The Eastern hemlock is the Pennsylvania state tree and plays a vital role in the health of cold-water streams with native brook trout populations, but like many trees throughout the state, it is under siege.

Sara Johnson, Forest Health Program Specialist, DCNR Bureau of Forestry, spoke to the devastation of wooded landscapes during the October meeting of Susquehanna Trout Unlimited.

Eastern hemlocks are very vulnerable to invasive species.

The trees, marked by their massive trunks and lush evergreen foliage, provide canopy for streams, introducing cooler water temperatures necessary for sustaining trout populations, according to Johnson.

Unfortunately, invasive species such as the Hemlock Woolly Adelgid and the Elongate Hemlock Scale are harming woodlands.

“Nothing can replace the function of a Hemlock except another Hemlock,” she said.

She pointed to the heavy decline of Eastern hemlocks throughout much of the state including in Bald Eagle State Forest in recent years.

Hemlock Woolly Adelig are tiny insects that arrived in the U.S. from Asia more than 50 years ago. They feed on healthy hemlocks sucking nutrient-rich fluids from needles and causing infested trees to die.

“When a tree is healthy, they overwhelm its defense,” Johnson said.

She noted that the Elongate Hemlock Scale has also taken its toll on forest lands.

They infest many different types of trees, but the hemlock is a preferred host, she said.

Fortunately, the Elongated Hemlock Scale has not shown to be in heavy populations in Lycoming County.

DCNR developed plans to counteract the Hemlock Woolly Adelgid through chemical and biological suppression approaches.

Insecticides such as Imidactoprid and Dinotefuran have been effective in somewhat controlling their populations.

The release of predatory beetles in forests populated by Elongated Hemlock Scale has also been employed.

Other trees experiencing negative impacts include the White Pine.

Spongy moths have been devastating to White Pine, although spraying efforts have helped stave off some of the damage.

Beech Leaf Disease caused by a microscopic nematode or roundworm invades the leaves of beech trees.

Johnson noted the infestation of Beech Leaf Disease was spread throughout the state by 2023.

Other threats to forest lands and their cold-water streams are invasive plant species such as Japanese Knotwood, Japanese Stiltgrass, and Purple Loosestrife.

A solid corridor of such invasive species, Johnson noted, negatively impact water chemistry and water flows, as well as streambank stabilization, and regeneration of tree populations.

Efforts to help restore the health of streams include the introduction of large woody debris in waterways including Kettle Creek in Potter County, a noted trout fishery.

Fallen trees and logs within the stream channel slow the flow of water, directing it over and around logs, reducing the water velocity and any erosion or sediment that might otherwise occur.

Large woody debris creates a more diverse aquatic habitat, including the cover and hiding places for fish and other aquatic life.

“It’s been shown to be a successful program,” Johnson said.

She noted that climate change and weather conditions also impact the sustainability of forests.