14. Effects on Forest Ecosystems of Changes in Climate, Insect Infestations, and Fire Regimes

Ecosystems of western North America are undergoing rapid and profound changes as the combined effects of drought, disease, and wildfire convert dense green coniferous forests into stands of red, brown, and black dead and dying trees.  Some of these changes may be related to change and variability in climate, and some may be due to more than a century of fire suppression and other forest management practices.  However profound these effects, they are an acceleration of processes that have occurred in the past, before large-scale intervention of humans on the landscape.

There remains much to be learned about the causes and effects of disturbance regimes in coniferous forests.  What are the long-term connections between climate change and the scale, frequency, and intensity of insect infestations, other diseases, and wildfires?  Have management practices inadvertently created forests that are much more dense than in the past -- forests that consequently have more ground-level fuel to feed wildfires?  Are the historic and ongoing disturbance events unusual when compared to what happened in the past?  What aspects of climate variability and change make individual tree species vulnerable to disease and fire?  These questions may be addressed by examining the long-term record of changes in climate and ecosystems. 

The sediments of lakes contain fossil pollen, macroscopic plant remains, and other paleoenvironmental indicators that provide the basis for reconstructing past changes in forest ecosystems in the mountains of the western United States.  Currently, U.S. Geological Survey (USGS) scientists and academic collaborators are conducting research on Holocene climatic variability in Colorado and adjacent States.  These studies include reconstructions of changes in:  1) climate (from sedimentological, paleontological, and isotopic data from lake sediments),  2) long-term changes in the composition and geographic distribution of forest ecosystems (from pollen and plant remains in lake sediments), 3) the elevations of upper treeline (from wood remains preserved at sites above the current treeline), and 4) regional climate and hydrologic response over the past two millennia (from a network of tree ring studies across Colorado;  Meko and others, 2007). This work, coupled with tree-ring based reconstructions of drought over the past two millennia, is aimed at providing a long-term perspective on the climatic and hydrologic effects that are occurring.  Current research activities do not include investigation of the landscape-transforming fire, disease, and other disturbance events that have occurred as a result of past climate change or as an intrinsic part of the dynamics of these forest ecosystems. 

A growing body of literature (for example, Swetnam and others, 1999; Whitlock and others, 2003) provides examples of how paleoecological studies can provide the basis for land and resource management practices.  The USGS can enhance its contributions in this area by increasing the scope of its paleoenvironmental research on the interconnections among climate change, disturbance regimes, and ecosystem dynamics.  With this objective, we seek a Mendenhall Fellow to investigate past disturbance regimes in Rocky Mountain coniferous forests.  Key questions that could be addressed include:

• can we, working as part of the larger community, devise or improve methods of detecting and characterizing past disturbance regimes from the information preserved in lake sediments?  (for example, can we calibrate data on wildfires from lake sediments using historic records or tree-ring based reconstructions of known fires?)
• can we provide insights into the probable trajectories of ongoing and future changes from the observed relations between climate change, disturbance, and resultant ecosystem modifications? 
• is the current high mortality of forest trees this area unusual for the Holocene?
• how do disturbance regimes vary through time in different forest ecosystems? (for example, lodgepole pine forests may require periodic landscape-scale fires whereas bristlecone pine forests may be highly vulnerable to fire)
• what were the characteristic intensities and return intervals of wildfires and other disturbances during past warm climates, such as the middle Holocene and the medieval warm period?

References

Meko, D.M., Woodhouse, C.A., Baisan, C.A., Knight, T., Lukas, J.J., Hughes, M.K., and Salzer, M.W., 2007,  Medieval drought in the upper Colorado River Basin:  Geophysical Research Letters, v. 34. p. L10705.

Swetnam, T.W., Allen, C.D., and Betancourt, J.L., 1999,  Applied historical ecology:  Using the past to manage for the future:  Ecological Applications, v. 9, p. 1189–1206.

Whitlock, C., Shafer, S.L., and Marlon, J., 2003, The role of climate and vegetation change in shaping past and future fire regimes in the northwestern US and the implications for ecosystem management:  Forest Ecology and Management, v. 178. p. 5–21.

Proposed Duty Station: Denver, CO

Areas of Ph.D.: Geology, biology, ecology, climate science, forestry

Qualifications: Applicants must meet one of the following qualifications: Research Geologist, Research Biologist, Research Ecologist

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Research Advisor: Robert Thompson, (303) 236-5347, rthompson@usgs.gov

Human Resources Office contact: Vanessa Chambless, (303) 236-9584, vchambless@usgs.gov

Summary of Opportunities