7944

• UCREFRP Catalog Number: 7944
• Author: Hoar, A. R. and M. J. Erwin.
• Title: Relationships Between The Expansion Of Agriculture And The Reduction Of Natural Riparian Habitat In The Missouri River Floodplain Of Northeast Montana, From 1938 To 1982, ‎(paper-North American Symposium on Riparian Ecosystems and Their Management)‎.
• USFW Year: 1985.
• USFW - Doc Type: April 16-18, 1985.
• Copyright Material: NO

In 1938, the riparian herbaceous type occupied
more than halt (52 percent) of the floodplain. It
was the dominant cover type. Agriculture, a devel-
opment type, occupied approximately a quarter (24
percent) of the floodplain. It was the second-
most dominant cover type. The shrub-scrub type
occupied a larger percentage (14 percent) of the
floodplain than did woodlands (10 percent).
Urban/ranchyards and rights-of-way occupied the
smallest percentages of the floodplain (0,6 and
0.2 percent, respectively).
In 1982, agriculture occupied over half (52
percent) of the floodplain. At this time, it was
the dominant cover-type. The herbaceous type
occupied approximately a quarter (26 percent) of
the floodplain. It was-the second-most dominant
type. The woodland type was the third most domi-
nant cover type, mile the shrub-scrub type was
the fourth. Woodlands occupied 13 percent of the
floodplain; the scrub-scrub type occupied only 5
percent. Urban/ranchyards and rights-of-way
ioccupied samil percentages of the floodplain.
These wire 0.8 and 0.5 percent, respectively.
This order of cover dominance was set before 1956.
General Changes
Between 1938 and 1982, the total acreage of
riparian cover declined by 58,910 acres (from
140,215 to 81,305 acres), while developed cover
increased by 57,789 acres (from 45,199 to 102,988
acres). However, most of the decline of riparian
cover occurred before 1956, by which time it had
been reduced by 47,164 acres (from 140,215 acres
to 93,051 acres). During this same time span,
(1938-1956) developed cover Increased by 41,884
acres (tram 45,199 to 67,083 acres). The average
annual decline of riparian cover between 1938 and
1956, wsa estimated to have been 2482 acres per
year. The average annual increase of developed
land was estimated to have been 2204 acres per year
during the same period. The changes that occurred
between 1938 and 1966 were the largest of the study
period.
A list of cover types, ordered by percent of
net change in screage, would have agriculture in
the ,.number one position. Agriculture increased
130,percent over the entire study period; rights-
of-way increased 120 percent; urban/ranchyards
increased 33 percent; foreata increased 26 percent;
herbaceous cover decreased 60 percent; and the
shrub-scrub type decresaed 61 percent.
Of those cover types that increased, only
agriculture increased throughout the study period.
The maximum acreages for rights-of-way,
urban/ranchyards, and woodlands appear to have
occurred during the mid-1970'x; by 1982, acreages
for the letter two types were less than they had
been since 1938. The rights-ot-way category
changed little between 1974 end 1982.
Observed changes in areal extent were not
uniform for each type, nor were they similar bet-
ween types, but a pattern. was observed. Data
presented in Table 2 provides evidence that the
herbaceous type declined until 1974 and then in-
creased; shrub-scrub declined throughout the study
period; and lorests increased until 1974 and then
declined. The largest decrease of herbaceous acre-
age took place between 1938 and 1956, when a net loss
of 54 percent took place (52,203 acres; from 96,804 to
44,601 acres). The largest decline in the shrub-scrub
type occurred between 1956 and 1974, when a net loss
of 37 percent took place (7455 acres; Prom 20,003
to 12,548 acres). Between 1974 and 1982, 37 percent
(13,893 acres; from 37,082 to 23,189 acres) of forests
were eliminated. Forest acreages declined more
than any other cover type between 1974 and 1982.
Also during this period, the herbaceous acreage
increased 9430 acres (from 38,849 to 48,279 acres).
These patterns of riparian decline appear to be
the result of the cumulative effects of several broad
categories aP change. The influence of each
category is not detectable from the data presented
in Table 2. Further analyses were necessary in
order to place in perspective the patterns and
causes of the riparian decline.
Causes of General Changes
The observed changes in the riparian Lypes
noted above resulted from three broad categories
of loss or gain. These categories of change were:
1) loss to development, 2) loss to the River, 3)
and loss (or gain) due to other causes.
An areal loss and a gain occurred whenever
the classification of a parcel changed from one
era to the next. For example, if woodland was
converted to cropland, a "loss" would have
occurred in the amount of woodland and a "gain"
would have occurred in the amount of cropland.
But, when a woodland was cleared to create new
pasture, a loss of woodland as well as a gain of
herbaceous area would have occurred, And, if a
stand of sappling cottonwoods had grown above the
height category for the shrub-scrub type, a loss
would have occurred for this type while a gain
would have occurred in the amount of woodlands.
Interactions such as these between cover types
were not investigated. But, evidence is provided
that adds another dimension to the broad patterns
of change described above. Specifically, data are
provided on the relative influence of each
category of change on each rfparian type.
` The artaunt of loss (or gain) attributable to
each category was measured for each riparian type
during each time period, these amounts were then
divided by the number of years in the period.
!Chronologically, these were 19, 18, and 8 years.
These rates are presented in Table 3 in terms of
acres per year. Estimating loss Land gain) as a
rate, rather than as the sum of change, facili-
tated comparisons of change between periods of
unequal length.
In order to simplify calculating the rates at
which individual rfparian types were lost, all
developed types were combined. Between 1938 and
1982, approximately 97.5 percent (85,894 acres) of
all riparian cover converted to a developed type
was converted to agriculture, 1.7 percent (1498
acres} was converted to urban/ranchyards, and 0.8
percent (698 acres) was converted to rights-of-