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Management of Agricultural Landscapes for the Conservation of Neotropical Migratory Birds

Recent Changes in Agricultural Habitats and Landscape Structure


The changes in agricultural landscapes that most concern conservation biologists are those that have occurred on a large spatial scale. We focus on changes in agricultural habitats in the last three decades, when bird-population trends in the Midwest were well documented (Herkert 1995). The major habitats in the Midwest are crops, including small grains (wheat, oats, etc.), corn, soybeans, sunflowers, and forage (hay). Other habitats are pastureland and rangeland, wetlands, woodlands, and strip cover (e.g., fencerows, roadsides, waterways, terraces). Idle cropland is not explicitly considered a habitat in this section but is covered below under land-use practices. The amounts and relative proportions of cropland, pastureland and rangeland, woodland, and other rural land vary across the Midwest (table 2).
Table 2. Estimated land use (thousands of hectares) of non-federal, rural land in the 12 midwestern States in 1992 (USDA 1994). Pastureland includes rangeland and excludes grazed forested land. Land enrolled in the Conservation Reserve Program is included with other rural land.

Region State Cropland Pastureland Woodland Other
Corn Belt
Illinois 9,761 1,119 1,385 563
Indiana 5,473 756 1,469 481
Iowa 10,120 1,503 782 1,196
Missouri 5,406 4,875 4,721 944
Ohio 4,831 919 2,683 516
Total 35,590 9,173 11,039 3,701
Lake States
Michigan 3,639 953 6,321 975
Minnesota 8,649 1,329 5,595 2,520
Wisconsin 4,379 1,196 5,431 1,301
Total 16,667 3,479 17,347 4,796
Northern Plains
Kansas 10,759 7,302 539 1,444
Nebraska 7,792 10,017 315 865
North Dakota 10,021 4,655 173 1,693
South Dakota 6,657 9,757 219 1,319
Total 35,228 31,731 1,245 5,321


The total area of cropland in the Midwest in the early 1980's was similar to that in the late 1940's (Frey and Hexem 1985). There was a steady decline in cropland area, associated with surplus production, from the late 1940's to the mid-1970's. The area then increased until the early 1980's, as exports expanded. The pattern of change varied geographically. The area used for crops in the Northern Plains (Kansas, Nebraska, North Dakota, South Dakota) in the early 1980's was similar to that in the late 1940's. In the Corn Belt (Illinois, Indiana, Iowa, Missouri, Ohio), there was a dip in the mid-1970's but an increase of 9.5% between the late 1940's and early 1980's. In the Lake States (Michigan, Minnesota, Wisconsin), there was an increase of 2.1% over the same period. The area of active cropland in the Midwest declined again from 1982 to 1992, mostly due to enrollment of cropland in the Conservation Reserve Program (CRP; USDA 1994).

Analysis of data from the National Resources Inventory (NRI), which has been conducted since 1967, also demonstrates declines in cropland area in the Midwest between 1967 and 1977 and between 1982 and 1992 (fig. 1). Analysis procedures changed between 1977 and 1982, so inventory data before 1977 cannot be directly compared with data after 1982 (USDA 1990).


gif -- Graphs of estimated land use changes

Figure 1. Recent changes in estimated land use of non-federal, rural land in three midwestern regions (USDA 1971b, 1982a, 1994). "Pastureland & Rangeland" excludes grazed forested land. Analysis procedures changed between 1977 and 1982, so inventory data before 1977 cannot be directly compared with data after 1982 (USDA 1990).

With the exception of the CRP, changes in the total area of midwestern cropland have been relatively small, particularly during the last three decades, when the best bird-survey data have been available (Herkert 1995). We focus on these decades in our presentation of changes at the level of major habitats.
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