8 Brazee and Marra: Nondestructive Detection of Internal Decay in American Elms (Ulmus americana) two other studies are comparable, however both uti- lized resistance drilling to detect decay. Luley et al. (2009) examined three species of maple across four cities in New York and found the frequency of decay at 53% for silver maple (Acer saccharinum), 62% for Norway maple (A. platanoides), and 63% for sugar maple (A. saccharum). Meanwhile, Koeser et al. (2016) determined decay incidence at 67% for laurel oak (Quercus hemisphaerica) and 29% for live oak (Q. virginiana) in Tampa, Florida. Aside from live oak, the incidence of decay for the other four tree spe- cies was 1.8 to 2.1 times higher compared to Ameri- can elm. A noteworthy difference between the two previous studies and this study is the size of the sam- pled trees, as the mean dbh of American elms sam- pled here was 105 cm. While Luley et al. (2009) do not provide mean dbh values, 69% of silver, 83% of Norway, and 81% of sugar maples had a dbh < 76.2 cm. For Koeser et al. (2016), mean dbh values for laurel oak (59 cm) and live oak (61 cm) were also substantially lower than the elms sampled here. The low incidence of decay is not altogether sur- prising, given that resistance to decay is a common characteristic of long-lived tree species, such as American elm (Bey 1990). Further, American elms do not experience any major root and butt rot diseases in natural and managed settings (Wargo and Houston 1981). Our findings support the commonly held view among arborists that American elm is a decay-resistant tree species, a desirable quality for urban and subur- ban environments. The decay resistance exhibited by American elms is most likely explained by the pres- ence of wetwood bacteria in the lower trunk. Of the four possible internal conditions determined by SoT and ERT, as outlined in the methods, nearly 50% of American elms exhibited maximum wood density and the presence of moisture in the heartwood (Cate- gory B). While relatively higher moisture in the heart- wood can indicate incipient decay or the presence of electrolytes, wetwood bacteria are known to be very common in American elm (Sinclair and Lyon 2005). Moreover, American elm sapwood colonized by wet- wood bacteria has been shown to possess higher decay resistance compared to uncolonized wood (Coleman et al. 1985). This is due to the anaerobic to hypoxic conditions created by wetwood bacteria in colonized wood tissues, preventing establishment by wood- decaying fungi (Sinclair and Lyon 2005). A final goal of this study was to support ongoing management efforts that seek to preserve American elms threatened by DED in urban and suburban set- tings. As surviving American elms continue to age in the landscape, their economic value and cultural sig- nificance will also continue to increase. Managing arborists should be particularly concerned about internal decay and the resulting risk of stem failure in large-diameter trees. Based on the results here, the poten- tial for injection-site wound colonization by wood- decaying fungi does not appear to outweigh the benefits of fungicide injection to prevent and manage DED. CONCLUSIONS The incidence of internal decay in American elms, determined nondestructively using SoT and ERT, was 63/210 (30%) with a mean percent decay of 39%. The proportion of American elms with decay under regular injection (28/91; 31%) was nearly iden- tical to non-injected elms (35/119; 29%). Mean per- cent decay was positively correlated to DSH and dbh, but diameter alone is not a reliable predictor of decay incidence and severity. Nearly half of all sampled American elms (104/210) exhibited maximum wood density and the presence of moisture in the heartwood, likely due to colonization by wetwood bacteria. The results show that American elms undergoing regular fungicide injection do not experience a higher fre- quency of internal decay compared to non-injected elms. LITERATURE CITED Andersen, J.J., R.J. Campana, A.L. Shigo, and W.C. Shortle. 1985. Wound response of Ulmus americana I: Results of chemical injection in attempts to control Dutch elm disease. Journal of Arboriculture 11(5): 137-142. Andrews, M.W., R.A. Blachette, and D.W. French. 1982. Effects of benzimidazole compounds for Dutch elm disease control on wood surrounding elm injection sites. Plant Disease 66: 495-498. Arciniegas, A., F. Prieto, L. Brancheriau, and P. Lasaygues. 2014. Literature review of acoustic and ultrasonic tomography in standing trees. Trees 28: 1559-1567. Benson, A.R., A.K. Koeser, and J. Morgenroth. 2019. Estimating conductive sapwood area in diffuse and ring porous trees with electronic resistance tomography. Tree Physiology 39(3): 484-494. Bey, C.F. 1990. American elm. In: R.M. Burns and B.H. Honkala (Eds.). Silvics of North America Volume 2: Hardwoods. USDA Agricultural Handbook 654. United States Department of Agriculture, Washington D.C., USA. ©2020 International Society of Arboriculture
January 2020
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
