Risks Associated with World Trade in Logs and Unmanufactured Wood

Borys M. Tkacz

Introduction
Increasing world trade in logs and unmanufactured wood articles has amplified the risks of inadvertent introduction of pests into new environments. Shipment of wood commodities has increased worldwide in the last century (Fig. 1). For example, in recent years there has been an increase in the amount of wood imported into the United States from abroad (Figs. 2 and 3). Unmanufactured wood, especially in raw log form, is a particularly high-risk pathway for movement of forest insects and pathogens into new environments. This paper reviews the impacts of two previous introductions of exotic forest pests that likely were transported on logs and summarizes the results of pest risk assessments to identify risks associated with international trade in logs and unmanufactured wood.

Case Histories of Previous Pest Introductions
Previous introductions of nonnative invasive organisms into new environments have resulted in severe outbreaks with economic and ecological disruption in forests. An example is the Dutch elm disease fungus, Ophiostoma ulmi, which was probably introduced into North America, along with its insect vector, Scolytus multistriatus, on unpeeled veneer logs from Europe. It was first reported in the United States in 1930 and by 1968 had spread throughout the eastern half of the North American continent. More than $11 million was spent over a 5-year period in the 1930s by federal and state agencies in attempts to eradicate the disease. By 1977, 60% of the 77 million planted elms had been killed by the disease. The nematode that causes pine wilt disease, B. xylophilus, was likely introduced into Japan early in the last century on pine logs from North America. It was effectively vectored by a native insect, M. alternatus, and spread at a rate of 20 miles per year through the pine forests of Japan, solely because of beetle movement. By 1979, 2.4 million cubic meters of standing timber had been killed in Japan, and by 1983, it was estimated that 25% of all Japanese pine forests had been infested. The nematode has been introduced into China where it was implicated in the death of 600,000 pines between 1983 and 1988, and has recently been found in Portugal.

Pest Risk Assessments for Log Imports into the United States
The United States Department of Agriculture (USDA) Forest Service (FS) and the USDA Animal and Plant Health Inspection Service (APHIS) have developed a pest risk assessment process that attempts to identify the risks associated with importation of logs and unmanufactured wood articles. Assessments have been completed for importation into the United States of larch logs from Russia, Monterey pine and Douglas fir logs from New Zealand, Monterey pine and native species logs from Chile, pine and fir logs from Mexico, and eucalyptus logs from South America. These risk assessments identified potential forest pests that could be introduced into the United States on logs and pose significant risks to timber resources, forest ecosystems, and urban trees in the United States. The results are considered in developing regulatory approaches to preventing introductions of nonnative invasive organisms.

Russian forest pests and pathogens that can be transported on logs and pose significant risks to North American forests include: the Asian gypsy moth (Lymantria dispar), nun moth (Lymantria monacha), spruce bark beetle (Ips typographus), pine wood nematodes (Bursaphelenchus spp.), larch canker (Lachnellula willkommii), and root rot (Heterobasidion spp.). The potential economic costs associated with the introduction of these forest pests and pathogens from Russia are high (Table 1). Costs would result from potentially reduced yields caused by growth loss, increased mortality, defects in the host species, and increased management costs. The introduction of these exotic pest organisms from Russia and their subsequent establishment in North American forests could result in significant changes in forest ecosystems, such as tree species conversion, deforestation, wildlife habitat destruction, degradation of riparian communities, increased fuel loading, and loss of biodiversity.

Table 1. Potential economic losses from the introduction of selected Russian forest pests (U.S. Department of Agriculture 1991).

The primary pests of concern identified during the pest risk assessment of Monterey pine and Douglas fir logs from New Zealand included the wood wasp (Sirex noctilio) and its associated fungus (Amylostereum areolatum), a root disease fungus (Leptographium truncatum), a drywood termite (Kalotermes brouni), pinhole borers (Platypus apicalis and P. gracilis), and the huhu beetle (Prionoplus reticularis).

The major pests of concern identified on Monterey pine from Chile included pine bark beetles (Hylurgus ligniperda, Hylastes ater, and Orthomicus erosus), the siricid wood wasp (Urocerus gigas), stain and wilt fungi (Ophiostoma spp.), and shoot blight (Sphaeropsis sapinea). Pine bark beetles from Chile could potentially be effective vectors of the native black stain root disease (Leptographium wageneri) and could lead to a 10% increase in losses caused by this disease (present value of $31 million) in the western United States. Organisms of concern on native trees in Chile included wood borers (Callisphyris semicaligatus and Chilecomadia valdiviana), bark beetles (Calydon submetallicum, Rhyephenes maillei and Epistomentis spp.), ambrosia beetles (Gnathotrupes spp.), and the complex of stain fungi (Ophiostoma spp. and Ceratocystis spp.).

The pest risk assessment for Mexican pine and fir logs identified numerous potential pest organisms. Some of these organisms are attracted to recently harvested logs, while others are affiliated with logs in a peripheral fashion. Insects that inhabit the inner bark and wood (Dendroctonus mexicanus, Ips bonansei and Scolytus mundus) have a higher probability of being imported with logs than the hitchhikers. Mexican insects of concern that can be found deeper in the wood included termites (such as Coptotermes crassus), the pitch moth, (Synanthedon cardinalis), and round-headed wood borers, (such as Monochamus clamator rubigineus). Because of their location deep in the wood, these insects may be more difficult to eliminate from logs.

Among the insects and pathogens found on Eucalyptus spp. in South America, eight organisms (or groups) were rated as having a high risk potential to the United States. The purple moth (Sarsina violescens) is a polyphagus species with a broad distribution in South America that has become one of the most important defoliators of plantation grown Eucalyptus in Brazil, Argentina, Peru, and Paraguay. Scolytid bark and ambrosia beetles (Scolytopsis brasiliensis, Xyleborus retusus, Xyleborus biconicus, and Xyleborus spp.) are not considered to be significant problems in South American eucalyptus plantations; however, they are considered a threat because of their broad host range and demonstrated propensity for human-assisted movement. Nonnative species of scolytids could potentially vector pathogens. The carpenterworm (Chilecomadia valdiviana) is a native insect that has crossed over to Eucalyptus nitens and other exotic forest and fruit trees in Chile from native Nothofagus spp. The round-headed wood borers (Chydarteres striatus, Retrachyderes thoracicus, Trachyderes spp., Steirastoma breve, and Stenodontes spinibarbis) are normally secondary associates of Eucalyptus in South America. Most of these beetles do have a broad host range and may find suitable hosts in the warmer regions of the United States. The eucalyptus longhorned borers (Phoracantha semipunctata, and P. recurva) are present in California but may be introduced into new areas. They are considered high risk due to their ability to survive during transport of wood, their wide host ranges, and the damage they (and other members of the genus) have caused when introduced into new environments. Pink disease (Erythricium salmonicolor) was rated high risk because of its broad host range and the high level of damage is causes under certain environmental conditions. Its introduction into Hawaii could result in major losses to the agricultural industry, as well as potential adverse impacts to native ecosystems. Ceratocystis canker (C. fimbriata) has a demonstrated ability to infect a wide range of hosts and cause considerable economic damage. Although this pathogen is currently widespread in the United States, the concern arises from the genetic diversity of this species and the potential for differences in pathogenicity and virulence of exotic strains or variants. Botryosphaeria cankers (Botryosphaeria dothidea, B. obtusa, and B. ribis) are present in the United States, but the current uncertainty regarding taxonomy of this group has led to concerns about pathogenicity and virulence of exotic strains or variants.

U.S. Wood Import Regulations
Once the potential pest risks associated with a particular pathway are identified through the pest risk assessment process, mitigation measures can be applied to prevent the introduction of non-native invasive forest pests. A detailed inventory of available pest mitigation measures was compiled by APHIS following the completion of the Russian pest risk assessment. This evaluation, along with the pest risk assessments for New Zealand and Chile, became the foundation for development of a Final Rule on Importation of Logs, Lumber, and Other Unmanufactured Wood Articles (Title 7, Code of Federal Regulations, Parts 300 and 319) in 1995. The regulations established general prohibitions and restrictions, general permits, procedures for permit applications, importation and entry requirements for specific articles, universal importation options, standards for treatments and safeguards, and pest risk assessment standards. APHIS has proposed and implemented amendments to these regulations based on the results of subsequent risk assessments. The FS and APHIS continue to cooperate on pest risk assessments of pathways for nonnative forest pests to ensure that the balance between protection of North American forest resources and free trade is sustained through sound, science-based decision processes.

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