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Forest Disturbance Processes

Silvicultural Options for Restoration of American Beech Resistant to Beech Bark Disease

Research Issue

Beech bark disease (BBD) is an insect-fungus complex involving the beech scale insect (Cryptococcus fagisuga Lind.) and one or two canker fungi.  The disease kills or injures American beech (Fagus grandifolia Ehrh.) when these fungi invade bark altered by the feeding activity of the beech scale insects.  Beech scale was accidentally introduced to Halifax, Nova Scotia from Europe, around 1890.  It has since spread into New England, New York, Pennsylvania, West Virginia, N. Carolina, Tennessee and Michigan.  Three phases of BBD are generally recognized: (1) the “advancing front,” corresponding to areas recently invaded by scale; (2) the “killing front,” representing areas where fungal invasion has occurred and tree mortality begins; (3) the "aftermath forest,” where the disease is endemic.  In the northeastern portion of the Allegheny National Forest (ANF), located in northwestern Pennsylvania, the advancing front has been present since the late 1980s and the killing front since around 1990.  Aftermath conditions are becoming evident. Dense understories of beech sprouts develop following decline and mortality of parent trees.

Some hardwood stands on the ANF harbor dense understories of American beech due to root suckering from parent trees that become infested with BBD.  The low-shade produced by these sprouts hampers silvicultural efforts to regenerate shade-intolerant species with higher economic value.  Yet, retention of potentially (genetically) resistant beech as a stand component is desirable due to important contributions to wildlife habitat.

Our Research

In stands where BBD is well established, silvicultural treatments attempt to retain large overstory trees which show visual resistance, remove all heavily infested/dying trees and then treat the understory with herbicides to kill all beech regeneration.  The residual, resistant parent trees will serve as future sources of resistant seed/sprouts. In 2003, the ANF surveyed all beech trees in stands that were targeted for shelterwood establishment cuts, used to create environmental conditions favorable for seedling regeneration.  Beech comprised 14-20% of the overstory basal area.  All visibly resistant beech stems larger than 6” dbh were reserved from harvest.  A total of 121 resistant trees were added to a database to track their survival and root sprouting response over time.

 As part of the shelterwood system, chainsaw site preparation and broadcast herbicide application are used to reduce the density of susceptible beech stems in the understory.  The most economical procedure is to apply this treatment uniformly throughout stands being regenerated, without avoiding potentially-resistant beech saplings.  However, it is unknown how the subsequent re-sprouting potential of the residual resistant trees is affected. We tested whether herbicides affected the sprouting potential of resistant trees, and whether killing resistant advance regeneration put beech at a competitive disadvantage in the new cohort.

In 2005, three stands received shelterwood establishment cuts.  Afterwards, circular vegetation sampling plots (0.1 acre) were established using each of the residual beech trees as the plot center to monitor subsequent new seedling development. Broadcast herbicide application was then intended to treat the entire understory, while avoiding the beech sprouts in the plot areas surrounding half of the resistant parent trees.  Plots were re-measured in 2008, 2010 and 2013.

Expected Outcomes

Broadcast application of herbicide to kill understory beech after shelterwood establishment cuts, did not decrease the subsequent density of resistant beech sprouts around visibly resistant parent trees.  Eight years after treatment, plots that had received herbicide treatment were adequately stocked with beech sprouts.  Broadcast herbicide treatment of understory vegetation does not hinder the density and height growth of beech sprouts from residual parent trees and may serve to perpetuate a new cohort of beech that is resistant to BBD where healthy parent trees are retained as a source of regeneration.  We recommend that broadcast herbicide application of the entire understory is the most economically feasible options and will not hamper the subsequent density of beech sprouts from resistant trees.

Research Participants

Principal Investigators

  • Mary Ann Fajvan, US Forest Service – Northern Research Station, Research Forester

Research Partners

Last Modified: April 7, 2016