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Why American Beech

The Ecology of American Beech

American beech (Fagus grandifolia Ehrh.) is an important component of the eastern deciduous forests of North America.  Beech has great shade tolerance and is moderately long lived, and together with sugar maple (Acer saccharum Marsh.) comprise the dominants in the climax “northern hardwood forest”.  Beech is widespread in all nine forest regions that comprise Lucy Braun’s classic 1950 treatise of the deciduous forests of eastern North America.  It is a characteristic species of four of those regions and is dominant in two northerly regions including the namesake beech-maple and beech-birch-maple regions.  It is prominent in most exemplary stands in the Northeast, as well as in many old-growth forests of the region. 

Despite its current abundance, it appears to have been much more abundant 200 years ago than it is today based on pollen records.  This decline in abundance does not appear to result from recent land use activities, and it predates beech bark disease (BBD).  Beech has consistently expanded northward since the last glaciation from refugia in the deep south.  The Southeast beech maximum faded between 11,000 to 8,000 ybp, but was accompanied by continued northward expansion at about 85 miles/year.  By about 1800 beech was abundant and common in the forests of the Northeast, but less common in the drier and warmer regions south of southern New England and northern Pennsylvania.  The modern distribution of beech covers temperate eastern US and southeastern Canada, with a distinct variety occurring in eastern Mexico.  It is found on most mesic sites within this range that have not been burned.  It occurs from sea level up to 2,000m elevation. There is a broad maximum of beech abundance scattered all along the Appalachian Mts from Kentucky to Maine and up into southeastern Canada and the Maritimes.  The range of beech has a sharp northern boundary, which suggests environmental limitation perhaps cold hardiness.  The western boundary in eastern Wisconsin seems constrained by moisture availability.  To the southwest beyond the Mississippi River scattered populations are found in riparian zones, cove forests, or on valley floodplains.  On moist acidic soils with low base saturation, beech is the overwhelming canopy dominant in late successional stands.  Canopy beech trees promote soil and forest floor conditions that favor beech regeneration at the expense of competitors such as sugar maple and hemlock.  The production of prolific beech sprouts promotes competitive exclusion of other species.

Throughout its range, beechnuts are an important food for many species of wildlife.  It is in the northern section of its range however, where other mast species are scarce that beechnuts have their greatest impact on wildlife populations.  Over the past 15 years increased intensive forest management as well as BBD are removing mature beech trees from the forests.  Wildlife managers in the Northeast are interested in learning how much mature beech is needed on the landscape to support black bear, marten, and other wildlife populations.  How should beech be managed to maintain it as an important forest component for wildlife?

Beech Bark Disease (BBD) and Its Impact

Sometime during the late 1800s a ship from England arrived at Halifax, N.S., Canada, carrying a shipment of European beech (Fagus sylvatica) saplings for the city’s gardens.  The trees thrived in the relatively mild maritime climate. By 1890 some of the trees were determined to be infested with the beech scale (C. fagisuga).  About 30 years later, large numbers of American beech in the nearby forests began dying of an unknown cause.  In the late 1920s, John Ehrlich began his graduate study of the problem at Harvard University.  His work was published in 1934, and in it he named the disease, described the causal insect-fungal complex so thoroughly that little additional work, except for some control trials and disease monitoring, was done on the disease until the early 1960s.  Ehrlich deduced that beech + scale insect + Neonectria fungus = BBD. 

What have we learned in the nearly 100 years since Ehrlich conducted his initial studies? The disease is slowly spreading southward and westward, and will likely encompass the range of American beech.  The consequences of BBD are still developing, and marked changes have occurred in the forests longest affected by it (i.e. the aftermath forests).  In the most recently affected forests, the disease is still causing heavy mortality.  But the aftermath forests are now composed of few, large, highly defective, residual trees; alongside many stands of small trees primarily of root sprout origin. Widespread beech mortality is rare in these forests. The aftermath forests are widespread in the beech forests of the Maritimes, New England, New York, and now in Pennsylvania and West Virginia.  The now endemic causal disease complex causes accumulating defect in these young, emerging beech thickets. 

BBD essentially has converted American beech into a native, invasive species with important resultant consequences for management of the northern hardwood forest types where beech is a significant component.  BBD killed or weakened trees of large and medium sizes, altering the structure and composition of these forests, and leaving aftermath stands with increased stocking of the smaller beech in understory and mid-story positions. Where management reduced the understory beech, or where it still remains sparse, a diverse array of woody and herbaceous species common to the site conditions remain abundant, and forest community structure has not shifted toward domination by beech.  But where dense, these beech thickets (colloquially referred to as “beech hell”) may threaten sustainable forest resources management and ecosystem integrity. Reproduction method cutting in these dense beech thickets commonly results in an abundance of that species in the new age class with the likelihood that beech may replace other species from northern hardwood stands, and biodiversity negatively impacted.

Mechanisms behind these responses and the implications for future stand conditions remain unclear. We also do not know if operational-scale treatments using mechanized harvesting equipment will have effects similar to those previously observed after cutting small experimental plots with brush saws. In addition, we do not yet know if cutting treatments might affect the progression of BBD itself, and if thinning the beech thickets might influence beechnut production and/or other tree responses. Effects on the faunal community also require attention, as well as reasons for changes in the diversity and abundance of those animals.

A possible usage of beech sprouts might be as feedstock for wood-fired boilers or other biofuel uses.  But the cost effectiveness of mechanized removal of understory and mid-story beech thickets on a commercial scale currently is unknown. Will coppicing of small beech lead to sustainable production of those biofuel materials?

The results of research plus anecdotal observation suggests that through recurring cycles of beech development, mortality, and suckering many northern hardwood ecosystems will likely become increasingly simplified in species diversity and structure. In turn, ecosystem functions and services, and related social values, seem likely to change as well.  So, beech is an important component of many different forest types with significant positive and negative ecological and economic impacts that justify a coordinated and integrated approach to address them.

Herbicide mistblowing has proven effective in reducing beech understory interference and promoting regeneration of other species following reproduction method cuttings (Kelty and Nyland 1981, Nyland et al. 2006b). Other trials by SUNY-ESF indicate that few stump sprouts, suckers, or seedlings form beneath closed canopy stands following understory cutting using brush saws during the growing season (Mallett 2002, Nyland et al. 2006b). However, research plots having a sizable canopy opening or a low-density overstory cover eventually developed root suckers, particularly in proximity residual overstory beech trees and when cutting occurred during the dormant season (Nyland et al. 2009).

Previous Work, Present Outlook, and Future Proposals

Beech Bark Disease (BBD) has killed or weakened large and medium-size American beech (Fagus grandifolia Ehrh.) trees across much of northeastern North America. Subsequently, the aftermath forest has developed dense understory and mid-story layers dominated by beech (Huston 1975), making that species an invasive native plant. When dense, this understory has interfered with other tree regeneration (Bohn and Nyland 2003), and dramatically reduced herb species diversity and abundance (Quinlan 1996, Forrester and Bohn 2007, Wightman et al. 2009). As a consequence, ecosystem complexity decreases, and particularly as cutting or natural causes remove other species from the overstory canopy and promote subsequent development of the small beech (Huston 1975, Forrester et al. 2003, McNulty and Masters 2005, Hane 2005, Nyland et al. 2006a, 2006b). Eventually the developing beech trees also become infected by BBD and generally succumb before reaching 10-12 in. in diameter. That halts tree community development at the pole stage, with replacement largely by beech root suckers from the understory (Houston 1975, Houston 2005, Nyland et al. 2006). Yet recent studies (Castello, Teal, and Leckowitz 2009) have suggested new hypotheses about the role of scale insects as a precursor to Nectria infection. Also, while beechnut production initially declined by 40% as the disease progressed into the aftermath stage (Costello 1992), it has subsequently increased to some degree despite absence of large upper canopy beech (McNulty and Masters 2005).

Foresters and ecologists have long known that American beech regeneration derives primarily from seedlings and root suckers, but stump sprouts may also occur off small trees following cutting (see Nyland et al. 2006a). Suckers develop from adventitious buds that form in callus on shallow roots after some kind of injury (Jones and Raynal 1988). Together, the suckers and sprouts can replenish cut trees, potentially facilitating long-term biomass production through a coppicing system. And while disturbance from logging and similar activities may increase their development (Houston 2001), many unmanaged stands also have abundant root suckers (Held 1980, Ward 1961). These also derive from shallow roots, possibly after wounds from natural causes (e.g., by animals, or movement of stones due to freezing and thawing of the soil). Some reports suggest that progression of beech bark disease also triggers increased suckering across a range of sites, resulting in development of a dense beech understory beneath many northern hardwood stands (Houston 1975, Hane 2005). Due to their high shade tolerance (Logan 1973, Tubbs and Houston 1990) these suckers and any interspersed beech seedlings may persist for years, and then develop into canopy positions beneath openings caused by a stand disturbance (Houston 1975, Canham 1988). So at least in northeastern portions of its range, American beech has a major negative effect on the stability, vigor, health, and sustainability of northern hardwood ecosystems.

The proposed research will initiate the next generation of investigations into beech biology and its effects within the northern hardwood forest by creating an instrumented Beech Field Laboratory to support longer-term observation of northern hardwood community dynamics, and serve as a diversity of additional future research by collaborating ESF scientists, such as:

  • changes in symptoms of BBD across treatments
  • differences in coverage of scale and Nectria, and changes of this through time
  • effects of spatial distribution and stand density on growth and survival of residual beech trees and coppice growth, and of overstory sugar maple
  • effects of beech on forest mychorrizal communities, including community dynamics through time
  • similarities and differences in fauna populations, and their dynamics through time
  • effects of beech on soil physical and chemical properties, and their changes through time

The resulting integrated approach will lend great breadth to the overall beech research program at ESF, giving it both applied and mechanistic dimensions.