Issue At Hand

Significant opportunities exist to improve the overall health and functioning of agricultural landscapes. To achieve the greatest efficacy, these opportunities should be evaluated at landscape scales and be attentive to where these landscapes have been in the past, as the history of a landscape has enduring effects on its present and future condition.

What We Accomplished

In studying landscape history and change, we expected to:

•  Establish a quantitative baseline for assessing present and future landscape change,

•  Delineate periods of rapid change, when landscape conditions are dramatically altered, and causes of this change, and

•  Provide a richer story of the interactions between humans and their environment for the purposes of furthering conservation initiatives.

How Went About It

We conducted this work in the Clear Creek watershed of east-central Iowa (~68,000 ac). Over the past 150 years, the majority of the land within the watershed has been converted from its natural state to row-crops or pasture. The hydrology of the watershed has also been highly modified through construction of drainage systems and the widespread channelization of streams and other waterways. More recently, the area has been experiencing significant urban growth, especially near the cities of Coralville and Iowa City. These and other factors make the region ideal for a study of causes and consequences of landscape change.

The primary data source for our analysis was historic aerial photography. We have scanned, georeferenced, and digitized landscape features from the aerial photos of Clear Creek watershed at four time periods (~1940, ~1960, ~1980, and 2002), with 1938 being the earliest date that aerial photos are available for the watershed.

What We Found

Our analyses quantify important ecological and social processes occurring in the watershed, including:

• Considerable landscape change has occurred within the Clear Creek watershed between the mid-1800s and today. From 1840 until approximately 1900, the mosaic of prairie, forests, and wetlands that had made up the native vegetation in the watershed was rapidly converted by settlers into fields, pastures, farms, and home sites. During this time period, forest cover declined within the watershed by approximately 44%.
• In the 20 th century, forest cover in the watershed increased by nearly 3,000 acres. As of 2002, there was about 5,800 acres of forest in the watershed, often concentrated along streams. This increase in the amount of forest may have positive implications for water quality in the watershed.
• Locations in the watershed that appear to have been continuously forested since mid-1800s. These remnant natural areas may contain critical components of biodiversity today.
• From 1940-2002, crop cover declined within the watershed—the total area of crop land declined by ~15%. At the same time, both urban cover and the density of houses increased dramatically, and at a growing rate in recent decades. The urbanization of formerly rural land in an important issue in Iowa.
• Adecline in the sinuosity of the main stream channel of Clear Creek was observed from 1940-1963, and many present day stream segments are much straighter than in 1940. While some Iowa waterways were historically straightened by natural forces, over 3,000 miles of rivers and streams in the state have been channelized since the early-to-mid 1800s, primarily to facilitate agricultural land use.
• The present-day watershed is dominated by agricultural land use, much as was the case in 1940. Increases in both urban and forest cover, especially in recent decades, suggest that these cover types may become more common within the watershed in the future. Shifts in relative dominance of these cover types (crop, forest, and urban) may have important ecological and social implications for residents.