The aggregate impact of an exotic species introduction, such as the zebra mussel (Dreissena polymorpha), may involve a large number of biotic and abiotic interactions within the recipient ecosystem. We used laboratory experiments and field data to assess effects of zebra mussels on both foraging success of yellow perch (Perca flavescens) and activity of the amphipod Gammarus fasciatus. In two laboratory experiments zebra mussel clusters reduced the rate at which yellow perch captured amphipods. Yellow perch captured fewer amphipods when zebra mussels were present at two light levels (<2.1 and >214 lx) and across a range of prey densities (76–1500 amphipods·m–2). The effect of zebra mussels on amphipod activity depended on light level. Yellow perch captured fewer amphipods in the presence of mussel clusters than when plants were present. The frequency of amphipods in the diets of adult yellow perch in Oneida Lake increased after zebra mussel introduction, but the increase was greater in low mussel density habitats. Our laboratory results and field observations suggest that zebra mussels affect yellow perch foraging on amphipods through increased structural complexity (negative) and increased light penetration ( positive), but not through increased prey density.

Assessment of tree health requires accurate estimates of crown condition and identification of specific biotic and abiotic agents that may affect crowns, stems, or roots. ForestHealth, an expert advisory system written in C language for the Macintosh™ platform, provides a diagnostic module and two training modules. The diagnostic module provides guidance in identifying foliar symptoms and the common insects, diseases, and abiotic disorders found on leaves of: sugar maple (Acersaccharum Marsh.), red maple (Acerrubrum L.), black cherry (Prunusserotina Ehrh.), northern red oak (Quercusrubra L.), and white oak (Quercusalba L.). Graphical user interfaces are central to both training modules. The Foliar Severity routine trains users to categorize injury (percent leaf area) on single leaves using a modified Horsfall–Barratt scale. The Crown Dieback routine displays different types and degrees of crown injury that users must identify and classify. Each crown is unique, generated in "real time" using tree–branch parameters selected by the user. Since the crowns are created on a three-dimensional basis, multiple views are possible. Written output from training sessions or periodic checks provide quantitative information for quality assurance and quality control. ForestHealth provides diagnostic assistance, training, quality assurance and quality control data, and standardization for research or survey projects involving forest health.