Linda M. Nagel

Multi-Criteria Risk Model for Garlic Mustard (Alliaria petiolata) in Michigan's Upper Peninsula

Abstract Throughout Midwestern forests, invasion by the exotic plant garlic mustard [Alliaria petiolata M. Bieb. (Cavara & Grande)] has become increasingly problematic. A multi-criteria risk model was developed to predict invasion in the Upper Peninsula of Michigan where garlic mustard is present but not yet widely distributed. The model uses geographic information system (GIS) data to predict the risk of invasion at three phases: introduction, establishment and spread. Known occurrence data for garlic mustard were used to validate the model predictions, with 89% of points correctly identified at moderate to high risk for invasion. The risk model predicted 13% of the Upper Peninsula to be at high risk and 33% at moderate risk for establishment of garlic mustard. Field sampling of randomly generated points across the Upper Peninsula provided only two additional observations of garlic mustard presence. The low encounter rate during field sampling may indicate that garlic mustard has not yet reached its full invasion potential in the Upper Peninsula. This presents an opportunity to use the model predictions and associated risk maps for monitoring and management in a relatively uninvaded region.

Silvicultural decisionmaking in an uncertain climate future: a workshop-based exploration of considerations, strategies, and approaches

Land managers across the country face the immense challenge of developing and applying appropriate management strategies as forests respond to climate change. We hosted a workshop to explore silvicultural strategies for addressing the uncertainties surrounding climate change and forest response in the northeastern and north-central United States. Outcomes of this workshop included identification of broad management strategies and approaches for creating forests that can adapt to rapidly changing conditions. Four themes were prevalent in the discussion of coping with climatic change: recognize relationships between site conditions and species vulnerability, maintain and increase diversity, increase discussion about assisted migration, and place a greater emphasis on monitoring. In this paper, we draw on the workshop to outline a process for presenting information and engaging land managers in discussion of forest management challenges in an era of climate uncertainty.

Community-Level Impacts of Management and Disturbance in Western Michigan Oak Savannas

Abstract Midwestern oak savanna systems are typically defined by their open canopy and the co-existence of scattered mature oak trees and a ground layer dominated by herbaceous vegetation. The structure of these systems is thought to be primarily maintained by disturbance such as fire. In this study we examined the plant community of 21 different oak savanna sites in western Lower Michigan, U.S.A., across a coarse disturbance gradient created by different management practices. Herbaceous community composition differed significantly across a variety of management approaches, while overall diversity remained similar. Indicator species analysis (ISA) identified several species commonly associated with mixed oak forest understories (e.g., Maianthemum canadense) as indicators for recently abandoned oak savanna sites, whereas the indicators identified for managed or heavily disturbed sites included common savanna-associates (e.g., Lupinus perennis). Variation in soil characteristics (C:N ratio and pH) and canopy cover may be driving these differences in plant community composition between management approaches. These results reinforce the importance of disturbance to Midwestern oak savanna ecosystems. Furthermore, if long-term management goals include encouraging the establishment and maintenance of herbaceous oak savanna-associated plant species, disturbance created through management activities, such as hand cutting, will likely yield better results over inaction, especially where using fire is not an option.