Background
In 1994-96, the old growth pine forests in Lake Itasca State Park sustained a sequence of heavy blowdowns from windstorms. The downed trees have provided abundant food resources for Ips bark beetles, leading to an apparent dramatic increase in the population size of Ips. Under some conditions, Ips are capable of attacking and killing trees that would otherwise survive. Limitations in soil water availability, such as characterize forests near the edge of the Great Plains in western Minnesota, have been hypothesized to exacerbate the risk of tree mortality from bark beetles. Thus, bark beetles pose a potentially severe risk for the remaining old growth forests of Lake Itasca State Park. The objective of this research is to assess that risk, evaluate potential strategies to mitigate the risk, and develop biologically sound models to guide our management and understanding of this unique and irreplaceable forest ecosystem. Research will be aided by a substantial existing knowledge base regarding interactions between pine trees and bark beetles. However, research will be unique in being the first scientific studies of bark beetles in old growth pine forests of the Great Lakes region. Because Lake Itasca represents one of the last remaining patches of primary forest from this once extensive forest type, results will also have great significance in advancing our understanding of the natural workings of unaltered forest ecosystems

General Objective
Research will be conducted in close cooperation with researchers at the State University of New York at Syracuse. Our integrated research plan includes two large studies designed to test the hypothesis that bark beetles kill mature pine trees and to evaluate the efficacy of potential control measures. The Dartmouth research team will contribute to these studies, which are described in detail in the Syracuse work plan. In addition, the Dartmouth research team will conduct studies to address the following objectives.

Specific Objectives

• The role of abiotic effects on bark beetle phenology and population dynamics. Climatic patterns are thought to exert strong effects on bark beetle population dynamics. We will develop models that predict the seasonal course of beetle development, the number of generations per year, and over-winter survival as a function of temperature. These models will allow an assessment of the climatic conditions that tend to increase and decrease beetle population growth and will provide a tool for scheduling beetle monitoring programs, beetle control programs, and blowdown salvage operations.
• Effects of tree physiological status. The attack success and oviposition rate of bark beetles is inversely related to tree resin flow. The survival, growth, and fecundity of their offspring is influenced by the nutritional attributes of the phloem, especially nitrogen content. The availability of water and mineral nutrients has strong effects on tree growth, secondary metabolism (e.g., oleoresin synthesis), and phloem chemistry. Thus, site characteristics that influence tree growth (e.g., water availability, nutrient availability, and basal area) are expected to influence tree susceptibility to bark beetles and the reproductive rate of colonizing bark beetles. We will test for correlations between site characteristics and tree attributes that are of relevance to beetles. This research will allow identification of sites and trees that are of relatively high and low risk from bark beetles. Studies will also provide comparisons of the relative suitability for bark beetles of the three pine species that occur in Itasca State Park and test for effects of tree size and age on host suitability.
• Effects of community interactions. Natural enemies and competitors can be potent forces in limiting the abundance of forest insects to levels below that of significant economic or ecological damage. Management strategies that incorporate these natural control agents can be cost-effective as well as environmentally friendly. However, this approach requires improved understanding of the structure and function of bark beetle communities in Itasca State Park. We will conduct replicated quantitative sampling of the bark beetle community within and outside of the blowdown area to address the following questions. Under baseline conditions (in the absence of blowdowns), what is the abundance of Ips bark beetles and their natural enemies? What is the relative abundance of the three Ips species that occur in the park (I. pini, I. grandicollis, and I. perroti). How does the abundance and species composition of the bark beetle community change in the presence of blowdowns and how do these changes influence the probability of tree mortality? Which of the bark beetle species are most effective in colonizing downed trees and attacking live trees?