Choosing a silvicultural system:
overview of the assessment process

General objective

To show how the silvicultural system selected will achieve forest management objectives established in higher-level plans, including those for promoting healthy, productive forests and for achieving landscape-level objectives for biological diversity.

When determining the silvicultural system for an area under a silvicultural prescription, you should:

• ensure that the silvicultural system for the area is consistent with the forest resource objectives contained in higher-level plans
• specify a silvicultural system that
  • is ecologically suited to the tree species being managed in the area
  • subject to higher-level plans, is capable of providing reasonable measures that promote and maintain a healthy and productive forest
  • is designed to achieve a specified stand structure that considers objectives for biological diversity contained in any higher-level plan for the area under the Forest Development Plan.

You must ensure that the silviculture prescription for an area:

• is consistent with the proposed silvicultural system, demonstrating that the specified free growing stand will be established to meet the specified target requirements within the specified free growing assessment period
• is consistent with the forest resource objectives in any higher-level plans or the Forest Development Plan for the area under the prescription
• demonstrates that the growth of ecologically suitable species will occur
• facilitates protection of the soil
• describes actions required to achieve known landscape-level objectives for stand structure and species composition
• demonstrates that natural regeneration will reliably reforest the area by the specified regeneration date, if natural regeneration is being considered
• demonstrates that there are sufficient suitable residual seed trees for maintaining or enhancing the genetic quality of the regeneration (if the silvicultural system proposed in the prescription is not clearcutting and natural regeneration is being considered).

Based on these principles, a suggested assessment process for choosing a silvicultural system follows.

The silvicultural system assessment process:
detailed considerations

Review higher-level plans and determine stand-level resource objectives

STEP 1

Locate higher-level plans and applicable resource maps, if available, for the area proposed for harvest. Obtain forest resource objectives and restrictions, if any, from these plans, and determine overall resource priorities. If a total resource management plan exists, the resource values and their priorities will be identified. Ensure that the plans are up-to-date.

Part 1 (Definitions) of the Forest Practices Code of B.C. Act defines a higher-level plan as:

(a) a plan formulated pursuant to section 4(c) of the Ministry of Forests Act,
(b) a management plan,
(c) an objective for a resource management zone,
(d) an objective for a landscape unit or sensitive area,
(e) an objective for a recreation site, recreation trail, or interpretive forest site, and
(f) a plan or agreement declared to be a higher level plan by

(i) the ministers, or
(ii) the Lieutenant Governor in Council under this or any other Act.

Forest resource objectives are stated in the higher-level plans listed above. The forest resource objectives in these plans are broad in scope. From these forest resource objectives, stand-level resource objectives must be developed and refined. This allows an appropriate, site-specific silvicultural system to be chosen.

Consultation with appropriate agencies

If higher-level plans are not available or appear inappropriate based on local knowledge, consult appropriate resource agencies and guidebooks to determine or refine forest resource objectives and priorities.

Setting stand-level resource objectives

Based on the recognized forest resource objectives and priorities, formulate preliminary stand-level resource objectives. Each forest resource objective should have at least one stand-level resource objective.

Consult appropriate agencies and guidebooks for guidance in setting stand-level resource objectives not specifically addressed by higher-level plans.

Stand-level resource objectives should be SMART (Specific, Measurable, Approved, Realistic, Time bound). The stand-level resource objectives for a site must be consistent with forest resource objectives stated in higher-level plans, and must be accommodated in the silviculture prescription (SP) and stand management prescription (SMP).

Converting forest resource objectives from higher-level plans to specific stand-level resource objectives may require the consultation of resource management agencies as well as relevant guidebooks. When higher-level plans do not exist, review guidebooks to identify which stand-level resource objectives are appropriate for a specific site, given its site and stand characteristics. These stand-level resource objectives must be documented in the SP.

Stand-level resource objectives must support your determining of specific, measurable stand structural objectives. For example, the objective of “maintaining mule deer winter range” is not specific enough. It would be more appropriate to state: “maintain mule deer winter range by maintaining thermal cover units of minimum height class 3 (20–30 m) with an average conifer thermal canopy greater than 70% over 40% of the cutblock area for the whole rotation length.”

Determine general stand structural goals

STEP 2

Determine the stand structural goals necessary to satisfy each of the stand-level resource objectives. Points to consider include, but are not limited to, the following:
• What are the regeneration requirements, shade tolerance and other relevant silvical characteristics of the existing and desired species?
• Is post-harvest forest cover necessary to satisfy stand-level resource objectives? Is the vertical or horizontal structure important? If so, what stand characteristics (stand structure, stocking levels, disturbance pattern, species composition) are adequate, and over what time frame and portion of the area is the forest cover necessary?
• Are specific stand structural attributes (e.g., standing live and dead wildlife trees, undisturbed coarse woody debris, vegetation, retention patches) required to meet the goals? Are stand structural goals consistent with biodiversity or other goals for the landscape unit?
• Are stand structural goals consistent with landscape-level objectives for the landscape unit, as set in higher-level plans?

Stand structural goals provide targets for the treatments that are to influence the short- and long-term development of the stand structure. The development and management of this envisioned future stand is to be projected for the entire rotation or one or more cutting cycles, as appropriate.

Long-term stand structural goals ensure that long-term forest resource objectives are achieved. Desired stand structural goals may be achieved after either the first entry or a specified number of future harvest entries or stand-tending treatments.

Stratify the proposed area and collect site-specific
field information

STEP 3

Pre-stratify aerial photographs to identify units potentially suitable for different silvicultural systems. Proposed treatment units will be based on species composition, stand structure, soils and ecosystem units, and possibly other pre-existing site-specific information.

Aerial photograph stratification is the initial process to check existing stand structure, block boundary location, road access, potential ecosystem units and slope stability, and to verify timber merchantability. Within and outside the proposed block boundary, the following types of units need to be stratified:

• environmental units (site series, forest cover, physiography and landforms)
• physical features (man-made structures, gullies, watercourses and natural barriers)
• resource features (for example, riparian reserve zones or riparian management zones).

Aerial photos of different strata in the area may indicate the potential for using different silvicultural systems, by providing visual evidence of differences in stand structure, broad forest cover types (tree species composition), and variations in stand height and density.

Stratify any differences in strata that can be visually identified on the aerial photograph. Some visual changes you detect may appear minor in the initial stratification, but in the final prescription this detail may aid in achieving certain stand-level resource management objectives. For example, subtle changes in stand structure and composition may help you identify portions of the stand appropriate for retention as uncut reserves. Field-checking of all strata identified at this stage will verify actual stand and site characteristics.

Collection of site-specific information

A recommended procedure for SP field data collection is:
1. collect site and ecological characteristics
2. identify and evaluate stand- and site-limiting factors (including, for example, windthrow hazard)
3. collect stand structure and species composition information
4. identify and evaluate site operational constraints
5. identify and evaluate site-specific integrated resource management concerns not identified in higher-level plans or preliminary stand resource management objectives.

Forest resource objectives from higher-level plans, stand-level resource objectives and stand structure goals will help to indicate which silvicultural system options must be considered for a proposed area. The silvicultural system options to be considered will therefore dictate what type of stand data to collect for each stratum in the area. Silvicultural prescription content requirements for different categories of silvicultural systems are summarized in the Silviculture Prescription Guidebook. Collection of information on existing stand structure will help determine if stand structural goals can be met for each general silvicultural system option.

Appendix 1 provides a checklist for required silvicultural prescription content and the recommended supporting information for different silvicultural systems.

For assessment of site windthrow hazard, a recommended reference is the Windthrow Handbook for British Columbia Forests (B.C. Ministry of Forests, 1994, Research Branch Working Paper # 9401).

For certain systems, and in particular seed tree and some shelterwood systems, potential mature seed trees and shelter-trees and the provision for natural regeneration need to be identified. Appropriate mature leave-trees for these purposes should be:

• larger dominant trees
• windfirm
• acceptable species
• capable of good seed production, and have
• desirable physical characteristics.

Notwithstanding these criteria, however, leave-tree acceptability criteria are to be site-specific, based on local site conditions and local past experience. Leave-tree acceptability criteria for the unit should be documented. For field assessment of the windfirmness of potential leave-trees, dig numerous soil pits, especially near identified leave-trees and within tree groups selected to be left.

Examine the existing stand structure to determine if future post-harvest stand structural goals are likely to be achieved. The number and condition of trees in all appropriate layers should be examined to determine at least the following information:

• amount and suitability of advance regeneration
• the dominants and codominants are capable of producing adequate natural regeneration, if required to achieve the regeneration objectives
• if suitable trees in any layer need to be reserved for resource management objectives
• if any trees need to be removed to improve stand health.

Review and refine stand structural goals

STEP 4

• Review existing stand structure and composition information for each stratum.
• Review windthrow hazard assessment in each stratum (refer to Windthrow Handbook mentioned in previous section).
• Review forest resource objectives as described in higher-level plans, and stand-level resource objectives derived from forest resource objectives.
• Integrate stand structure, windthrow hazard information and other site data with stand-level resource objectives to formulate specific and achievable stand structural goals. Refer to applicable guidebooks for guidance on specific goals, constraints for specific stand-level objectives, and required standards and actions.
• If warranted, refine the stand-level resource objectives and stand structural goals in consultation with appropriate agencies. Any modifications at this stage must be supportable by sufficiently detailed field data, or will cause and direct further investigations.

Sometimes it is not possible to design an achievable stand structural goal, given all of the factors to be considered. It may be possible to modify stand-level resource objectives in consultation with appropriate agencies or the authors of higher-level plans, based on the field assessment. Feedback from field work is essential to ensure that higher-level plans translate into the appropriate choice of silvicultural systems.

Note that, according to Section 9 (Management Plans) of the Forest Practices Code of B.C. Act:

“If an objective, specification or measure in a management plan differs from those provided under this Act, the regulations, the standards or the objectives established under this Part, the more stringent objective, specification or measure prevails.”

Compare silvicultural system options

STEP 5

List and consider the attributes of the silvicultural systems (stand structures and silvicultural treatments) appropriate for each stand-level resource objective, in keeping with:
• ecological conditions and stand or site limiting factors
• forest resource objectives as described in higher-level plans
• stand structural goals
• natural stand developmental processes
• wind exposure, windthrow hazard and possible risk mitigation measures.

Once the desired sequence of stand structures over time has been determined, consider alternative combinations of silvicultural treatments (including harvest strategies and methods) that will allow the stand to develop, with the aid of the treatments, from its existing structure and composition to the desired condition. These treatment combinations include, but are not limited to, the harvest and regeneration processes for which the silvicultural systems are named.

During this analysis, keep in mind the overall resource objectives, site and stand limiting factors, natural stand development processes that will continue without management intervention, the risk of the loss of stand values, and risk mitigation measures.

Table 3 provides a preliminary checklist of a variety of stand and site limiting factors and considerations that may need to be addressed.

The silviculture treatments that are chosen as components of the silvicultural system must have treatment objectives that contribute to the development of the desired stand structure and composition. Many of these treatments will be carried out to aid the establishment and growth of regeneration. Some examples of objectives for these treatments are:

• increasing soil temperature
• shading to decrease soil surface temperature
• increasing the volume of the rooting zone
• increasing the ease of root penetration in the rooting zone
• controlling competing vegetation.

From feasible alternatives, select the most appropriate combination of treatments for achieving the long-term stand structural goals, in light of all stand-level objectives and site conditions. Different strata on the area may require differing combinations of treatments.

Finalize the choice of proposed silvicultural system

STEP 6

Review the series of silvicultural treatments chosen to ensure that it provides the most advantageous opportunity for achieving the desired stand structural goals over time, and that treatments are logically consistent with each other.

In contentious cases, propose two or more options for review.

Develop any final treatment refinements.

Name the silvicultural system, using terminology defined in this guidebook.

In the silviculture prescription, describe the selected silvicultural system, post-harvest stand structural goals, desired leave-tree characteristics, and other required and supporting information.

If no silvicultural system appears to be desirable at this time, recommend deferral of the area from harvesting. Further investigation of possible options may be warranted in some situations.

While more than one combination of treatments may achieve the stand structural goals over time, in most cases only one prescription for a silvicultural system will be proposed for each stratum. This proposed site-specific treatment combination (the final proposed silvicultural system) will have been developed step-by-step and incrementally from the start of the process to consider Forest Practices Code requirements, higher-level plans, stand-level objectives and specific site characteristics. In contentious cases, however, it may be necessary to develop two or more possible silvicultural system options for further review or for use in a public involvement process.

In some instances, individual silvicultural treatments chosen to achieve different stand-level objectives on the same site may appear to be mutually incompatible. In such cases, make the final combination of treatments chosen an appropriate compromise, based on ranking stand-level objectives. Consider, evaluate and determine a balance among:

• silvics of suitable regeneration species, with respect to stand structural objectives
• insect, regeneration, windthrow, disease, climatic and economic risk
• viable harvesting systems
• stand-tending activities and schedule to achieve stand structural objectives
• administrative, legal and other operational constraints
• public perception
• requirements of higher-level plans.

If evaluation of all considerations and potential risks demonstrates that there is no suitable silvicultural system for the site, recommend to the district manager that the area be deferred from harvesting. Ensure that any such decision is adequately recorded in the forest inventory database.