US-2: Holocene records from the Rocky Mountains

Title: Millennial-scale variations in disturbance and biogeochemical cycling in subalpine forests in Colorado and Yellowstone National Park

Investigators: Whitlock, Higuera

Students: Dunnette (MS UIdaho), Krause (PhD MSU).

Project description:

A rise in the frequency of large fires in western U.S. forests has been tightly linked to climate change, and predictions of further warming have raised concerns about feedbacks with disturbance, vegetation, and key ecosystem processes (Westerling et al. 2006, Bonan et al. 2008, Littell et al. 2009). For example, although nitrogen limits primary productivity in Rocky Mountain forests, little is known about relationships between fire and nitrogen cycling over multidecadal and longer time scales (Smithwick et al. 2009, Turner et al. 2007). Similarly, associations between climate and fire regimes over centennial to millennial time scales are not well understood in regions hardest hit by recent drought, fire, and mountain pine beetle activity.

This goal of this research is to develop and apply paleoecological methods to elucidate relationships among climate, vegetation change, and the patterns and biogeochemical impacts of fire within subalpine forests in Rocky Mountain and Yellowstone national parks. Analyses of existing paleoclimate records and new and existing lake sediment records of charcoal, fossil pollen, and biogeochemical proxies will be used to inferred the causes and ecological impacts of past disturbances at decadal to millennial time scales. This research will help elucidate the long-term controls on fire and vegetation change, as well as the impacts of stand-replacing fire on key ecosystem processes and increase understanding of the controls on fire regimes in one of the most widely distributed forest types in western North America. The specific objectives are to:

(1) Quantify fire regimes over centennial to millennial timescales and if and how variability in fire activity is related to coincident changes in climate and vegetation.

(2) Quantify the ecological impacts of past disturbances (primarily fire) and disturbance regimes on terrestrial and aquatic ecosystem using biogeochemical proxies of productivity, nutrient cycling, and erosion.

Related Activities

These projects are largely supported on other research grants, although PIRE has contributed some funding in Year 1.  The research in Rocky Mountain National Park has been supported by a NPER fellowship to Higuera as well as PIRE support in Year 1. Studies in Yellowstone National Park are supported by a NSF grant (EAR0818467) and National Park Service funding to Whitlock. 

This project links to ongoing or planned PIRE research in two ways: (1) Holocene records fire and vegetation history will relate to PIRE US-3, focusing on lower treeline dendroecology in the Greater Yellowstone Ecosystem and interregional comparisons and syntheses (e.g., PIRE Syn-2 and PIRE Syn-3). (2) Work developing and interpreting isotopic disturbance signatures are directly applicable to PIRE-related research in Tasmania (PIRE TAS-2/ARC) and potentially New Zealand (PIRE NZ-2) focused on quantifying ecological impacts of fire and other large-scale disturbances.

Year 2 Update


The objective of this project is to build on existing research, funded by the National Science Foundation and National Park Service, to reconstruct the fire history of Rocky Mountain forests.  The project provides a comparison to the fire history of similar vegetation types in New Zealand, Australia, and Patagonia.  Our focus in the US is on middle-elevation and subalpine forest history of Yellowstone National Park and Rocky Mountain National Park and the project includes the participation of graduate students Krause and Dunnette. These two regions should provide high-resolution reconstructions of paleoenvironmental changes since the last glaciation, and an opportunity to look at drivers of past fire regimes. 

In Yellowstone National Park, analytical work funded by a separate NSF grant to Whitlock has been largely completed for four sites.  These data form the core of MSU PhD student Krause‚Äôs dissertation. MSU MS student Dave Firmage is undertaking research that complements the Krause study by examining sediment cores from two small lakes (Foster and Floating Island lakes) that span the last few centuries.  High-resolution charcoal, pollen, and magnetic susceptibility from these lakes will help assess changes in fire regimes during and just before the establishment of the national park.  Two papers were submitted and published on Yellowstone (Whitlock et al. 2012; Mumma et al. 2012) that help clarify the role of climate and people on long-term fire activity. 

In Rocky Mountain National Park, attention has focused on the environmental history of a small lake in subalpine forest, Chickaree Lake.  Field sampling of terrestrial organic matter pools and measurement of basic limnological parameters in and around Chickaree Lake in August 2011 enabled characterization of lake trophic status and elemental and isotopic composition of terrestrial organic matter.  This information will aid in interpreting these variables in the lake-sediment record currently being analyzed. Dunnette spent the year developing hypotheses and carrying out laboratory sampling and analyses of an 8-m sediment core collected from Chickaree Lake in 2010. Results are now available on sediment radiocarbon dating, sediment C and N, elemental and isotopic geochemistry, accumulation rates of fossil pollen and macroscopic charcoal, and organic matter (OM) concentration. Two undergraduate students, Ryan Moran and Shannon Pauli, were involved in the lab portion of this work.  Dunnette and lab technician Maggie Ward developed and executed a subsampling scheme for isotopic analyses of tree-ring records previously collected around Chickaree Lake by Dr. Jason Sibold (Colorado State University). These samples are currently being analyzed at Central Appalachians Stable Isotope Facility; the results will help constrain and complement the isotopic analyses from the lake-sediment record.