The Effect of Arboreal Diseases onHemlocks and Oaks in SoutheasternPennsylvania
Aria Kovalovich
Academy of Notre Dame
Over the last century, regions of theUnited States’ deciduous andconiferous forests have been wipedout by pests and introduced diseasesWhat is the prevalence of twocommon tree diseases, Oak Wilt andthe Woolly Adelgid, in SoutheasternPennsylvania?
Problem
Background Information – Oak Wilt
Oak Wilt is a fungus that kills deciduousRed and White Oaks.
Its spores are carried to freshlywounded or cut trees by beetles or theroot grafts of another infected tree.
Once it has invaded, the Oak Wiltfungus blocks the tree’s conducting(water) system and causes the leavesto brown inwards from the sides.
Background Information –Hemlock Woolly Adelgid
The Hemlock Woolly Adelgid is a soft-bodied,microscopic insect that was introduced from Japan andinfests coniferous Eastern Hemlock Trees, which have noresistance to it.
The insects lay their eggs on the tree’s branches, andthe newly hatched nymphs migrate to the youngbranches and settle at the base of the needles.
They feed on the stored starches that are critical to thetree’s growth and long-term survival by inserting theirfeeding stylets into the base of the needles, which turngrey and fall off.
The insects travel slowly up the tree, until the whole treeis infested.
This map shows that Oak Wilt originated in the northerncentral states and has since been spreading eastward.(1996)
http://www.nrs.fs.fed.us/disturbance/invasive_species/hwa/risk_detection_spread/
This map shows that the Woolly Adelgid originated in theeastern states and has since been spreading westward.(2010)
http://www.nrs.fs.fed.us/disturbance/invasive_species/hwa/risk_detection_spread/
Hypothesis
If oaks are surveyed within forests in eastern,central, and western parts of Chester County,Pennsylvania, then there will be a greaterpercentage of infected trees in the westernforest than in the eastern forest.
If Eastern Hemlocks are surveyed within forests ineastern, central, and western parts in ChesterCounty, Pennsylvania, then there will be agreater percentage of infested trees in theeastern forest than in the western forest.
Materials
Science Notebook
Camera
Pencil
Car with Driver
Calculator
Procedure
Drive to each park or forest.
Observe each tree, identifying whether the treeis an Eastern Hemlock or a Red or White Oak.
If it is one of the subject trees, look for signs ofdisease or infestation, such as peeling bark ordying branches.
If it is one of the subject trees, mark down whichspecies it is, and whether or not it is infected.
Repeat steps 2-4 for each tree in a 60-acre area.
Calculate the percentage of trees that are infected foreach part of Chester County.
This graph shows the number of healthy and diseased Eastern Hemlock trees surveyed within sixtyacres of three different forests arranged from west to east in Chester County. Notice that theEastern Hemlock is a rare species of tree within the surveyed forests across Chester County, andthat the Woolly Adelgid infestation is present within Chester County. This suggests either that theclimate of Chester County is not conducive to the abundant growth of Eastern Hemlock or that thepopulation of the Eastern Hemlock has been essentially destroyed, in part by the Woolly Adelgid.
This graph shows the number of healthy and diseased oak trees surveyed within sixty acres ofthree different forests arranged from west to east in Chester County. Notice that Oak Wilt isprevalent in both the Eastern and Western forests, but has not infected the Central Forest. Thissuggests that Oak Wilt has not infected Chester County forests in a west to east pattern, thusindicating that the factors causing the spread of Oak Wilt are more complex than simpledirectional movement.
Possible Errors
Misidentification of a tree as diseased orhealthy
Misidentification of a tree’s species
Not counting a tree in the data
Also, the oaks were surveyed in the fall,which could have affected the identificationprocess because oaks are deciduous,meaning their leaves die and fall off inautumn.
Conclusion
Both Oak Blight and the Woolly Adelgid do occur in ChesterCounty, but there is no directional trend in the percentage ofdiseased trees.
In order to decrease the spread of Oak Blight, it may beimportant to encourage people not to prune their trees in thespring or summer when the beetles that carry the fungus aremost active.
To avoid spreading disease, people should distribute treeswidely apart when planting them.
Trees become a hazard when they become diseased due tothe risk of dead limbs falling. It is important for localgovernment and property owners to maintain healthy treesto prevent serious injury to people and property.
Further Questions & Study
What is the prevalence of the WoollyAdelgid in counties where there is a largerpopulation of Eastern Hemlock trees?
Are there natural predators of the WoollyAdelgid that are safe to introduce intoinfested areas to preserve the EasternHemlock population?
An incidence study of oaks and hemlockscould be done
More diverse variables as to the effect onthe spread of disease should be studied.
Works Cited
Bowen, K. L., & Merrill, W. (1982, February). Oak Wilt Foci Related to Bearing and Aspect in Pennsylvania [Scientific Research Paper]. Retrieved from http://www.apsnet.org/publications/plantdisease/backissues/Documents/ 1982Articles/PlantDisease66n02_137.PDF
Billings, R. F., & Appel, D. N. (2007, June 7). The Proceedings of the 2nd National Oak Wilt Symposium [Proceedings]. Retrieved from http://www.texasoakwilt.org/NOWS/conference_assets/conferencepapers/Strakey.pdf
Department of Conservation and Natural Resources, Bureau of Forestry, & Division of Forest Pest Management. (2007). 2007 Pennsylvania Annual Pest Conditions Report [Pest Conditions Report]. Retrieved from http://pfa.cas.psu.edu/ pdfs/Natural%20Resources%20Information/Forest%20Pests/2007_DCNR_Pest_Survey.pdf
Dirr, M. A. (Ed.). (1997). Dirr's Hardy Trees and Shrubs: An Illustrated Encyclopedia. Timber Press, Inc.
Eastern Hemlock (Tsuga Canadensis). (n.d.). Retrieved October 7, 2010, from Ohio Department of Natural Resources website: http://www.dnr.state.oh.us/Home/ trees/hemlock_est/tabid/5372/Default.aspx
Egan, S. (2011). Camping at Valley Forge Historic National Park. Retrieved from Lance Armstrong Foundation; Demand Media Inc. website: http://www.livestrong.com/article/ 235905-camping-at-valley-forge-historic-national-park/
Godman, R. M., & Lancaster, K. (n.d.). Eastern Hemlock. Retrieved October 7, 2010, from http://www.na.fs.fed.us/pubs/silvics_manual/volume_1/tsuga/ canadensis.htm
Kelemen, C. R. (n.d.). Black Rock Sanctuary: A Model of Wetland Reclamation. Retrieved from Chester County Department of Parks and Recreation website: http://dsf.chesco.org/ccparks/cwp/ view.asp?a=1578&q=621974&ccparksnav=%7C34615%7C&tx=0
Lenox, A. T. (2001). Invasive Insects: Woolly Adelgid [Fact Sheet]. Retrieved from Pennsylvania State University website: http://rnrext.cas.psu.edu/PDFs/ adelgid.PDF
Lincoln, M. (2010). Plant Fact Sheet: White Oak - Quercus Alba L. [Text Document]. Retrieved from http://plants.usda.gov/factsheet/doc/fs_qual.doc
Nesom, G. (2000). Plant Guide: NORTHERN RED OAK - Quercus rubra L. Retrieved
from United States Department of Agriculture website: http://plants.usda.gov/plantguide/pdf/cs_quru.pdf
O'Brien, J. G., Mielke, M. E., Starkey, D., & Juzwik, J. (n.d.). How to Identify, Prevent, and Control Oak Wilt. Retrieved October 4, 2010,from United States Department of Agriculture website:http://www.na.fs.fed.us/ spfo/pubs/howtos/ht_oakwilt/toc.htm
Orwig, D. (2010). Eastern OLDLIST Introduction [Database]. Retrievedfrom Eastern OLDLIST: a Database of Maximum Tree Ages for NorthAmerica
Pokorny, J. (n.d.). How to Collect Field Samples and Identify the OakWilt Fungus in the Laboratory. Retrieved from USDA Forest Service,Northeastern Area State and Private Forestry website:http://www.na.fs.fed.us/spfo/pubs/ howtos/ht_oaklab/toc.htm
Roberts, Ph.D., D. L. (2004). Oak Wilt: A Threat to Red Oaks and WhiteOaks Species. Retrieved 2004, from Michigan State University Extension website: http://www.anr.msu.edu/robertsd/oakwilt/index.html
Tree Species in the Park. (n.d.). Trees of Valley Forge National HistoricPark [Brochure]. Retrieved from National Park Service website: http://www.nps.gov/vafo/planyourvisit/loader.cfm?csModule=security/ getfile&PageID=281030
United States Department of Agriculture. (2005, August). Pest Alert:Hemlock Woolly Adelgid. Retrieved fromhttp://www.na.fs.fed.us/spfo/pubs/pest_al/ hemlock/hwa05.htm
Valley Forge National Historical Park Information & History. (2007).Retrieved from Hillclimb Media website: http://www.valley.forge.national-park.com/ info.htm
What is the Hemlock Woolly Adelgid? (n.d.). Retrieved October 7, 2010,from Pennsylvania Department of Conservation and Natural Resourceswebsite: http://www.dcnr.state.pa.us/forestry/woollyadelgid/index.aspx
Willen, M. (2004). French Creek State Park Campground - Elverson PACamping. Retrieved from All Getaways website: http://www.allgetaways.com/ view_destination.asp?destinationid=HTU534-031