Conifer Alternatives for Eastern Hemlock

White spruce ready for planting

With the prevalence of hemlock wooly adelgid and the hemlock mortality it is causing across the state the question often comes up concerning what, if anything, to plant in it's place. Most often if nothing is done we see hemlock stands being replaced by black birch. The Allegheny National Forest (Warren, Forest, Elk and McKean counties in NW Pennsylvania) has completed some small supplemental plantings under hemlock to enhance the conifer component in anticipation of hemlock mortality. In addition, PSU Forestry Extension just completed a stream corridor planting, where all the hemlock was lost, looking at white and red spruce as possible replacements.

The information below compares different coniferous species as a general guide for supplemental plantings. A special thank you goes out to Andrea Hille, Forest Silviculturist, on the Allegheny National Forest (ANF), for compiling and sharing this information. One species I have heard mentioned as a supplement to hemlock is Norway spruce. This species is not included in the list below because it is not native to the United States although it has been planted extensively.

Plant bare-root seedlings once frost leaves the ground and prior to bud break, when seedlings are dormant. In Pennsylvania this is generally between early March and early May. It is essential to plant bare root seedlings before buds begin to swell and new growth starts to emerge. There is more flexibility when planting potted or balled and burlapped trees which can be planted later into the growing season. Planting early in the spring helps ensure seedling root system establishment before the hotter drier summer months. Trees planted after mid-May might not survive summer’s intense heat and water stress. Planting in the fall may expose trees to severe winds and cold temperatures which can desiccate seedlings as well as frost heaving when the ground freezes and thaws.

For additional information on tree planting check out the Penn State Extension publication entitled: Forest Landowner Guide to Tree Planting Success. This guide is a great resource to help you get started planning your tree planting project for next year.

Species Considerations for Conifer Plantings:
Potential Alternatives to Eastern Hemlock

Red Spruce (Picea rubens)
Red spruce lacks the lower limb structure and the thermal characteristics of hemlock. It is the best replacement species for northern flying squirrel, as it supports lichens (bryoria fremontii) required by northern flying squirrel for food and nesting material. Its native range is north of PA and at higher elevations in the northern Appalachian mountains. Specimens found in McKean County occur at higher elevations and in locations with good moisture. Red spruce grows well on poor sites with acidic and shallow soils preferred. It is shade tolerant to very tolerant. Red spruce is long-lived (350-400 years) and slow growing. Browsing by deer does occur, but it is not a preferred browse. Its biggest pests are spruce budworm, eastern spruce beetle, and eastern dwarf mistletoe. It is potentially sensitive to pollution (sulphur dioxide, nitrogen oxides and ozone).

White Spruce (Picea glauca)
White spruce retains its lower limbs. It is primarily found north of PA with specimens in a few counties south of the ANF. White spruce was planted on the ANF in the past. It is tolerant of a wide range of sites in northern North America, from moist to dry, alkaline and acidic. It is intermediate in shade tolerance and long lived (250-300 years). White spruce is not preferred as browse. White spruce can be susceptible to frost heaving. Its seedlings can be damaged by rodents. Its biggest pests are spruce budworm, European spruce needleminer, Tomentosus root disease, and various bark and wood boring beetles. It is considered a hardy tree and has a strong affinity to local environments. 

Black Spruce (Picea mariana)
Black spruce is a smaller tree, with a small diameter at maturity. It retains its lower limbs and is shallow rooted. It is primarily found north of PA with specimens occurring in Tioga County. Moisture is important to black spruce and it prefers dark brown peat, boggy areas, and wet organic soils. It is a common inhabitat of swamps or bogs. Black spruce is a pioneer species, though shade tolerant. A 200 year lifespan is typical. It is not preferred as browse. Its primary pests are eastern dwarf mistletoe, spruce budworm, bud and needle rusts.

Balsam Fir (Abies balsamea)
Balsam fir retains its lower limbs and has a fairly small crown area. It provides food and cover for wildlife and is the second best species on this list for northern flying squirrel. Generally found north of PA and at higher elevations in the Appalachian mountains, specimens do occur in the area. Balsam fir requires abundant moisture and prefers slightly acidic sites. It is very shade tolerant and slow growing with a typical lifespan of 80 years. Browsing by deer does occur, but it is not a preferred browse. Its primary pest is balsam wooly adelgid; it has an intermediate sensitivity to sulphur dioxide and is tolerant of ozone.

Pitch Pine (Pinus rigida)
Pitch pine lacks the lower limb structure and thermal characteristics of hemlock. It is usually found on dry, low quality sites with poor sandy soils. Pitch pine requires a mineral soil seedbed for regeneration. It is a pioneer species and is shade intolerant. A typical lifespan is 200 years. Browsing by deer is limited to seedlings and sprouts. Its primary pests are Sirex wood wasp and various wood boring bark beetles. Pitch pine is very good at surviving injury, and has the ability to “green up” after fire or pests.

Virginia Pine (Pinus virginiana)
Virginia pine also lacks the lower limb structure and thermal characteristics of hemlock. It requires well drained sites and prefers poor sandy soils. A mineral soil seedbed is essential for its regeneration. Virginia pine is shade intolerant with a typical lifespan of 100 years. It is not preferred as browse. Its primary pests are Sirex wood wasp and various wood boring bark beetles. Virginia pine is sensitive to air pollution (ozone) and sometimes suffers from meadow mouse girdling. It grows well in old fields as a pioneer species and can successful outcompete other species.

Eastern Redcedar (Juniperus virginiana)
Eastern redcedar has a general bush-like appearance though it may lose its lower limbs in forest grown areas. It is widely distributed through the eastern and midwestern U.S. Eastern redcedar can grow on a wide variety of conditions, but it prefers deep, moist, well drained sites and calacareous soils. It is shade intolerant to very intolerant and has a typical lifespan of 150 years. It is a pioneer species and can tolerate drought and temperature extremes. It is of intermediate preference for deer browse. Its primary pest is cedar gall and it is tolerant of air pollution (sulphur dioxide and hydrogen fluoride). 

Red Pine (Pinus resinosa)
Red pine lacks the lower limb structure and thermal characteristics of hemlock. It prefers dry sites but will grow on wetter sites. Red pine is shade intolerant to very-intolerant and has a typical lifespan of 200 years. It is not preferred by deer. Its primary pests are Sirex wood wasp and various wood boring bark beetles. It is sensitive to sulphur dioxide but tolerant of ozone.

Northern white-cedar (Thuja occidentalis)
Northern white-cedar has a general bush-like appearance, but it may lose its lower limbs in forest grown areas. It provides an abundance of food and cover for wildlife, especially in winter. It prefers moist, nutrient rich sites, such as those along streams and it prefers calacareous soils. Northern white-cedar is shade tolerant, slow-growing, and persistent. A 300 year lifespan is typical. It is a preferred browse for deer. Its primary pests are carpenter ants and leafminers. It is tolerant of sulphur dioxide and ozone and can withstand suppression for long time periods.

Eastern White Pine (Pinus strobus)
Eastern white pine lacks the lower limb structure and thermal characteristics of hemlock. It prefers well drained, drier sites, with coarse textured soils. White pine is intermediate in shade tolerance. A 200 year lifespan is typical, but it can be long-lived (450 years). It is preferred browse for deer and does not tolerate browsing well. Its primary pests are white pine weevil, Sirex wood wasp, white pine blister rust and it is sensitive to ozone and sulphur dioxide. White pine grows rapidly and is considered an excellent tree for reforestation projects.

Shortleaf pine (Pinus echinata)
Shortleaf pine lacks the lower limb structure and thermal characteristics of hemlock. It is native to the ridge and valley region of southeastern PA and south. It occurs on a wide range of sites from dry sites to deep well-drained soils. It is shade intolerant with a typical lifespan of 200 years. Browsing by deer is limited to seedlings and sprouts. Its primary pests are Sirex wood wasp and various wood boring bark beetles, and it has intermediate sensitivity to air pollution. It is a pioneer species and competes better on dry sites.