The treeline as a refuge: are elevational gradients in Mountain Pine Beetle-caused mortality common in Pinus albicaulis populations at treeline?

Abstract:

Climate change-induced mountain pine beetle outbreaks are a major cause of recent declines in high-elevation whitebark pine in the US Northern Rocky Mountains. Whitebark pine is a major component of subalpine forests in western North America. It is often the dominant tree species at treeline, where it readily forms krummholz, a stunted, shrub-like growth form. Whitebark pine appears to be relatively naïve to beetle attack; it has poor physical defense compared to that of lodgepole pine. However, anecdotal accounts suggest that whitebark krummholz may be resistant to beetle attack. I investigate the potential for treeline habitats to serve as a refuge from mountain pine beetle attack. I sampled recent beetle-caused whitebark pine mortality across treeline ecotones at 10 sites. I compared treeline mortality gradients with other forest edges to determine if mortality patterns are unique to treeline edges. Preliminary results from this study indicate that treeline habitats evaded mountain pine beetle attack during recent outbreaks. If treeline individuals are long-lived or can reproduce, treeline habitats may be viable refugia for whitebark pine populations.