Allegheny Defense Project ...working for the protection of the natural heritage of the Alleghenies...

Black Cherry Tree Farms
Threaten Healthy Forests

Research Indicates that increased amounts of black cherry lead to forest health problems

Forest Conversion - Losing Native Forests

Over the last 150 years - a blink of the eye on a geologic time scale - Allegheny Plateau forests have undergone a dramatic transformation at the hands of turn-of-the-century timber barons and the modern day US Forest Service.

The beautiful Eastern Hemlock-Northern Hardwoods forests of the Allegheny Plateau once towered over early settlers in northern Pennsylvania. At that time, black cherry (Prunus serotina) was hardly a speck on the map, making up less than 1% of the original forest canopy.

President Calvin Coolidge established the Allegheny National Forest in 1923 for watershed protection. However, the forest’s first Supervisor defied this direction and declared management for the commercially valuable black cherry a priority.

As logging escalated in the 1960s, so did management for black cherry. The Forest Service’s Northeast Research Station in Irvine developed methods to create nearly pure stands of taller, straighter black cherry trees. These crop-perfected black cherry trees fetched more than $2,000 per thousand board feet - ten times more than other native northern hardwood forest trees.

By 1970, more than 20% of the Allegheny National Forest consisted of black cherry trees. The Forest Service nearly doubled timber goals in the 1986 forest management plan and by the mid 1990s more than a quarter of all canopy height trees were black cherry. At present this one species accounts for more than half of the forest’s young trees.

Clearcuts, Herbicides, and Fertilizers Create Black Cherry Tree Farms

Black Cherry tree farms do not occur naturally. The “science” of logging for black cherry is outlined in a 1990 manuscript drafted by Forest Service researcher David Marquis - a fact that a District Court in Pittsburgh found “troubling”.

The Forest Service uses a two stage clearcutting process in the Allegheny National Forest. “Shelterwood” cuts open up the canopy to produce immediate regeneration. Clearcuts remove most of a forest stand’s seed source, so if you can’t get immediate tree regeneration you don’t even get a tree farm - let alone a forest. Natural forests have centuries during which they can develop successful regeneration and are therefore guaranteed of greater success.

After the so-called “shelterwood” cut, native tree species such as American Beech and Striped Maple dominate the understory. These valuable native trees are labeled “undesirable” by the Forest Service, which uses the herbicides RoundUp and Oust to eradicate them. Black cherry seeds remain viable in forest soils for longer periods than do the seed sources for other important native species killed byt he herbicides allowing black cherry to dominate the site.

After regeneration of black cherry is deemed successful the Forest Service initiates the “Overstory removal” - the second half of what is, in reality, a delayed clearcut. In order to guarantee success for black cherry, foresters then apply nitrogen-based chemical fertilizers to accelerate growth of cherry seedlings. This has a dramatic effect, with black cherry seedlings growing several feet during a single growing season and outcompeting other native tree species. The entire clearcut area must then be fenced for deer, at considerable taxpayer expense.

During the next 80 years, a series of cutting methods including “crop tree release” and “thinning” cuts are used to remove any competition for the black cherry trees. These methods allow monocultures of black cherry trees to develop.

Pure Black Cherry Stands Create Potential Threats

Scientists have given extensive warning to the Forest Service that management practices which dramatically increase concentrations of black cherry in the Allegheny Plateau Region make the forest more susceptible to natural catastrophes:

“One may question the value, however, of increasingly converting much of the forest to nearly pure stands or monocultures of black cherry.” - Whitney, 1990.

“If vast areas of pure black cherry stands were to develop throughout this region, the potential threat from an outbreak of an insect or disease epidemic would be great.” - Tilghman 1989.

Monocultures Cause of Biodiversity Crisis

Although plant diversity problems are typically blamed on white-tailed deer researchers have documented decreased plant bio-diversity in forest stands associated with black cherry management. Research has also shown that old growth forests are more diverse than second growth forests even when both are exposed to high deer pressure:

“These pure black cherry stands are more likely to have understories dominated by plants that interfere with the establishment and growth of herbaceous and woody vegetation.” - USFS Timber Harvest Capability Report (THCR).

“Current stand regeneration treatments result in stands which are less diverse, are changing in forest type, and are composed primarily of either black cherry or black birch. The total impact of a major shift of tree species cannot easily be measured, but we know that there are related effects to wildlife habitat and wildlife species habitation.” - Forest Service Adaptive Management Program Summary.

“Forest type conversion will likely occur in the Northern hardwood stands where a black cherry component exists, and where shelterwood systems and herbicides and/or fences are used to establish advanced regeneration.” - USFS THCR

Black Cherry is also considered less valuable for wildlife habitat. Logging for black cherry contributes towards:

  • a dearth in standing dead trees important for the Indiana bat,
  • a deficiency in large downed logs important to small mammals;
  • overpopulations of Hayscented and New York ferns which have been associated with amphibian population declines in forest stands; and
  • overpopulations of white-tailed deer which contribute towards plant biodiversity problems.

Research on the Northern Goshawk found that this large, fierce bird sought out Amiercan Beech trees and avoided using black cherry trees for its nests despite the dominance of black cherry across the studied landscape. Forest Service field biologists have found that black cherry monocultures with their thin canopies are often devoid of the diverse vegetation that makes a forest healthy. The native Northern Hardwood forests are considered more valuable habitat.

More Black Cherry Means Insect Infestations

Current research is now indicating that increased amounts of black cherry lead to “statistically significant increases” in defoliations from cherry scallopshell moth and elm spanworm.

A decade of research in the Allegheny has shown that the amount of black cherry that is in the forest today is having negative impacts on forest health. The graph to the left shows that the higher proportion of black cherry the more defoliations occur.

Interestingly, an overlay of maps showing black cherry density in the Allegheny National Forest with the area affected by forest health problems shows a direct correlation. The maps below show black cherry densities on the left with crown dieback on the right. The relationship is obvious with the only outliers on the right being dieback on oak types.

Black Cherry More Susceptible to Windthrow

Windthrow is part of the natural disturbance regime within the Allegheny National Forest. However, given the Forest Service’s emphasis on windthrow as an alleged forest health problem it is significant to note that black cherry is the tree species in the Allegheny that is most susceptible to windthrow due to its shallow root systems. Field work also suggests that logged areas are more susceptible to windthrow than uncut areas.

Black Cherry Health Threatened by Ozone

Research documents that black cherry is highly susceptible to ground level ozone, the main component in smog. This research has found that when exposed to ground level ozone black cherry suffers from canopy deterioration and growth stunting. This, in combination with deer overbrowsing and cation loss as a result of logging and acid rain, has helped promote an understory of hayscented and New York ferns. Thus, one monoculture helps promote another, with severe consequences for many native plants and wildlife.

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