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THE PRACTICE OF ECOFORESTRY: TENDING AND HARVEST -
Part 3 of 3

Paul Kalisz, Ph.D.

1. Introduction

Silviculture is the art and science of tending individual
trees and entire forest ecosystems with the objective of
producing conditions and products that are pleasing or essential
to people, while maintaining, restoring, or at least not
degrading, the health, integrity, and natural biodiversity of the
ecosystem. The silvicultural prescription or silvicultural plan
defines specific goals and provides a schedule of activities
designed to achieve the goals. Although detailed, the plan must
be case-specific and flexible, and should be used as a working
hypothesis rather than as a cookbook. All techniques and
technology used in the plan should be sustainable, and should
represent an appropriate blend of scientific, traditional, and
intuitive knowledge.

This paper is the third in a series on THE PRACTICE OF
ECOFORESTRY and deals with concepts and techniques of
silviculture. Important terms and concepts not previously
discussed in this series of papers are printed in bold-face and
are defined in the text. The emphasis of this paper is on the
hardwood-dominated forests of Appalachia, and on providing
principles and ideas that may serve as stimuli for innovation, or
that may be modified to suit local conditions.

2. Stand Evaluation

Species Characteristics

Silvical characteristics (the life history, requirements,
and general characteristics and responses of trees) may differ
dramatically even among tree species occurring in a single stand.
Since a treeþs silvical characteristics determine its functioning
within the ecosystem, its utility to people, and its response to
management, it is essential that you become familiar with the
silvical characteristics of at least the most important tree
species encountered during your forest inventory. This may be
done by consulting knowledgeable local residents, field guides or
books on local flora. Agriculture Handbook Number 654, Silvics of
North America (1990; Volume I. Conifers and Volume II. Hardwoods;
produced by the USDA Forest Service and available from the U.S.
Government Printing Office), is relatively inexpensive and
provides up-to-date information on the silvical characteristics
of all North American tree species. The Tree Species Chart in the
center of the present technical paper also provides some
information on the silvical characteristics of 30 important
Appalachian tree species.
Stand Characteristics

Stand structure refers to the distribution of trees in a
stand (number of trees per acre) into categories based on age,
DBH or some other variable of interest. Age distribution (Figure
1) is particularly interesting since a major goal of ecoforestry
is to re-establish uneven-aged conditions in stands that have
become even-aged due to management. Tree age may be determined
by counting annual rings. These are concentric color and
texture patterns observable in tree cross-sections and caused by
differences in the sizes of the cells produced during the early
and late part of a single growing season In regions where trees
become dormant in the winter. Annual rings are often counted on
increment cores collected with an increment borer (a coring
device that extracts a thin cylinder of wood extending from the
bark to the center of a tree). This is not recommended since
increment boring harms living trees by producing entry points
through the bark for fungi and other organisms that may decay
wood, cause disease or reduce the usefulness of the tree for
lumber. For this reason living trees should only be bored under
exceptional circumstances. Reasonably good estimates of age may
be obtained non-destructively by questioning people familiar with
local forest history, by collecting increment cores from trees
that have died recently enough that the wood is still sound, or
by counting the annual rings on the stumps of harvested or wind-
thrown trees.

Figure 1. Distributions of diameter classes for: A, even-aged
stand; B, uneven-aged stand. Note that diameter (DBH) is used in
place of age (see text).
Given the problems involved in determining tree age, DBH has
conventionally been used in place of age when constructing age-
distribution graphs such as Figure 1. This convention is based
on the assumption that DBH and age are well-correlated, that is,
that larger-diameter trees are older than smaller-diameter trees.
In general, this assumption holds, but care must be taken since
some small trees may be very old, or, due to differences in rates
of growth, two individuals of the same age may have very
different DBHs. Misjudgment of age is a problem when it affects
the results of tending operations as, for example, when small
trees judged to be young and vigorous are released (a cutting
made to free the crown of a selected tree from competition by the
crowns of other trees) but turn out to really be too old to
respond to the release. Such a misjudgement would lead to
inappropriate and ineffective tending, and would waste time and
energy.

Age-distribution of a stand can be visually evaluated by
plotting the average numbers of trees per acre (vertical axis)
versus 2-inch DBH classes (horizontal axis). Your graph should
have a shape similar to curve þBþ of Figure 1, otherwise the
stand is probably not uneven-aged, and you will need to restore
uneven-aged conditions prior to practicing uneven-aged management
or harvesting (see þTending Standsþ and þHarvestingþ below). If
you use the inventory procedures described in þInventory and
Description,þ Part 1 of this series of technical papers, the
trees tallied in DBH-classes wider than 2 inches should be
divided proportionally into 2-inch classes starting with the 2 -
3.9 inch class (see Example 1).

EXAMPLE 1
Refer to the sample data presented on p. 5 of Part 1 (þInventory
and Descriptionþ) of this series of technical papers, and to the
total number of tally trees recorded by DBH-class in the bottom
line of the sample tally sheet :

Of the 16 trees tallied in the 2-4.9 inch DBH-class, two-thirds
(11) would be assigned to the 2-3.9 inch class and one-third (5)
to the 4-5.9 inch class

Of the 29 trees tallied in the 5-9.9 inch DBH-class, one-fifth
(5) would be assigned to the 4-5.9 inch class, two-fifths (12) to
the 6-7.9 inch class, and two-fifths (12) to the 8-9..9 inch
class

11 trees were tallied in the 10-11.9 inch class

5 trees were tallied in the 12-13.9 inch class

8 trees were tallied in the 14-15.9 inch class

3 trees were tallied in the 16-17.9 inch class

Of the 1 trees tallied in the 22-27.9 in DBH-class, one-third of
a tree would be assigned to the 22-23.9 inch class, one-third to
the 24-25.9 inch class and one-third to the 25-27.9 inch class

NOTE: These are numbers of tally trees only; trees per acre must
be calculated from the tally data separately for each DBH class
.

3. Tending Stands

Intermediate cuttings (cuttings made for any purpose other
than the final
harvest of a tree) may be carried out for many reasons including:
to re-establish an uneven-aged DBH-distribution in stands that
are initially even-aged; to maintain an uneven-aged DBH-
distribution once it has been established; to release crop trees
(any tree selected to be intensively tended to produce forest
products); and to release selected young trees growing in natural
gaps or in openings created by tree harvest. Intermediate
cuttings provide an opportunity to regularly harvest firewood and
other small products, and occasionally sawtimber, while cutting
to improve the overall quality of the stand or of selected trees
in the stand.

A patch cut that removes all or most of the trees from the
upper- and mid-canopy levels is an effective way to harvest
firewood or other small products while increasing the
biodiversity of a stand. Such cuts help convert an even-aged
stand to an uneven-aged condition by increasing the light and
temperature levels on the forest floor which, in turn, stimulate
the growth of young trees in lower canopy levels and the
germination of seeds in the soil seed bank (the reservoir of
dormant but viable seeds that accumulate over many years in the
upper soil and litter layers, and that may be þshockedþ into
germination by drastic alterations in the environment such as
disturbance of the forest canopy, burning, and fertilization).
Patch cuts may also increase species diversity if the species
that are released or stimulated to germinate in the patch differ
from the common species composing the stand. Increases in species
diversity may also be encouraged by follow-up treatments that
release selected species that have established by natural
regeneration (renewal of a tree crop by natural seeding or
sprouting) in the patches, or by artificial regeneration
(planting seedlings or sowing seeds) or enrichment plantings of
rare or valuable tree species in the patch. In any case, the
size of a patch cut should approximate the natural size of a
canopy gap that would occur from the death or blow-down of one or
a few trees. In general, patches approximately one tree-height
in diameter seem ideal in that they are large enough to allow for
the growth of a variety of species including intolerant species
(see definition of tolerance at bottom of Tree Species Chart),
and are of such a size to prevent the gap from functioning as a
þfrost pocketþ or a þheat pocketþ (climatological phenomena
whereby small openings in the forest serve as þtrapsþ for cold or
hot air and adversely affect the growth of some plants). Patches
that are one tree-height in diameter could range in size from as
little as 50 feet for poletimber-sized trees or for scarlet oak
or pitch pine growing on dry and infertile sites, to more than
150 feet for yellow-poplar or white pine growing on moist and
fertile sites.

Intermediate cuttings made to establish or maintain uneven-
aged DBH distributions would remove trees from DBH-classes that
have excessive numbers of trees, and would leave extra trees of
appropriate size to grow into DBH-classes that have deficient
numbers of trees. The goal would be to maintain a DBH-
distribution similar to that shown in curve þBþ of Figure 1. The
following guidelines represent a convenient way to determine
which sizes classes have deficient or excessive numbers of trees.
Such a determination is the first step in marking (the process of
determining which trees are to be cut, and of painting or
otherwise marking these trees) a stand for an intermediate cut
that is designed to maintain an uneven-aged DBH-distribution.

GUIDELINES FOR UNEVEN-AGED STANDS

(1) There should be about 2 times as many
seedlings as saplings;
(2) There should be about 2 times as many
saplings as poletimber trees;
(3) There should be about 5 times as many
poletimber trees as sawtimber trees;
(4) About three-fourths of all sawtimber
trees should be less than 15 inches DBH,
and about one-fourth should be larger
than 15 inches DBH.

Frequent fire is a natural process in some dry ecosystems
dominated by pine and oak. On such sites prescribed fire may be
used during tending to encourage natural regeneration, to thin
out dense understories, or to reduce heavy accumulations of
forest litter (decomposing foliage, bark, twigs, and other plant
materials on the forest floor). The season and frequency of
burning, the intensity of the fire, and the size of the area to
be burned are among the variables that must be carefully chosen
if the prescribed fire is to mimic natural fires in the same
ecosystem. Before ever considering fire as a tool in your
silvicultural plan, check with your state forestry agency and
with your local fire marshall concerning restrictions and safety
rules, and determine where you will recruit a fire crew of
sufficient size and experience to safely monitor and control the
fire.

In order for uneven-aged management to be successful, new
trees must become established beneath a canopy or in gaps left by
the harvest of one or a few trees. During tending consideration
should therefore be given to assuring that sufficient numbers of
seeds germinate and grow into established seedlings that can
eventually grow into the upper canopy. In cases where
regeneration is lacking due to consumption of seeds by seed
predators such as chipmunks and squirrels, it may be possible to
divert these small mammals from feeding on native tree seed by
providing large amounts of another type of seed that is easily-
available, inexpensive, and incapable of surviving to become a
pest in the forest. For example, the sowing of large numbers of
sunflower seeds seems to cause small mammals to key-in on
sunflower seeds and to refrain from consuming pine seeds. Similar
responses may occur if seeds are added to hardwood stands,
although it may be that small seeds such as sunflowers will never
be more attractive to mammals than larger seeds such as acorns
and hickory nuts. Since seeds germinate and seedlings establish
more dependably in mineral soil than in litter, regeneration may
be encouraged by soil scarification (exposing bare mineral soil
in small spots or strips on the order of 12 inches in size). To
some degree this will be achieved in the course of normal
operations, and especially during intermediate cuttings and
harvest of crop trees. Advance regeneration (seedlings less than
2 inches DBH and greater than 4.5 feet tall) stems have well-
established root systems and are generally capable of rapid
growth when released, and are one of the most dependable ways of
naturally regenerating many tree species including oaks. For this
reason, if seedlings and saplings are scarce intermediate cuts
should be made to release stems of advance regeneration,
individually or in patches, as they are encountered during the
course of other tending operations.

Tending Crop Trees

Crop trees may be selected for intensive tending with the
goal of maximizing their health and longevity, and encouraging
them to grow large clear boles (a lower trunk free of branches,
knots, decay, or other blemishes). Unless dealing with species
that are in danger of disappearing from the stand, it is best to
delay selection of crop trees until they are at least 20 years
old and have begun to exhibit their physical characteristics and
potential for growth. If production of sawtimber is the goal,
individuals of desirable species should be selected as crop
trees based on their having high vigor (Figure 2); cylindrical
stem form (shape and taper of the tree trunk;) and a low apparent
tendency to produce epicormic branches or epicormic sprouts
(branches originating in suppressed buds buried beneath the bark
on the trunk of a tree, and stimulated to develop by increased
temperature or light levels). Trees that are likely to produce
abundant epicormic branches once released may be identified by
the presence of numerous small branches on the trunk and by the
occurrence of small bumps and bark irregularities that indicate
that clusters of suppressed buds are hidden below the bark. Note
also that of the 30 species listed in the Tree Species Chart,
white, red, and chestnut oaks, and basswood and black cherry,
have the greatest tendency to produce epicormic branches
following release. Up to 80 crop trees per acre may be selected,
but remember that crop tree tending is labor-intensive and time-
consuming.

High Tree crown appears thick and dark green for the
species; large or abundant dead branches are lacking in the
crown; excessive numbers of epicormic sprouts are lacking from
lower portion of tree trunk; evidence of disease and mechanical
injury is lacking; twigs have good color and normal appearance
for the species; bark is relatively smooth with shallow fissures.

Medium Tree crowns appear more open or less healthy than
those of "high" vigor trees in terms of dead or dying branches,
excessive numbers of epicormic sprouts on the lower trunk, etc.

Low Tree crowns appear to be thin and unhealthy, and
excessive numbers of epicormic sprouts may occur on the lower
trunk and at the base of the tree; evidence of excessive decay
may occur along with sign of increased excavating activity by
woodpeckers, bark beetles, and other animals; bark is rough with
broad plates and deep fissures.

Figure 2. Tree vigor classes.


In order to maintain high vigor and rates of growth, the crowns
of crop trees should be kept free of competition from the crowns of
surrounding trees. Growth increases of 25-100%, highest for more
tolerant species, have been recorded for crop trees during the first
decade after release. The goal of crop tree release is to maintain a
live-crown ratio (the proportion of the total tree height that is
clothed with live branches, expressed as a percentage) of at least
35%. During the period of vigorous tree growth, whenever the live-
crown-ratio of a crop tree approaches this threshold, it is time to
again release the crown of that tree. Once height growth has peaked,
however, trees expand their crowns very slowly. Beyond this age,
release of crop trees will be ineffective and should cease since the
trees will not be able to take advantage of additional open space
created in the canopy.

Once the crop trees have been selected, there are two simple
methods of marking these trees for release. The þcrown-touchingþ
method simply cuts every tree whose crown touches the crown of the
crop tree. Trees with crowns in canopy levels beneath the crown of the
crop tree do not offer serious competition and are never cut; these
subordinate trees may also conceivably function as þnurse treesþ that
shade the lower trunk of the crop tree and reduce the formation of
epicormic branches. If it is desirable to create more open space in
the canopy than is formed by the þcrown-touchingþ approach, the
following guidelines may be used to determine the release radius (the
radius of the circle surrounding a tree which should be kept free of
the crowns of competing trees) for individual crop trees. Note that
the crowns of 30 Appalachian tree species are classified as narrow,
medium, and broad in the Tree Species Chart.

Release Radius (feet )

DBH (in) Narrow Crown
Medium Crown Broad Crown

8 14 16 19
12 17 20 25
16 19 23 31
20 21 26 35
24 23 29 39
28 24 31 43
32 25 32 44
36 26 33 45

Table 2. Recommended release radii for crop trees with narrow, medium
and broad crowns.

To guarantee that clear wood is produced, the lower 18 feet of
all crop trees should be pruned (the artificial removal of selected
branches from trees) at the time of release and kept free of epicormic
branches by repeated pruning as often as necessary. The Natural Target
Pruning method (described below) should be used to remove living and
dead branches, both of which produce knotty wood. Branches should
ideally be pruned before reaching 2 inches diameter, and no more than
25% of the live crown length should ever be removed in one year.

Harvesting.

Trees are considered candidates for harvest after reaching some
large DBH that is site- and species-specific, normally in the range of
30 to 36 inches for trees on good sites. Trees that die before
reaching this critical DBH are not harvested, but are left to become
snags and logs. Harvesting is by single-tree selection (uneven-aged
cutting method in which scattered individual trees are harvested
throughout the stands) with individual trees evaluated on a cutting-
cycle (the interval between visits to the stand to evaluate trees for
harvest) of 10 years, and never harvested until judged not to be
vigorous enough to survive another 10 years. This means that every
tree has its own individualized rotation (the period of time over
which a tree is grown before being harvested), and that an individual
of a long-lived species such as white oak (See þlongevityþ column in
Tree Species Chart) could conceivably be tended for 3 or 4 centuries
before harvest.

Logging should be done using directional felling and other low-
impact harvesting techniques described by Gary Anderson in SUSTAINABLE
LOGGING AND LUMBER PRODUCTION (Supplement 4). Such methods minimize
the length of roads needed on the forest and the amount of damage done
to the remaining trees during logging. Skidding (hauling logs from the
stump to the collection point) with horses or other draft animals and
a logging arch (see TP-35) is least damaging to the soil and the
remaining trees. Horse-logging is a practical and economical
alternative on at least three-fourths of all Appalachian logging jobs.

Estimating Growth

Rough predictions of the volume growth of a tree for the next 10-year
period may be made by making reasonable estimates of DBH- and height-
growth rates. As described in Part 1 of this series, DBH and
merchantable height are used in conjunction with a volume table to
first obtain board-foot sawtimber volume at the beginning of a 10-year
period. DBH-growth rates for the next 10-year period may be obtained
from the Tree Species Chart, and height growth may be estimated using
the rules given below. Finally, using these growth predictions, DBH
and merchantable height at the end of the 10-year period may be
estimated and a volume table again consulted to obtain tree volume at
the end of the period.

RULES FOR PREDICTING MERCHANTABLE HEIGHT-GROWTH

(1) Trees with DBH-growth greater than 2 inches during the next
10 year period could increase as much as 1 log (16 feet) in
merchantable height over the same period
(2) Trees with DBH-growth less than 2 inches during the next 10
year period could increase as much as « log
(8 feet) in merchantable height over the same period.
(3) Trees greater than 30 inches DBH will not increase in
merchantable height during the next 10 years.
(4) Maximum merchantable height is 5 logs for tall-growing
species such as yellow-poplar and white pine,
and 4 logs for other species.
(4) Trees with merchantable height limited by forks or large
branches will never increase in merchantable height.

Conclusion. As with all predictions, these growth estimates assume
that environmental conditions remain stable over the 10-year period of
interest. This assumption was probably sound 50 years ago, but is
questionable today due to widespread pollution of the air leading to
global climate change, poisoning of soils and waters, destruction of
native biodiversity (including pollinating and seed-dispersing
animals) and other human abuses of the Earth.