Biodiversity losses: The downward spiral

Abstract

The dramatic decline of whitebark pine ( Pinus albicaulis ) populations in the northwestern United States and southwestern Canada from the combined effects of fire exclusion, mountain pine beetles ( Dendroctonus ponderosae ), and white pine blister rust ( Cronartium ribicola ), and the projected decline of whitebark pine populations rangewide (Chapters 10 and 11) do not simply add up to local extirpations of a single tree species. Instead, the loss of whitebark pine has broad ecosystem-level consequences, eroding local plant and animal biodiversity, changing the time frame of succession, and altering the distribution of subalpine vegetation (Chapter 1). One potential casualty of this decline may be the midcontinental populations of the grizzly bear ( Ursus arctos horribilis ), which use whitebark pine seeds as a major food source (Chapter 7). Furthermore, whitebark pine is linked to other white pine ecosystems in the West through its seed-disperser, Clark's nutcracker ( Nucifraga columbiana ) (Chapter 5). Major declines in nutcracker populations ultimately seal the fate of several white pine ecosystems, and raise the question of whether restoration is possible once a certain threshold of decline is reached.