Impacts of Beech Bark Disease and Climate Change on American Beech

Abstract

American beech (Fagus grandifolia Ehrh.) is a dominant component of forest tree cover over a large portion of eastern North America and this deciduous, mast-bearing tree species plays a key role in these forest ecosystems. Beech bark disease (BBD) is a scale insect-fungus complex that has caused the decline and death of afflicted beech trees. This disease has become a common feature in North American forest landscapes. Resistance to BBD is at the level of the beech scale (Cryptococcus fagisuga Lind.). Beech scale attack predisposes the tree to subsequent infection by Neonectria fungi. The impact of this tree disease has been shown to be significant, particularly in beech dominated forests. Scale-free trees (resistant to BBD) have been reported to range from only 1% to 3% in infested stands, with estimates ranging from 80–95% for overall infestation (for all beech within the current North American range). In addition to BBD, overall beech health will be directly impacted by climate change, if one specifically considers the expected fluctuations in precipitation leading to both drought periods and flooding. Beech is particularly sensitive to both extremes and is less resilient than other broad leaf tree species. Although the increase in global temperatures will likely shift the current range of the American beech, milder winters and less snowpack will favor propagation and survival of the beech scale. This review aims to present the current outlook for American beech in light of climate change. The natural history of the American beech and the onslaught of BBD during the last century will be covered, followed by the potential effects of a changing climate on BBD-infested forests. Evidence from models of European beech (Fagus sylvatica) and other host-pathogen systems will supplement data directly gathered to evaluate BBD in American beech. We present the case that although climate change is likely to be a confounding factor in the continued loss of American beech, increasing our understanding of possible mechanisms of resistance and environmental factors that may influence susceptibility of American beech to BBD can inform proactive management strategies.