Among terrestrial ecosystems, forests contain the largest and most long-lived components. The long lives of trees, the large spatial extent of forests and their planning, and the social perceptions of forests combine to create particular diffi culties in managing forests to sustain biodiversity. Bunnell et al . (2009a) recognized fi ve, as follows:

1 For historical and social reasons, forest practitioners bear an uncommon responsibility for sustaining biodiversity. In western North America, for example, both forestry and agriculture provide highly valued crops, but only forestry is consistently charged with sustaining biodiversity.