Silvicultural Systems

Silvicultural Systems and
Terminology
Tony D’Amato
Module 3: Certificate Course in Ecosystem
Silviculture
May 2011

Silvicultural Systems
– Planned program of treatments over the
entire life of the stand
– Includes regeneration treatments, tending
operations, intermediate treatments, and
protection measures

Silvicultural Systems
• Regeneration method
– Procedure by which the stand is established and
renewed
– Silvicultural systems are named after the
regeneration method (e.g., shelterwood system)
Shelterwood method
Seed tree method

Stand initiation stage
Stem exclusion stage
Understory reinitiation stage
From Nyland (1996)

Young Growth-stage 0-35 years
M
R
R
Extended Transition-stage 35-115 years
Old-Growth-stage >115 years
T
T
• Determine
outcomes of
treatments for
maintaining species
and structures
M
M=maintenance harvest
T=transition harvest
R=regeneration harvest

Regeneration Methods

Classification of Regeneration Methods
• Based on two factors:
1. Distinction between sprouts (i.e., suckers,
stump sprouts) and seedlings (from seed) as
sources of regeneration (Low- vs. Highforest
methods)

Classification of Regeneration Methods
• Based on two factors (cont.):
2. The arrangement of cuttings in time (Evenvs.
Uneven-Aged Methods)

Low-Forest Methods
• Rely largely on vegetative regeneration from
stump sprouts, root suckers, or layered
branches
– Coppice method – any type of cutting in which
dependence is placed mainly on vegetative
reproduction

High-Forest Methods
• Regeneration of stands based on sexual
reproduction (germinated seed)
– Even-aged methods - entire community of mature
trees is removed in one or more cuttings over a
short interval of time to allocate growing space to a
new, even-aged cohort

Even-Aged, High-Forest Methods
• Clearcutting Method
– Removal of the entire stand in one cutting
– Regeneration occurs following harvest, either
through artificial means (seeding, planting) or seeds
germinating after harvest

Even-Aged, High-Forest Methods
• Seed-Tree Method
– Removal of the old stand in one cutting, except for a
small number of seed trees left singly or in small
groups
– Seed trees provide for establishment of advance
regeneration

Even-Aged, High-Forest Methods
• Shelterwood Method
– Removal of old stand in a series of cuttings
extending over a relatively short portion of the
rotation
– Encourages the establishment of one cohort of
advance regeneration under the partial shelter of
seed trees

Two-Aged, High Forest Methods
• Most of the mature forest is removed, but
widely spaced vigorous trees are left to
grow above the new cohort
Shelterwood with Reserves
Clearcut with Reserves

Irregular shelterwood methods
• “Irregular” refers to stands in which distribution of
age classes is unbalanced
‣ Irregular heights and spatial arrangement of trees

Group shelterwood
components (small gaps)
Baden Femelschlag

Matrix surrounding gaps
(uniform shelter)
Baden Femelschlag

Uneven-Aged, High Forest Methods
• Uneven-Aged Methods – only some trees in a
community have reached maturity and are
removed over an extended time period to
allocate space to a new age class

Uneven-Aged, High Forest Methods
• Selection methods – occasional
replacement of single trees or small groups
of trees with regeneration from any source
Single-tree selection
Group selection

SHADES OF GRAY
• Depending on objectives and stand conditions,
hybrid approaches can be applied that combine
multiple regeneration methods in same stand or
harvest unit

Intermediate Treatments

Intermediate Treatments
• Treatments applied to improve the existing
stand, regulate its growth, and provide for early
financial returns, without any effort directed
at regeneration.

Release Treatments
• Weeding: treatment applied during the
seedling stage to eliminate or suppress mainly
herbaceous plants or shrubs before they
overtop or interfere with desired trees

Release Treatments
• Cleaning: treatment applied during the sapling
stage to free selected trees of better species
and quality from overtopping trees of
comparable age

Release Treatments
• Liberation cutting: freeing young trees not
past the sapling stage from competition from
older overtopping trees
– Often corrects problem not addressed by earlier site
preparation (poor quality, undesirable trees left
during past logging)

Thinning Treatments
• Thinning: the removal of live trees from a
stand with the intention of improving growing
conditions on the site for the uncut or leave
trees

Thinning Treatments
• Pre-commercial thinning (PCT): thinning
before the cut trees have sufficient
merchantable volume to yield adequate volume
for commercial harvesting
– Early investment to increase the net return from
the whole crop

Commercial Thinning Methods

Thinning Methods
• Based on how individual trees are chosen for
removal
– Crown position in canopy (crown classes – Kraft
classification)
• Low, crown, and selection thinning
– Predetermined spacing or pattern of removal w/o
regard for crown position or quality
• Geometric (mechanical) thinning

Thinning Methods
• Low Thinning (thinning from below)
– Favors development of dominants and codominants
through the removal of lower crown classes
– Leave more valuable trees
– Emulates natural development processes

Thinning Methods
• Crown thinning (thinning from above)
– Favor dominants and codominants by removing
other dominants and codominants
• Favoring best quality crop trees in stand
– Intentionally make holes in canopy around crop
trees

Thinning Methods
• Selection thinning (dominant thinning)
– Removal of trees in dominant crown classes in
order to favor lower crown classes
– Relies on smaller trees to respond to open growing
conditions (risk of windthrow, thinning shock)
– Can become high-grading

Thinning Methods
• Geometric Thinning (mechanical thinning)
– Trees are removed in proportion to their occurrence
(no crown class considerations)
– Removals are made to maintain a predetermined
spacing among trees
– Operationally efficient (thin in rows, every other
tree)

Thinning Methods
• Free thinning
– When faced with stand with irregular structure, it
may not make sense to do any of the above
thinnings
– Apply all other elements of thinning at once
– Thin to approve stand structure

Variable Density Thinning
– Thinning regime in which thinning intensity and tree
marking rules are varied within stand of interest
• Increases heterogeneity in stand density and cover
– Emulates natural variation in stand structure
resulting from competitive mortality and small-scale
canopy disturbance

Variable Density Thinning
– Often called “skips-and-gaps” approach
• Portions of stand are left lightly or completely unthinned
(“skips”)
– High stem density, heavy shade
• Other portions are heavily harvested (“gaps”), including
removal of dominant trees
– Increases understory development (REGENERATION)
• Remaining matrix is often thinned to intermediate levels
(e.g., 70% of initial basal area)

skip
thinned
matrix
gap

Final Point
• Silvicultural systems are an expression of
your collective creativity in meeting a desired
future condition
– Well-defined approaches exist; however, these
methods should be applied with flexibility and
creativity to meet ever-evolving objectives