INTRODUCTION

Simulation models predict that habitat loss may reach a threshold level below which ecological processes change abruptly (Fahrig 1998; With and King 1999; Flather and Bevers 2002). Effects of fragmentation sensu stricto are then detected, whereby increasing distances among patches and matrix resistance reduce the likelihood of recolonization after local extinctions (Lande 1987; With and King 1999). By definition, models simplify reality; therefore, they do not always represent appropriate metaphors for real landscapes because they tend to assume sharply contrasted habitat mosaics. None the less, different species perceive the same landscape differently and those specializing on habitat types dramatically altered by management may exhibit actual fragmentation effects and species-specific thresholds.

Surprisingly few studies have examined the landscape-scale effects of forest management on animals and plants. Previous landscape-scale studies have mainly examined species response to different landscape contexts or landscape structures in forests fragmented by agriculture (see Chapter 8, this volume, for a review). Managed forest landscapes are thought to be more permeable to the movements of vertebrate forest animals because contrasts among forest stands are generally softer than between forests and cropfields or pastures, for example. Indeed, fragmentation effects have mainly been detected in forests fragmented by agriculture or in island archipelagoes (Mönkkönen and Reunanen 1999). Clearcuts may become relatively permeable to forest bird movements as soon as the regeneration provides some cover (Sieving et al. 1996), although juveniles may not move across them as readily as adults.