Iowa is located near the center of the United States and experiences a temperate climate. The state encompasses 145,744 km2 (56,272 mi2) and is bounded to the east by the Mississippi River and to the west by the Missouri and Big Sioux rivers. Minnesota borders Iowa to the north and Missouri to the south. A more complete description of the land and climate during BBA I was provided by Jackson et al. (1996) and our intent here is to provide more detailed information about the climate and habitat conditions during BBA II.
Temperature and precipitation data during BBA II varied annually and illustrate a period that was slightly warmer and wetter than the long-term averages (Table 2). The climate in Iowa has been slowly warming. The mean annual temperature since 1895 was 47.5˚F through the end of BBA I (1985–1990) and 47.6˚F through 2012. The average annual temperature during BBA II (2008–2012) was approximately 48.2˚F, which is significantly warmer (Iowa Department of Agriculture and Land Stewardship 2020, National Oceanographic and Atmospheric Administration 2020). By the end of BBA I (1985–1990), the average annual precipitation for Iowa since 1895 was 80.5 cm (31.7 inches). By the end of 2012, Iowa was experiencing slightly wetter conditions and that average had risen to 82.0 cm (32.3 inches). The average annual precipitation during BBA II (2008–2012) was approximately 94 cm (37 inches; Iowa Department of Agriculture and Land Stewardship 2020, National Oceanographic and Atmospheric Administration 2020). Notably, the first three years of the atlas were wetter than normal while the last two were moderate drought years.
Annual temperature and precipitation during Iowa’s second Breeding Bird Atlas, 2008–2012
|These totals are from Iowa Department of Agriculture and Land Stewardship data for this period and differ slightly from the same totals reported by the National Oceanographic and Atmospheric Administration.
The vegetation and land use patterns in Iowa are complex and include many changes since settlement. Our intent here for BBA II is to update the descriptions in Jackson et al. (1996) by making use of geographic information system (GIS) technology that was not available in the 1990s. Using the 2009 High Resolution Landcover of Iowa raster dataset (Iowa Department of Natural Resources 2017), we calculated the area and percent of all breeding bird atlas blocks in each of fifteen habitat classes, combined those into broader habitat classes (e.g., water and wetland into “Water,” grass_1 and grass_2 into “Grass”), and then recalculated the area and percent separately for grid and habitat blocks. In each calculation there was a small amount of the landscape that could not be classified, most often because the underlying habitat type was obscured by clouds or reflection. This simple comparison illustrates that there were important habitat differences between the grid and habitat blocks, as expected from our method of selecting blocks. As expected, grid blocks had a greater percentage of their area in grass and crops than did habitat blocks. The high grass number includes some agricultural lands as well as pasture. Also, as Iowa was historically mostly grass habitats, there are more grasslands across the state than the other habitat classes (wetlands and forests) thanks to USDA Farm Bill Programs for private lands. Conversely, grid blocks had less forest, shrub, and wetland cover than did habitat blocks. Recall that our block stratification scheme was designed to select habitat blocks in part based on these more specialized habitats. Finally, the area covered by structures, roads, and bare soil did not differ appreciably between grid and habitat blocks.
Area (ha) and percent of breeding bird atlas blocks in each of seven habitat classes, calculated for all blocks and then separately for grid and habitat blocks
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