Erie insect infestation poised to decimate Eastern hemlocks in the region, we must act now

If you ever made friends with a tree, then you will understand why I wrote this. The Eastern hemlock became my friend when I was a child, playing on a forested slope behind the house that my dad built on Blue Mountain near Harrisburg. On the ridge behind my home was an old double-trunk hemlock tree, with exposed roots atop a massive chunk of weathered sandstone, where I set up my toy soldier armies. I later built a treehouse in that hemlock, using scraps of lumber and nails salvaged from my father's construction projects.

That tree was one of a pair of big hemlocks 100 feet apart on the ridge, with the second one standing on the adjacent parcel where my grandfather had built his house in the 1930s. The lower branches of the second tree had died and broken off up to 15 feet above the ground, but a few pieces of furring strip had been nailed to the trunk, spaced to allow a kid to scramble up to the living limbs and ascend toward the sky. I'm sure that those "rungs" had been affixed by my dad and his brother when they were kids.

Tree climbers know that hemlock branches are spaced just right to allow a person to move up toward the crown and find a perch to look down on the earth below. My usual climb would get me up to the point where I could feel the tree sway in the breeze — and I could look out to see out beyond Fishing Creek Valley to the Second Mountain. It was an awesome perspective for a 10-year-old to gaze onto a mountain wilderness miles away.

An invasive aphid arrives

Years later, after our mountain forest oaks had been ravaged by the gypsy moth invasion, I returned to my childhood home and found my beloved hemlock trees under siege by another invasive insect — an aphid named the Hemlock woolly adelgid (HWA). Eventually all the big hemlocks died on the ridge, leaving only stumps of the old giants.

I remember a feeling of dread that the invasive HWA was going to spread from central Pennsylvania to the rest of the state and Erie, where I had moved my family for a biology teaching position at then-Mercyhurst College. Luckily, winters in northwestern Pennsylvania in the 1980s and 1990s were too cold for the HWA to establish, and the Eastern hemlocks there were safe.

Eastern hemlock a 'foundation species'

Eastern hemlock was a perfect selection for Pennsylvania's state tree. Besides its beauty and historical utility for the lumber and tanning industries, ecologists consider it a foundation species — meaning it provides key support for other forest creatures. In the riparian habitats surrounding streams, hemlock trees provide shade to keep the water cool during the summer, allowing cold-water fish like brook trout to thrive (https://bit.ly/3I3sbcQ). When hemlocks drop their needles, they provide important food for stream insects. Low branches are a source of winter browse for our state mammal, the white-tailed deer, and the trees offer breeding habitat for migratory songbirds, like the Acadian flycatcher and black-throated green warbler.

The pest was first detected in Erie in 2017, and reported by the Erie Times-News  (https://bit.ly/4bTFw5p), but several mild winters in a row since then have given the tiny six-legged enemy of the hemlock a stronger foothold. Our failure to address climate change has ended the "cold protection" that Erie previously enjoyed from the HWA, which is now poised to decimate hemlocks throughout our community.

Hemlock woolly adelgid spread in Erie County

Penn State Extension's Amber Stillwell organized an educational program to alert people about the insect last fall (https://bit.ly/4bIiHBd), after an extensive infestation of the HWA was spotted in Millcreek Township's Scott Park. I recruited environmental science student Mackenzie Kiker at Mercyhurst University to map locations in Erie County where the invasive pest was attacking hemlock trees. Mackenzie graduated in December, but I continued the search over the Christmas break. Besides Scott Park, other locations with HWA-infested hemlocks include Zuck Park, Glenwood Park, Headwaters Park, Presque Isle and Erie Bluffs State Parks, Wintergreen Gorge, Asbury Woods, and Erie Cemetery.

We did not detect HWA anywhere south of I-90 or east of Harborcreek, but the pest has been found in Fairview, Girard and Springfield townships, including the eastern end of State Game Land 314 (the Roderick Preserve). Street and sidewalk tree surveys done in various parts of the city of Erie and Millcreek Township indicate infested trees on private property in residential neighborhoods. Heavily infested trees on the brink of death are noticeable close to the lake. This is logical since Lake Erie moderates fall and winter temperatures, and during mild winters when the lake doesn't freeze, the HWA thrives in trees near the lakeshore.

It doesn't help that our hemlock trees face other threats that weaken them, including diseases and other invasive insect pests including the elongate hemlock scale. The hemlock trees dying in Zuck and Glenwood parks in Erie were already infested with that before the HWA appeared. It makes me sad to see the sick hemlock trees in residential yards in Erie, and I've felt overwhelmed at the prospect of knocking on doors to let people know that one or more of their trees are possibly going to die if they don't do something about the HWA infestation. The mild winter we are currently experiencing is going to make things worse again this year.

What can you do to help?

There are options for managing the pest on infested trees, including pesticides and biological controls. Guidance for property owners on controlling the HWA is available from Penn State Extension (https://bit.ly/3wlbmaT). The cost to treat a tree is going to be less than the cost to have a dead tree removed, not counting the value of unrecoverable ecological services if hemlocks disappear from our urban forest in Erie.

My other worry is that in the future, we might lose the hemlock forests that sustain aquatic life in our Lake Erie tributaries. The HWA is already established at sites along the interstate, and it won't be long until we find it south of I-90. The red flag on HWA was raised last fall in the Allegheny National Forest, where the Forest Service is using biological controls to combat the adelgid as reported by the Warren Times Observer (https://bit.ly/49j1tJ3).

Damage done by the HWA elsewhere in Pennsylvania had prompted the Pennsylvania Department of Conservation and Natural Resources to craft a conservation plan for the Eastern hemlock, with a strategy for monitoring and managing the invasive pest (https://bit.ly/42MxEyi). The DCNR's website on the HWA indicates that the Bureau of Forestry "has been treating high value hemlocks in state parks and forests since 2004."  Those treatments have not stopped the spread of the Hemlock woolly adelgid or address the root cause of it reaching Erie — climate change. We all need to do our part to address that.

Mike Campbell, Ph.D., is a professor of biology at Mercyhurst University.

This article originally appeared on Erie Times-News: Mercyhurst professor warns of HWA hemlock decimation in Erie region