Agricultural landscape change (1937–2002) in three townships in Iowa, USA

While agricultural landscape change over the course of 20th century has generally resulted in substantial gains in productivity, there is growing concern that the spatially uniform, functionally homogenized agricultural landscapes lack both environmental resilience and socioeconomic sustainability. The State of Iowa, USA provides a specific example where agriculture is highly developed and functions in a highly modified, human-dominated landscape; yet, few spatially explicit, comprehensive, and consistent data are available from which to assess change. To begin filling this gap, we digitized land cover information from aerial photographs for three Iowa townships (Orient Township in Adair County, Bloomfield Township in Clinton County, and Denmark Township in Emmet County) at five time steps between 1937 and 2002 and analyzed landscape change using a case study approach, landscape metrics, and graphical analysis. Results showed several consistent patterns across townships, including increased area devoted to row crops; decreased area devoted to small grains, hay, and grass; decreased numbers of farm fields concomitant with an increase in average field size; and a loss of rural infrastructure, such as farmsteads and rail lines. This generalized pattern describes an overall loss in agricultural landscape diversity over time, which is clearest in Denmark Township, while more detailed analysis reveals fine-scale diversification in Orient and Bloomfield Townships due to the adoption of conservation practices. A comparison of the three case study landscapes suggested that technology, economics, and federal farm policies, as meditated by variability in natural resource constraints, were drivers of the changes we observed.

Research highlights
► Several patterns of landscape change were consistent across our three study townships, all of which contributed to the overall loss in agricultural diversity over time; however, more detailed analysis revealed some fine-scale diversification due to the adoption of conservation practices.
► A comparison of the three study landscapes suggested that technology, economics, and federal farm policies, as meditated by variability in natural resource constraints, were drivers of the observed changes.
► Federal policies emerged as key drivers of landscape change in two study landscapes, while the lack of constraints to technology adoption appeared as more salient in the third.
► Initiatives that foster the diversification in agricultural landscapes, rather than further homogenization, may be more likely to achieve the common goal of enhancing agricultural sustainability.