Relationships between spatial environmental variability and black bear occurrence in the continental United States of America

The American black bear (Ursus americanus) historically occurred throughout the forested regions of the continental United States of America (USA). However, today black bears only occur in a fraction of their former range. I investigated the relationship between spatial environmental variability and black bear occurrence in the continental USA. The objectives of this study were to determine if spatial environmental variability influences the distribution of black bears and, if so, develop a model to predict the spatial distribution of suitable bear habitat and potential relocation areas. I used logistic regression to model bear occurrence. I divided the continental USA into two areas; the Southeastern coastal plain, termed lowland environments, and the remainder of the continental USA, termed upland environments. I found that bear presence was correlated with 10 variables in upland and lowland environments. In upland environments, bear presence was positively correlated with all macrohabitat types (except grassland-shrubland mosaic), wild lands, snowfall >122 cm, and increasing levels of spring-summer normalized difference vegetation index (NDVI). In contrast, bear presence was negatively correlated with forest fragmentation, road density index, human densities >10 persons/km2, greater distances from streams, and increasing levels of wetness. In lowland environments, bear presence was positively correlated with deciduous and evergreen forests, grassland-shrubland mosaic, perforated through edge levels of fragmentation, wild lands, human density <43 persons/km 2, increasing soil nitrogen levels, and increasing levels of spring NDVI. In contrast, bear presence was negatively correlated with herbaceous-woodland wetland, sparsely vegetated areas, increasing road density index, and increasing levels of wetness. The relative probability of bear occurrence models identified about 2.8 million square kilometers of suitable bear habitat and 981,061 km 2 of vacant suitable habitat, including 34 high priority (≥5,000 km2) relocation areas. This study describes bear-habitat use patterns across a broad spatial extent and identified landscape variables that may influence bear occurrence. In so doing, the study provides a new interactive model that can be adapted and used to predict the relative probability of bear occurrence due to changing spatial conditions and identify potential relocation areas.