The impact of timber harvest on wildlife distribution patterns and population vital rates: Does structural retention ameliorate the negative effects of clearcutting

Anthropogenic habitat degradation is a primary threat to global biodiversity. The overarching theme of my dissertation is one of conservation-based research for reducing the impacts of anthropogenic disturbances, specifically timber harvesting, on forest wildlife. Although the primary objective of my dissertation is to assess the effectiveness of structural retention ( i.e., canopy green trees and coarse woody debris) for conserving wildlife in harvested forests, it also provides valuable insight to other areas of ecology and wildlife management. Throughout my dissertation I highlight the need to use design- and model-based approaches for minimizing bias associated with the limited detectability of wildlife. Doing so allowed me to achieve stronger inference when determining how wildlife interacts with their environment. For my first two chapters I use species occupancy models and multiple sampling techniques to estimate detection probabilities of forest-floor wildlife. These chapters demonstrate the need to incorporate species detectability when comparing the effectiveness of different trapping methodologies. Furthermore, these studies highlight the utility of power analyses for exploring study design tradeoffs for research and monitoring programs. I used results from these chapters to develop a strong sampling design for Chapter 5. In Chapter 3 I lead a detailed investigation into the performance of wildlife occupancy models when model assumptions were openly violated. Analyses from Chapter 3 revealed general sensitivity of estimates from single-season occupancy models to violations of closure. This chapter highlights the importance of addressing the population "closure" assumption and non-random organism movements in wildlife occupancy studies. I provide multiple solutions for minimizing bias associated with non-random changes in occupancy within a field season. For my final two chapters I assess the effectiveness of structural retention for conserving wildlife in harvested forests. Both studies represent an empirical evaluation of the Michigan Department of Natural Resources (MDNR) structural retention guidelines in harvested aspen stands. Results from Chapters 4 and 5 suggest that broad-scale conservation goals for forest songbirds and terrestrial salamanders will not be accomplished by simply retaining structure within individual harvest units. Rather, successful conservation efforts for these species may also require conservation of late-successional forests as part of managed landscapes. Future management objectives in aspen forests should reflect the value of clearcutting to early-successional and generalist bird species while recognizing that green-tree and coarse woody debris retention, as observed here, did little to promote site occupancy of interior forest bird and terrestrial salamanders. However, if the management goal is to reduce mortality of local salamander populations following timber harvest, then my research suggests that implementing structural retention prescriptions is a viable management option.