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<br />ciated with farm or ranch sites. Cottonwood typically consisted of the Burlington Northern
<br />(Pooulus app.) was the predominant tree species in Railway; and transmission, pipeline, and Inter-
<br />this category. state Highway corridors. Miscellaneous paved and
<br />gravel roads were not included here, but were
<br />included with whatever cover type was adjacent to
<br />Shrub-scrub ,them.
<br />The riparian shrub-scrub category consisted
<br />of woody plants up to flue meters tall with erect
<br />single or multiple stems in areas containing less
<br />than ten percent woodland canopy closure $nd.more
<br />than 30 percent shrub rover. Where the canopy
<br />closure of shrubs did not fall wlthin the bounds
<br />of these criteria, the area was classified
<br />according to the dominant vegetation type; e.g.,
<br />deciduous woodland or herbaceous.
<br />Some dominant shrub species were willow
<br />(5alix app.), dogwood (Corpus stolonifer~), green
<br />ash (Fraxinus aennavlvenica) and cottonwood
<br />(Pooulus app.) saplings, western wild rose (
<br />woodsll), and snowberry ($y,~g oricaroos
<br />occidentalis). Other common woody shrub species
<br />,included Russian olive (Elaeaanus anaustifolla),
<br />butfaloberry ( eo~erdia graentea), and choke-
<br />cherry (P,Tunua virciniana).
<br />Aerial Photography
<br />Coverage
<br />Complete physical Coverage for the 1938,
<br />1956, 1974, and 1982 time periods was acquired
<br />from several sources. The photographic products
<br />for the three older eras consisted of 9x9 inch,
<br />black and white, contact prints. The 1982 coverage
<br />was Kodak 2443 color infrared (CIR) film, The
<br />scale of all aerial photography was 1:24,000.
<br />These years were chosen because 1) photographic
<br />coverage for the entire area was available; 2) the
<br />Fort Peck Dam was completed in 1938, and 3) the
<br />years span a reasonable time period within which
<br />change could be assessed.
<br />Adequacy
<br />Herbaceous
<br />The riparian herbaceous category consisted of
<br />areas with a woodland-canopy cover of less than ten
<br />percent r~ a shrub cover of less than 30 percent.
<br />Small, non-shrub clearings wlthin a woodland or
<br />large arena of low vegetation outside the woodland
<br />boundary with no visible evidence of farming such
<br />as furrows or hay piles, were included within the
<br />herbaceous category. Grazing was a common land-
<br />use in areas classified as this type. This cate-
<br />gory included herbs, grasses, young willows and
<br />cottonwood seedlings, wildrose, and snowberry, as
<br />well as wetland species such as rattail (Tvpha
<br />latifolia). Many emergent wetlands were included
<br />within this cover type as was permanent water in
<br />oxbows, natural and man-made ponds, channels that
<br />had been dammed or naturally arrested, depressions,
<br />or excavations. This lumping was necessary because
<br />these features could pat be reliably interpreted
<br />on the 1938-era photography; thus reliable caepari-
<br />sons could pat have been made with successive eras.
<br />The black and white aerial photography used
<br />tar this project was the best available. The
<br />resolving quality was generally adequate for fea-
<br />ture identification, but considerable time was
<br />required for "keying-out" the textural, depth, and
<br />height characteristics of the surface-cover types.
<br />Poor exposure control of the black and white photo-
<br />graphy reduced the contrast on some frames, espe-
<br />cially those of 1938 vintage. In some cases, gray
<br />tones were not consistent for the same feature on
<br />two adjacent frames-and there was lack of full
<br />stereo coverage. Quality of the negatives improved
<br />substantially for eras after 1938.
<br />The 1982 CIR film had excellent resolving and
<br />exposure qualities, but no stereo coverage. Over-
<br />all, the 1982 film presented distinct contrasts
<br />between features, very sharp resolution, and appro-
<br />priate mid-day shadows, which assisted in making
<br />height determinations. However, classifying dense
<br />stands of cottonwood trees was difficult 1f they
<br />approached the height limits of the shrub-scrub
<br />and woodland categories.
<br />Agriculture
<br />Agriculture was defined as any land visibly
<br />disturbed for the purpose of producing or harvest-
<br />ing crops. Three types of agriculture were in-
<br />cluded in this feature: flood-irrigated, center-
<br />pivot irrigated, and non-irrigated. Pastureland
<br />for grazing was difficult to identify on a black
<br />and white print. It was not tonsidered as a
<br />separate feature, but was incorporated into this
<br />and other cover types, such as the herbaceous,
<br />shrub-scrub, and declduou§ woodland types.
<br />Rights-of-way
<br />Rights-ot-way included areas developed as
<br />transportation and utility corridors. This type
<br />Oats Processing
<br />Photointerpretation and digitizing was done
<br />by the U.S. Fish and Wildlife Service in Fort
<br />Collins, Colorado. The process of interpreting
<br />the aerial photography was divided into several
<br />phases: field orientation, interpretation, over-
<br />lay production, field verification, and quality
<br />control.
<br />Field orientation was conducted during late
<br />July of 1981. Reference points for most features
<br />in the classification system were located on the
<br />ground, photographed, and marked on aerial photo-
<br />graphs. These reference points provided a standard
<br />for interpretation throughout the project.
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