The Effect of Arboreal Diseases on Hemlocks and Oaks in Southeastern Pennsylvania

1. The Effect of Arboreal Diseases on Hemlocks and Oaks in Southeastern Pennsylvania Aria Kovalovich Academy of Notre Dame

2. Over the last century, regions of the United States’ deciduous and coniferous forests have been wiped out by pests and introduced diseasesWhat is the prevalence of two common tree diseases, Oak Wilt and the Woolly Adelgid, in Southeastern Pennsylvania? Problem

3. Background Information – Oak Wilt • Oak Wilt is a fungus that kills deciduous Red and White Oaks. • Its spores are carried to freshly wounded or cut trees by beetles or the root grafts of another infected tree. • Once it has invaded, the Oak Wilt fungus blocks the tree’s conducting (water) system and causes the leaves to brown inwards from the sides.

4. Background Information – Hemlock Woolly Adelgid • The Hemlock Woolly Adelgid is a soft-bodied, microscopic insect that was introduced from Japan and infests coniferous Eastern Hemlock Trees, which have no resistance to it. • The insects lay their eggs on the tree’s branches, and the newly hatched nymphs migrate to the young branches and settle at the base of the needles. • They feed on the stored starches that are critical to the tree’s growth and long-term survival by inserting their feeding stylets into the base of the needles, which turn grey and fall off. • The insects travel slowly up the tree, until the whole tree is infested.

5. This map shows that Oak Wilt originated in the northern central states and has since been spreading eastward. (1996) http://www.nrs.fs.fed.us/disturbance/invasive_species/hwa/risk_detection_spread/

6. This map shows that the Woolly Adelgid originated in the eastern states and has since been spreading westward. (2010) http://www.nrs.fs.fed.us/disturbance/invasive_species/hwa/risk_detection_spread/

7. Hypothesis If oaks are surveyed within forests in eastern, central, and western parts of Chester County, Pennsylvania, then there will be a greater percentage of infected trees in the western forest than in the eastern forest. If Eastern Hemlocks are surveyed within forests in eastern, central, and western parts in Chester County, Pennsylvania, then there will be a greater percentage of infested trees in the eastern forest than in the western forest.

8. Materials • Science Notebook • Camera • Pencil • Car with Driver • Calculator

9. Procedure • Drive to each park or forest. • Observe each tree, identifying whether the tree is an Eastern Hemlock or a Red or White Oak. • If it is one of the subject trees, look for signs of disease or infestation, such as peeling bark or dying branches. • If it is one of the subject trees, mark down which species 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 for each part of Chester County.

10. This graph shows the number of healthy and diseased Eastern Hemlock trees surveyed within sixty acres of three different forests arranged from west to east in Chester County. Notice that the Eastern Hemlock is a rare species of tree within the surveyed forests across Chester County, and that the Woolly Adelgid infestation is present within Chester County. This suggests either that the climate of Chester County is not conducive to the abundant growth of Eastern Hemlock or that the population of the Eastern Hemlock has been essentially destroyed, in part by the Woolly Adelgid.

11. This graph shows the number of healthy and diseased oak trees surveyed within sixty acres of three different forests arranged from west to east in Chester County. Notice that Oak Wilt is prevalent in both the Eastern and Western forests, but has not infected the Central Forest. This suggests that Oak Wilt has not infected Chester County forests in a west to east pattern, thus indicating that the factors causing the spread of Oak Wilt are more complex than simple directional movement.

12. Possible Errors • Misidentification of a tree as diseased or healthy • 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 identification process because oaks are deciduous, meaning their leaves die and fall off in autumn.

13. Conclusion • Both Oak Blight and the Woolly Adelgid do occur in Chester County, but there is no directional trend in the percentage of diseased trees. • In order to decrease the spread of Oak Blight, it may be important to encourage people not to prune their trees in the spring or summer when the beetles that carry the fungus are most active. • To avoid spreading disease, people should distribute trees widely apart when planting them. • Trees become a hazard when they become diseased due to the risk of dead limbs falling. It is important for local government and property owners to maintain healthy trees to prevent serious injury to people and property.

14. Further Questions & Study • What is the prevalence of the Woolly Adelgid in counties where there is a larger population of Eastern Hemlock trees? • Are there natural predators of the Woolly Adelgid that are safe to introduce into infested areas to preserve the Eastern Hemlock population? • An incidence study of oaks and hemlocks could be done • More diverse variables as to the effect on the spread of disease should be studied.

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