Participants:

Steve Oberbauer: Principal Investigator

Lorraine Ahlquist: Graduate Assistant

Tracey Baldwin: Graduate Assistant

Sarah Colby: Graduate Assistant

Inga Parker: Graduate Assistant

This material is based upon work supported by the National Science Foundation under OPP-9615845 and OPP-9907185. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Project Summary:

Climate warming may substantially increase the length of the active season for high latitude ecosystems, but many plant species in these areas have phenological patterns adapted to short growing seasons. Some, but not all, of the factors that affect phenological stages will change with climate warming. Those species constrained by factors that will be unchanged by warming, such as photoperiod, may be unable to take advantage of additional resources that become available. As a result, species composition, productivity, and carbon fluxes from these ecosystems are expected to change substantially.

Using Alaskan tussock tundra, this project addresses the questions: 1) What are the constraints on phenological patterns for the dominant species? 2) What physiological adjustments will species make in response to an extended period of resource availability? 2) How will growth of the dominant species, ecosystem productivity, and ecosystem carbon fluxes change under field-simulated extended seasons? These questions are being addressed using a combination of field modifications of season length and controlled-environment studies.

The main project is a snow-removal and soil heating experiment at Toolik Field Station, Alaska, designed to extend the growing season at both ends of the season. In two additional sets of plots early season and late seasonal extensions are tested separately. Quantitative phenology, community composition, and ecosystem carbon fluxes are monitored along with relevant climate and soil parameters. In addition, constraints on phenology of the dominant species are being tested under controlled environmental conditions.

Key findings to date include: 1) early season snow removal affects thaw depth and soil temperatures for the entire growing season. 2) bud break and growth are accelerated for nearly all species under study in response to snow removal. 3) late-season senescence of deciduous shrubs and forbs is accelerated in the early-season snow-removal treatments. 4) leaf area development is increased on the extended season and extended season + heating plots. 5) the graminoid, Eriophorum vaginatum, appears to be increasing its dominance on the treatment plots. 6) seasonal net carbon fluxes among the treatments are fairly similar, but the similarity results from increases in both the aboveground carbon uptake capacity and belowground respiration. 7) treatments testing separately the effects of early season and late season snow removal indicate that both types of seasonal extension contribute to increases in ecosystem uptake. 8) root and leaf growth of the dominant tussock tundra species are affected by photoperiod. 9) a model of bud break of the deciduous species was calibrated and tested using field and growth chamber data. Model simulations indicate that warming in the arctic will result in earlier bud break in these species but is unlikely to affect their winter chilling needs.

We have recently started a new program that includes collaboration with Michigan State University personnel at Barrow Alaska.

Publications:
Oberbauer, S.F., G. Starr, and E.W. Pop. 1998. Effects of extended growing season and soil warming on carbon dioxide and methane exchange of tussock tundra in Alaska. Journal of Geophysical Research 103:29075-29082

Arft A.M., M.D. Walker, J. Gurvitch, J.M. Alatalo, M.S. Brete-Harte, M. Dale, M. Diemer, F. Gugerli, G.H.R. Henry, M.H. Jones, R. D. Hollister, I.S. Jonsdottir, K. Laine, E. Levesque, G. M. Marion, U. Molau, P. Molgaard, U. Nordenahll, V. Raszhivin, C.H. Robinson, G. Starr, A. Stenstrom, M. Stenstrom, O. Totland, P.L. Turner, LJ. Walker, P.J. Webber, J.M. Welker, P.A. Wookey. 1999. Responses of tundra plant species to experimental warming: meta-analysis of the International Tundra Experiment. Ecological Monographs. 69:491-511

Starr, G., S.F. Oberbauer, and E. W. Pop. 2000. Effects of extended growing season and soil warming on the phenology and physiology of Polygonum bistorta.. Global Change Biology 6:357-369.

Pop E. W., S. F. Oberbauer, and G. Starr, 2000. Predicting vegetative bud break in two arctic deciduous shrub species, Salix pulchra and Betula nana. Oecologia 124: 176-184.

Gorsuch, D.M, S.F. Oberbauer, and J.B. Fisher. 2001. Comparative vessel anatomy of arctic deciduous and evergreen dicots. American Journal of Botany. 88:1643-1649.

Gorsuch, D.M. and S.F. Oberbauer. 2002 Effects of mid-season frost and elevated growing season temperature on stomatal and specific xylem conductance of the arctic shrub, Salix pulchra. Tree Physiology22:1027-1034.

Starr, G. and S. F. Oberbauer. (in revision). The photosynthetic response of two arctic graminoids to changes in soil temperature: the role of abscisic acid. Plant, Cell, and Environment.

Starr, G. and S.F. Oberbauer. (submitted ). Photosynthetic activity under the snow in arctic evergreens: implications for ecosystem carbon balance. (Ecology).

Oberbauer, S.F. and Starr, G. 2002. The role of anthocyanins for photosynthesis of Alaskan arctic evergreens during snow melt. In: Anthocyanins in leaves. D.W. Lee and K. Gould. Advances in Botanical Research. Vol 37. Academic Press.

Hobbie, J. E., G. Shaver, J. Laundre, K. Slavik, L. A. Deegan, J. O'Brien, S. Oberbauer, and S. MacIntyre. In press. Climate forcing at the Arctic LTER Site. In: D. Greenland, D. Goodin and R. Smith (eds.), Climate Variability and Ecosystem Response at Long-Term Ecological Research (LTER) Sites. Oxford University Press, New York.

Theses and Disserations:

Pop, E. W. 1997. Salix pulchra and Betula nana in a globally warmed climate: a model for bud break of two key arctic plant species. M.S. Thesis. Florida International University, Miami FL.

Starr, G. 1998. Effects of extended growing season and soil warming on the ecophysiology of Polygonum bistorta: a global warming perspective. M. S. Thesis. Florida International University, Miami FL.

Gorsuch, D.M. 2000. Analysis of xylem susceptibility to cavitation in arctic plants: physiological and anatomical studies under natural and simulated climate conditions. M. S. Thesis. Florida International University, Miami FL.

Starr, G. 2000. A multi-scale assessment of physiological processes in arctic tundra plants under natural and simulated climate change scenarios. Ph.D. Dissertation. Florida International University, Miami FL.

Presentations at national and international meetings:

Oberbauer, S.F., G.H. Henry, M.D. Walker, P.J. Webber, J.M. Welker, C.E. Tweedie, J.T. Fahnestock, E. Elmore and A. Kuchy, and G. Starr. 2002. Tundra carbon fluxes in response to experimental warming along moisture and latitudinal gradients. ARCSS all hands meeting, Seattle Washington.

Oberbauer, S.F., C. Tweedie, A. Kuchy, P. Webber, B. Hollister, and E. Elmore. 2001. Tundra carbon fluxes in response to experimental warming along moisture and latitudinal gradients. LAII all hands meeting, Salt Lake City, Utah.

Oberbauer, S.F., G. Starr, E.W. Pop, L.E. Ahlquist, and I. Parker. 2001. Contrasting responses of tussock tundra to early season snow melt: growth acceleration versus frost damage. LAII all hands meeting, Salt Lake City, Utah.

Oberbauer, S.F. 2001. Effects of ITEX warming experiments on ecosystem carbon fluxes. LAII all hands meeting, Salt Lake City, Utah.

Oberbauer, S.F. 2001. La Selva site update. Ameriflux annual workshop. Argonne National Lab, Illinois.

Starr, G. and S.F. Oberbauer. 2000. Photosynthetic activity of arctic evergreens under the snow: implications in the ecosystem carbon budget. Annual meeting of Ecological Society of America, Snowbird, Utah.

Gorsuch, D.M., S.F. Oberbauer, and J.B. Fisher. 2000. Effects of early summer frosts on the hydraulic and stomatal conductance of a deciduous arctic species. Annual meeting of Ecological Society of America, Snowbird, Utah.

Starr, G, S.F. Oberbauer, and D.S. Neuman. 2000. Physiological response of two arctic sedges to changes in soil temperature. International Tundra Experiment Workshop, Abisko, Sweden.

Ahlquist, L.E. S.F. Oberbauer, and G. Starr 2000. Using digital imaging to determine NDVI on small scale plots. International Tundra Experiment Workshop, Abisko, Sweden.

Ahlquist, L.E. S.F. Oberbauer, and G. Starr 2000. Using digital imaging to determine NDVI on small scale plots. Arctic System Science LAII workshop, Seattle Washington.

Oberbauer, S.F., Gregory Starr, L. E. Ahlquist 2000. Ecosystem responses of tussock tundra to extended growing season length and soil warming: leaf area and carbon exchange. Arctic System Science LAII workshop, Seattle Washington.

Ahlquist, L.E., E. Rodriguez, B. Shamblin, and S.F. Oberbauer. 1999. Phenological and physiological responses of eight northern Alaska species to decreased summer irradiance. 9th International Tundra Experiment Meeting, January 1999, East Lansing.

Oberbauer, S.F. 1999. Effects of increased season length on plant phenology, community composition, productivity, and ecosystem carbon fluxes in Alaskan tundra . U.S. International Tundra Experiment workshop, September 1999, Boulder

Oberbauer, S.F., G. Starr, E. W. Pop, and L. E. Ahlquist. 1999. Phenological influences on ecosystem gas exchange: response to extended growing season. Annual Meeting of South Florida Plant Biologists, April 1999, Davie FL.

Oberbauer, S.F., G. Starr, E. W. Pop, and L. E. Ahlquist. 1999. Phenological influences on ecosystem gas exchange: response to extended growing season. Arctic System Science LAII meeting, March 1999, Seattle

Oberbauer, S.F., G. Starr, E.W. Pop, and L.E. Ahlquist. 1999. Linking leaf phenology and gross ecosystem production in Alaska tussock tundra. 9th International tundra experiment Meeting, January 1999, East Lansing.

Pop, E.W. Steven F. Oberbauer, and Gregory Starr. 1999. Predicting bud break in two Arctic deciduous shrubs, Salix pulchra and Betula nana.. Annual Meeting of South Florida Plant Biologists, April 1999, Davie FL

Pop, E.W. Steven F. Oberbauer, and Gregory Starr. 1999. Predicting bud break in two Arctic deciduous shrubs, Salix pulchra and Betula nana. Arctic System Science LAII meeting, March 1999, Seattle

Rodriguez, E., R. B. Shamblin, S.F. Oberbauer, G. Starr, and L.E. Ahlquist. 1999. Phenological and physiological responses of eight northern Alaska tundra species to decreased summer irradiance. Annual Meeting of South Florida Plant Biologists, April 1999, Davie FL

Rodriguez, E., R. B. Shamblin, S.F. Oberbauer, G. Starr, and L.E. Ahlquist. 1999. Phenological and physiological responses of eight northern Alaska tundra species to decreased summer irradiance. Arctic System Science LAII meeting, March 1999, Seattle

Pop, E. W., S.F. Oberbauer, and G. Starr. 1997. The effects of extended growing season and soil warming on plant canopy development in arctic tundra. ESA Annual Meeting, Albuquerque, NM.

Pop, E. W., S.F. Oberbauer, and G. Starr. 1997. Effects of extended season on canopy leaf area and NDVI. Eight Annual International Tundra Experiment Workshop, London, April 19-22 1997.

Starr, G, S.F. Oberbauer, and E.W. Pop. 1997. Effects of early extended season on carbon and nutrient use efficiency of Polygonum bistorta. Eight Annual International Tundra Experiment Workshop, London, April 19-22 1997.

Oberbauer, S.F., G. Starr, and E.W. Pop. 1997. Effects of increased season length and soil heating on carbon exchange of tussock tundra in Alaska. ESA Annual Meeting, Albuquerque, NM.

Oberbauer, S.F., G. Starr, and E.W. Pop. 1997. Effects of increased growing season length and soil warming on carbon dioxide and methane exchange of tussock tundra in Alaska. Arctic System Science Land-Air Interface Interactions workshop, Seattle Washington, March 1997.

Oberbauer, S.F., G. Starr, and E.W. Pop. 1997. Effects of increased growing season length and soil warming on carbon dioxide and methane exchange of tussock tundra in Alaska. Eight Annual International Tundra Experiment Workshop, London, April 19-22 1997

Starr, G., Oberbauer, S. F., and E.W. Pop. 1997. Phenological and physiological responses of Polygonum bistorta to a lengthened growing season and soil warming in Alaskan tussock tundra. ESA Annual Meeting, Albuquerque, NM.

Oberbauer, S.F., G. Starr, and E.W. Pop. 1996. Effects of early-season snow removal on soil temperature, thaw depth, canopy development, and ecosystem CO2 exchange in arctic Alaska. Seventh Annual International Tundra Experiment Workshop, Copenhagen Denmark.

Pop, E.W., S.F. Oberbauer, and G. Starr. 1996. Effects of extended season on leaf flushing, timing of bud break, and flowering in several dominant species of tussock tundra. Seventh Annual International Tundra Experiment Workshop, Copenhagen Denmark.

Starr, G, S.F. Oberbauer, and E.W. Pop. 1996. Early season snow removal and its effects on the physiology of Polygonum bistorta. Seventh Annual International Tundra Experiment Workshop, Copenhagen Denmark.

Oberbauer, S.F., G. Starr, and E. Pop. 1996. Effects of early-season snow removal on soil temperature, canopy development, and ecosystem CO2 exchange in arctic Alaska. ARCS-LAII workshop, Seattle Washington, March 1996.

Oberbauer, S.F. Effects of decreased season length on plant phenology, community composition, productivity, and ecosystem carbon fluxes in Alaskan tundra: implications for climate warming. 1995. Arctic System Science -Land Air Interface Interactions workshop. Orcus Island, Washington. March 1995.

Study site is near Toolik Lake Alaska on the Dalton Highway north of the Brooks Range.	View of Brooks Range south of study site
Gas exchange chamber on study plot surrounded by boardwalks	Study plot

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This page is under contruction by S.F.O. Last updated 10 Feb 2003

Send mail to:oberbaue@fiu.edu