Elise G. Pendall - US grants

This project explores the role of centennial to millennial-scale climate variability, particularly wet and dry extremes, in governing the tempo, rate, and spatial pattern of invasion and expansion of three economically and ecologically important tree species (yellow birch, hemlock, beech) near their northwestern range limits in the western Great Lakes region. Geographic ranges and population sizes of these species have expanded episodically in the last 5000 years, and preliminary evidence indicates that these expansions were paced by climate variability. We will use paleoecological methods (analysis of pollen, macrofossils, and stomates from lake and peatland sediments) to delineate the spatial and temporal patterns of these expansions, and paleoclimatological methods (analyses of paleontological and geochemical indicators from peatland sediments) to develop detailed, independent records of spatial and temporal patterns of climate variability. Comparison of the paleoecological and paleoclimatological data will link the ecological responses to climate variations across a range of timescales. Understanding ecological and climatic dynamics of the past will contribute to our ability to predict ecological responses to ongoing and future climatic change.

This award funds a project to investigate the utility of peatland in eastern North America as archives of climate information. The researchers will conduct multi-proxy paleoclimate studies in peatland areas located in the Canadian Maritime provinces, northern Minnesota, and southwest Ontario. Stable isotope studies will examine the unique hydrology of ombrotrophic peatlands and further understand late Holocene climate variability based on tree-rings and pollen. Most tree-ring records from the region extend only a few centuries and pollen sequences record responses to climate change but often lag and/or mask abrupt changes. The researchers aim to develop high-resolution and climate-sensitive datasets from peatlands to document climate variability during the past 3,000 years in the region.

The research will help quantify regional responses of forest ecosystems to climate change and support interdisciplinary training for a post-doctoral researcher and several undergraduate students.

This award provides partial support of the of two new stable isotope ratio mass spectrometers to be placed in the University of Wyoming Stable Isotope Lab. This will be the only facility in the state capable of analyzing stable isotope ratios of the light elements (H, C, N, O,and S). The two isotope ratio mass spectrometer systems will be coupled with peripheral devices for automated and rapid sample processing and will be fully capable of accepting additional peripheral systems as needed in future applications. The instrumentation will augment the capabilities of this lab by providing the means for analysis of the isotopic composition of atmospheric trace gases and of organic substances and microwater (<1mL) samples. The new instruments will enable the Stable Isotope Lab to meet a growing demand for stable isotope ratio analyses from researchers at the University from elsewhere in the state and region. Among the immediate uses of the new instruments will be investigation of the physiological responses of plants and animals to environmental change, organism-environment interactions across space and time, food-webs and feeding patterns in terrestrial, aquatic, and marine systems, biogeochemistry in terrestrial and aquatic ecosystems, hydrological flow paths in arid and semiarid landscapes and biosphere-atmosphere interactions. In addition to their use in research, the instruments will be used to enhance the training and educational experiences of undergraduate and graduate students, postdocs, and visiting scientists at the University of Wyoming. The users of the facility are committed to bringing cutting-edge analytical approaches to traditionally underrepresented student, advanced researcher, and faculty groups on campus.

Global climate change models predict higher temperatures and increased variability in precipitation in the coming century, which could affect drought frequency and intensity. A relatively long-term drought has persisted throughout the central Rocky Mountain region of North America with negative impacts on the environment and the livelihood of local communities. Increasing the accuracy of future drought projections requires a glimpse into the past to look at long-term variability in precipitation and other factors associated with drought. Droughts are well documented in instrumental climate records from 1895 to present, while tree-ring widths have been used successfully to extend these climate records back in time for hundreds of years. This research project will characterize the climatology underlying recent droughts, and will reconstruct temporal and spatial patterns of drought in the central Rocky Mountains. Tree cores have already been collected and preliminary results suggest that climate and tree growth relationships are becoming more complacent at the mid to high elevation sites starting around 1955. This increasing complacency over time complicates the climate-tree growth relationship and subsequent drought reconstruction. Previous research suggests that combining stable carbon isotopes with tree-ring widths may strengthen the climatic signal necessary for reconstructions, and carbon isotopes have been found to correlate strongly with drought cycles in semi-arid regions. Thus, research objectives will be to use instrumental climate records (temperature, precipitation, and the Palmer Drought Severity Index), a multi-proxy approach (tree-ring widths and stable carbon isotopes), an elevation gradient sampling scheme, and dendroclimatic time series analysis to develop drought reconstructions for the central Rocky Mountains. It is the multi-proxy design of this project which will address a knowledge gap as to whether carbon isotopes will actually strengthen the predictive ability of tree-ring widths over time and space.

Results of this project will provide new insights into the complex ecological responses of tree-ring widths and carbon isotope composition to climate. Inferences from these proxy records of annual and seasonal climate across an elevation gradient will improve the ability to identify spatiotemporal patterns of drought in the central Rocky Mountain region. This project will also benefit local communities by identifying the historical context of drought occurrence which can be incorporated into land use planning and water conservation strategies currently being reviewed at both the local and regional level.

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

There is increasing evidence that ecological processes at high latitude are just as sensitive to the timing of events as to their magnitudes. In the boreal forest, moisture availability in summer affects both tree growth and the fire regime. Summers are brief and seasonal transitions rapid, so even slight shifts in the timing of precipitation patterns can have large impacts. One of the most striking, seasonal phenomena in the Alaskan boreal forest is the onset of frequent frontal storms in late summer. This event usually comes in mid-July but is delayed into August or even September in some years. Summers when the rains are delayed have a greater chance of being mega-fires seasons when >1.6 million ha burn. This project will test the hypothesis that shifts in the seasonality of warm-season precipitation could be a key driver of the boreal forest?s responses to future climate changes. The effect of late-summer precipitation on tree growth and fire in Alaska will be quantified in two ways: First, by analyzing interactions between climate, fire, and tree growth (specifically ring-width, ring density, and wood-isotope composition); second, by analyzing fire-climate relationships using a new statistical approach. Together, these results will improve parameterization of the forest model ALFRESCO, which will then be used to test additional hypotheses about the interconnections among future climates, tree growth, fire, and their collective feedbacks to the global climate system.

The shifting seasonality of water availability during the warm season may be of key importance in determining how the global boreal forest responds to future climate changes. The multidisciplinary research proposed here represents a new approach to answering a novel question. No one has examined the impacts of seasonal shifts in the timing and magnitude of warm-season precipitation on vegetation distribution, tree growth, and fire regime in the boreal forest before. This will be the first time that tree rings from deciduous species in the boreal forest are used to describe past variations in summer rainfall through measurements of ring-width, late-wood density, and wood isotopes. The generalized boosting technique we propose using has not been previously applied to climate-fire records. The results of these tree-ring and statistical analyses will improve parameterization of the ALFRESCO forest model and allow us to explore the interactions among components of this part of the Arctic system with greater realism.

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

Quantifying the Effects of Large-Scale Vegetation Change on Coupled Water, Carbon and Nutrient Cycles: Beetle Kill in Western Montane Forest
We are quantifying how rapid, extensive changes in forest structure and composition associated with Mountain Pine Beetle (MPB) infestation of western montane forests affect the coupling of water, carbon, and nitrogen cycles. MPB infestation and associated fungal pathogens radically change ecosystem structure by killing host trees, altering surface energy and water partitioning, reducing carbon uptake, and putting organic matter into soil on short and long time scales. The widespread extent of this disturbance presents a major challenge for governments and resource managers who must respond to the changes, yet lack a predictive understanding of how these systems will respond to the disturbance over various temporal and spatial scales. This disturbance allows us to test emerging theories of direct and indirect effects of vegetation change on coupled biogeochemical cycles following a disturbance that initially changes only the amount of living biomass while leaving soil hydrologic and chemical characteristics unchanged. By working at sites with different levels of MPB impact, we are evaluating how the dramatic loss of tree function both directly (i.e. transpiration and carbon fixation) and indirectly (i.e. snow capture, redistribution, and surface energy balance) affects water, carbon and nitrogen cycling.

Our work is organized around two, broad questions that require both an interdisciplinary approach and close integration of observation and modeling. How do changes in vegetation structure associated with MPB alter the partitioning of energy and water? And How do these changes in energy and water availability affect local to regional scale biogeochemical cycles? We have assembled a diverse team of biogeochemists, ecologists, hydrologists, and atmospheric scientists to address these questions using measurements, modeling tools, and conceptual approaches from each discipline. Our approach includes intensive, coordinated hydrological, biogeochemical, and ecological observations designed to quantify the internal coupling of water, carbon, and nutrient cycling, as well as how these processes are expressed in both land surface-atmosphere exchanges and catchment solute export. These observations are closely integrated with two process models, one from the landsurface community and one from the catchment community, to evaluate our current understanding of how vegetation change alters coupled cycles. To extend our work beyond the relatively short time-scale of our observations, we coordinate with several ongoing projects, including the Boulder Creek CZO and the Niwot Ridge LTER.

By quantifying both the biological and physical controls that forest vegetation has on water and biogeochemical cycles, our project will both improve our basic understand of the coupling between water, energy, carbon, and nitrogen. Through coordination with land surface and catchment modeling communities we will incorporate this knowledge into the broader community. Our educational activities build on successful efforts at all institutions, while coordination with land and water resource managers will ensure our knowledge is transferred to the applied science community.

Support from the National Science Foundation has allowed the purchase of a GC-combustion-isotope ratio mass spectrometer (GC-C-IRMS) and integrated quadrupole mass spectrometer (GC-MS) system with an interface supporting on-line coupling of HPLC and IRMS (LC-IRMS) to allow for stable isotope analysis (SIA). The SIA of bulk biological materials allows the integrative study of processes at scales that range from the biochemical to the biospheric. This instrumentation will add capacity for CSIA to the University of Wyoming Stable Isotope Facility (UWSIF), a core, multi-user research and training facility currently supporting 16 research groups from 8 departments and 3 colleges. The instrumentation will provide a core group of users in the capacity for CSIA on fatty acids, lipids, amino acids and carbohydrates, and be flexible enough to allow LC-IRMS on polar, non GC-volatile or thermolabile compounds without the requirement for derivatization. The major users conduct research in three areas that integrate biological and geochemical systems: 1) organismal and ecosystem ecology; 2) paleo-ecology and paleo-environmental studies; and 3) energy research. Studies with the new instruments will focus on animal physiology, diet, food webs, plant and ecosystem carbon cycling, diets and environments of extinct organisms, reconstruction of past climates and ecosystem responses, and geochemical tracing of environmental contaminants associated with energy extraction. A graduate course taught every fall semester by Williams (PI) and Sharma (co-PI) provides hands on training using the instrumentation acquired through NSF funding. High school students in the NSF EPSCoR sponsored Summer Research Apprenticeship Program (SRAP) and the NSF sponsored Science Posse program at UW have and will continue to conduct isotope-related research involving analyses in the UWSIF. These faculty also currently advise 26 graduate students (10 are women) and 4 postdocs (3 are women), and all include undergraduates in their isotope oriented research projects. Results from the research projects will be disseminated through student and faculty presentations at regional or national meetings, and through publications in peer-reviewed journals.

Grassland ecosystems comprise over 30% of the Earth's terrestrial surface, and provide a resource base for extensive agricultural activities such as ranching. Grasslands are sensitive to climate change because they exist where hot, dry weather is common and rainfall is unpredictable, and because their plant communities may rapidly shift in response to rising climate and atmospheric CO2 concentrations. Grassland soils contain large stores of long-lived carbon, which could either buffer climate change, or accelerate it if this carbon is released to the atmosphere. Soil microbial communities are the ultimate drivers of soil carbon uptake or loss. This project investigates how plant-microbe interactions regulate soil carbon cycling within an ongoing, state-of-the-art, manipulative climate change experiment in grasslands near Cheyenne, Wyoming, the Prairie Heating and CO2 Enrichment (PHACE) experiment. Thirty plots are exposed to combinations of climate conditions, including warming and CO2 conditions expected to occur before the end of the 21st century, and altered precipitation. An important component of the experiment is the comparison of carbon and nutrient cycling between native and disturbed grasslands with distinct plant communities, including invasive species. Laboratory and growth chamber experiments applying molecular and isotopic methods will test specific hypotheses generated from observations and measurements in the field. This project is expected to reduce uncertainties related to interactions between soil nutrients, biological communities and climate change, leading to improved predictions of future atmospheric CO2 concentrations and associated warming effects.

This project will reach out to agricultural resource management agencies, ranchers and landowners who are concerned about impacts of climate change, disturbance and weed invasion on rangeland productivity, by conducting annual Field Days at the PHACE site and publishing articles in the popular press. Cross-site collaboration and data synthesis will be promoted by incorporating soil data into a comprehensive database. The project will provide strong interdisciplinary training to two graduate students, several undergraduates, and two postdoctoral scientists from under-represented groups. In-service middle school science teachers participating in the University of Wyoming Master's of Science in Natural Science degree program will be invited to the field site for hands-on lesson development, and minority high school students will be mentored. The new Summer Soil Institute at Colorado State University (http://soilinstitute.nrel.colostate.edu) will bring students to the PHACE field site for sampling and analyses.

In seasonally snow covered regions, the metabolism of living roots and microorganisms in the soil over the winter may be an important part of the total annual transfer of carbon dioxide from ecosystems on land into the atmosphere. This project will measure wintertime soil respiration in southeast Wyoming and determine the factors that control it. Measurement plots have been established across a range of ecosystems from short grass prairies to subalpine forests that experience a wide range of winter weather conditions. The highest elevation site, at about 10,000 feet, is a subalpine forest that has snow cover for more than eight months at depths up to ten feet. The lowest elevation site, at 5400 feet, has only four months of snow that is shallow and patchy. This results in contrasting midwinter soil environments. At the high elevation site, snow provides a deep insulating layer that effectively insulates the soil from extremely cold air temperatures and prevents soil freezing. In contrast, soils at the lowest elevation site are often directly exposed to the air and often freeze in midwinter. This has the counterintuitive result that soils in the coldest, snowiest ecosystems at the highest elevations are actually the warmest in midwinter. The organisms responsible for soil respiration, mainly bacteria, fungi and plant roots, rely on the presence of liquid water to be biologically active. Therefore, it is expected that the highest elevation sites will have higher rates of soil respiration during the winter than the lowest elevation sites. Measurements will be made of soil respiration at the different study sites in ways that will enable the relative amounts coming from microbes and roots to be determined. Laboratory experiments will be done to determine the controls over respiration at cold temperatures.

Over a year the flux of carbon dioxide from the land into the atmosphere is many times greater than the amount released by the burning of fossil fuels. Over the earth, most of the released carbon is taken back up by plants. But small shifts in the relative rates of release and uptake can have a large impact on atmospheric concentrations of carbon dioxide. Current computer models generally contain overly simple descriptions of soil processes and how they may respond to climate change, particularly at cold temperatures. Therefore, it is important to learn about the interacting biological and physical factors that control these processes. In addition to addressing the socially relevant issue of global climate change, this project will help educate and train a new generation of scientists through the employment of an undergraduate research assistant.