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Recognizing and restoring open forests of savannas and woodlands

Date: April 25, 2019

Open forests, or oak and pine grasslands, are distinctive ecosystems composed of both a forest overstory and grassland understory. Recognition of these unique ecosystems will limit ecological misunderstandings and restoration misapplications

A picture of open oak forest with grassland understory treated by fire in Missouri, showing greenery and trees (photo courtesy of C. Kinkead).
Open oak forest with grassland understory treated by fire in Missouri. (Photo courtesy of C. Kinkead)
















Historical forests of the eastern US were open old growth forest ecosystems, not closed forests and not successional. Fundamental ecology and silviculture of temperate open forest ecosystems remains ill-defined because these forests do not match traditional silvicultural or ecological concepts. Open forests are characterized by simple internal stand structure consisting of overstory trees of fire-tolerant oak and/or pine species. Limited tree densities below the overstory trees allow co-existence of grasslands in the groundlayer. Frequent surface fire provides a mechanism to maintain open oak and pine forests with a grassland ground layer through removal of tree regeneration, which otherwise would capture the growing space from herbaceous plants and fill in the midstory. We have proposed that declining early successional bird species are instead open forest bird species that relied on the relatively permanent grasslands ground layer in historical open forests. Open forest ecosystems bridge the canopy spectrum between treeless grasslands and closed forests. Delivering this research has the potential to be transformative to pedagogy and management, in ecology, silviculture, and wildlife ecology, by providing an alternative ecosystem and management option that is not a clearcut or closed forest.

Closed forest with treed understory in Missouri. The photo shows a green, forested area. (Photo courtesy of C. Kinkead)
Closed forest with treed understory in Missouri. (Photo courtesy of C. Kinkead)
Western oak savannas in Oregon. The photo shows a forested, green area. (photo courtesy of B. Hanberry).
Western oak savannas in Oregon. (Photo courtesy of B. Hanberry)

Key Findings

  • Open forests of oak and/or pine species were the most abundant type of forest historically in the United States.
  • Fire controlled tree growth in the understory, creating open forests with an herbaceous understory.
  • Since fire exclusion during the first half of the 1900s, trees have captured the growing space from herbaceous vegetation and filled the vertical profile, resulting in closed forests.
  • Many bird species that are considered ‘early successional’ probably are associated with the herbaceous layer of open forests, which dominated landscapes for thousands of years, while early successional vegetation historically was rare.

Open pine forest in Washington. The photo shows a grassy area with pines behind it. (photo courtesy of B. Hanberry).
Open pine forest in Washington. (Photo courtesy of B. Hanberry)

Featured Publications

Hanberry, Brice ; Thompson, Frank R. , 2019
Hanberry, Brice ; Brzuszek, Robert F. ; Foster, H. Thomas I ; Schauwecker, Timothy J. , 2018
Hanberry, Brice ; Kabrick, John M. ; Dunwiddie, Peter W. ; Hartel, Tibor ; Jain, Terrie B. ; Knapp, Benjamin O. , 2017

Principal Investigators: 
Principal Investigators - External: 
Marc Abram - Pennsylvania State University
Forest Service Partners: 
Don Bragg, SRS
Dan Dey, NRS
John Kabrick, NRS
Todd Hutchinson, NRS
Frank Thompson, NRS
Greg Nowacki, Eastern Regional Office