The indirect human influence on western mountain environments: Vulnerabilities and resiliencies

Background/Question/Methods

In our 2002 book, Rocky Mountain Futures, we assessed the direct and indirect impacts of humans to mountain landscapes.  We also made projections of future indirect effects, such as climate change.  A decade later, it is clear that the pace of climate change has quickened beyond our earlier estimates, that parts of the Rocky Mountains have warmed 1.8 times the global average, and that ecosystems are responding in ways we didn’t anticipate. 

Results/Conclusions

Trophic cascades have proven sensitive to cryospheric changes driven by warming and have added additional stress to species of concern.  In the northern Rockies, retreating glaciers and earlier snowmelt not only affect timing and magnitude of run-off, but change stream temperature profiles.  Late summer warming water temperatures change the distribution and abundance of thermally-sensitive stream macroinvertebrates, the foraging behavior of the associated salmonids, such as bull trout, and their competitive interactions with invasive lake trout (which are better adapted to warmer temperatures).  Ultimately, warming will restrict bull trout distribution to higher elevations where genetic isolation will occur as populations are trapped in montane headwaters.   Retreating glaciers have been recently shown to add additional nitrogen to high-elevation aquatic systems as they exposure new substrate, further causing indirect changes.  As seasonal snow persistence becomes more variable, research of the past decade has underscored the snow dependence of mountain organisms, ranging from wolverines to alpine poppies, on snow cover.  The landscape is snow-dependent as well.  Snow avalanches provide critical wildlife habitat through frequent disturbance and there has been a post-2000 shift toward wetter avalanches that may presage eventual changes in this dynamic. Climate change has  exposed the vulnerability of some phenological patterns such as snowshoe hares still having white pelage in early spring when the snow is gone.   As we’ve documented the complex and often subtle mountain ecosystem vulnerabilities to accelerating climate change, we have found resilience as well.  The behavioral plasticity of some organisms has allowed them to adapt to changing climates and ecosystem processes.  Compensatory processes also dampen the full impact of climate change.  An example is  increased fire prevalence in some subalpine areas where trees are invading meadows valued for biodiversity – both the fire occurrence and invasion are tied to climate changes.  In addition, resiliency is being enhanced by protection of critical habitats such as the North Fork of the Flathead River, a transboundary effort between the U.S. and Canada.