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

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RELATIONSHIPS BETMEEN THE EISPANSION OF AGRICULTURE AND THE REDUCTION OF NATURAL
RIPARIAN W48ITAT IN THE MISSOURI RIVER FLOODPLAIN OF NORTHEAST MDNTANA
FROM 1938 TO 19821
Alexander R. Boar and Michael J. Erwin2
Abstract.--The fioodplain composition is described for
four points in time over a 45-year period. Broad changes 1n
the area, density, and percent of the fioodplain represented
by agricultural and other developed land and three general
riparian cover types are documented. Evidence is provided
on the patterns and rates at which riparian cover types were
lost and gained, Including the conversion to agriculture and
other developed types.
INTRODUCTION
Human use of the fioodplain zone has often
resulted in the removal of the natural riparian
vegetation. This reduction has been complete and
permanent in some areas of the grid west (Ohmart
et ai. 1977). In the Sacramento River Valley. of
California, the riparian forests have been reduced
from •n estimated 775,000 acres in the 1850's to
less than 13,000 acres in 1980 (Haugen 1980).
Approx4mately 90 percent of the cottonwood forests
along the lower Colorado River was eliminated
between 1600 and 1967, the mayor decline occurring
between 1940 and 1967. Similar declines occurred
on the Rio Grand River 1n New Mexico and Texas
(Ohmart et a1. 1977) and on the South Platte River
in Colorado.
M1-y these changes have occurred is sometimes
confounding, at other times strafghtfarward.
Ohmrrt et a1. (1977) concluded that the demise of
eottonwood torsata on the lower Colorado River was
directly related to changes in that system caused
by upstream dams. Taylor (1982) studied a series
of aerial photographs taken in 1940, 1954, and
1963 of a small mountain stream in California from
which water had been diverted since 1940. He
found that the riparian zone declined steadily
throughout the 24-year period, failing to reach a
state of ec~ilibrium. He attributed the observed
changes to the reduction of streambank recharge
resulting from the annual dewatering of the
stream. This in turn stressed the vegetation in
the riparian zone. Johnson et a1. (1976) found
that tree growth below dams on the Missouri River
became less vigorous following control of river
flows and flooding. Other contributing factors
were reduction of groundwater recharge, soil mois-
ture, soil nutrient enrichment, and seedbed avail-
ability.
The most permanent destruction of riparian
habitat on the middle end upper portions of the
Missouri River has been caused by federal water
development projects. Between Gavins Point, South
Dakota and the function of the Madison, Gallatin,
and Jefferson Rivers in Montana, 838 of the 1510
river miles (or 55 percent) must now be claaaified
sa reaervolr rather than as free-flowing river
(MfONRC 1979, USCOE 1977 and 1981c). A compila-
tion of land-cover types flooded by six dams (Fort
Peck Dsm not Included) in this river reach pro-
vides evidence that 27 percent (219,800 acres) of
the total peal areas formerly consisted n1 trees,
shrubs, and marsh; 35 percent (293,800) was grass-
land; 19 percent (158,400 acres) was agriculture;
18 percent (152,000 acres) was river channel;
while less than one percent (5000 acres) consisted
of forb and upland cover types. Thus, approxi-
mately 62 percent of the area flooded by six dams
on this reach was occupied by woodland/grassland
vegetation {USCOE 1981 (a and b); USFWS 1946,
.1948, 1950, and 1952).
Little is known about how much riparian vege-
tation has existed in those areas of the upper and
middle Missouri River fioodplain that have not
been inundated by reservoirs. The largest concen-
tration of remnant gallery forests and other
riparian vegetation types on the Missouri River
upstream from Gavins Point, South Dakota is be-
Tleved to exist now along 190 river miles in
northeast Montana and northwest North Dakota.
This paper documents how much riparian cover,
agriculture, end other development existed 1n this
area at different times between 1938 and 1982.
1Paper presented at the first North American
Symposium on Riparian Ecosystems and Their
hMnagemento Reconciling Conflicting Uses, Tuscon,
Arizona, April 16-18, 198b.
2W11dlife biologists, Ecological Services,
U.S. Fish and W)1d11fe Service, Billings, Mont.