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Sustaining Forests

Site, Stress, Nutrition, and Forest Health Interactions

Research Issue

[photo:]  Sugar Maple Decline on the unglaciated Allegheny Plateau in northern PennsylvaniaA range of stressors including defoliating insects, pathogens, droughts, inadequate soil base cations, and changing climate have interacted to affect the health and regeneration of selected northern and central hardwood forest species.  In the 1980s and 1990s sugar maple dieback and mortality was extensive across the unglaciated Allegheny Plateau in northern Pennsylvania.  Subsequent research established the critical role of landscape position and soil base cation nutrition (calcium and magnesium) as predisposing stresses, and defoliation from elm spanworm and forest tent caterpillar as inciting stressors that caused this extensive sugar maple dieback and mortality.  Other factors such as poor seed production and antagonistic cations (manganese and aluminum) may also be affecting sugar maple health and regeneration. 

In oak forests across unglaciated portions of southern Ohio, white oak mortality became prominent in 2003 and 2004.  While the spatial pattern of mortality severity varies considerably, lower slope and bottomland sites have experienced the most dieback and mortality.  Predisposing stresses include the 1998-1999 drought, while inciting stresses are related to defoliation from forest tent caterpillar and common oak moth.  The association of mortality with bottomlands, lower slopes and drainage ways, suggests that soil and waterborne pathogens might be contributing stressors.  Research was initiated in 2006 to evaluate this hypothesis.

Our Research

Northern Hardwoods:  Since the 1990s we have developed a suite of studies to investigate the causal factors associated with sugar maple decline using a network of more than 75 sites from northern Pennsylvania to New Hampshire.  From this work, we identified the key causal factors associated with sugar maple decline and are developing tools for land managers to select sites suitable for sugar maple using vegetation indicators.  Other studies include a long-term assessment of the effects of forest liming on northern hardwoods, an assessment of soil base cation depletion over 30 years, and a regional study comparing Ca, Mg, and Mn nutrition in Pennsylvania and New York with New Hampshire and Vermont.

Central Hardwoods:  White oak decline and mortality is being investigated at Scioto Trail and Zaleski State Forests in southern Ohio.  Extensive white oak mortality occurred at Scioto Trail State Forest (STSF) and only scattered patches have been detected at Zaleski State Forest (ZSF).  White oak crown condition was evaluated and soils and roots were sampled at both state forests from plots located along topographic transects.  The exotic soil pathogen Phytophthora cinnamomi has been isolated from soils and roots of declining trees.  This pathogen is limited by freezing soil conditions and is not found north of 42° latitude.  Milder winters may enhance survival of this organism in the soil, and excessively wet conditions such as those that prevailed in 2003 and 2004 may favor development of this soil pathogen.      

Expected Outcomes

We expect our work to result in tools for land mangers to assist in identifying sites on which sugar maple should be protected from stresses such as insect defoliation and sites on which sugar maple growth and health can be expected to be good. We also expect to increase our understanding of the role of antagonistic cations, Mn and Al.

The sustainability of oak forests is threatened by a range of factors in addition to the white oak decline phenomenon.  The white oak decline research will focus on strategies for land managers to minimize impacts of this problem on sites with specific soil and moisture regimes.  Other oak species less susceptible to Phytophthora cinnamomi can be favored on such sites or conversion to other hardwood species such as sugar maple and yellow-poplar can be considered. 

Research Results

Inadequate base cation nutrition of Ca and Mg and high levels of Mn have been identified as predisposing stressors for sugar maple decline, but an inciting stress such as defoliation is needed to trigger crown dieback and decline. 

Stands with foliar Ca > 5500 mg/kg, Mg > 700 mg/kg, and Mn < 1900 mg/kg, can withstand stresses associated with defoliation and drought and remain healthy.

Depending on the quality of bedrock minerals, soil supplies of base cations may have been depleted by acidic deposition inputs on some plateau top, shoulder, and upper slope landscape positions on the unglaciated Allegheny Plateau in northern Pennsylvania; mid and lower slope sites may be enriched and can support healthy stands of sugar maple.

Liming northern hardwood stands has been shown to benefit sugar maple growth and crown health, have no effect on American beech, and negatively affect black cherry growth.

Results from the sugar maple decline research have been incorporated into the Allegheny National Forest’s revised Forest Plan, and similar management guidelines were adopted by the Pennsylvania Bureau of Forestry. 

Soils sampled at Scioto Trail State Forest (STSF) yielded four species of Phytophthora organisms, but P.  cinnamomi was isolated from 67% of the samples; only a few roots yielded isolates of P.  cinnamomi.  At Zaleski State Forest (ZSF) 29% of the plots yielded P. cinnamomi.

There was no association of P. cinnamomi with elevation, but Phytophthora spp. were found to occur at a greater frequency on sites with higher integrated moisture index values (more mesic sites) at STSF and ZSF.

Total root mass was significantly lower for white oaks sampled at declining sites compared with white oaks from non-declining sites and  P. cinnamomi population densities were seven times greater on declining sites at STSF compared with densities found on non-declining sites.


Long, Robert P.; Horsley, Stepphen B.; Halett, Richard A.; Bailey, Scott W. 2009. Sugar maple growth in relation to nutrition and stress in the northeastern United States. Ecological Applications, 19(6), 2009, pp. 1454–1466.

Hallett, Richard A.; Bailey, Scott W.; Horsley, Stephen B.; Long, Robert P. 2006. Influence of nutrition and stress on sugar maple at a regional scale. Canadian Journal of Forest Research 36(9):2235-2246.

Long, Robert P.; Horsley, Stephen B.; Halett, Lilja, Paul R. 1997. Impact of forest liming on growth and crown vigor of sugar maple and associated hardwoods. Can. J. For. Res. 27: 1560-1573.

Research Participants

Principal Investigators

  • Robert Long, USDA Forest Service- Northern Research Station Research Plant Pathologist
  • Stephen Horsley, USDA Forest Service- Northern Research Station Plant Physiologist emeritus
  • Scott Bailey, USDA Forest Service- Northern Research Station Geoecologist
  • Richard Hallett, USDA Forest Service- Northern Research Station Research Ecologist

Research Partners

  • Todd Ristau, USDA Forest Service- Northern Research Station Research Ecologist
  • Thomas W. Hall, PA Bureau of Forestry, Forest Pathologist
  • Robert White, Allegheny National Forest, Silviculturist
  • Yilmaz Balci, West Virginia University, Division of Plant and Soil Sciences
  • William MacDonald, West Virginia University, Division of Plant and Soil Sciences
  • Enrico Bonello, Ohio State University, Department of Plant Pathology
  • Dan Balser, Ohio Division of Forestry, Forest Health Administrator

Last Modified: 01/27/2010