Diseased beech increasing, other hardwoods declining in NE North America – could a 2nd exotic beech pest to enter NA via Nova Scotia redirect change again?

There’s lot’s about tree pests and diseases to observe and think about as we approach a new season in Nova Scotia’s forests

American beech, although highly affected by the beech bark disease that got its start in Nova Scotia in the late 1800s, is pretty abundant in many hardwood and mixed Acadian forest stands in Nova Scotia. So an item highlighted on forestindustry.com Volume 3, Issue 5 piqued my interest:

Beech trees are booming in New England. Here’s why that’s a bad thing There’s no easy answer to this one. By Patrick Whittle, AP, February 25, 2018

…The authors… used U.S. Forest Service data from 1983 to 2014 from the states of Maine, New Hampshire, New York and Vermont to track trends in forest composition. They found that abundance of American beech increased substantially, while species including sugar maple, red maple and birch all decreased.

That’s a problem not only because of beech’s lower value, but because of the spread of beech bark disease, which causes the trees to die young and be replaced by newer trees that succumb to the same disease.

The authors found that the rise of beech and the decline of other species is associated with “higher temperature and precipitation” in the forests. The dominance of beech was also especially notable in some key tourist areas — the White Mountains of New Hampshire, the Adirondack Mountains of New York and the Green Mountains of Vermont.

More detailed information is available in the journal paper reporting on the study:

A three decade assessment of climate-associatedchanges in forest composition across the northeastern USA. Arun K. Bose, Aaron Weiskittel1 and Robert G. Wagner. 2017. Journal of Applied Ecology 54, 1592–1604. A PDF of the article is available here. From the paper:

…Occurrence and abundance of American beech have increased substantially over the past three decades, whereas the occurrence and abundance of three other deciduous species have decreased in all ecological provinces of the north-eastern USA, except the Midwest Broadleaf ecological province. Consequently, a clear shift in species composition is currently underway in the beech-maple-birch (BMB) forests of the north-eastern USA, with uncertain consequences for future ecosystem structure and function.

…Increasing dead tree basal area positively influenced the abundance of beech, but was negatively related to the abundance of other deciduous species…When a beech sapling was present in the understorey, overstorey tree mortality (creation of canopy gaps) benefited the beech saplings more than the three other deciduous species (sugar maple, red maple, and birch).

While the evidence the authors present for increased abundance of beech and reduced abundance of the other hardwoods is strong and is consistent with other studies, their evidence that climate change (an “abiotic” factor) is a major driver looks to me to be pretty thin (although I would defer to a more professional assessment of that claim). Rather, increased abundance of beech appears to be associated mainly with the “biotic” factors listed by Bose et al. and studied by other researchers:

Old, dead beech

In the forests of north-eastern USA, several factors have been reported as beneficial to beech with respect to competition with sugar maple, red maple and birch, namely:
(i) beech is more shade tolerant than the three other studied species (Canham 1989), therefore, small-scale overstorey openings that occur by natural mortality due to beech-bark disease, self-thinning and senescence, and by selection harvest are more beneficial to beech saplings than other species,
(ii) unlike the three other species, beech is able to regenerate vegetatively from root suckers, which is often promoted by the beech-bark disease and root injuries during harvesting (Houston2001; Nyland et al. 2006). Beech seedlings originated from suckering have shown a higher rate of growth and survivability than beech seedlings originated from seed (Beaudet& Messier 2008),
(iii) beech is a less palatable species for browsers (Tripler et al. 2005), and
(iv) beech forms an interconnected root system, which effectively generates higher survivability of beech regeneration than other hardwood species (Nyland et al. 2006).

Bose et al. note in the introduction that “…the increasing beech dominance may significantly reduce the future diversity, productivity and value of northern hardwood forest stands” and in the discussion section they advocate “large-scale harvesting/disturbances (i.e. large-scale canopy opening)” – and herbicide use to control/eliminate beech.

Two beech trees, one heavily cankered and dead; the adjacent tree with much less beech bark disease and living

A different approach with a focus on promoting disease-resistant beach over disease-susceptible beach is pursued in a paper by Amanda Farrar and W.D. Ostrofsky, 2006. Dynamics of American Beech Regeneration 10 Years following Harvesting in a Beech Bark Disease-Affected Stand in Maine Northern Journal of Applied Forestry; Bethesda Vol. 23, Iss. 3, (Sep 2006): 192-196; view also the related thesis by Amanda Farrar: Ten Years of Change in Beech Stand in North Central Maine Long Affected with Beech Bark Disease MSC Thesis by Amanda Farrar, University of Maine, 2003. (The thesis is available in full, the journal article only via library subscriptions).

From introduction to the thesis:

Beech bark disease is an introduced disease complex that affects American beech (Fagus grandifolia Ehrh.) throughout much of its range in North America The disease was first found in Maine’s forests in 1931 (Ehrlich 1934, Houston 1994a). Beech bark disease is incited by the beech scale insect (Cryptococcus fagisuga Lindinger), which feeds on the living phloem of the host tree. The feeding alters the bark tissue and predisposes the tree to infection by one of several species of canker hngi in the Nectria genus including N. coccinea var faginata Lohrn., Watson, and Ayres, N. gallingena Bres., and N. ochroleuca (Schweinitz) Berkeley. The scale insect and most likely N. coccinea var. faginata were first introduced to North America in Halifax, Nova Scotia around 1890 on imported ornamental beech from Europe (Ehrlich 1934, Spaulding et al. 1936, Cotter and Blanchard 1981, Houston and O’Brian 1983, Houston 1994b).

Understory, younger beech stand out in the fall, their leaves retained after those of most other species have fallen

This disease has had numerous detrimental effects on northern hardwood stands containing American beech. In contrast to other introduced diseases such as chestnut blight, which largely eliminated the host tree from its range, beech bark disease has not caused widespread, consistent declines in beech abundance. Instead, the disease has led to an increase in the percentage of beech in many stands in terms of basal area and stems per acre (Houston 1994b). This increase in abundance in response to beech bark disease can be attributed to the species powerful sprouting ability after experiencing root disturbance and ability to persist due to its extreme shade tolerance.

Both papers illustrate the complexity of ecological interactions in the northern hardwood forests, and how exotic pests and diseases can radically alter the interactions.

Beech with leaf miner, Halifax area 2017

As described above, beech bark disease got its start in North America in Nova Scotia in the late 1800s. Now another exotic pest, the beech leaf-mining weevil, has recently been recorded in Nova Scotia, the first record in North America. It is making it’s way through the province, causing severe defoliation and hitting the remaining somewhat healthy beech pretty hard where it has become established.

Beech leaf-mining weevil Kathleen Ryan on www.invasiveinsects.ca
“The beech leaf-mining weevil (Orchestes fagi), also known as the beech flea weevil, was first detected in Canada in 2012 in Halifax, Nova Scotia. There it was causing severe defoliation on American beech trees (Fagus grandifolia). Subsequent surveys detected the presence of the insect near Sydney, Nova Scotia as well. The weevil is native to Europe where it is common. Currently, this insect is only known to be established in Nova Scotia, where several counties are infested.” Read more. View also: European insects ravaging Nova Scotia beech trees CTV Atlantic July 26, 2017.

In a perverse way, perhaps this second exotic pest will provide a “solution” to the negative impacts of beech on other species cited in the papers above. On the other hand, it may bring the final demise of this once very important and desirable species of the Acadian forest.

There’s lot’s about tree pests and diseases to observe and think about as we approach a new season in Nova Scotia’s forests.

A Few More Links

Invasive Insects in Canadian Forests
“Tools for forest managers and landowners”

Pests
Page on this website

What a beech: Evil weevil lands in Halifax
Francis Willick, for Chronicle Herald, Jun 12, 2012

NOVA SCOTIA NATURALLY: Healthy N.S. beech trees spell hope
Jamie Simpson, Chronicle Herald, Oct 17, 2014

Beech bark disease: spatial patterns of thicket formation and disease spread in an aftermath forest in the northeastern United States
Lisa M. Giencke et al. 2014. Canadian Journal of Forest Research, 2014, 44(9): 1042-1050

Tolerant hardwood natural regeneration 15 years after various silvicultural treatments on an industrial freehold of northwestern New Brunswick
Martin Béland and Bruno Chicoine, 2013. The Forestry Chronicle, 2013, 89(4): 512-524

The Speed of Invasion: Rates of Spread for Thirteen Exotic Forest Insects and Diseases
Alexander M. Evans Forests 2016, 7(5), 99