The introduction of lodgepole pine as a major forest crop in Sweden: implications for host-pathogen evolution

Theoretical and experimental investigations of natural selection in host-pathogen systems are reviewed and the general principles emerging from these studies are used to analyse the possible pathogenic consequences of introducing lodgepole pine into Sweden. Introduction of lodgepole pine alone is likely to pose a relatively low disease risk for native forests. The possible evolution of more aggressive populations of native Scots pine pathogens on highly stressed lodgepole pine plantations is, nevertheless, of some concern. These pathogens could, subsequently, transfer back on to Scots pine and cause an increase in damage levels within native forests. The risk of this form of destabilising pathogen evolution occurring is, however, similar to the risk of evolving more aggressive pathogens on stands of native Scots pine growing under stressed conditions. In contrast to the conclusions drawn above, the introduction of lodgepole pine pathogens from North America into Sweden has the potential to cause very severe damage not only to native Scots pine, but also to lodgepole pine growing as an exotic. The most important measures needed to guard against pathogenic problems are those that minimise the risk of introduction of lodgepole pine pathogens into Sweden. One practical step that can be taken is to curtail importation of lodgepole pine seed and encourage the development of well adapted Swedish 'land races' of lodgepole pine from germplasm already present in the country. (C) 2001 Elsevier Science B.V. All rights reserved.