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Where does it hurt?

A yearly "physical" is fast becoming a reality for our nation's forests. Because a variety of assaults, including the specter of acid rain, may be working synergistically to spell trouble for our trees, a sweeping federal-state campaign called the National Forest Health Monitoring Program has recently gotten underway to assess the health of America's forests.

Although monitoring is not expected to lead to an immediate bill of health (clean or otherwise), the program does promise a comprehensive national--even global--framework for addressing critical questions about forest health.

In the development of this new program, human health care has been a useful model. Joseph Barnard, the program's national manager, explains: "We went into the public health sector and sought out human epidemiological approaches to help develop the thought process."

But taking a health reading on a forest is not straightforwardly analogous to something like taking a human patient's temperature. With humans, the reading is compared to a well-established average of 98.6 degrees; with forests, no highly corroborated knowledge base exists to which we can compare the resource's current state in order to make a diagnosis of broad problems. For now, research must be concerned principally with building the data base for future comparisons.

The National Forest Health Monitoring Program is the latest and possibly most ambitious national effort in forest-health assessment. It began as a regional effort--the New England Forest Health Monitoring Program--in the summer of 1990 with the establishment of sampling plits for data collection. Monitoring will continue through the '90s and beyond.

If New England's forests are in the health-care equivalent of the examination room, those in other parts of the country are in the waiting room. Six additional states (Delaware, Maryland, New Jersey, Virginia, Georgia, and Alabama) were included in the monitoring program this year, and plans call for adding new states by regional groupings each year until the contiguous 48 states are all on line. The timeframe for inclusion of Alaska, Hawaii, and Puerto Rico is subject to funding. Pilot projects have been established this year in California and Colorado (10 projects in each state) to test monitoring methods in the West.

The program functions through a multiagency nexus composed of the U.S. Forest Service, U.S. Environmental Protection Agency, and the six New England states (Connecticut, Massachusetts, Maine, New Hampshire, Rhode Island, and Vermont).

The Forest Response Program (FRP), which began in 1985 under the auspices of the National Acid Precipitation Assessment Program (NAPAP), was a precursor to this new monitoring effort. The FRP has in effect been superseded by the comprehensive new monitoring program, but the legacy of previous efforts like the National Vegetation Survey, a component of the FRP, is anything but lost. In fact, these undertakings helped set the groundwork for the new program.

In a broader sense, Barnard says, forest-health monitoring falls under the umbrella of global change. Two main facets of the FRP--epidemiological concerns on the one hand and detailed studies of forest-response mechanisms to problems like global warming on the other--are being coordinated with the health-monitoring effort, as is the Forest Service's Global Change Research Program.

The new forest-health monitoring program is three-tiered in design, according to Margaret Miller-Weeks of the agency's Forest Pest Management division (recently renamed "Forests Heath Protection"). Miller-Weeks is the Forest Service's forest-health-monitoring coordinator for New England and New York. She explains that the program's first tier is direct "detection monitoring" of the plot network and seeks to answer the what, where, and when of forest health.

"Evaluation monitoring" and "ecosystem monitoring" complete the series. Evaluation addresses the "how," endeavoring to track the nature and cause or causes of anomalies that may have turned up in the detection phase; it also keeps one eye directed at remediation. Ecosystem monitoring, the "why," examines cause-and-effect relationships in depth.

In practice the three tiers work as an integrated whole, says Miller-Weeks, along with a fourth component--research on monitoring techniques--that serves as a basis for fine-tuning the other three.

The monitoring program in New England is really just beginning, but a report on the first year's results was released last summer. The report concluded that there is no major pattern of unexplained helath decline in New England for any tree species. But some ongoing problems remain, including sugar-maple decline, high-elevation spruce forest decline in northern New England, and stressed-out oaks in the southern part of the region.

Much of southern ANew England's forestland is within the central hardwood forest type. As the name suggests, hardwoods--predominantly several species of oak--occupy many of the area's ridges, with a transition on the slopes through a fairly diverse mix of species and, in the lowlands, to red-maple swamps. Although this general pattern is an oversimplification to be sure, it is repeated throughout the region.

Another pattern is unmistakable on the ridges, one of past cycles of gypsy-moth population booms. The evidence--dead oaks--is a familiar sight. Mature oaks, conspicuously gaunt amid the otherwise healthy-looking woodland, stand as troublesome reminders to those concerned about the health of our forests.

The oaks' decline is not as much of an enigma as other declines, since the main offender, the gypsy-moth caterpillar, is so conspicuous and suggests a straightforward cause and effect--caterpillars killing trees. But in matters such as forest health, even events that appear unambiguous often warrant a closer look.

Natural senescence is, of course, a factor in tree mortality, especially in trees that are overmature for the prevailing site conditions. Pete Merrill, lead forester with the division of forestry in Connecticut's Department of Environmental Protection and one of the cooperators in the monitoring effort, compares the situation to its human-health counterpart: "When you've got a population that averages 60 years old, you can expect to see more heart disease than in a population that's averaging 30. And the same thing is happening on this forest." Nonetheless, Merrill concedes that this decline is part of a complex involving several factors.

To develop a working explanation for the probable cause of mortality in a given tree, it is necessary to examine known or suspected factors such as soil conditions. In southern New England many oaks grow on soils developed from glacially deposited sand and gravel, or no shallow glacial-till soils with bedrock a few inches below the surface. Such conditions predispose trees to the ill effects of periodic drought. An otherwise healthy tree that is partly defoliated by caterpillars stands a good chance of recovery. However, with a diminished water supply, attrition begins to show, particularly if the pattern repeats itself the next year.

Unfortunately, the list of stresses doesn't stop here. Another insect among the cast of oak enemies is the two-lined chestnut borer, a beetle that benefits from the same set of misfortunes for the tree. The beetle larvae tunnel beneath the bark, their galleries eventually girdling and killing branches. An unstressed tree is not normally susceptible to attack from this insect, so an infestation is really symptomatic of the broader process.

All the sets the stage for the finishing stroke. It may come as no surprise that the final player in the oak's demise is often a fungus, in this case Armillariella mellea, the cause of Armillaria root rot. Its omnipresence in the forest as mycelium, fruiting bodies, or spores ensures an eventual host. They gypsymoth caterpillar, drought, and the two-lined chestnut borer work--unwittingly, of course--to provide an opportunity for the virulent potential of this fungus.

Robert Brooks, research wildlife biologist with the Northeastern Forest Experiment Station, coordinates the work plan for New England monitoring. Brooks says this kind of decline "frequently is a complex of many stressors and many responses. It's not a simple thing that you can just go out and identify, and if you had to prioritize, probably the gypsy moth is one of the most important attributes. That's one of the things we're trying to capture in this survey."

So what killed the oak tree? The fungus may have finally dispatched it, but clearly, defoliation by the caterpillar opened the way for other agents that otherwise probably would not have posed a serious threat. Any conclusions contain elements of uncertainty, however, since there may be other important factors. Does stress from atmospheric pollution, for example, need to be factored into the lethal lineup?

One effective way to minimize uncertainties is to have copious, reliable data of the right sort. It is axiomatic that decades of prior data would be just what the collective forest doctor would order for our mix of forest maladies.

Indeed the U.S. Forest Service would seem to have such data from its periodic Forest Survey, the most recent for New England from the early 1980s. Unfortunately, this information is not generally considered suitable for health-monitoring applications because it has been collected according to more traditional measurements that look at items like timber yield.

The plot design of the National Forest Health Monitoring program is part of a global grid developed by EPA through its Environmental Monitoring and Atmospheric Program (EMAP), which divides the globe's surface into polygons like a gargantuan soccer ball. The grid for the continental United States contains sample locations of 40-square-kilometer hexagons.

Brooks notes, "Across the continetal United States and near coastal waters (including the continental shelf), there are something like 12,500 of these hexagons. We asked EPA to provide us the center point for those hexagons that occur in New England." New England has 206 forested sample locations.

Using the EPA information coupled with aerial photograph points already established by the Forest Service for its Forest Survey, plot locations are installed on the ground. This allows the monitoring program to be tied to the Forest Survey information.

The design also can be integrated into a Geographic Information System (GIS) to further enhance analysis. Overlays depicting various data sets can be analyzed on computer displays for patterns that might show important correlations. A map showing locations where ailing trees have been documented, for example, might overlay another depicting elevated ozone levels.

Before high-quality monitoring data can show up on the screen, though, a lot of work must be done in the field. Field crews use survey techniques to establish plots. Each plot on the ground consists of four quarter-acre circular subplots--three at equally spaced points around a central one--forming a cluster that is collectively considered one plot.

Annually, during a time window of approximately 10 weeks, the crews conduct detailed sampling on each plot cluster. They use electronic data recorders so the data can be uploaded later to PCs. Subplots within the main quarter-acre circles are designed to host different sets of activities. For example, on the fourt largest subplots, workers document types of forest cover. Inside smaller 24-foot-radius nested subplots, they record data on individual tree condition; items here include three species and diameter at breast height (dbh), as well as distance and azimuth from the plot center. Trees are also assigned a condition class denoting the degree of dieback present in their crowns.

Crews examine certain plant indicator species--including trembling aspen, poison ivy, and bracken fern--for foliar lesions and necrotic tissues that represent damage caused by sulfur dioxide and ozone. On the smallest nested subplots--so-called microplots--information on three reproduction is observed and recorded. Data are collected annually on some parameters, while others require less frequent documentation.

Besides direct vegetational observations, soil profiles are documented, and soil is analyzed for pH and cation-exchange characteristics. Cations, as important as they may be esoteric, include the electrically charged forms of potassium, calcium, magnesium, iron and a host of other plant nutrients. They play a vital role in tree physiology. An upset in the "normal" dispositions of these cations--which can be brought about by acid deposition--may have insidious effects on tree physiology.

Joe Barnard points to some important monitoring components that, even this early in the program, offer a sense of how things look. The condition of the crowns, for example, is a good early indicator of the overall health and vigor of forest stands as well as individual trees. One important parameter is "crown transparency"--how thin or dense the crown of a given tree is--measured by two observers from ground points beneath the tree. Foliar discoloration also is assessed, and on conifers observers determine needle retention time by counting annual nodes back from twig tips, noting the age at the point where needles become sparse.

Based on initial impressions, Barnard says, "Things look to be in pretty good shape. We didn't identify any major problems." He particularly notes that nothing "unexpected" was found, and adds, "A species that's been of significant interest internationally in New England and Canada--sugar maple-seemed to look pretty good on the stands that we measured." This finding was consistent, he said, with studies done in the Forest Response Program. Sugar-maple decline continues to be a problem, but one that is apparently linked to stresses such as soil compaction peculiar to sugarbush operations.

One problem did turn up in an unspecified number of American beech trees, adds Brooks. Beech complex, also called beech bark disease, causes lesions on the bark that can girdle branches. The beech trees seen in the sample were recorded as exhibiting dieback and thin crowns. A confirmation of whether the cause is, in fact, beech complex awaits further scrutiny.

In important ways, of course, the monitoring program is not all new. It is actually a synthesis of a diverse set of previously valuable but not necessarily integrated activities, and it adds new components. The result will undoubtedly be significant advances in our knowledge and understanding of forest ecosystems, their intrinsic dynamics and relationships to stresses imposed by modern society.

An almost pensive Joe Barnard says of the Forest Response Program's National Vegetation Survey, of which he was the program manager, "The sun set on those programs. . . ." But with the dawn of an aspiring new campaign, one planned to span 50 or 100 years, eyes are on the future. Fruits of the National Forest Health Monitoring Program, besides being of increasing value to us in the short term for intelligent policy-making, will become part of an informational legacy to the next generation. Future forest scientists will have something those of today can only long for--comprehensive historical data on forest health.

Through this program, we may hope to gain answers where there are now only questions.

Glenn Miller is a freelance writer in Plainfield, Conneticut.
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Title Annotation:National Forest Health Monitoring Program
Author:Miller, D. Glenn
Publication:American Forests
Date:Nov 1, 1991
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