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Goal: Sustain Our Nation’s Forests and Grasslands Redefining the spectrum of open forest ecosystems

Fire in a forest
Frequent surface fires are a vital ecological driver for the development of open forest ecosystems, as they help to regulate understory and midstory species composition and dynamics. (Forest Service photo by Don C. Bragg)

Introduction

Open forests range from nearly treeless savannas to fairly closed woodlands, with a wide range of tree densities in between. Historically, these open forests arose more from the interactions of fire tolerance than competition for light, and many were multi-aged, self-replacing systems. They were often dominated by shade-intolerant overstory species, making them particularly challenging to study and manage.

Summary

There is abundant historic evidence that many landscapes of eastern North America were dominated by open oak and pine forests. Ecologically, these were markedly different from the closed canopies of early and late successional managed—or even old-growth—forests frequently considered as models of the past.

Despite the historic abundance of savannas and woodlands, the ecology of open forest ecosystems remains ill-defined when compared to either closed forests or grasslands because of a lack of research on this forest type. SRS research suggests that the open forests of eastern North Americas had simple internal stand structures consisting of a single layer of variably-spaced, often very old, overstory trees and limited midstories. These open forests were maintained by understory disturbance, particularly surface fires, that controlled tree regeneration and encouraged a taxonomically rich herbaceous groundlayer.

In contrast, closed canopy forests have dense woody growth throughout the vertical profile, limiting herbaceous plants. To better describe and manage for open forest ecosystems, researchers developed a canopy closure spectrum model dependent on the interactions between prevailing disturbance regimes of historic and current eras. This model depends on the effects of disturbances on either the tree understory (regeneration) or overstory, along with tree traits of fire and shade tolerance. The recognition of different stand structures, disturbance regimes, and their interrelationships can improve our understanding of open forests and limit ecological misunderstandings and restoration misapplications, thereby improving management of these once historically extensive ecosystems.

Principal Investigator
Don Bragg, Project Leader
RWU
4159 - Southern Pine Ecology and Management
Strategic Program Area
Resource Management and Use
Publication
A reconceptualization of open oak and pine ecosystems of eastern North America using a forest structure spectrum
Research Partners
Brice Hanberry (RMRS)
Todd Hutchinson (NRS)