Ecosystem Management Study: Restoration of Mixed-oak Forests with Prescribed Fire

Research Issue

Historically, fire was a frequent disturbance process in the mixed-oak forests of the central hardwoods region. Fire control has altered forest structure and composition. Forests are more dense and the sustainability of oak and hickory dominance is now threatened by an abundance of shade-tolerant and fire sensitive tree species such as red maple, sugar maple, and beech. Prescribed fire has been advocated to promote and sustain open-structured mixed-oak forests and the plants and animals that have adapted to these communities. However, long-term research on fire effects is lacking. Our Ecosystem Management Study was initiated in 1995 to quantify the effects of frequent and periodic prescribed fires on the structure, composition, and function of oak forest ecosystems. 

Our Research

Four 75 ha study sites are located in the Allegheny Plateau of southern Ohio, on the Vinton Furnace Experimental Forest (VFEF) and the Ironton Ranger District of the Wayne National Forest.   Each site has three experimental units:  unburned, frequent burn, and periodic burn.  Vegetation plots, stratified by an integrated moisture index, were established in each unit to monitor vegetation and soils.  Prior to treatments, the overstory of all sites was dominated by oaks and hickories, but shade-tolerant species (e.g., red and sugar maple, blackgum, beech) dominated the midstory and understory.  

Phase 1 (1995-2005):
Pretreatment data on vegetation, soils, and breeding birds were collected in 1995 and results were published in a Forest Service technical report.  Low-intensity dormant-season prescribed fires were applied from 1996 to 1999.  During that period, frequent burn units were burned annually (4 times) and periodic burn units were burned twice, in 1996 and 1999.  Extensive postreatment data were collected during this period on vegetation, belowground processes, and breeding bird populations.  Additional fires were conducted from 2003 to 2005, resulting in units that have now been burned 2 to 5 times.  

Phase 2 (Begins 2008):
We will continue the study by applying a shelterwood harvest treatment to all four burn units at VFEF after the 2008 growing season.  This treatment will reduce tree basal area from ~110 to ~55 ft2/acre.  We will continue to monitor overstory and understory tree populations before and after the shelterwood treatment. 

Prior to the shelterwood treatment, we will study tree regeneration within canopy gaps on burned and unburned units.  Numerous gaps have developed recently as a result of mortality from a regional white oak decline.  In the gaps on burned sites, where the maple-beech midstory has been largely eliminated, we have observed the development of oak and hickory advanced regeneration.  By contrast, on unburned sites we’ve observed that gaps are being filled by the midstory tolerant species.  

Expected Outcomes

Phase II.  This study will provide new information about how hardwood regeneration  responds when repeated prescribed fires are followed by a canopy-opening disturbance.  

Research Results

• Annual vs. periodic fires.  We found that annual fires were operationally feasible but fire intensity increased significantly with two or more fire-free years between burns.  
• Forest structure and composition.  Repeated low-intensity fires caused virtually no overstory tree mortality but greatly reduced the density of the maple-dominated sapling layer.  However, with the persistence of closed-canopy conditions, oak and hickory advanced regeneration generally failed to develop.
• Herbaceous layer vegetation.  Both annual and periodic burns resulted in greater small-scale species richness, as fire stimulated the germination of disturbance-adapted species from the seedbank.  Fire cause very little direct damage to herbaceous plants because the burns occurred when the great majority of the flora was dormant.  
• Soil chemistry and nutrient cycling.  Neither annual nor periodic fires altered soil organic matter, available P, or nitrogen cycling rates.  In contrast, both fire regimes increased soil pH and exchangeable calcium, compared to unburned controls.  Thus fire appears to offset the effect of atmospheric deposition by increasing pH and calcium, although increased nitrate fluxes through the soil from nitrogen deposition may negate this positive effect of fire.  
• Soil temperature and root production.  During a fire, we found that very little heat was transferred to the mineral soil.  However, the postburn blackened litter layer resulted in soils that warmed earlier and to a greater extent in the growing season.  This earlier soil warming was accompanied by an earlier increase in root biomass in the soil.  
• Decomposer organisms (springtails and mites).  These microarthropods play a major role in the decomposition of leaf litter in forests.  In the short-term, four annual fires reduced springtail and mite abundance in the soil.  However, their abundance on sites burned twice in four years was no different than on unburned control sites. 
• Breeding birds. Of 30 bird species monitored, only 6 were affected positively or negatively by fire over a five-year period.  Densities of Eastern Wood Pewees and American Robins increased on burned sites.  Populations of several species that nest on the forest floor and the low shrub layer decreased in abundance:  Ovenbirds, Worm-eating Warblers, and Hooded Warblers.  

Selected Publications 

Research Participants

Principal Investigator

• Todd Hutchinson, USDA Forest Service- Northern Research Station Ecologist

Research Partners

• Dan Yaussy, USDA Forest Service - Northern Research Station Supervisory Research Forester
• Robert Long, USDA Forest Service- Northern Research Station Research Plant Pathologist
• Joanne Rebbeck, USDAUS Forest Service- Northern Research Station Plant Physiologist
• Ralph Boerner, Ohio State University
• Mike Bowden, Ohio Division of Forestry
• Greg Wilhelm, Forestland Group, LLC

For further details log on website :
http://www.nrs.fs.fed.us/sustaining_forests/conserve_enhance/biodiversity/regeneration_other_species/