America’s Favorite Trees Are Under Attack

The Dogwood Tree

A fungal disease, dogwood anthracnose, is steadily eliminating the eastern, or flowering, dogwood from North American forests. The dogwood is a beloved ornamental tree of suburban yards in the most densely settled portion of the East Coast. In addition, dogwood fruits are a valuable food source for migratory birds and mammals, and the twigs are browsed by a variety of animals.ⁱ The tree’s fallen leaves provide a significant amount of calcium to forest soils.ⁱⁱ

The Oak Tree.

At least 40 North American tree, shrub and herb species are susceptible to the imported disease known as sudden oak death. More than one million trees in California and southwestern Oregon have died alreadyⁱⁱⁱ, and millions more are at risk along a 1,500-mile stretch of the Pacific Coast. The size of the infestation in California is expected to grow 10 fold by 2030 according to a study issued this past summer. In 2004, millions of nursery plants exposed to the disease were shipped throughout the country. APHIS adopted more stringent regulations to prevent a repetition of this event, however, small numbers of infected plants continue to be found in nurseries in Alabama, Mississippi, Florida and Georgia. If sudden oak death gets out of nurseries into eastern states, several species of oak, black walnut and sugar maple, as well as rhododendrons and mountain laurel, might be killed. Oaks alone comprise 38 percent of the total hardwood saw timber volume in the United States^iv. The timber value of oaks is estimated to be $3 billion annually.^v

The Pine Tree

White pine blister rust, a disease, was introduced early in the 20th century on pine seedlings imported for forestry plantings.^vi It attacks a dozen North American tree species^vii, including one of the most important timber species in the West: western white pine. In the first half of the 20th century, authorities spent more than $100 million in a largely futile effort to contain the disease. White pine blister rust is believed to have killed or damaged 80 to 95 percent of western white pine, sugar pine and eastern white pine. Forests on 9 million acres in Idaho, Montana, Oregon, Washington and California have been affected by losses that range from reduced timber values because of damaged wood to the death of both mature and seedling trees. In some areas, the Douglas-fir and grand fir trees that have replaced white pines experience chronic poor health and are vulnerable to native root diseases and insects.^viii The USDA Forest Service has spent decades breeding rust-resistant pines for the western timberlands, an endeavor described as “expensive but promising.” However, there are credible concerns that the pathogen might evolve to overcome these forms of resistance.^ix

Maple, Willow and Poplar Trees

The citrus long-horned beetle kills a wide range of hardwood species, including maple, oak, willow and poplar. The beetle was discovered in 2001 on quarantined, imported maple trees in a plant nursery near Seattle. During the summer of 2002, APHIS and the Washington Department of Agriculture cut and chipped 1,000 trees -- located on nearby city streets and in yards -- in hopes of eradicating this dangerous pest.^x Subsequent surveys appear to confirm that the insect was eradicated, but government agencies remain concerned and vigilant.

The Hemlock Tree

The Asian hemlock woolly adelgid was first reported in the 1920s, when it was observed attacking western hemlock (Tsuga heterophylla) in the Pacific Northwest (Annand, 1924). A separate introduction established the pest in Virginia, where it spread to attack eastern and Carolina hemlocks. Extensive populations of hemlock trees died in Virginia, Pennsylvania, New Jersey, and Connecticut within ten years of the first detection (Orwig & Foster, 1998). At Shenandoah National Park in Virginia, where hemlock woolly adelgid has been present since 1988, less than 10% of hemlocks sampled still have 90-100% of foliage intact and very few stands are entirely free of the adelgid (Barr, 2002). Hemlock populations in Connecticut were infested in 1985, and mortality ranged up to 95% in the sample stands studied (Orwig & Foster, 1998). Hemlocks play an important ecological role. In northern New Jersey, 96 bird and 47 mammal species are associated with hemlock forests (USDI NPS EIS, 2000). These forests shelter more than 12 species of small mammals, more than 14 species of amphibians and at least 152 species of terrestrial invertebrates. Salamanders, in particular, depend on the unique habitat under a hemlock canopy (Brooks, 2001). Hemlock-lined streams also keep water temperatures cool enough for brook trout (USDI NPS EIS, 2000).

The American Beech Tree

American beech is common in eastern North American forests. The exotic beech scale insect was introduced into Nova Scotia at the end of the 19th Century. It has since spread to central Pennsylvania with outlying infestations on the Virginia/West Virginia border, in the Great Smokey Mountains, and on Michigan’s Upper Peninsula. The insect wounds the tree’s bark, allowing an associated fungus to enter the tree. The tree is girdled from the resulting multiple cankers. The scale and associated fungus are easily transported over long distances by animals and humans, which has resulted in isolated outbreaks and establishments in West Virginia (1981). There is no practical chemical control of the beech scale in natural forests. The scale has several natural predators, but none has been sufficiently effective to stop the spread of beech bark disease. There is some hope of breeding trees resistant to beech scale insect attacks.

The Port-Orford Cedar Tree

Port-Orford cedar grows in a limited area along the Pacific coast from southern Oregon to northern California. Port-Orford cedar populations have been heavily damaged by a root disease caused by the exotic algal fungus Phytophthora lateralis. The disease was first reported in 1923 near a Seattle nursery (Hunt in Zobel et al., 1985); the disease had entered natural populations of the tree by 1952 (Roth et all, 1987) and has since spread throughout the host’s range. How Phytophthora lateralis entered the country or even the exact country of origin is uncertain. Partial resistance in Asian Chamaecyparis species suggests an eastern Asian origin (Roth et al., 1987). The fungus invades the tree’s roots, then spreads to the root collar – after which the tree dies from girdling. Fungal spores are spread by surface water or rain splash, and through movement of spore-contaminated soil. The USDA Forest Service at the Oregon Dorena Tree Improvement Center, in conjunction with the USDI Bureau of Land Management and Oregon State University, have been working since 1996 on breeding resistance to this disease.

Floridian Bromeliads

The introduced bromeliad weevil (Metamasius callizona) is killing native bromeliads (air plants) throughout southern Florida’s forests. Already, the state has declared two species of bromeliads endangered because of the impact of the weevil. The weevil appears likely to spread to all vulnerable parts of Florida, including the Big Cypress National Preserve and the Everglades National Park.

For more information

Please contact Faith Campbell, Senior Policy Representative, The Nature Conservancy, fcampbell@tnc.org, 703-841-4881.