The sampling procedure used during this current
inventory involved a two-stage approach, and a
sample of both new and remeasured plots. Aerial
photos were first stratified into current land-use
and cubic-foot volume classes, for both new and
previously sampled photo points.
This was
followed by the establishment of new plot
locations on the ground, and the remeasurement
of plots established during earlier inventories.
The Green Mountain National Forest was
included in this sample base (Fig. 1).
Abstract
In 1996-1998, the Forest Inventory and Analysis
Research Unit of the Northeastern Research
Station conducted its fifth forest inventory of
Vermont.
This inventory of forest resources
included a sample base within the Green Mountain
National Forest. After analyzing the data for only
National Forest land within Vermont, results
showed that there were almost 337 thousand acres
of forest land in the Green Mountain National
Forest. Vermont has over 114 thousand acres in
reserved status, but almost all of that is within the
National Forest – over 82 thousand acres. Mature
forests dominate it’s landscape, timber quality is
high, and average annual growth to removals are
positive – the forests are growing almost one and a
half times more than are being removed.
This report highlights the results from the most
inventory of forest land conducted in Vermont, as
it relates to the Green Mountain National Forest.
However, it is not the intention of this publication
to analyze temporal data, or the overall changes
in Vermont’s forest resources. A separate and
comprehensive statistical report has been
published (Frieswyk and Widmann, 2000), and a
report analyzing the State’s forest resources in
greater detail is being prepared.
Introduction
The forests of the Green Mountain National Forest
are a dynamic resource. Information about the
extent, condition, and use is essential to effectively
manage and allocate the goods and services
potentially available from it’s forests. To assess
these basic forest characteristics, inventories are
periodically conducted.
Forest Inventory and Analysis Research Units
(FIA), USDA Forest Service, are responsible for
conducting periodic forest inventories, in order to
provide current information on the forest resources
of the Nation. This is done under the authority of
the McSweeney-McNary Forest Research Act of
1928, and subsequent acts that include the
Renewable Resources Planning Act of 1974 and
the Renewable Resources Research Act of 1978.
The Forest Inventory and Analysis Research Unit,
located at the Northeastern Research Station (NEFIA), effect forest inventories in 13 northeastern
states. The first such inventory of Vermont’s forest
resources was conducted in 1948 (McGuire and
Wray, 1952). Succeeding inventories were carried
out in 1966 (Kingsley, and Barnard, 1968), 1973
(Kingsley, 1977), and 1983 (Frieswyk and Malley,
1985). The most recent, the fifth such inventory in
Vermont, was conducted between 1996 and 1998.
It was done with the cooperation of the Vermont
Department of Forests, Parks and Recreation, the
Green Mountain National Forest, and the
landowners of Vermont.
Figure 1. Location of Forest Inventory and
Analysis Plots, Green Mountain National Forest
1
In addition, several associated studies related to
Vermont’s forest resources were carried out in
conjunction with this inventory and with the general
program of research conducted by NE-FIA. The
most notable of these are a study in private forestland ownership (Birch, 1996), and timber industry
studies.
precision of each estimate is described by its
sampling error. Sampling errors are given with
several tables in this report. The others are
available upon request.
Here is an example of how the sampling error is
used to indicate reliability. The estimate of total
forest land for the Green Mountain National
Forest is 336,899 acres. It has an associated
sampling error of 5 percent, or 16,845 acres.
This means that if there are no errors in the
procedure, we are 68 percent confident that the
true area is 336,899 + 16,845 acres (at one
standard deviation), or that it is between 320,054
and 353,744 acres. Similarly, we are 95 percent
confident that the true area is 336,899 + 33,690
acres (at two standard deviations).
Not all of the information that was collected is
contained within this publication. Forest area,
numbers of trees, timber volume, biomass, and
change statistics reported here, are only a
summary. Other information may be available, and
additional summaries may be developed upon
request. For more information, contact:
USDA Forest Service
Forest Inventory and Analysis
11 Campus Boulevard, Suite 200
Newtown Square, PA 19073-3200
However, estimates become less precise with
increasing detail, both spatially and in terms of
more specific forest and tree attributes. For
example, while the sampling error for all forest
land on the Green Mountain National Forest is 5
percent, the sampling error for the area in
sawtimber stands is 11 percent, for the area in
poletimber stands is 24 percent, and for the area
in seedling and sapling stands is 51 percent.
Phone: 610-557-4075
Fax:
610-557-4200
Web: www.fs.fed.us/ne/fia/
Reliability of the Estimates
The data in this report are based on a carefully
designed sample of forest conditions throughout
Vermont. However, because the field crews did
not measure every tree or every acre in the state,
the data are estimates. The reliability of the
estimates can be judged by two important
statistical criteria: accuracy and precision.
The reason for these higher sampling errors is
that as the size of the sample in a particular
condition decreases, sampling error increases.
County estimates were not provided in this report
for that reason. In many cases, the sampling
errors were too large for the estimates to be
meaningful.
Estimates with sampling errors
greater than 25 percent are suspect, and those
larger than 50 percent are unusable because the
resulting estimate is not significantly different
from zero (at two standard deviations).
Accuracy refers to the success of estimating the
true value; while precision refers to the clustering of
sample values about their own averages or to the
variation among repeated samples.
We are
interested primarily in the accuracy of the inventory
but in most cases we can only measure its
precision.
For many of the tables in this report, both the last
column and last row are labeled "SE." These
values are the sampling errors of the column and
row totals. The last sampling error (SE) given is
for the table total. As a helpful tool, individual
table cells have been annotated to indicate their
level of reliability. Those marked by (†) have
between a 25 and 49 percent sampling error, so
are suspect and should be used with caution.
Those marked by (‡) have a sampling error of 50
percent or greater, and as such should not be
used unless combined with another table cell
estimate with a smaller sampling error.
Although accuracy cannot be measured exactly, it
can be checked. Preliminary tables are sent to
other agencies and to outside experts familiar with
the forest conditions in Vermont. If questions arise,
the data are reviewed and reanalyzed to resolve
differences. Great care is taken to minimize
sources of procedural error through careful training
of both field and office personnel, frequent
inspection of field and office work, and application
of the most reliable inventory methods.
However, its possible to approximate the actual
sampling error for a table cell within certain
tables.
To do so, use the following formula:
Because of the care exercised in the inventory
process, estimates of precision afford a reasonable
measure of the inventory's adequacy.
The
2
estimates of change because this procedure was
not used at the previous occasion.
NOTE: this formula is reliable only for estimating
sampling errors of individual cells in the area
tables.
Land Area Determination
SEij = 1/Pij((Pij (1- Pij))/n)1/2
FIA uses Bureau of Census estimates of total
land area in a state or county as the basis for
estimating land area by various classes. But
between 1980 and 1990, the Bureau of Census
changed its estimating procedures. Previously,
the minimum width for streams had been 660
feet, and the minimum area for bodies of water
was 40 acres. Now, inland-water streams more
than 200 feet wide and bodies of water 4.5 acres
and larger in area are identified. Changes to this
procedure resulted in a reduction in total land
area.
where:
SEij
n
Pij
Aij
A
ij
=
=
=
=
=
=
actual sampling error) for a table cell
total number of samples in a population
Aij / A
cell estimate
total land area of a population
row(i) and column(j)
Comparison Between Inventories
Levels of Stocking
As a result of ongoing efforts to improve the
efficiency of the inventory, several changes in
procedures and definitions have been made since
the previous inventory. These changes prevent
direct comparison between some of the current
estimates with those published previously. The
changes in methods and definitions include: (1) a
new plot design, (2) changes in land area
determination, and (3) procedures to calculate
levels of stocking as it relates to stand size and
forest type.
Stocking is a quantitative expression of live tree
stand density. It may be expressed in absolute or
relative terms (Arner and others, 2000). For the
1983 inventory statistics, the stocking value of a
tree was calculated using the basal area of the
tree as a percent of 75 square feet per acre,
which is the basal area standard for full use of the
site (USDA Forest Service, 1967).
Basal area stocking describes current timber
volume well, but inadequately measures present
site utilization, stand composition, and smalldiameter stands. A relative measure of stand
density is more appropriate for interpreting
findings of extensive inventories where a variety
of stands are sampled, such as those performed
by FIA. It more adequately reflects species
composition, stage of development, and the
social position of the trees present. A procedure
using relative density to calculate stocking using
relative density, which represents site occupancy
based on normal yield tables, was developed and
accepted as a standard for FIA units throughout
the country.
New Plot Design
To improve data consistency at the national level, a
standard plot design is being used by FIA units
throughout the country. The new plot design, a
cluster of four 24-foot-radius subplots covering a
1/6-acre area, was used during the most recent
inventory on both new and previously measured
plot locations.
In addition to the new plot configuration, field crews
recorded different conditions on the plot if certain
attributes (land use, forest type, stand origin, stand
size, tree density, owner) differed from those at plot
center, along with information that described the
boundaries of the conditions. This procedure was
designed to reduce bias in the estimates. In
previous inventories, ground plots were wholly
within the condition that the plot was chosen to
represent.
Stand size is a classification (sapling/seedling,
poletimber, sawtimber, or nonstocked) of forest
land based on the size of the trees that dominate
an area, and forest type is a classification of
forest land based on the species found in the
area.
Both stand size and forest type are
calculated based on stocking of all live trees, and
were therefore affected by the change in the
procedure to calculate stocking. In addition, there
were minor refinements with respect to how
several species were allocated to local types
since the previous inventory.
On all remeasured plot locations, a subsample of
trees that were recorded in past inventories was
reconciled, and growth and removals estimates
were calculated using these data.
Differing
conditions were ignored for calculations of
3
Highlights
 Significant reserved forest-land area
Total Forest Land Area
The Green Mountain National Forest is almost
completely covered by forests. Of its 337.3 acres
of total land area, 336.9 thousand acres are
forested, or 99 percent. Forest land includes
timberland (not withheld from timber production),
reserved forest land (such as wilderness areas),
and unproductive forest land. There is minimal
unproductive forest land in the National Forest, so
the difference between forest land and timberland
is reserved forest land. The National Forest
contains a higher proportion of reserved forest
land than Vermont does as a whole.
Approximately 78 percent of Vermont is covered
by forests, almost all of which can be classified
as timberland, or 76 percent. Only a little more
than 2 percent is reserved. But in the National
Forest, 76 percent is classified as timberland,
while almost 24 percent is reserved.
Reserved
(wilderness)
24%
Timberland
76%
Timberland = 254,585 acres
Reserved Forest Land = 82,313 acres
Total Forest Land = 336,899 acres
 Mature forests dominate
Area by Stand-size Class
250
Thousand Acres
The forests of the Green Mountain National
Forest also contain a mature resource. Most of
the area is contained in sawtimber-size stands.
On forest land within the National Forest, 68
percent of the area is contained in mature, or
sawtimber stands; 25 percent is contained in
intermediate, or poletimber stands; and 7 percent
is contained in regenerating, or sapling and
seedling stands.
This distribution remains
essentially unchanged on the timberland
component, although there is a slightly higher
percentage in the sawtimber-size stands on
timberland within the National Forest.
200
150
100
50
0
Forest Land
Sawtimber
 Sugar maple dominates growing-stock
Timberland
Poletimber
Sapling &
Seedling
Leading Tree Species
Beech
In terms of the total number of trees greater than
1-inch diameter at breast height (d.b.h.), Beech is
by far the leading species – accounting for almost
65 million trees. The softwood species of balsam
fir and red spruce follow closely. But when
looking at the leading species in terms of trees
greater than 5-inch d.b.h. (commonly called
growing-stock trees), these species quickly drop
out.
Sugar maple – an important species
throughout Vermont and much of New England –
becomes the leading species. On the Green
Mountain National Forest, there are over 13
million sugar maple trees greater than 5-inch
d.b.h. That’s 21 percent of all trees encountered.
Balsam fir
Red spruce
Sugar maple
Red maple
> 5-in d.b.h.
Yellow birch
> 1-in d.b.h.
Paper birch
0
4
20
60
40
Million Trees
80
 Diameters peak at the 10-inch class
Diameter Class Distribution of Live Volume
The distribution of tree diameters in the forests of
the Green Mountain National Forest follow a
normal curve. On forest land, a significant
amount of cubic-foot volume exists in the 10-16
inch diameter classes. This is where most of the
volume differences are between what is growing
on forest land as opposed to what is growing on
timberland. Although, there is also an apparent
difference in the largest diameters. Trees in the
30-inch and larger diameter class account for
almost 16 million cubic feet on forest land, but
only 2 million cubic feet on timberland. This is
expected since a large portion of this forest land
is reserved and tends to contain more mature
trees.
120
Million
Cubic Feet
100
Forest Land
80
60
Timberland
40
20
0
8
6
 Most sawtimber of high-quality tree grade
12
16
20 30+
18 22-28
10
14
Diameter Class
Distribution of Tree Grade in
Sawtimber Trees >15 Inches d.b.h.
Almost half of the sawtimber volume in trees 15inch d.b.h. and larger is in tree grades 1 and 2 –
47 percent on forest land and 49 percent on
timberland. The distribution of quality in all tree
grades is virtually identical between forest land
and timberland – the only difference being that
there is slightly less grade 5 material on
timberland than on forest land. Most of the
resulting difference is distributed through all tree
grades. Land set aside for timber production will
include more of the high-quality material than
land that is reserved for other multiple-use
treatments.
24%
Grade 5
19%
11%
Grade 4
13%
18%
Grade 3
19%
24%
Grade 2
24%
23%
Grade 1
25%
Forest Land
 Growing stock half of total woody material
Timberland
Components of Biomass on Forest Land
Forest inventories typically measure only growing
stock. Yet, growing stock accounts for only 52
percent of the total biomass of woody material
contained in the forest of the Green Mountain
National Forest. The tops, branches, foliage, and
stump-root system of these growing-stock trees
account for an additional 25 percent. That means
more the three-quarters of the total-tree biomass
can be found in these trees. The remainder of
the forest biomass – 23 percent – is contained in
cull trees, dead trees, and small trees such as
seedlings (< 1-inch d.b.h.) and saplings (between
1-inch and 5-inch d.b.h.).
Growing
stock
52%
Non-growing stock of
growing-stock trees
25%
Cull and
dead trees
13%
Small
trees
10%
5
 Positive growth to removals ratio
Components of Change in Live Volume
The ability of forests to sustain themselves is
measured by their ratio of growth to removals.
Net growth is the total growth of trees, plus gains
from land converting to forest, minus losses to
mortality from insect and disease outbreaks, and
disturbances such as wind and ice storm
damage. There is more growth than there are
removals in the Green Mountain National Forest
– its forests average a ratio of 1.4:1. Balsam fir
and red maple have the highest ratio at 4.3:1 and
3.6:1, respectively. A few major species, though,
have ratios of less than 1:1, and as such are
cause for concern. Red spruce, beech, and the
birches all have high rates of both mortality and
removals compared to their amount of growth.
Sugar Maple and Beech show the highest levels
of mortality. Beech trees, in particular, are dying
faster than they are growing. Of the major
species, it is the only one that exhibits a negative
net growth, evidence of the damage brought
about by Beech Bark Disease.
12
Million
Cubic Feet
8
4
0
-4
-8
Net
growth
Gross
growth
Mortality
Net
change
Removals
Removals due to
harvesting
31%
 Most removals not due to harvesting
Removals include harvesting, as well as losses
due to the conversion of forest land to a reserved
status (such as wilderness), and the change from
forest land conversion to a non-forest land use.
On the National Forest, there is a significantly
higher volume being lost to administrative
withdraws than there is to harvesting – 69 percent
and 31 percent, respectively. If the volume
resulting from the conversion of forest land to a
reserve status were subtracted out, the resulting
growth to removals ratios paint a more positive
picture.
Removals resulting from a change to
reserved status or a change through the
conversion of forest land to a non-forest use
69%
Average Annual Growth, Removals, and Mortality of Live Volume on Timberland
Species
Balsam fir
Red spruce
Hemlock
Sugar maple
Red maple
Birches
Beech
Ashes
All species
Gross Growth
Mortality
Net Growth
Removals
Net Growth : Removals
331
606
1,099
2,997
1,711
1,758
1,146
290
10,350
-74
-317
0
-1,641
-308
-974
-1,560
0
5,229
256
289
1,099
1,356
1,402
784
-414
290
5,121
-59
-357
0
-625
-386
-1,011
-801
-193
-3,741
4.3 : 1
0.8 : 1
-2.2 : 1
3.6 : 1
0.8 : 1
0.5 : 1
1.5 : 1
1.4 : 1
6
Index to Tables
Table
Page
Total Land Area
1
Total land area by land class, Vermont and Green Mountain National Forest
8
Forest-land and Timberland Area
2a Area of forest land by forest type, forest type group, and stand-size class
9
2b Area of timberland by forest type, forest type group, and stand-size class
9
Number of Trees
3a Number of all live trees (1.0-inch d.b.h. and larger) on forest land by species and diameter class
10
3b Number of all live trees (1.0-inch d.b.h. and larger) on timberland by species and diameter class
12
Growing-stock Volume
4a Net volume of all live trees (1.0-inch d.b.h. and larger) on forest land by species and diameter class
14
4b Net volume of all live trees (1.0-inch d.b.h. and larger) on timberland by species and diameter class
16
5a Net volume of growing-stock trees (5.0-inch d.b.h. and larger) on forest land by species and diameter class
18
5b Net volume of growing-stock trees (5.0-inch d.b.h. and larger) on timberland by species and diameter class
20
Sawtimber Volume
6a Net volume of sawtimber trees on forest land by species and diameter class
22
6b Net volume of sawtimber trees on timberland by species and diameter class
23
7a Net volume of sawtimber trees (15.0-inch d.b.h. and larger) on forest land by species and tree grade
24
7b Net volume of sawtimber trees (15.0-inch d.b.h. and larger) on timberland by species and tree grade
25
8a Net volume of sawtimber trees on forest land by species, size class, and tree grade
26
8a Net volume of sawtimber trees on timberland by species, size class, and tree grade
27
Total Tree Biomass
9a Net sound biomass of growing-stock trees on forest land by species and component
28
9b Net sound biomass of growing-stock trees on timberland by species and component
29
10a Net sound biomass of all trees on forest land by species and component
30
10b Net sound biomass of all trees on timberland by species and component
31
10a Net biomass of all live trees (1.0-inch d.b.h. and larger) on forest land by species and diameter class
32
11b Net biomass of all live trees (1.0-inch d.b.h. and larger) on timberland by species and diameter class
34
Growth and Removals
12 Average annual net change of live tree volume on timberland by species and component of change
Note: In the tables, a zero indicates that the data are negligible or the condition was not encountered in
the sample. A dash indicates that the condition is not possible under current Forest Service
definitions. Rows and columns in all tables may not sum due to rounding.
7
36
23