The future of subalpine forests in the Rocky Mountains is uncertain following widespread and severe bark beetle outbreaks [primarily mountain pine beetle (Dendroctonus ponderosae) and spruce beetle (Dendroctonus rufipennis) in lodgepole pine (Pinus contorta) and Engelmann spruce (Picea engelmannii) trees, respectively] in recent decades. Many subalpine forest trajectories will depend largely on survival of subalpine fir (Abies lasiocarpa), the primary tree species not attacked in recent outbreaks. Yet, subalpine fir has experienced escalating mortality since the mid-1990s across the US Rocky Mountains. The causes of this mortality and consequences for subalpine forest integrity are largely unknown, but such information is critical for designing and successfully achieving conservation goals in the face of novel climate and disturbance combinations.
We are using a long-term dataset on tree demography (e.g., establishment, growth, and mortality on >6,000 individual trees) located at the Niwot Ridge NSF-Long Term Ecological Research (LTER) site and combining these data with with satellite/aerial imagery, climate data, and forest simulation modeling to better understand the causes and consequences of accelerating rates of tree mortality in the subalpine forest zone of the US Rocky Mountains. Specifically, we are asking the following questions:
1) What are the spatio-temporal patterns of recent subalpine fir mortality and relationships with potential causal mechanisms?
2) What are the effects of recent tree mortality on future forest trajectories and susceptibility to disturbance?
3) How can different management treatments foster ecological resistance and resilience?