• The changes imposed on Iowa's native ecosystems by nineteenth-century settlers were overwhelming in extent and rapidity, as demonstrated by these dramatic woodland alterations:

• In the early 1800s, about 19% of Iowa (6.7 of the state's 35.8 million acres) was wooded; much of this was savanna.

• Early immigrants described oaks with trunks 3 to 4 feet wide covering miles of the landscape. Roosting passenger pigeons were so thick that they broke off branches the size of small trees.

• Already by 1860, over 500 local sawmills had cut the choice trees throughout the state.

• By 1875, Iowa's original woodlands were reduced to 2.5 million acres.

• A few decades later, railroads consumed entire woodlands, using 6 acres of oaks for a mile's worth of ties.

• Following World War II, Iowa's woodlands plunged (by 1974) to only 1.6 million acres, 4.3% of Iowa's land.

• Iowa's woodlands have been expanding recently, as cattle herds shrink and trees invade prior pastureland. By 1990, woodlands covered 2.1 million acres.

• Iowa's current oak woodlands are destined to disappear if they are not managed by burning and opened to sunlight.

• Walnut Creek National Wildlife Refuge, southeast of Des Moines, is one of the nation's largest savanna restoration projects.