The Effect of Arboreal Diseases on Hemlocks and Oaks in

Southeastern Pennsylvania

Aria KovalovichAcademy of Notre Dame

Over the last century, regions of the United States’ deciduous and

coniferous forests have been wiped out by pests and introduced

diseases

What is the prevalence of two common tree diseases, Oak Wilt and the Woolly Adelgid, in Southeastern

Pennsylvania?

Problem

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.

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.

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/

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/

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.

Materials

Science Notebook Camera Pencil Car with Driver Calculator

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.

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Western Forest French Creek State Park

Central Forest Black Rock Sanctuary

Eastern Forest Valley Forge National

Park

Name of Forest Surveyed

The Prevalence of the Hemlock Woolly Adelgid Across Chester County

Healthy EasternHemlocks

Eastern HemlocksInfested With WoollyAdelgid

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.

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Western Forest French Creek State Park

Central Forest Black Rock Sanctuary

Eastern Forest Valley Forge National Park

Name of Forest Surveyed

The Prevalence of Oak Wilt Across Chester County

Healthy Oaks

Oaks Infected With OakWilt

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.

Diseased Hemlock branches