go to glossary section A-C D-I J-S S cont R-Z


SILVICULTURAL SYSTEMS/PRESCRIPTIONS: Defined as the art and science of growing trees, silviculture allows forest managers to imitate natural processes of dynamic forest ecosystems (Fraser Inc.).  Natural regeneration occurs through seed or vegetatively, as even-aged and uneven-aged processes, depending mostly on species characteristics.  Silvicultural systems based on reproduction by seed (the so called "high" forest methods) are well recognized as the silvicultural prescriptions listed below.

EVENAGED SYSTEMS: Acceptable in areas larger than 200 acres (where the untreated portion is large enough to provide the required area of functional shelter (Vermont guide)), with established rotation ages and cutting intervals. 

 #5.   UNIFORM SHELTERWOOD SYSTEM:     Two or more cuts designed to either release advanced regeneration or to establish new natural regeneration.  A transitional (to regen stage) cutting to remove volume in a first cut without making the residual stand unsuitable for seeding in or sheltering the new stand, and prohibiting another cut after adequate reproduction of desirable species became established (Thomson 1950).


     First Cut as a seed cut:


     -leave at least 18 m2 of BA/ha, releasing final crop (seed) trees, yet provide shade to limit development of intolerant shrub/tree regeneration (Fraser's Maine Timberlands).

     - remove up to 35% of the BA (Vermont Guide)

     - remove 30 to 60% of the trees (Fraser's)

     - Cut from below to remove low shade

     - includes submerchantable hardwoods down to 1 inch

     - leave larger and vigorous trees for seed and shade

     - late summer logging to prepare seedbed & reduce damage

     - leave windfirm, healthy seed trees as final crop trees



       First Cut as a release cut:


     - employ regeneration protection methods (winter, etc)

     - remove up to 45% of the BA

     - remove low grade materials first plus some higher grades

     - leave windfirm, final crop trees, ie minimize windthrow

     - follow-up with final felling in 3 to 5 years after release

     -three stage where functional shelter is limited, or on exposed sites with windthrow hazards (20% BA 1st

       cut, and in 5 to 10 years, 20% BA in 2nd cut, etc.).


     Final Cut: (Vermont)

     - complete removal of merchantable volume

     - after adequate regeneration (1-2 ft) has been established

     - winter logging with regen protection measures

     -to establish even-aged regenerating stand

SHELTERWOOD This group of treatments is often practised in stands with an objective of promoting natural regeneration, salvaging mortality or eliciting growth response in the residual overstory. In most situations this prescription is even-aged management; however, in some cases the long-term objective may be to create all aged stands. Generally up to 40% of the area ( and volume) is removed in the first pass ( modelled as 33% removal), focusing on the shorter lived species and lower quality or less vigorous trees. The second entry is normally delayed by 5-10 yrs depending on the specific stand conditions and objectives. There are some variations on the standard shelterwood that may be prescribed in specific circumstances including irregular shelterwood and some group selection methods. (JD Irving) Wind firmness is a primary concern limiting the implementation of this treatment particularly in stands dominated by red spruce. Serious blowdown in post treatment red spruce stands over the past years has discouraged this teatment while encouraging the use of patch cutting as an alternative.

 #6.   STRIP OR PATCH SHELTERWOOD: Is the shelterwood system described above except it is done in strips, separated by uncut strips.  In stands of 60+ years and 70% balsam fir (Vermont), or other areas where uniform shelterwood is inappropriate.  Strip cutting should proceed from the windward side to enhance seed dispersal and minimize windfall along the edge of the mature timber (Baker, 1934).  Once regeneration has occurred, the stand can be managed by uneven-age group selection, or even-age shelterwood (ie final cut as above).  Cut strips to be 20 to 40 ft wide, uncut strips 40 to 80 ft wide (Vermont).  Strip orientation should be east-west to northeast-southwest depending on windthrow hazard.  Use harvesting method which scarifies the ground to favour spruce regeneration (Vermont).

     - follow guidelines for uniform shelterwood above

 #3.   SEED TREE: Requires leaving a suitable number of good seed producing trees per hectare, which are harvested after regeneration has become established.  This system favours light demanding regeneration and windfirm species.

 #2.   STRIP OR PATCH CLEARCUTTING: This is a variation of clearcutting where the cuts are orientated in strips or patches.  Clearcutting is done in the presence of established advanced regeneration, or in areas unrestrained by manaagement objectives and wood supply calculations.  In a DMAMU, area cut must meet area regulation calculations (Vermont).  Logging in the winter to protect advanced regeneration.

 UNEVENAGE SYSTEMS: (see uneven-aged definition below)  Uneven-aged management systems, by area regulation are the best method for managing DWAs (Vermont), the authors state that individual tree selection is not preferred because it may reduce overall shelter values through the uniform nature of the disturbance.  Suitable in healthy stands 60 years (bF) to 100 years (sp, Ce, He) old.

#7 SINGLE TREE SELECTION The objective of this prescription is to create and maintain an un-even aged stand condition. Tolerant Hardwood TH, Tilerant mixed wood THSW, and cedar dominated stands CE are usaully targeted, but this treatment may also be used in stands with signicant components of red spruce, white pine or hemlock. In addition, non timber primary management objectives in riparian zones or in recreational and aesthetically important areas may result in a single tree selection treatment being utilized. Depending on specific stand conditions, uneven aged management typically removes 20-40% of the stand volume each entry ( modelled as 33%), with rentries normally seperated by 15-30yrs (modelled as 20yr re-entries). The objective of these treatments is generally to improve stand quality while maintaining a full range of age and diameter classes and a suitable diversity of species at all times. The single tree selection prescription is often used in TH and THSW stand types where maintenance of the existing covertype is an important management objective. This treatment is usually eligible for a royalty discount.(JD Irving)

Single Tree Selection: A continuous harvesting operation based on 5 to 10 year intervention cycles, where individual trees (hence small periodic allowable cut) are selected and harvested as they mature.  Shade tolerant seedlings or sprouts regenerate in the openings.  Theoretically, single tree selection stands contain trees of all age classes with fair crown closure.  Changes in the stand's appearances from one cutting to the next is often not readily apparent.  General improvement cutting practices are followed. (DNR choices), ie over time remove poor quality trees.  (remove mature individual vs. remove all size ranges?)

#8  GROUP SELECTION Like a single tree selection, the objective of the group selection is also to create and maintain an uneven aged stad condition, The latter is usually directed to stand conditions that will be managed on a single-tree selection basis in the long-term. The group selection treatment often targets stands where the long-term objective is to promote a different species composition than is presently occuring on the site; eg promoting yellow birch over beech, or spruces over balsam fir. Ideally, the opening size in a group selection is less than one hectare and in many specific cicumstances it is much smaller than that. Individual trees may be left standing in the opening, particularly if they contribute to the long-termmanagement objectives for the stand (eg. pole sized hardwoods or saplings of the desired species) Similar to single tree, group selection typically removes 20-40% of the stand volume each entry (modelled as 33%), with rentries normally seperated by 10-30yrs ( modelled as 20yr re-entries) The earlier re-entry prescriptions will be used in some situations to accelerate transition to uneven aged management. In some situations, an entire stand may be operated in one entry using a combination of single tree and group selection prescriptions. (JD Irving)

GROUP SELECTION: Also a continuous harvesting operation on a periodic intervention cycle, except groups of trees are removed as they mature.  Characterized by:


       - Uniformly distributed removals,

       - 20 to 40 feet in diameter, associated with

         undisturbed adjacent areas. (Vermont)  The cut patches

         will be shaded favouring spruce-fir regen.

       - 1/4 to 1 acre patches (Fraser)

       - Ten to 20 year intervention schedules.  Favour long

         lived species such as cedar, hemlock and spruce.

     - Summer longing to scarify seedbed which favours

         spruce regeneration. (Vermont) Winter logging only on

         wet sites.

 INTERMEDIATE CUTTINGS: Partial cuts aimed solely at the    improvement or tending of an established stand, especially those under even-aged management.  These cuttings serve rather well defined purposes and are classified and named accordingly.  Often intermediate cuttings are the first intervention in a previously "unmanaged" stand, and are usually referred to as an improvement or low grade cut, or  thinning.  For example a precommercial thinning.  In some cases, the operation may be in the form of a release cut or residual removal.   

 #9 Precommercial Thinning (PCT): Should be done before the stand is a functional shelter, and at a heavy or frequent intensity so that thinning will not be essential during the last half of the rotation.  Especially useful to promote crown development and stem growth leading to the earlier development as a functional shelter.  Done before the trees reach 15 ft tall and 2 inches in size, to improve stand growth and quality, softwood composition, merchantable volume and rotation age or intervention schedule.

  For example:    - long rotation age (80+ yrs)

(Vermont)  - 15 to 20 year operating interval

Prescription: PCT 700-800 trees/ac @ age 15 to 20
Com. Thin to 400 trees/ac @ age 35

or,             - shorter rotation (60 yrs)

Prescription: PCT to 400 trees/ac @ age 15 to 20

# 10 COMMERICAI THINNING Commercial thinning is generally prescribed in the managed stands (planted or pre-commercially thinned), but some unmanaged natural areas are also treated where conditions are appropriate (eg. natural jack pine of fire origin). The primary objective of this treatment is to maintain vigorous growth rates by removing a portion of the trees, usually focusing on the lower quality stems.. This prescription generally removes 20-40% of the area (and volume) in the first treatment (modelled as 30% removal). Depending on the species, density and site productivity, commercial thinning may be prescribed in stands varying from 20 -50 yrs old. This treatment is usually eligible for a royalty discount. (JD Irving)


Commercial Thinnings: The rule of thumb, "thin early or don't thin at all." (Vermont).  Not to be done in large pole to sawlog sized stands.  Commercial thinning is done in a immature stand and generates pulpwood products, leading to a final sawlog harvest.  For DWA's, repeated thinnings not recommended due to adverse effect on shelter.  The amount of functional shelter and the duration (window of suitability) afforded are interdependent.  If half the area is to provide functional shelter, thinning must ensure that crown closure (70%) is recovered before 1/2 of the rotation age is reached.

#11  Sanitation/Salvage Cutting: These are improvement cuttings in stands in order to salvage trees which are dead or near death due fire, maturity, ice or wind storms, insects or disease. (ie imminent mortality, JDI).  Remove poorest quality trees and some good quality trees in order to leave adequate growing space for the residual trees and the establishment of shade tolerant regen (Fraser).

SALVAGE HARVEST Salvage harvesting is prescibed in specific situations to salvage recent or imminent mortality ncluding blowdown in stands that would otherwise not be sceduled for harvesting in the very near future. this prescription would most often be utilized along roadsides and block edges. These prescriptions are not blocked in the management plan. See salvage operations below. This treatment is usually eligible for a royalty discount. (JD Irving)




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Last Updated 08/06/2004