Canadian Forest Service Publications
Impact of the Invasive Beech Leaf-Mining Weevil, Orchestes fagi, on American Beech in Nova Scotia, Canada. 2020. Sweeney, J.D.; Hughes, C.; Zhang, H.; Hillier, N.K.; Morrison, A.; Johns, R. Frontiers in Forests and Global Change
Issued by: Atlantic Forestry Centre
Catalog ID: 40591
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The beech leaf-mining weevil, Orchestes fagi (L.), is native to Europe where it commonly attacks European beech. The weevil was discovered infesting American beech in Halifax and Cape Breton Island, Nova Scotia, Canada in 2012, but anecdotal reports of defoliated beech in the Halifax area as early as 2006 suggest it established 5–10 years prior to its discovery. Our objectives were to estimate the impact of O. fagi on American beech in forested sites and urban areas, as well as its economic impact on owners of residential properties with mature American beech. In 2014, we established fifteen plots in forested sites containing a total of 260 American beech at Sandy Lake, Oakfield, and Mount Uniacke (n = 5 plots per site), where weevil infestation levels were moderate, low, and nil, respectively. At the same time we recorded the degree of cankering by beech bark disease on the main stems of each tree. Plots were visited annually to record tree mortality (2014–2019) and percentage of leaves with larval mines or adult feeding (2016–2019). Between 2016 and 2019, the percentage of leaves mined by weevil larvae increased from 6 to 59% at Mount Uniacke and from 48 to 83% at Oakfield. During the same period, cumulative beech mortality increased from 35 to 48% at Mount Uniacke and from 10 to 70% at Oakfield. At Sandy Lake in 2016, 88% of the beech trees had died and there were too few living beech to collect a leaf sample in our plots so estimates of weevil damage (87% of leaves with mines) were obtained from life table plots in the same area. Tree mortality was associated with severity of cankering by beech bark disease only at Mount Uniacke, the site with the fewest years of defoliation by the leaf-mining weevil. We also surveyed residents of Halifax in 2016 and 2018 to determine the rate of beech mortality and costs of tree removal in urban residential areas in the same region (within 40 km) of the forest areas. Relative to the forested sites at Sandy lake and Oakfield, mortality rates were lower in urban areas (32% in 2016, 44% in 2018), even though signs of weevil defoliation had been apparent to residents as early as 2011–2012. Direct costs ($CAN) to property owners who hired arborists to remove dead beech trees averaged $1934 ($300–$6600) per resident in 2018. Options for mitigating the impact of O. fagi on American beech are briefly discussed.
Plain Language Summary
The beech leaf-mining weevil, Orchestes fagi, is native to Europe where it commonly mines the leaves of European beech. The weevil was discovered infesting American beech in Halifax and Cape Breton Island, Nova Scotia, Canada in 2012, and often causing heavy defoliation. Because the adult weevil spends most of the year in dormancy in nooks and crannies of bark of trees of several species, it can be spread by human transport of firewood and logs. We set up sample plots in 2014 in three Nova Scotia forests to monitor annual defoliation and tree mortality and estimate the weevil’s impact on American beech. We also surveyed residents of Halifax who had American beech on their properties to determine the weevil’s impact on in urban forests. In 2014, there were 217 live American beech in our forest fifteen plots; by 2019, only 80 beech remained alive, an overall mortality rate of 64% over five years. Tree mortality was positively correlated with the percentage of leaves mined by the weevil. Mortality rates were lower in urban areas, with 44% of beech on residential properties dead in 2018, but direct costs to property owners who hired arborists to remove dead beech trees were significant, averaging $1934 ($300–$6600) per resident in 2018. We briefly discuss potential options for mitigating the impact of the beech weevil on American beech.