Hemlock Trees of Hocking Hills: The Evergreen Backbone

Walk into any gorge in Hocking Hills and you'll notice them immediately — the eastern hemlocks. While the hardwoods around them cycle through seasonal change, the hemlocks stay green year-round, their dark, dense canopies creating the cool, damp microclimate that makes the gorges feel like a different world from the ridgetops above. These trees are the ecological backbone of the Hocking Hills landscape. And they're under threat.

Why Hemlocks Matter Here

Eastern hemlocks (Tsuga canadensis) thrive in the cool, humid conditions of Hocking Hills' gorges and ravines. They're shade-tolerant evergreens that grow slowly, live for centuries, and create the dense canopy shade that keeps gorge floors cool even in summer. This microclimate supports plant and animal species that wouldn't survive in the warmer, drier conditions of the surrounding hardwood forest.

The hemlocks moderate stream temperatures (critical for aquatic species), stabilize steep slopes with their root systems, and provide year-round cover for wildlife. In fall, they play a distinctive visual role: while every other tree in the gorge is turning color or dropping leaves, the hemlocks remain deep green, creating the contrast that gives Hocking Hills its signature autumn look — fire-colored hardwoods against a dark evergreen backdrop.

The Hemlock Woolly Adelgid Threat

Hemlock woolly adelgid (HWA) is a tiny, non-native invasive insect from East Asia that feeds on the sap of eastern hemlock trees, weakening and eventually killing them. First detected in the United States in Virginia in 1951, HWA has caused the decline of millions of hemlocks across the eastern states. It was first found in Ohio in 2012 and has since been detected in 24 Ohio counties, including Hocking County.

The adelgids appear as small white, cottony masses on the underside of hemlock branch tips — they're most visible between fall and spring. An infested tree typically declines over several years as the adelgids drain nutrients and sap, eventually leading to death if untreated.

According to Tom Macy, forest health program manager for ODNR's Division of Forestry, Ohio is still in the relatively early stages of the HWA invasion. Most Ohio hemlocks remain in good health, and significant decline from the insect hasn't been widely observed yet. But without intervention, the trajectory observed in other eastern states — where HWA has devastated hemlock populations — is expected to repeat.

ODNR Treatment Efforts

ODNR's Division of Forestry is taking a two-pronged approach to fighting HWA:

Chemical treatment: Systemic insecticides (primarily imidacloprid) applied through soil injection or trunk treatment can protect individual trees for approximately five years per application. ODNR has focused survey and treatment work in the Hocking Hills area because of its ecological and tourism importance.

Biological control: ODNR has released predatory beetles that specialize in feeding on adelgids as a longer-term biological control strategy. These tiny beetles target HWA specifically and are intended to establish self-sustaining populations that keep adelgid numbers in check without ongoing chemical treatment.

In 2026, ODNR launched a first-of-its-kind cost-share program offering private landowners $700 per acre to treat hemlock forest for HWA. The program, funded by a USDA Forest Service grant, covers 1 to 25 acres per applicant.

What You'd Lose

If hemlock woolly adelgid decimated the hemlocks of Hocking Hills the way it has in parts of the southern Appalachians, the changes would be dramatic:

• Gorge temperatures would rise as the dense, year-round canopy shade disappears. The cool, humid microclimate that defines the gorge experience would fundamentally change.
• Stream temperatures would increase, stressing cold-water aquatic species.
• The visual character of the gorges would shift. The contrast between evergreen hemlocks and colorful hardwoods in fall — one of the most photographed features of the region — would be gone.
• Erosion on steep gorge slopes could increase as hemlock root systems die and lose their grip on the soil.
• Species that depend on hemlock habitat — certain warblers, amphibians, and understory plants — could decline or disappear from the region.

The stakes are real, and they're visible. Next time you're on a gorge trail, look up at the hemlocks and check the branch tips for white masses. You can report suspected HWA infestations to the ODNR Division of Forestry at 614-265-6694.