98 



5 



The APHIS assessment demands that we identity potentially damaging foreign pests. 



We can identify many, but as in the past it is the unlcnown or unidentified ones that may be 

 the real threats. 



As for the known disease-causing agents, we are just beginning to realize how little 

 we really know about them. As an example, until recently, we believed that one of the 

 world's most devastating root diseases was caused by a single fungus species. With new 

 technology, including DNA analysis, we now know that there are at least 10- U different 

 species throughout the world and that some of them are still confined to relatively small 

 geographic areas. 



In agriculture, we have a much simplified system with respect to both the plants and 

 the environment. Tlie plants often axe almost identical genetically, the crops are usually 

 monocultures and the environment is as unifonn and simple as cultivation will make it The 

 natural forest is a diverse ecosystem which tends to suppress pest populations. Disease- 

 causing agents of forest trees may be very obscure in their native habitat, compared to those 

 in agricultural systems. Thus, to overlook a potentially dangerous pest in its native habitat is 

 rather easy. It is inappropriate and unwise to base assessments only on the known. Past 

 history should have taught us a better lessoiu 



Second, the means by which we can control or manage introduced pests in the forest 

 are much more limited than those in agricultural systems. The values of the forest resources 

 at risk are enontious, probably in the many trillions of dollars even without considering the 

 multiple values and uses. Yet, the economics of growing long-lived trees are such that we 

 can rarely afford to spray them every year to protect against pests, even if it is 

 environmentally sound (Rarely Is it.). Genetic resistance, a common approach in agriculture 



