Thomas L. Schmidt

BACKGROUND

The North Central Research Station’s Forest

Inventory and Analysis Program (NCFIA) began

fieldwork for the fifth forest inventory of Missouri in 1999, in cooperation with the Missouri Department of Conservation. This

inventory initiates a new annual inventory

system. Under this new system, one-fifth of

the field plots in the State are measured each

year. As a result, the current inventory of

Missouri’s forest resources will not be completed until 2004. However, because each

year’s sample is a systematic sample of the

State’s forest and because timely information

is needed about Missouri’s forest resources,

preliminary estimates of Missouri’s forest

resources have been prepared from data

gathered during the first year of the inventory.

Due to the limited number of field plots

measured, future estimates using data in

this report are subject to change when

ensuing annual inventories are completed

and data compiled. The results presented are

estimates based on sampling techniques. As

additional annual inventories are completed,

the precision of the estimates will increase and

additional data will be released.

THOMAS L. SCHMIDT is a Research Forester

with the North Central Research Station, St.

Paul, MN.

Missouri’s Forest Resources in 1999

Reports of previous inventories of Missouri are

dated 1947, 1959, 1972, and 1989. Data from

new inventories are often compared with data

from earlier inventories to determine trends in

forest resources. However, for the comparisons to be valid, the procedures used in the

two inventories must be similar. As a result of

our ongoing efforts to improve the efficiency

and reliability of the inventory, several

changes in procedures and definitions have

occurred since the last Missouri inventory in

1989. Some of these changes make it inappropriate to directly compare portions of the 1999

data with those published for 1989. When

comparisons are made or estimates presented

from past inventories in this report, data from

previous inventories are recomputed using

current methods to ensure that comparisons

are valid.

RESULTS

Before European settlement, forests occupied

an estimated 70 percent of the total land area

in Missouri (King et al. 1949). Between initial

European settlement and the first inventory of

Missouri’s forests in 1947, area of forestland

declined to about 35 percent of the State. The

second inventory in 1959 of Missouri’s forestlands estimated that about 3 out of every 10

acres were forested. The trend of declining

area of forestland continued with the third

inventory of Missouri’s forests in 1972. Between the 1959 and 1972 inventory, the area

of forestland declined by more than a million

acres. The decrease in forestland was primarily due to agricultural expansion as forests

were cleared for crops and pastures. However,

the 1989 inventory showed a reversal in the

declining trend in area of forestland in Missouri because of land-use practices and

wildfire control. Between 1972 and 1989, area

of forestland increased by 8 percent in Missouri.

Forest Service

North Central

Research Station

Research Note

RN-NC-375

ABSTRACT.—The North Central Research

Station’s Forest Inventory and Analysis Program began fieldwork for the fifth Forest

Inventory of Missouri in 1999. This inventory

initiates a new annual inventory system. This

Research Note contains preliminary estimates

of Miouri’s forest resources prepared from data

gathered during the first year of the inventory.

KEY WORDS: Annual inventory, forestland,

forest type, growing-stock volume, Missouri.
The Missouri River marks the southern terminus of glacial expansion, which had a profound effect on topography, soils, drainage

systems, and resulting vegetation. Before

European settlement in Missouri, the area

north of the Missouri River was primarily

prairie with a mix of woodlands along rivers

and streams. Northern Missouri has historically been dominated by grassland ecosystems

due to frequent wildfires. Native Americans

commonly used fire as a tool to attract and/or

herd buffalo and other wildlife. This limited

trees in northern Missouri to being mainly

along streams and rivers where they were

somewhat protected from wildfires. As Europeans settled the area, the number of wildfires

decreased in northern Missouri but the area

dedicated to agricultural practices increased,

which continued to limit the extent of forests

in the region. If disturbances are limited,

trees can grow in almost all locations across

northern Missouri.

The area south of the Missouri River was more

heavily forested before European settlement

than the area north of the Missouri River.

Fires also occurred in southern Missouri but

not with the same frequency and severity as in

northern Missouri. The combination of a

different fire regime with different topography

and soils allowed southern Missouri’s vegetation to be predominately forest.

In both regions, agricultural practices have

changed. Marginal croplands have been

allowed to convert back to grasslands or

forests. Domestic livestock grazing methods

have changed, as more operations switch from

Figure 1.—Area of timberland in

 Missouri by inventory year (Note:

 sampling errors associated with

 each inventory are represented

 by the vertical lines at the top

 of each bar).

2

open grazing to confinement systems. These

changes, combined with effective wildfire

control, have allowed forests to become established on formerly forested sites in southern

Missouri and to expand into new areas in

northern Missouri.

Results of the 1999 inventory of Missouri show

a slight increase in the area of forestland.

While forestland area continues to increase,

the rate of conversion from other land uses to

forestland has slowed. It appears that in the

10 years between inventories (1989 to 1999),

the area of forestland increased by approximately 5 percent. Timberland, a subset of

forestland, has followed the same trend in

Missouri. Timberland is forestland that is

capable of growing trees at a minimum level

(20 cubic feet per acre per year) and that is not

restricted from harvesting. Currently, it

appears that the area of timberland in Missouri may have reached or exceeded the 1959

level (fig. 1).

Missouri is well known for its oak-hickory

forests. Every inventory conducted in the

State has shown this to be the dominant forest

type. The 1999 inventory estimates almost

three-fourths of the timberland in Missouri is

oak-hickory and associated species (fig. 2).

The area of publicly owned forestland in

Missouri increased between 1989 and 1999.

Publicly owned timberlands are a critical

component of the landscape because they are

major sources of wildlife habitat, outdoor

recreation, and other social and environmental

benefits. On average, these public forests also

0

4

8

12

16

1947 1959 1972 1989 1999

Million Acres of Timberland

0

4

8

12

16

Historical Area
Figure 2.—Area of timberland in Missouri by

 forest type, 1999.

Missouri’s timberlands continue to mature,

resulting in increases in the number of acres

classified as sawtimber and poletimber and

decreases in the area of sapling-seedling-size

stands (fig. 3). Forests have been maturing

due to a lack of natural or human disturbances. As mentioned, the number of disturbances from fire has declined in Missouri over

time. Historically, harvesting methods in

Missouri ranged from clearcutting to individual tree selection (individual trees were

selected for harvest but the entire stand was

not removed). However, harvesting methods in

Missouri are now undergoing some changes,

which may influence the future distribution

among the three classifications of stand size.

Figure 3.—Stand-size classification

 as a percentage of total timberland

 area in Missouri, 1989 and 1999.

With the increase in average stand-size class,

growing-stock volume has also increased.

Growing-stock volume is the amount of solid

wood in trees 5 inches d.b.h. and over, from 1

foot above ground to a minimum 4-inch top

diameter. As trees increase in diameter and as

the timberlands increase their stocking rate,

the volume of wood also correspondingly

increases. Both hardwood and conifer growing-stock volumes have increased between

every inventory of Missouri’s timberlands (figs.

4, 5). The increase in growing-stock volume is

a reflection of both increased stocking and tree

size. Another factor in the increase of growing-stock volume between inventories is the

conversion of some non-growing stock (primarily either having rough form or having rotten

portions of the live tree) to growing stock

because of improved quality.

In 1999, the majority of the growing-stock

volume in Missouri was in oak species. The

second greatest volumes were in hickory

species, followed by maples, black walnut,

hackberry, sycamore, and ash. Hardwoods

dominate in Missouri, representing more than

90 percent of the total growing-stock volume.

In summary, it appears from the initial annual

inventory of Missouri completed in 1999 that

area, stand-size class, stocking, growing-stock

volume, and most other measures related to

forestland and timberland continue to increase. This is a positive note for the condition of the State’s forests as we await further

implementation and completion of additional

annual inventories in Missouri.

3

0

10

20

30

40

50

60

70

Sawtimber Poletimber Sapling-seedling

1989

1999

Percentage

currently appear to have better stocking rates

(stocking is a measure of the density of tree

cover) and more volume per acre than most

privately owned timberlands in Missouri.

Maplebasswood

Elm-ashcottonwood

Conifers

Oakhickory
INVENTORY METHODS

Changes Between Inventories

Since the 1989 inventory of Missouri, several

changes have been made in NCFIA inventory

methods to improve the quality of the inventory as well as meet increasing demands for

timely forest resource information. The most

significant difference between inventories was

the change from periodic inventories to annual

inventories. Historically, NCFIA periodically

inventoried each State on a cycle that averaged

about 15 years. However, the need for timely

4

Figure 4.—Hardwood growing-

 stock volume in Missouri by

 inventory year (Note:

 sampling errors associated

 with each inventory are

 represented by the vertical lines

 at the top of each bar).

Figure 5.—Conifer growing-

 stock volume in Missouri

 by inventory year (Note:

 sampling errors associated

 with each inventory are

 represented by the vertical

 lines at the top of each

 bar).

and consistent data across large geographical

regions, combined with national legislative

mandates, resulted in NCFIA’s implementation

of an annual inventory system. Missouri was

one of the first States in the North Central

region, and one of the first States in the Nation, to be inventoried with this new system,

beginning with the 1999 inventory.

With an annual inventory system, about onefifth of all field plots are measured in any one

year. After 5 years, the entire inventory will be

completed. After the first 5 years, NCFIA will

report and analyze results as a moving 5-year

Hardwood Growing-Stock Volume

0

3

6

9

12

15

1947 1959 1972 1989 1999

Billion Cubic Feet

0

3

6

9

12

15

Conifer Growing-Stock Volume

0

0.5

1

1.5

2

1947 1959 1972 1989 1999

Billion Cubic Feet

0

0.5

1

1.5

2
average. For example, NCFIA will be able to

generate a report based on inventory results

for 1999 through 2004 or for 2001 through

2006. While there are great advantages for an

annual inventory, one difficulty is reporting on

results in the first 4 years. With the 1999

inventory, only 20 percent of all field plots

have been measured. Sampling error estimates for the 1999 inventory results are 8.43

percent for timberland area and 12.7 percent

for growing-stock volume. Thus, caution

should be used when drawing conclusions

based on this limited data set. As ensuing

measurements are completed, we will have

additional confidence in our results due to the

increased number of field plots measured. As

each measurement year is completed, the

quantity and quality of results will expand.

Other significant changes between inventories

include the implementation of new remote

sensing technology, implementation of a new

field plot design, development of new volume

equations, and gathering of additional remotely sensed and field data. The advent of

remote sensing technology since the previous

inventory in 1989 allowed NCFIA to use computer-assisted classifications of Multi-Resolution Land Characterization (MRLC) data and

other available remote sensing products to

stratify the total area of the State and to

improve estimates. Previous inventories used

manual interpretation of aerial photos to

stratify the sample.

The new volume equations, developed by

USDA Forest Service research scientists and

other cooperating researchers, more accurately

estimate the true growing-stock and sawtimber volumes. As additional annual inventories

are implemented and comparisons between

the current inventory and previous inventories

become possible, FIA will update the 1989

inventory using the new volume tables.

New algorithms were used in 1999 to assign

forest type and stand-size class to each condition observed on a plot. These algorithms are

being used nationwide by FIA to provide

consistency from State to State and will be

used to reassign the forest type and stand-size

class of every plot measured in the 1989

inventory when it is updated. This will be

done so that changes in forest type and standsize class will reflect actual changes in the

forest and not changes due to a change in

algorithms. The list of recognized forest types,

grouping of these forest types for reporting

purposes, equations used to assign stocking

values to individual trees, definition of

nonstocked (stands with a stocking value of

less than 10 percent for all live trees), and

names given to the forest types changed with

the new algorithms.

Another change with the current inventory is

the determination of the exact plot location of

every ground plot in the inventory. For plots

that are visited in the field, this is done using

a geographic positioning system (GPS) device

at plot center. For plots not visited in the field,

the plot location is determined by transferring

the old plot location from the aerial photography to an unclassified, geo-corrected remotely

sensed image. Both procedures provide an

accurate location that is used to link the

ground plots to the classified remotely sensed

data used for stratification.

PROCEDURES

The 1999 Missouri survey used a two-phase

sample for stratification that included remeasuring inventory plots from the 1989

inventory and new field plots. Two-phase

sampling, also called double sampling, consists of a phase-one sample used to estimate

area by strata and a phase-two sample to

estimate the average value of parameters of

interest within these strata. The estimated

population total is the sum across all strata of

each stratum’s estimated area multiplied by its

estimated mean per unit area.

The only land that could not be sampled was

private land where field personnel could not

obtain permission from the owner to measure

a phase-two field plot. These denied access

plots were somewhat rare in Missouri (about 2

percent of the total forest plots statewide), and

the methods used in the preparation of this

report make the necessary adjustments to

account for sites where access was denied.

Phase One

Phase-one and phase-two plots were placed

systematically across the entire State without

regard to specific land characteristics. All

lands have the same probability of being

sampled under this inventory system. The

1999 inventory used a computer-assisted

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6

classification of satellite imagery for classification. FIA used the imagery to form two initial

strata—forest and nonforest. Pixels within

60 m (2 pixel widths) of a forest/nonforest

edge formed two additional strata—forest/

nonforest and nonforest/forest. Forest pixels

within 60 m on the forest side of a forestnonforest boundary were classified into forest/

nonforest strata. Pixels within 60 m of the

boundary on the nonforest side were classified

into nonforest/forest strata. An overlay of all

National Forest land ownership was used to

identify all lands owned by the Mark Twain

National Forest. These National Forest lands

were treated separately but were also stratified

into one of the above four strata. Stratification

and estimation were conducted at the State

level for National Forest Lands and at the unit

level for other lands. In the National Forest

stratum, forest and forest/nonforest strata

were combined because there were fewer than

five ground plots in one of these strata. Final

estimation of area by stratum was based on

these five strata—National Forest, forest,

forest/nonforest, nonforest/forest, and

nonforest for all lands.

In the 1989 inventory, aerial photographs were

assembled into township mosaics, and a

systematic grid of 121 one-acre photo plots

(each plot representing approximately 190.4

acres on the ground) was overlaid on each

township mosaic. Each of these photo plots

was stereoscopically examined by aerial photo

interpretation specialists and classified based

on land use, forest type, and stand-size density. From these photo plots, a systematic

sample of plots (without regard to their aerial

photo classification) was selected as ground

plots and further examined by survey crews to

verify the classification and to take further

measurements. These 1989 ground plots

formed the basis for the remeasured ground

plots in the 1999 inventory. Additional information related to procedures for the 1989

inventory can be found in Spencer et al.

(1992).

The move to satellite imagery changed NCFIA’s

phase-one sample from being based on one

photo plot every 190.4 acres to a sample based

on a classified pixel every 0.22 acres. The

increased intensity of the phase-one sample

greatly improved estimates of the area with

each stratum, particularly at the county level.

Also, because classification was conducted

using a computer-assisted algorithm across

the entire State, biases in the photo plot

sampling method that resulted from differences in photo quality, age of photography,

and experience of the photo interpreter were

eliminated and classification was consistent

across the entire State.

Phase Two

Phase two of the inventory consisted of the

measurement of an annual sample of field

plots in Missouri. Current FIA precision

standards for annual inventories require a

sampling intensity of one plot for every 5,937

acres. To satisfy this requirement, the geographical hexagons established for the Forest

Health Monitoring (FHM) program were divided

into 27 smaller NCFIA hexagons, each of

which contained 5,937 acres (McRoberts

1999). A grid of field plots was established by

selecting one plot from each smaller hexagon

based on the following rules: (1) if an FHM

plot fell within a hexagon, it was selected as

the grid plot; (2) if no FHM plot fell within a

hexagon, the existing NCFIA plot from the

1989 inventory nearest the hexagon center

was selected as the grid plot; and (3) if neither

FHM nor existing NCFIA plots fell within the

hexagon, a new NCFIA plot established at the

hexagon center was selected as the grid plot

(McRoberts 1999). This grid of plots is designated the Federal base sample and is considered an equal probability sample; its measurement in Missouri is funded by the Federal

government.

The total Federal base sample of hexagonal

grid plots was systematically divided into five

interpenetrating, non-overlapping subsamples

or panels. Each year the plots in a single

panel are measured with panels selected on a

5-year, rotating basis (McRoberts 1999). For

estimation purposes, the measurement of each

panel of plots may be considered an independent random sample of all land in a State.

Field crews measured vegetation on plots in

the forested and straddler (nonforest/forest

and forest/nonforest) categories; plots classified as non-forested were checked to ensure

correct classification.

NCFIA has two categories of field plot measurements—phase-three plots (FHM plots) and

phase-two field plots to optimize our ability to

collect data when available for measurement.

It is imperative that each type of plot be uniformly distributed both geographically and
Figure 6.—Current NCFIA field plot design.

temporally. Phase-three plots are measured

with the full array of FHM vegetative and

health variables collected (Mangold 1998).

Phase-three plots must be measured between

June 1 and August 30 to accommodate measurement of non-woody understory vegetation,

ground cover, soils, and other variables. We

anticipate that in Missouri the complete 5-year

annual inventory will involve about 150 phasethree plots. On the remaining plots, only

variables that can be measured throughout

the entire year are collected. In Missouri, the

complete 5-year annual inventory is expected

to involve about 2,350 phase-two forested

plots and about 500 phase-two straddler plots.

The new national FIA 4-point cluster plot

design was used for data collection (fig. 6) in

1999 and will be used in subsequent years.

The old NCFIA 10-point cluster plot design will

be phased out over the next 5 years. For all

remeasured field plots in the Federal base

sample, the new 4-point cluster plot was

established and measured at the old plot

(1989) location. In addition, the first five

subplots of the old 10-point (subplot) cluster

plot were also remeasured in 1999 to estimate

change. All trees previously measured on

these plots were remeasured or otherwise

accounted for on these five subplots. These

measurements form the basis for change

estimates between the 1989 and current

annual inventories for characteristics such as

average annual net growth, mortality, and

removals. Thus, until a complete cycle of

annual inventories for Missouri has been

accomplished, both the new 4-point cluster

plots and part of the old 10-point cluster plots

will be measured. If the anticipated 20 percent of the State is sampled each year, by the

sixth year of annual inventories in Missouri,

the new 4-point cluster plots will begin to be

remeasured and the former plot design will be

abandoned. The national plot design also

requires mapping forest conditions on each

plot. Due to the small sample size (20 percent)

each year, precision associated with change

factors such as mortality will be relatively low.

Consequently, change estimates will not be

reported until at least three annual inventories

are completed, and even then we anticipate

that estimates of change will be limited in

detail. When the complete annual inventory

has been implemented in 2004, the full range

of change variables will be available.

The overall plot layout for the new design

consists of four subplots spaced 120 feet apart

in a triangular arrangement. Subplots 2, 3,

and 4 are spaced 120 degrees apart. The

center of the new plot is located at the same

point as the center of the previous plot if a

previous plot existed within the sample unit.

All trees less than 5 inches in diameter at

breast height (d.b.h., or 4.5 feet above ground

level) are measured on a 6.8-foot-radius

(1/300th acre) circular microplot located at the

center of each of the four subplots. Trees with

diameters 5 inches and larger are measured

on a 24-foot-radius (1/24th acre) circular

subplot. The forest condition of each subplot

is recorded. Factors that can determine a

change in condition from subplot one are

changes in forest type, stand-size class, land

use, ownership, and density. Each condition

that occurs anywhere on one of the subplots is

identified, described, and mapped if the condition in total meets or exceeds one acre in size

(the one acre minimum size for a condition to

be identified could include land off the subplot). Each condition is assigned a condition

number and condition information is recorded.

Field plot measurements are combined with

phase-one estimates in the compilation process and table production. The number of

tables generated from a single year’s data is

limited, but as additional annual inventories

are completed the number of tables will increase until year 5, when all statewide inventory summary tables will be available in both

printed and electronic format. If additional

7

MAGNETIC

1

4 3

2

Plot

center

N
8

Printed on recyclable paper.

information is desired, requests may be directed to:

Program Manager

Forest Inventory and Analysis

North Central Research Station

1992 Folwell Ave.

St. Paul, MN 55108

or

State Forester

Missouri Department of Conservation

2901 West Truman Blvd.

P.O. Box 180

Jefferson City, MO 65102

LITERATURE CITED

King, D.B.; Roberts, E.V.; Winters, R.K. 1949.

Forest resources and industries of Missouri. Res. Bull. 452. Columbia, MO:

University of Missouri, College of Agriculture, Agricultural Experiment Station.

89 p.

Mangold, R.D. 1998. Forest health monitoring

field methods guide (National 1998).

Research Triangle Park, NC: U.S. Department of Agriculture, Forest Service, National Forest Health Monitoring Program.

429 p. (Revision 0, April 1998)

McRoberts, R.E. 1999. Joint annual forest

inventory and monitoring system, the

North Central perspective. Journal of

Forestry. 97(12): 27-31.

Spencer, J.S., Jr.; Roussopoulos, S.M.;

Massengale, R.A. 1992. Missouri’s forest

resource, 1989: an analysis. Resour. Bull.

NC-139. St. Paul, MN: U.S. Department of

Agriculture, Forest Service, North Central

Forest Experiment Station. 84 p.