Managing invasive forest insects and pathogens: Slow the spread or proactively adapt?

Background/Question/Methods

Forests throughout the world are being invaded by non-native insects and pathogens, and many of these organisms are fundamentally transforming native ecosystems. The dominant management response to such invasions has been slow-the-spread campaigns (concerted efforts to limit local expansion within affected areas and/or prevent colonization of susceptible regions that have not been invaded). For instance, slow-the-spread programs are currently targeting invaders ranging from the emerald ash borer (Agrilus planipennis) in the eastern US to the pathogen that causes sudden oak death (Phytophthora ramorum) on the US west coast. This is a very understandable reflexive response given that non-native disturbance agents such as these have the potential to permanently reduce or eliminate populations of susceptible species and create novel ecosystems. However, there has been little serious investigation of the efficacy of these programs or consideration of alternatives. In this paper, I first address the following question: Under what circumstances, if any, are slow-the-spread campaigns effective?  Second, I define and develop an alternative approach and explore both its scientific validity and social palatability.

Results/Conclusions

While slow-the-spread campaigns may sometimes be able to reduce the rate of expansion (thus technically living up to their name), available data suggest that established pests and pathogens are likely to eventually reach most or all areas in which they can thrive. As an alternative - and potentially complementary - strategy, I propose the “Accept The Inevitable And Proactively Adapt” approach (ATIAPA), which consists of the following steps: 1) predict the relative abundances of tree species that will result after the invading organism has established; 2) identify key ecosystem functions that will be lacking in the invaded ecosystem; and 3) employ strategic efforts to restore or maintain these functions (e.g. by planting non-susceptible seedlings of species that will provide such functions, possibly including resistant genotypes of susceptible species). Potential challenges to implementing ATIAPA include: 1) public relations (“sorry, these trees are going to die and there’s nothing we can do”); 2) the need for accurate predictions of forest dynamics; and 3) willingness to manipulate the species composition of “wild” ecosystems. Nonetheless, these issues may ultimately be less problematic than flawed slow-the-spread campaigns, and thus ATIAPA and similar approaches deserve serious consideration.