148 



Exotic insects and diseases have damaged North American forests for more than 100 

 years (cf. Crandal] et aL 1945). In a recent forest health survey for the Northeast, Biirk- 

 man et at (1993) found that forest types covering more than 60 percent of the total 

 forested area (which covers about 165 million acres) have been seriously damaged by 

 introduced insects or pathogens. While the true economic costs of forest damage 

 caused by all forest pests are diiJCicuIt to calculate, lost timber revenue alone amoimt. 

 to S2 billion annually (Pimcntcl 1986). The impact on industries that are connected 

 with recreational forest use is more difficult to estimate. Industries associated with 

 hiking, hunting, fishing, and other outdoor activities can be seriously affected if the 

 forest is no longer suitable for a particular recreational activity. The ecological cost, 

 in terms of an altered forest ecosystem, cannot be adequately measured. According to 

 Ledig (1992), Hntroduction of exotic diseases, insects, mammalian herbivores, and 

 competing vegetation has had the best-documented effects on genetic diversity [of 

 forest ecosystems], reducing both species diversity and intraspeciCc diversity." Their 

 impact has been greater than that of other, more widely recognized, humanoused 

 factors, including forest fragmentation, changed demographic structure, altered 

 habitat, pollution, and favoring of certain "domesticated" species of trees. Elxotic 

 pests have virmally eliminated important species such as the American chestnut and 

 American elm (Ulmus americana) as viable components of eastern forests and have 

 radically altered the eastern forest ecosystem (Ledig 1992). 



The majority of exotic forest pests in North America have been introduced on 

 imported nursery stock or logs. Past problems with imported pests resulted in the for- 

 mation of the Animal and Plant Health Inspection Service (APHIS) in the United 

 Stales Department of Agriculture (USDA). Strict regulations on imporution of nurs- 

 ery stock were implemented decades ago (Plant Quarantine Act 1912).* Until recent- 

 ly, however, there were no specific timber import regulations to insure protection 

 against exotic pest introduction. APHIS relied on visual inspection of logs enterinf 

 U.S. ports to detect insects and pathogens. Importers were required to eliminate any 

 pests found prior to bringing the logs into the country for processing. This policy 

 reflected the fact that log shipments usually were relatively small or from countries 

 considered to be substantially free from pests that could damage American forests, 

 eg., countries with a tropical climate. Now. however, the reduction of harvesting in 

 U.S. National Forests and increasing controversy about logging in the United Slates, 

 especially in old-growth forests of the Pacific coast, have created an interest in import- 

 ing large quantities of logs from Siberia, New Zealand, Chile, and other countries 

 with similar climates and forest types as in North America. 



In ihe context of this paper, the most important question raised by such proposals is the 

 possibility of introducing exotic pests into North America. Although USDA has 

 begun to lake steps to control or respond to the introduction of alien pests, their 

 efforts to date arc inadequate in the face of this serioiu ihreaL Pests could have ex- 

 tremely high economic and ecological costs if they became established in the widespread 

 coniferous forest ecosystems of the American west. In 1961, Boyce predicted that "(a] 

 virulent introduced parasite is inflnitely more destructive to pure than to mixed 

 stands. ... no more potentially dangerous simation for disaster can be imagined than i' e 

 extensive pure Douglas-fir forests of the Pacific Northwest or the far-flung pure stands 

 of ponderosa pine and lodgepole pine in other parts of the WesL" Unfortimately, this 

 prediction has been realized, as western forests arc currently threatened by exotic 

 pests such as the Asian gypsy moth. Some examples of past and current exotic pest 

 devastations are listed below to illustrate the magnitude of exotic pest problems. 



* See Appendix A for a lummary of solutes governing exclusion 2nd control of alien forest pest spedes. 



