Glossary
-
Annual Increment, Mean Annual Increment, and Culmination
of Mean Annual Increment
-
Mean annual increment (MAI) is the average annual growth of a stand up
to a given age, generally measured in units of volume (typically cubic
feet or board feet in Montana). MAI is determined by dividing total
stem volume by age.
Stand MAI rises, then levels, then falls as the stand tends toward
maturity. This pattern results from the life cycle of an even-age
stand or cohort, which begins with minimal biomass production (little
trees growing a little bit), and rises more each year until it levels
off and eventually decreases.
Annual Increment, or Periodic Annual Increment (PAI) is determined by
dividing a stand's volume growth over a year or other given time
period by that given time period.
As with MAI, stand PAI rises, levels, and falls over its lifecycle.
As long as annual or periodic growth continues to rise, PAI will
exceed MAI (since the mean includes those slower early years).
However, as the stand matures and annual growth slows, MAI overtakes
PAI. By mathematical necessity, when PAI (inevitably) falls below
MAI, MAI begins to fall. This moment is said to be the culmination of
mean annual increment, or CMAI.
- Basal Area
-
Basal Area (BA) is a measure of the total area, per acre, of tree-stems measured
in cross-section at breast height (conventionally 4.5 feet from the
groundline). Basal area is based on diameter values and reported in units
of square feet per acre.
The basal area of an individual tree is the area of a cross-section of the
tree stem derived from its
DBH.
With radius measured in linear inches and Basal Area reported in square
feet, the formula for the basal area of an individual tree is:
BA(in ft2) = (Pi * Radius2)/144
For perspective, a tree with a 12-inch diameter at breast height (dbh)
has a basal area of 0.79 ft2. A stand with one-hundred trees with 12-inch
dbh would have a BA of 79 square feet per acre.
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- Canopy Density
-
Canopy density is a measure of the density of tree material in the crown,
measured in pounds per acre feet. This is an important measure for
determining a stand's susceptibility to crown fire and as a measure of
available biomass.
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- Clumpiness
-
Clumpiness is the measure of the lack of uniformity in a stand's
distribution of trees. In other words, clumpiness is a measure of a stand's
variability. Trees, in vivo, normally grow in clumps interspersed with small
openings. In these clumps, trees are more dense (more trees per area) than they
are on the average stand level, as openings are not accounted for at the clump
level. (Clumps are the opposite of openings.) A clumpy stand with 100 trees
averaging 12-inches
DBH
will be sometimes be less productive (in terms of growing volume) than a uniform
stand with the same stand growing uniformly, since the clumped trees will provide
more shade, decreasing photosynthesis and overall productivity.
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- Diameter at Breast Height
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Diameter at breast height (DBH) is the diameter of the stem, measured
in inches at a point 4.5 feet (4-feet, six-inches) above
ground level.
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- Diameter Class
-
A diameter class is a class of trees falling within a certain diameter
range at breast height. Generally, diameter classes are designated in
one-inch increments
starting halfway between any whole inch. Thus, a 12-inch
diameter class would include trees ranging from 11.5 inches to 12.4
inches in diameter at a point 4.5 feet from the ground.
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- Fire Regime
-
A fire regime is the fire pattern characterizing a particular cover type
or ecosystem. It includes these parameters:
-
Fuel Consumption and Spread Patterns (for instance, ground,
surface, or crown).
-
Flame Intensity (a measure of the heat in the flame front).
-
Severity (including measures of post-fire effects, i.e.,
consequences of the fire, especially upon plant life).
-
Frequency (the range of fire-free intervals in years in
a specified area).
-
Seasonality (the time of year when fires are common in the
given ecosystem).
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- Fixed-Radius Plots
-
Fixed-radius plots are sample plots with a fixed area representative
of the larger stand. For example, a fixed-radius plot with an area
equal to 1/100th, or 435.6 feet2, would have a
radius of c. 11.8 feet. We generally used fixed-radius plots for measuring
regeneration trees (smaller than 4.5 inches
DBH
).
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- Forest Cover Type
-
A Forest Cover Type is a classification of forest type based upon either its
current or potential
structure and composition.
Forest cover types based on current conditions generally use criteria
based on dominant species or species mix, age and size, uniformity, and
density. Distinctions between cover types should be clear in the field
or on aerial photographs. Fortunately, these distinctions result from the
same differences that mark stand boundaries, such as geographical
boundaries. Thus, cover type boundaries and stand boundaries often are
easily discernable to the practiced eye.
Forest cover types based on potential conditions might include various
methodologies. For instance, criteria for defining a cover type might be
linked to the expected stand structure and composition of a stand
given a
natural fire regime.
Conversely, criteria might be linked to the
habitat typing
methodology, which classifies cover types in terms of their long term potential
structure and composition in the absence of disturbance (like wildfire).
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- Forest Stand
-
A parcel of land, bounded by geographical boundaries,
administrative or property boundaries, use boundaries, roads,
apparent distinctions in stand structure and composition, or other
significant boundaries.
A stand is typically part of a discernable watershed or
drainage.
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- Fuel Characteristics
-
Fuel characteristics are the factors that affect fire behavior,
including:
- Fuel Moisture
- Size and Shape. This characteristic breaks into light fuels
(shrubs, grasses, pine needles, and other fast-burning fuels)
and heavy fuels (logs, tree trunks, and limbs). For a more
detailed classification of size and shape, see the glossary
item on
fuel classes.
-
Fuel Loading. This characteristic refers to the quantity, in
tons per acre, of fuel in each fuel class.
-
Horizontal Continuity and Vertical Arrangement. Horizontal
continuity refers to the uniformity or clumpiness of fuel,
while vertical continuity refers to the vertical levels of
fuel, including:
-
Ground fuels include combustible materials beneath the
ground surface, ranging from duff to roots and buried
logs.
-
Surface fuels are include the combustible materials on
or immediately above the forest floor, light and heavy.
-
Aerial fuels include all fuels found in the tree canopy
(crown area).
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- Fuel Classes
-
A fuel class is a category of ground fuel (down and woody debris,
leaf litter, and undergrowth flora), usually (in the field) based
on size (diameter of a cross-section of wood). The usual breakdown
is thus:
Fuel Classes and Fuel Size
| Fuel Class |
Dimensions |
| 10-hr fuels |
0.25 to 1-inch diameter |
| 100-hr fuels |
1 to 3-inch diameter |
| 1,000-hr fuels |
greater than 3-inch diameter |
Technically, 10-hour, 100-hour, and 1,000-hour refer to
"time lag periods," which means that a given piece of
wood, depending upon its size, will lose 63% of its moisture up to
an equilibrium point beyond which it will not stay dry. So, if a
3.5-in piece of wood has an equilibrium moisture of 1-2%, then
starting from any given time, that piece of wood will dry 63%
towards that target (1-2%) in more than 1,000 hours.
One time lag period is the amount of time necessary for a fuel
component to lose (or gain) 63% of the difference between the
current level of moisture within the fuel and the equilibrium
moisture content, assuming constant atmospheric conditions
(temperature and relative humidity) for an extended period of time.
The larger the fuel, the more time needed to reach the equilibrium
moisture content with the atmosphere. Conversely, the larger the
fuel, the more time needed for moisture to penetrate the fuel during
wet weather.
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- Fuel Type
-
Fuel types are the four general categories of surface fuels (see
directly above) that "carry" a fire by providing it with
the minimum fuel necessary to sustain flame. The four fuel types
are:
- Grasses.
- Shrubs. (Includes herbs and larger shrubs, like sagebrush.)
- Timber Litter. (Includes pine needles, twigs, branches, other
down and woody debris.)
- Logging Slash.
Each of these fuel types has its own further sub classifications,
each with a unique set of
fuel characteristics.
These sub classifications are called fuel models,
and each represents a unique set of measured conditions that have
been empirically demonstrated to affect fire behavior in measurable
ways given measurable variables (including but not limited to fuel
moisture and wind).
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- Geographical Information System
-
A Geographical Information System (GIS) is a computerized mapping
system supported by a relational database. In more specific terms,
it is a relational spatial-database that renders data in table and
graphic form. Data can be fixed or rendered on-the-fly.
For our mapping needs, Interface Forestry uses
Manifold System GIS
.
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- Georeferenced Photo-image
-
A georeferenced photo-image (GPI) is a virtual photo-image that has been linked
to a longitudinal and latitudinal coordinate system. Every point
on the image corresponds to a latitude and longitude. A GPI can be
printed to paper-copy with a coordinated system specific to any project.
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- Global Positioning System
-
The Global Positioning System (GPS) is a system of satellites all
transmitting via microwave their precise location and the
precise time of transmission (which of course changes at extremely
small increments). When a GPS receiving unit picks up signals from
at least four satellites, it uses the location data and time data to
determine the location (in latitude and longitude) of the receiving
unit.
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- Habitat Typing
-
Habitat typing is an approach to assessing the productivity of a stand
by determining the structure and composition that would characterize it
in a
climax
state. The process begins with cataloging the proportional presence of
all tree plant species on a site. The forester uses this information and
a reference key to determine the site's current
successional stage
from which is deduced its final
climax state.
The hypothetical climax state (its potential for production) is
described in terms of the site's (or stand's)
structure and composition,
particularly, volume (the most important measure of production).
The values of this hypothetical site are based on reference sites
established by researchers.
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- Ladder Fuels
-
Ladder fuels are fuels that carry a surface fire into a tree's
crown. They often consist of saplings and pole-sized trees with
low-lying limbs, though shrubs and slash can provide ladder fuels.
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- Natural Interpretation
-
Natural Interpretation is a field-based management activity that educates
and sometimes guides visitors in a natural setting. Landowners can use
natural interpretation to meet several sub-objectives, from providing a
calm or beautiful place for a stroll, to demonstrating or explaining natural
features or processes, to diverting visitors away from ecologically sensitive
or dangerous places. Natural interpretation can use signs, trails, canopy
openings and other physical structures to bring attention to beautiful,
important, sensitive, or interesting natural features -- and in some
instances, cultural and historical features.
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- Selection Cutting
-
Selection cutting, also known as
selective thinning, is the practice
of selecting and cutting individual trees
or groups of trees in a pattern and volume consistent with a long-term stand plan.
In this planning and management context, the primary concern is the structure and
composition of retained or "residual" trees. Harvested trees may or may not
include merchantable logs, and in some cases may include the largest and oldest
trees on a stand. (However, the practice or removing the oldest and largest trees
is barely distinguishable from
selective cutting,
also known as high-grading, discussed below.) Landowners can
use selection cutting to harvest individual trees throughout the
stand(single-tree selection) or harvest them in clumps
(group selection).
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- Selective Cutting
-
Selective cutting, also known as high-grading, is the practice of removing the
most valuable trees. This practice is usually done ad hoc for immediate
profit. Because the largest and most productive trees are an important seed source
for the ongoing health of the stand, high-grading is considered a dysgenic practice,
leading to the long-term degeneration of its genetic stock. The results of high-
grading often become apparent within one rotation.
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- Shade Tolerance
-
A tree's growing space and its associated access to
sunlight, water, and nutrients is commonly obstructed
only by other trees. Some tree species (and individuals)
can thrive in shade better than others. These shade
tolerant trees can thrive and reproduce in the shade
and actually receive benefits from shade and other aspects
of crowding, while shade intolerant trees cannot
thrive and reproduce. Thus, on a given site, over time,
the shade tolerant species will replace the intolerant
species. For example, in Montana, a common scenario is a
mixed species stand composed of Douglas-fir and ponderosa
pine, wherein the ponderosa pine (shade intolerant) is
succumbing to the Douglas-fir (shade tolerant). Over more
time, perhaps, a tree species even more shade tolerant
will replace the original replacers. For example,
subalpine fir, Abies lasiocarpa, is more shade
tolerant than Douglas-fir, and we frequently encounter both
species on the same stand. In time, such a process, known
as
succession,
will result in a
climax
stand or forest, wherein the species dominating the site
will be the most shade tolerant species that can survive
and reproduce given site conditions.
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- Site Index
-
Site index (SI) is an estimation of stand productivity based on
how much height a tree can grow over the long-term. We usually
express SI in terms of feet (or meters) per 50 years or 100 years.
For example, a measured stand might have an index of 85
feet per 100 years. Usually, we estimate a stand's SI by
measuring a sample of well-formed (straight) open grown trees
of each species. The process of determining SI for a species involves averaging the
SI measurements for each sample tree. We calculate individual SI
measurements by dividing tree height by age and multiplying by
100:
SI = Age (years) / height (feet) * 100
We usually measure tree height from breast height (4.5 feet above
ground level) to the tree tip, and we measure age at breast height
by counting rings in a core sample.
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- Stand Density
-
Stand density is an index of how crowded (with trees) a stand is.
Stand density is important because it determines how productive a
stand can be (independent of other variables, like
site index)
in terms of growing tree volume.
Conventionally, foresters have used any of several approaches, each with their
own advantages and disadvantages. Most approaches calculate a value
based on average
DBH
in relation to the number of trees per acre (TPA). As a stand's
average DBH increases, or as its TPA count increases, its index
of stand density increases. Typically, a subjective interpretation
accompanies this numerical index, such that one can determine
whether or not a stand is overcrowded, under crowded, or some
condition in between.
Most measures of stand density have assumed "stand uniformity"
and "distance-independence." That is, most stand density indices
assume that trees are evenly spaced and that their distance from
other trees does not affect their productivity (volume growth
over time). They also assume that stands are even-aged, with trees
roughly the same age or size. With these models, the stand's
clumpiness
does not affect productivity. However, evidence that clumpiness
does significantly affect productivity makes this distance-independence
problematic. In a stand where trees grow in clumps, leaving open spaces,
many trees are more shaded than they would be in a uniform stand. This
shading definitely affects productivity. In effect, the trees in these
clumps are much more dense than reflected in the average density figures,
which fail to account for the open spaces.
In contrast, Crown Competition Factor (CCF) does take
proximity of trees and distribution of diameters into effect. CCF is based
on the "Competitive Stress Index" (CSI). CSI is a measure of a
single-tree's shade from other trees. A tree's potential crown area (as
seen from above), is proportional to its diameter, and these ratios are well
documented for each species. If 35% of a tree is shaded by other trees, its
CSI is 135. CCF reflects this single-tree CSI on the stand level. Thus,
if the average tree in the stand has a CSI of 135, the stand's CCF is 135.
A stand with a CCF of 135 will be made up of trees that, on average, have
35% of their potential crown space taken by other crowns.
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-
Stand Structure, Composition, and Function
-
Structure, composition, and function, generally, are the three main
analytical components of forest ecology.
Stand structure refers to several parameters of tree size, volume,
and distribution that are compiled, analyzed, and reported in per
acre (or hectare) units: trees per acre(tpa)(self explanatory),
average
diameter at breast height
(dbh),
basal area,
merchantable
board feet,
volume
(cubic feet measurement of tree stems), and sometimes
canopy density.
Usually, stand structure is disaggregated into
diameter classes
and species, such that dbh, basal area, cubic feet,
and board feet would be reported for each diameter
class for each species. Two other parameters often
reported (but not by diameter class) include
clumpiness
and
crown competition factor
Stand composition refers to the relative mix of tree species represented in a
stand.
Stand function refers to the biological processes and relationships
that occur and are necessary in a forest stand, for example,
nutrient exchange, transformation of sunlight into transferable
compounds (like glucose), microbial decay of detritus,
and countless others.
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- Stand Table
-
A table reporting stand structure parameters, usually broken
disaggregated into species and diameter classes.
Example: a simple stand table
| Species |
DBH
Class |
BA/ac. |
CF/ac.
(stem) |
Board/ac.
Feet |
TPA |
|
93 |
1361 |
2941 |
180 |
| D.-fir |
9 |
22 |
265 |
470 |
50 |
|
10 |
16 |
258 |
570 |
30 |
D.-fir
total |
|
38 |
523 |
1040 |
80 |
| p. pine |
9 |
27 |
408 |
1134 |
60 |
|
11 |
20 |
300 |
567 |
30 |
|
12 |
8 |
130 |
200 |
10 |
p. pine
total |
|
54 |
838 |
1901 |
100 |
In addition, a stand table will often report clumpiness and stand
crown competition factor (a measure of stand density).
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- Stand Volume
-
Conventionally, stand volume has referred to timber volume -- the
volume of wood found in the stem of the tree. Foresters have
conventionally reported timber volume in cubic feet and board feet.
A board foot is 144 cubic inches, the equivalent of a one-inch thick
board, with 12-inch sides.
A cubic foot is 1,728 cubic inches, the equivalent of a block of wood
measuring 12-inches on all sides.
In the near future, volume measures will be extended to include branch,
twig, and leaf volume to account for biomass and carbon sequestration
objectives.
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- Succession Theory
-
Succession theory is a fundamental theory in ecology arguing that
a forest unit (we'll use stand) will change in
structure and composition
until reaching the state of a climax forest,
from which it will not change independent of disturbance or
climate change. (The term "climax" derives from the term "climate.")
A climax state is a theoretical state of
equilibrium that a forest reaches after the most
shade tolerant
species displace the shade intolerant species and reach a state
of maturity. The ecological states preceding the climax forest are
successional states. These states begin with the establishment
of pioneer species, the first species to colonize a site after
a severe, stand-replacing disturbance. These trees are usually
shade intolerant and need full sunlight to germinate, survive, and grow.
Gradually, trees that are more shade tolerant "invade"
these stands, and since the shade intolerant trees cannot reproduce,
the shade tolerant species gradually replace them. Theoretically, the
cycle continues until the most shade-tolerant species or species mix that
can grow on the site is growing on the site.
Of course, this undisrupted succession unfolds only in the absence
of a significant disturbance or climate change.
However, disturbance is the rule rather than the exception
in forest ecology. Disturbance vis-a-vis wildfire is especially
prevalent in most forest types found in the northern Rockies --
particularly the ponderosa pine, Douglas-fir, western larch,
and lodgepole pine forests. And, evidence indicates that our
climate is changing, and forests are already changing in response.
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- Target Stand
-
A target stand is a description of the desired condition of a stand
at a chosen time in the future, and is useful for long term stand
planning. The target stand is described in terms
of
stand structure and composition.
Of course, the forester must consider the site's limitations when
designing a target stand, and management activities must be consistent
with these limitations to meet the desired future conditions.
Often, the target date for a target stand corresponds to the time
period when the oldest trees in the stand will reach some level of
maturity (for instance,
culmination of mean annual increment).
Target stands are very useful when managing for the restoration
of old-growth forest structure and composition.
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- Uneven-aged Management
-
Uneven-aged management is a silviculture practice that maintains
two or more well-defined age groups or cohorts of well-defined
diameter classes. Ideally, time intervals between age groups are
evenly spaced. Generally speaking, older or larger cohorts have
fewer trees per acre though they might occupy equal or more area
in terms of growing space. Uneven aged stands can mix individual
trees from all cohorts or distribute them in discrete clumps.
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- Urban Interface
-
The Urban Interface, otherwise known as the Wildland-Urban Interface, is
the area where residential development occurs on forested lands,
particularly near the boundaries of public lands. Often, the transition
from urban and suburban development to wildlands is gradual, but a defining
characteristic is the presence of wildland trees and vegetation. The
Firewise Communities
program defines the Urban Interface as "any location where a fire
can spread from vegetation (wildland fuels) to buildings (urban fuels)
resulting in multiple house fires that overwhelm fire protection efforts."
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- Variable-Density Thinning
-
Variable Density Thinning (VDT) is the method of thinning some sub-stand
units to a different density than other sub-stand units. For example, a stand of
lodgepole pine might be broken into 3-5 acre units, with some units clear
cut and others lightly thinned. Another possible scenario could include
thinning a pine-larch mixed forest with a patchwork of with a resulting
stand of relatively young western larch intermixed with pockets of
old-growth ponderosa pine.
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- Variable-Radius Plots
-
Variable-radius plots are points from which the surrounding
trees are observed. If these trees are large enough, in
relation to their distance from the point, they are tallied.
If not, they are ignored. The further from the plot center
(the point of observation) that a tree grows, the larger that tree must be
to count in the tally. To illustrate the point, imagine
I am in a forest stand looking at my thumb, which is almost
touching my nose and is pointing up to the sky. As I turn in a
circle and look at each tree I can see, my thumb will
visually block some tree trunks, while only partially
blocking others. The partially blocked trees would be
tallied in a variable-radius plot. The totally blocked
trees would be ignored.
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- Watershed (or Drainage)
-
A watershed is the water catchment area for a water stream or any
tributary of that stream. In Montana, a watershed typically
includes the headwaters (beginning) of a tributary creek or river and
the lands between the stream and the surrounding ridges. All
precipitation falling on a watershed or drainage flows toward the
stream, and thus, forest activities affect the stream from great
distances.
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