Forest Disturbance, Succession and Modeling

Research Issue

Oak-dominated forests of northern Arkansas are complex ecosystems that became established 5 to 10 thousand years ago. Both human and natural disturbances have played a role in their development. Studies of witness trees prior to the European settlement in this area provide a snapshot of species composition and distribution. Qualitative comparisons of historical and present vegetation data reveal a much higher proportion of red oak and black oak today. Such a shift may be attributed to nearly a century of fire suppression and recent management actions, which has resulted in higher than historic stem densities of relatively old trees in these forests.

High stem densities combined with a three-year drought likely led to the recent and extensive oak decline event in Arkansas and surrounding areas. Trees most vulnerable to decline are 70-90 years old or older, on poor sites (e.g., shallow, rocky soils, ridge tops), and dry slopes (e.g., south and west facing slopes). Short-term, severe drought and repeated insect defoliation can further stress the oaks that are vulnerable.

In a preliminary study, we have parameterized a spatially explicit forest landscape model, LANDIS, to assess the spatial and temporal variation of oak species composition, age structure, and spatial pattern. We have developed methodologies to delineate current and potential areas of vulnerability under current and historic fire regimes.

Our Research

We will employ a factorial design of simulation experiments. There is a factor for prescribed fire (fuel) treatments (P), a factor for harvest (H), and a factor for natural and current fire regimes (F), each representing a treatment action. Combined, they represent a set of management alternatives. Each experimental treatment will be independently simulated for 150 years and each simulation experiment will be replicated 10 times.

Oak Decline Risk Categories in the Boston Mountain Landscape

Expected Outcomes

The overall objective of this study is to evaluate viable landscape-scale management alternatives and their effects on improving forest ecosystem health in the Ozark National Forest within the Boston Mountains of northern Arkansas.

Research Results

• Spetich, Martin A.; He, Hong S. 2008. Oak decline in the Boston Mountains, Arkansas, USA: Spatial and temporal patterns under two fire regimes. Forest Ecology and Management 254: 454-462

Research Participants

Principal Investigator

Martin A. Spetich, Research Forest Ecologist, US Forest Service, Southern Research Station at 501-623-1180 ext 105

Research Partners

• Hong S. He, University of Missouri
• Stephen R. Shifley, Research Forester, US Forest Service, Northern Research Station