Implications for management of eastern larch beetle and emerald ash borer and their impact on lowland forest types across the Great Lakes region

Abstract

Climate change and insect disturbances pose a great challenge to forest management in the Great Lakes region. Here, I evaluate some of those challenges with an invasive insect, emerald ash borer (Agrilus planipennis Fairmaire[EAB]) and a native insect eastern larch beetle (Dendroctonus simplex[ELB]). EAB is remarkable in the level, intensity, and extent of mortality it has caused in ash species in North America. Within the Great Lakes, it threatens to induce site conversion in northern black ash wetlands. This research identifies potential replacement species with adequate cold and flood tolerance to plant in such sites by analyzing survival and growth metrics in an experimental greenhouse and nursery study in Wisconsin. The impact of ELB on its primary host tamarack has become an emerging concern due to an increase in epidemic level outbreaks, largely attributed to warmer temperatures and longer growing seasons, which allow for increased reproduction. This research sought to explore the detection and dynamics of ELB in north central Wisconsin through observational studies. Ground surveys of two methods of detection, aerial sketch map surveys and a satellite imagery remote sensing algorithm, were conducted to assess forest mortality in these detection areas. It was determined that in this region of Wisconsin, detection methods are likely underperforming due to the variable and heterogeneous nature of tamarack forests. Fixed radius plot inventories were also conducted in randomly selected tamarack stands and stands identified via detection methods to evaluate relationships between ELB and tamarack structure and composition. Several significant relationships were discovered between ELB and tamarack structure and composition, such as between ELB and stand density, percent host species composition, and small tamarack tree presence. This knowledge can be implemented by forest managers across the region to assist in efforts to manage forests appropriately in the face of climate change and insect disturbances.