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Forest Health in the United States
SOURCE: R. Neil Sampson and Lester A. DeCoster © 1998 American Forests

Forest Health Concerns

Forest Health Concerns There are many different forest types, but as noted earlier they generally differ between East and West due to the differences in climate, elevation, and geology. Some of the major types, and some of the forest health concerns generally associated with them, are listed in Table 2 below.
This is not an exhaustive listing, nor is it meant to suggest that all of any forest type is characterized by the problems listed. This is followed by some brief regional discussions. The regional boundaries are established by the Forest Service, and the basic data and maps of general forest types come from Powell et al. (1993). As will be noted, some of the more extensive forest types, such as ponderosa pine in the West and oak in the East, extend across several regions. The Great Plains region was omitted from the regional roundup, which overlooks the ponderosa pine forests in South Dakota and Nebraska, as well as the riparian hardwoods that inhabit the region.

The regional discussions are included to provide some idea as to the types of forest health issues being discussed by people who know the forests of the region. They are not exhaustive, of course, and much of the discussion in some places focuses on the indications of a forest health problem-insect and disease epidemics, extraordinarily large and hot wildfires, or problems with forest regeneration. Taken together, however, they illustrate the enormous range and complexity of America's forests.

The most general forest health problem across different forest types and regions today is the preponderance of dense forest structures and the lack of an adequate proportion of the savanna, open, and complex structures (Oliver et al. 1997). The reasons for this vary by region, forest type, historical factors, and past management and ownership patterns. Where dense forests dominate the landscape, however, managers are faced with similar challenges, such as:

  • Species diversity---in terms of plants, mammals, birds, and fish---is likely to be low, since the dense structure is the least-used of the major structure types. If other structures (such as savanna or complex) are totally absent, species that depend on them may be on the threatened or endangered species lists.
  • Plant stress is likely to be observed in the trees, particularly as they grow larger and more competitive. If this begins to kill a few trees or small patches, it may be part of a transition to an understory structure. If it sets up the stand for an insect or disease epidemic that kills most or all of the trees, or if conditions support a wildfire that kills all, succession will begin again as an open structure.
  • Where dense stands slow or stop tree growth before the trees reach a merchantable size, the response often prescribed is to thin the trees so that the remaining individuals have adequate light, moisture and nutrients for growth. But often there is little economic opportunity to do thinning, because the trees that need to be removed are the smaller, less valuable ones that do not pay for the work involved. Unless the owners are willing to invest for long-term values in these stands, they may stay in this condition until fire, wind, or pests disturb them.
  • Reproduction and survival of new plants may be largely limited to shade-tolerant species in a dense forest. Thus, as the larger, more dominant trees die for various reasons, they are replaced by the shade-tolerant species that have grown in under them. Such transitions move pine forests toward fir or hardwoods, coastal Douglas-fir toward hemlock, oak toward maple. Where these transitions reduce forest values that people feel are important, or set the forest up for new kinds of disturbances that people feel are damaging, intentional management of the trees may be the only way the transition can be halted.

Table 2. Western Forest Health Concerns
ForestType PrimaryRegion* Health Concerns
Spruce Alaska Large uniform areas of dense, mature stands with insect epidemics and major wildfire risk
Douglas-fir (coastal) PNW (west side) Concerns with retention of complex stands and excess fragmentation on low-elevation lands. Major windstorms can create large areas of dead & down trees, followed by large, hot fires. Endangered species include northern spotted owl, several species of salmon and trout.
Douglas-fir (inland) PNW (inland);
Invades ponderosa pine and western white pine sites when fires are suppressed. Dense, stressed stands encourage root rot and mistletoe, setting the stage for large, lethal crown fires.
Ponderosa pine PNW (inland);
Savanna structures severely lacking; large areas of dense and understory stands exhibit stress, particularly during droughts. Wildfires burn as lethal crown fires instead of nonlethal ground fires due to ladder fuels that carry ground fires into treetops.
Mixed conifers PNW, PSW'
Changes in fire regimes and historical high-grade logging have led to large areas of dense stands. Savanna and complex structures are lacking in many areas, and the amount and arrangement of dead fuels can lead to lethal crown fires that will foreclose their development for centuries.
Western white pine InlandWest, PSW The exotic white pine blister rust has nearly wiped out the species across its range. Resistant strains have been selected and planted, but there is worry about the narrow genetic base being used. (Blister rust also threatens sugar pine and whitebark pine in these regions.)
lodgepole pine
PNW (inland);
Fire suppression has led to larger areas of uniform, dense stands. Lack of open structures and reduced meadow area affects diversity and increases risk of landscape-level wildfires. Wildfires are no more lethal than historical, but less frequent, and much larger when they happen.
Western hardwoods PNW, PSWI
Often associated with riparian areas or lowland valleys, many of these forest types have been dramatically reduced by agricultural and urban development; strearnside forests are often in need of restoration.
Tropical forests PSW (Hawaii) Only fragments remain. Exotic species have replaced most natives, often by more aggressive growth following hurricane disturbances.
Aspen InlandWest Fire suppression has allowed conifers to invade, while heavy elk and deer browsing has limited regeneration. Aspen reproduces f rom root sprouts rather than by seed, and there are predictions that much of the region's aspen will be lost unless seasonal fire management is restored and animal populations controlled (Kay 1997).
Pihon-juniper InlandWest Fire suppression has allowed P-J to expand onto grass and brush lands, increasing soil erosion and runoff due to reduced ground cover. The aggressive root system eliminates grass, making prescribed fire difficult.
*PNW - Pacific Northwest; PSW - Pacific Southwest.


In this generally and region (often called the Inland West, to include similar forests in eastern Washington, Oregon, and California), the forests grow in the snow and rain-catching mountains. Most people live in the valleys, where they rely on mountain watersheds for municipal, agricultural, and power-generating water.
Cold winters and dry summers restrict microbial decomposition of dead wood and other vegetation, and most of the carbon recycling must be performed by fire. Suppressing historic wildfire patterns has led to a buildup of dead and dry leaves, twigs, bark flakes, and other litter that provide fast-burning fuels and volatile, dangerous conditions in many areas.

(left) Aspen needs periodic fire to remove conifer competition and encourage resprouting.

There is great interest in protecting forest watersheds for water supply, wildlife, and recreation. In their current condition, many forests face big die-offs and lethal wildfires that can damage both watersheds and human health. In large, remote areas, such treatment requires road construction, which can have negative impacts on watershed and wild-life conditions. There are few easy answers to these complex trade-off issues.

Federal ownership and projects dominate the region---70 percent of forests are federally owned. Federal dams and lakes attract intense recreation activity. Mountain recreation---primarily skiing---attracts a worldwide clientele, bringing burgeoning populations into remote mountain valleys with fairly limited human carrying capacity. High quality-of-life values, coupled with modem communications and access to regional airports, attract a fast-growing population of "lone eagles" professionals who can work anywhere their computers will function.

Low-elevation forests adapted to a historical regime of frequent, low-intensity fires are now mainly dense forest stands that support large, lethal wildfires. Where super-hot fires occur, forest recovery may be slowed or absent on the damaged soils.
There's also considerable potential for economic damage and loss of human life. Areas of rapid population growth often overlap closely with areas of high wildfire hazard. Forest health, wildfire, and population growth are entwined in a complex pattern of rapid change. Addressing forest health questions with intentional treatment has been difficult, even where public opinion supports action.

Cumbersome federal decision processes-coupled with intensely controversial political battles over wilderness, endangered species, roadless areas, timber harvest, and salvaging dead timber-tend toward gridlock. This is exacerbated by enormous distances, remote and isolated forests, and a weak forest products industry, diminished in recent years as federal timber sales dwindled.

Even if those problems were solved, there is still the challenge of disposing of the excess biomass that needs to be removed to restore fire-tolerant conditions. Much of the excess is only suited for energy production and today's biomass technology cannot economically compete with natural gas and coal.
Unless biomass energy can be made fea-sible, the region has few treatment options. After the inevitable wildfires, some land may return to forest over the coming decades. Some could also, under adverse weather, deteriorate into brush fields or desert due to soil damage. The risks are high, and the decisions difficult.

Table 3. Major forest types on unreserved forest land, Intermountain region
Major Forest Type Estimated Area (1000ac) Percent of total forest
Rhon-juniper 41,667 35
Douglas-fir 15,754 13
Ponderosa pine 15,278 13
Fir-spruce 12,975 11
Western hardwoods 12,484 10
Other forest types 9,863 8
Total unreserved forest 119,016 100

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