high timber volumes by growing for long periods-in some cases, hundreds of years. However, the forests that will regenerate on these sites will likely be harvested in the future at younger ages, and so will yield lower volumes per hectare. Consequently, in most areas of the province, the level of harvesting will decline over time as the forest industry shifts from harvesting higher volume, old-growth forests, to harvesting younger forests of lower volume. This transition from harvesting older to younger forests does not mean that all of British Columbia's old-growth forests will be harvested.

As well, while the volume harvested over time may decrease significantly in some locations due to the change in harvest age, less change is expected in the area harvested.

Of the province's 90 million hectares of Crown land, approximately 49 million hectares are forested. About half of this area is managed for commercial timber production in timber supply areas and tree farm licences. This timber harvesting land base is managed according to the Forest Practices Code and other forest policies. Roughly one-quarter of the timber harvesting land base is managed primarily for other values-such as maintaining old-growth ecosystems and visual features, and managing riparian areas.

Factors influencing timber supply

The amount of timber that a forest produces depends on the size and productivity of the landbase, the tree species growing there, and the way that the forest is managed. Changes in land-use designations, management objectives, and forest policies also affect British Columbia's timber supply. For instance:

• increasing the timber harvesting land base, or improving its productivity through treatments such as fertilizing, can increase the amount of timber available for harvesting
• changing the management objectives for an area-such as to maintain visual features-may reduce the timber available for harvesting or the rate at which harvesting can occur
• implementing new forest management guidelines (e.g., for roadbuilding and harvesting) may affect the availability of timber for harvesting
• harvesting some stands that were previously unprofitable may be feasible if the price of wood products increases.

Forces shaping the long-term harvest level

Timber supply analysis

Timber supply analysis is a process that explores the effects on timber supply of existing or possible forest management strategies and alternative timber harvesting levels. The process uses a computer model to forecast potential harvest levels in the forest, decade by decade, given a specific schedule of management activities. This analysis makes it possible to compare how alternative management strategies affect forest structure and timber production over time.

Timber supply analysis is carried out to support many types of planning in British Columbia, including:

• land-use planning
• forest management planning
• the determination of an allowable annual cut.

Timber supply analysis and AAC determination

The allowable annual cut is an administrative instrument used to set the maximum allowable rate of harvesting in a management unit such as a timber supply area or tree farm licence.

British Columbia's chief forester is responsible for setting the allowable annual cut in each of the province's 37 timber supply areas and 34 tree farm licences. Determining an allowable annual cut is a lengthy and complex process in which the chief forester considers technical forestry reports, analyses, and public review, as well as the government's social and economic objectives and other criteria specified in the Forest Act (Section 8).

An analysis of timber supply under current management practices is one source of information considered by the chief forester. The timber supply analysis measures the effects of current forest management practices on timber supply and assesses the sensitivity of timber supply to changing forest management practices and uncertainty in data.

AAC determination and apportionment

STEPS IN TIMBER SUPPLY ANALYSIS TO SUPPORT AAC DETERMINATION

Step 1 · Categorize the landbase
The productive forest land in a management unit is separated into the timber harvesting land base and the lands unavailable or inappropriate for timber production (e.g., lands designated for other uses, lands with sensitive or inaccessible terrain). Lands outside the timber harvesting land base still contribute to and are managed for other forest values (e.g., wildlife habitat, old growth).

Step 2 · Project growth and yield
Management activities such as tree planting and fertilization affect the way forests grow. Stand growth and timber yield are projected for each stand, based on current management. These projections are represented as timber yield curves that show the characteristics of a stand (e.g., timber volume per hectare, average stem diameter) at different ages.

Step 3 · Identify management activities and requirements
Current management activities, including those that enhance timber production (e.g., planting), and those that maintain or enhance other values (e.g., wildlife habitat, visual quality), are identified. The amount, timing, and location of each management activity is specified. Due to resource interactions (e.g., effects of timber harvesting on wildlife habitat), it is often necessary to restrict some activities to achieve several objectives. Some management requirements are designed to protect a resource or landscape feature; others are designed to create or enhance a resource characteristic.

Step 4 · Model timber supply based on current management
Timber supply analysis done by the Ministry of Forests uses the Forest Service Simulator-a computer model that simulates the way a forest grows and is harvested over time. Analysts evaluate the simulation results by examining how much volume was harvested, how much area was treated, and how some key characteristics of the standing forest (e.g., volume of growing stock, the area in each age class) were affected in every decade.

Step 5 · Run sensitivity analyses
Sensitivity analysis is carried out to evaluate sources of uncertainty in the data and management assumptions used in timber supply analysis. It is used to highlight the factors that most affect analysis results (e.g., where small changes in a management objective can cause large changes in timber supply). Such knowledge helps to establish priorities for collecting new information, and indicates where caution is required in interpreting results.

Alternative rates of harvest to the long term harvesting level (LTHL)

In setting the allowable annual cut in most management units, the chief forester is choosing a transition strategy from current harvest levels to the long-term harvest level. In some management units, this transition will be characterized by a decreasing allowable annual cut and in others by an increasing allowable annual cut. In other management units, the allowable annual cut is already at the currently forecast long-term harvest level.

Many possible rates of harvest may be followed from a current harvest level to the long-term harvest level. Four alternatives are illustrated here. Scenario 1 maintains the allowable annual cut for one decade, followed by a steep rate of decline to the long-term harvest level. Scenario 2 reduces the allowable annual cut in a series of smaller steps to the long-term harvest level which can be maintained for a number of decades. The dotted line represents the unmanaged long-term harvest level, i.e. no special silviculture practices are applied. However, when enhanced forest management is practiced, it results in higher productivity from second-growth forests and in a higher long-term harvest level (solid line). Scenario 3 shows an immediate drop to the long-term harvest level. Scenario 4 maintains current harvest levels for approximately three decades, then makes a steep drop in cut to a level below the long-term harvest level; the harvest level then gradually increases to the long-term harvest level.

In evaluating these alternatives, the chief forester must consider the state of the forest, the factors identified in Section 8 of the Forest Act, and the minister of forests' statement of the economic and social objectives of the Crown. These objectives include minimizing adjustment costs to communities and limiting decreases in allowable annual cut to those necessary to avoid compromising long-run sustainability.

In this context, the chief forester would likely consider Scenario 3 inappropriate since it represents a major, immediate drop in harvest and production with consequent effects on the local economy. Scenario 4 would probably be considered inappropriate since it involves a sharp drop to below the long-term harvest level. In choosing between scenarios 1 and 2, the chief forester would consider the characteristics of the affected communities (e.g., economic diversification) and of the forest (e.g., age-class distribution), as well as any uncertainties in the data.

The chief forester determines how much wood, in aggregate, can be cut in each management unit. Once an allowable annual cut has been determined for a timber supply area, the minister of forests apportions that cut to various forms of agreements (timber tenures) under the Forest Act.

Timber supply analysis and land-use planning

Forest planning on Crown land involves both resource professionals and the public. Processes such as land and resource management plans and local plans bring together interest groups to identify forest values and management objectives for a designated area. Based on these findings, participants develop broad statements of management direction and, eventually, a land-use proposal or options for the area. The land-use proposal or options are then referred to various agencies for analysis. Timber supply analysis is carried out or administered by the BC Ministry of Forests.

Timber supply analysis supports the planning process by assessing the extent to which each land-use proposal or option meets specified management objectives under specified forest policies and practices. The analysis also forecasts the implication of each proposal or option for the timber supply in the area. Therefore, timber supply analysis is a tool used to support planning, but the plan itself is developed by participants through a planning process.

Timber supply analysis and forest management planning

Different factors or combinations of factors limit the supply of timber in different timber supply areas or tree farm licences. For example, the productivity of the land may be the determining factor in one area, while the age of existing stands may be important in another. As a result, specific management activities, such as planting with genetically improved seedlings, may influence the short- or long-term timber supply in some areas more than in others.

Timber supply analysis can support silviculture program planning by allowing managers to explore different combinations of treatment type (e.g., fertilization), treatment amount (e.g., area fertilized each year), and treatment timing (e.g., the years or decades in which fertilizing should be done). Without analysis it would be impossible to predict the outcomes and time frames of incorporating new information and silviculture practices. Timber supply analyses show that with careful planning and management it may be possible to affect the size and duration of the fall-down in a given management unit.

Three different management units are illustrated here. The dash and dotted lines represent the potential outcomes and time-frames resulting from enhanced forest management regimes.

This type of harvest forecast is very stable and it is possible that information and practises which improve the volume of regenerated stands can actually result in an increase in the harvest level across all time horizons. Alternatively, if a short-term benefit cannot be obtained, then at the very least one can expect an increase in the future as shown at the point where the small, dotted line departs from the solid black line.

In this situation, changes in information or practises which improve the yields of regenerated stands generally do not affect the short term, but may result in future increases as shown by the small dotted line, or, in a best case scenario, may even offset the fall-down entirely as shown by the dashed line joining the small, dotted line.

In the type C forecast, changes in information or practices which increase the yields of regenerated stands generally cannot offset the fall-down but may have the benefit of either lessening the duration or depth of all-down as shown by the dashed line, or may not have any benefit until fat into the future as shown by the small, dotted line.

Timber Supply Review program

In 1992, the Ministry of Forests initiated a review of the province's timber supply. The Timber Supply Review program was established to regularly provide an up-to-date assessment of timber supply in each of British Columbia's timber supply areas and tree farm licences based on the best available information and current management practices.

The Timber Supply Review should not be confused with land-use planning processes, such as land and resource management plans or local resource use plans, whose purposes are to identify and make decisions about resource values, land use, and management in designated areas.

As part of the Timber Supply Review, timber supply analyses assess how current forest management practices will affect the supply of wood available for harvesting over time. They also examine how timber supply may be affected by changes in management practices and uncertainties about forest inventory and growth.

The chief forester also uses other information gathered through the Timber Supply Review, including social and economic implications, and public input in determining allowable annual cuts. In all, the process takes about 20 months for timber supply areas and for tree farm licences.

The 1992-1996 Timber Supply Review assembled a great deal of new information and identified where additional information and research are needed. It developed an important benchmark against which future changes in forest management can be assessed. This first review showed significant changes in allowable annual cuts for the Nelson, Prince George, Vancouver, Kamloops forest regions.

B.C. Ministry of Forests
Timber Supply Branch

location:
3rd Fl, 595 Pandora
Victoria, BC, Canada V8W 3E7
Phone: (250) 953-3631

mailing address:
PO Box 9512
Stn Prov Govt
Victoria, V8W 9C2

tel: (250) 356-5947
fax: (250) 953-3838

This site was last updated: August, 2002