Tree-Ring Formation, Isotopes, and El Niño
in Ponderosa Pine of the Southwest

(NSF GRANT #(NSG-ESH-)ATM-9810474 1 Oct. 1998 to 30 Sept. 2002)
Principal Investigators:
Steven W. Leavitt, Austin Long, Harold C. Fritts, Wm. Edward Wright, and Deborah Hemming (Post-Doc)

      The southwestern United States is an important climatic transition region between "genetic climate regions" (Bryson and Hare, 1974), whose boundary varies seasonally and from year to year. Important meteorological phenomena contributing to the inter-annual climatic variability in this region include El Niño/La Niña events, which are particularly influential in winter precipitation, and the more erratic summer influence of the western limb of the North American monsoon system. Prospects for reconstructing long-term incidence, extent and strength of these climate events can be improved by using proxy tools such as tree rings, on which a wide variety of parameters may be measured, such as ring width, wood x-ray density, cell size, and isotopic composition.
     We have used stable isotope analysis of tree rings in the Southwest in this and the preceding grant to derive empirical relationships between the isotopic composition of ponderosa pine wood cellulose and environmental parameters such as drought, precipitation amount, humidity and sea-surface temperature. These relationships were developed for stable oxygen and carbon isotopes on a largely spatial scale involving a network of sites whose rings were analyzed for an 11-y period, and on a temporal scale at one site where a 100-y chronology was developed. Furthermore, seasonal relationships were explored by subdividing the rings into 3 subdivisions (Fig. 1) anchored on the inside and outside of the ring and a false-latewood band occurring within the growth band and signifying the onset of the monsoon season (about the first week in July).

Fig. 1. Subdivisions of rings based on false-latewood band (FLB). Post-false segment is indicated, and there are 2 equal pre-false subdivisions ("Pre-1" and "Pre-2")

    Additionally, we improved the mechanistic TREERING 3 growth model and employed it to advance our understanding of processes and mechanisms by which tree rings acquire an isotopic composition related to these environmental signals. The basic model takes the raw materials of photosynthesis (carbon dioxide and water) together with climatic inputs (sunlight, soil water, and sensible heat) to manufacture photosynthates and then sequentially initiate and mature wood cells with those photosynthates. By adding isotopic subroutines according to the current theoretical models of isotope incorporation in plants, changes in climate or isotopic composition of CO2 and water during the growing season were then be incorporated into the isotopic composition of both individual cells as they develop over some finite period and the sequence of cells formed during the growing season. Implementation of the isotope subroutines was guided (calibrated and verified) with seasonal tree-ring isotope data and with precise plant-growth-isotope data derived from field experimentation. We were particularly interested in how the process model might guide our understanding of the interaction of multiple factors producing the distribution of isotopes measured within tree rings and ultimately better reconstruction of environment from isotopic measurements.
    The project contributes to the focus of SWLs research on stable isotopes in tree rings, leaves and soils as tracers and indicators of the environment in modern, historical and prehistorical contexts. Specifically, the research has 1) developed seasonal isotope (d¹³C [link to Data],d¹⁸O) chronologies of ponderosa pine (and related Apache pine) from about 1985-1995 in 7 mountain ranges in S. Arizona and New Mexico, with subsampling of periods formed before and after the onset of the summer monsoon, 2) developed a 100-yr seasonal isotope (d¹³C, d¹⁸O) chronology from ponderosa pine a site in the Santa Catalina Mts. near Tucson, 3) monitored environment and collected precipitation, soil water and plant water at the Santa Catalina site to better understand the mechanisms contribution to d¹⁸O in the tree rings, 4) conducted double-labeling isotope tracer (d¹³C, d¹⁸O) experiments in the Santa Catalina Mts. to better understand the timing of incorporation of isotopes generated during photosynthesis into the tree rings themselves, 5) collected needles samples at biweekly intervals during the 1998 and 1999 growing seasons to better link d¹³C and d¹⁸O in the needles to those in the rings, 6) added mechanistic algorithms for dD, d¹³C, d¹⁸O into the tree-ring growth model TREERING 3.0 for the purpose of modeling of cell-by-cell development and isotopic composition as related to primary input variable of temperature, precipitation and sunlight. This data is being linked together through the model to properly represent processes producing the isotopic compositions we are measuring in seasonal segments of ponderosa pine rings.

Publications and Presentations:

Hemming, D.L., H.C. Fritts, S.W. Leavitt, W.E. Wright, A. Long. (1999) Modelling tree ring d¹³C. American Geophysical Union. Abstracts - San Francisco, December 1999.

Hemming, D.L., Fritts, H.C., Leavitt, S.W., Wright, W.E., Long, A., Shashkin, A. (2000) Incorporating stable isotopes into the 'TreeRing 2000' model of tree ring formation. International Conference on Dendrochronology. Abstracts - Mendoza, March 2000.

Hemming, D., Fritts, H.C., Leavitt, S.W., Wright, W., Long, A., Shashkin, A., 2001. Modelling tree-ring d¹³C. Dendrochronologia 19(1): 23-38.

Hemming, D., Fritts, H., Leavitt, S., Wright, W., Shashkin, Long, A., 2001. A process model of tree-ring d¹³C, d¹⁸O and dD applied to 20th Century ponderosa pine growth in southern Arizona. 18th Pacific Climate Workshop, Asilomar Conference Center, Pacific Grove, CA, 18-21 March (abstr).

Hemming, D., Jalkanen, R. and Leavitt, S.W., 2001. Preliminary relationships between climate and the apical extension, needle production and ring width of Pinus ponderosa in Arizona, USA. The Palaeobotanist 50(1): 125-131.

Leavitt, S.W., 2002. Moisture availability and water-use efficiency in d¹³C of pine tree rings of the U.S. Southwest. 6th International Conference on Dendrochronology, Quebec City, Canada, 22-27 August.

Leavitt, S.W. and Baisan, C.H., 2001. Variability of seasonal d¹³C patterns in Apache pine from southern Arizona, USA, The Palaeobotanist 50(1): 117-123.

Leavitt, S.W., Wright,W.E., Hemming, D., Long, A., 2002. Micro-variation of d¹³C in tree rings of ponderosa pine from S. Arizona. Ecological Society of America Annual Meeting, 4-9 August, Tucson.

Leavitt, S.W., Wright, W.E. and Long, A., 1998. ENSO signal in d¹³C of pre- and post-false latewood of ponderosa pine tree rings in southeastern Arizona. Proceedings of the 14th Pacific Climate (PACLIM) Workshop, 6-9 April 1997, Two Harbors, Santa Catalina Island. Eds. Wilson, R. and Tharp, V., Technical Report #57 of the Interagency Ecological Program for the Sacramento-San Francisco Estuary, pp. 61-68, April 1998.

Leavitt, S.W., Wright, W.E. and Long, A., 1999. Evidence for ENSO in Tree-Ring d¹³C Along a 500-km E-W Transect in Southern Arizona and New Mexico. Proceedings of the 15th Pacific Climate (PACLIM) Workshop, 27-30 April 1998, Two Harbors, Santa Catalina Island. Eds. Wilson, R. and Buffaloe, L.D., Technical Report #64 of the Interagency Ecological Program for the Sacramento-San Francisco Estuary, pp. 61-68.

Leavitt, S.W., Wright, W.E., Long, A. (2000) Seasonal d¹³C variability in ponderosa pine tree rings in southern Arizona and New Mexico. International Conference on Dendrochronology. Abstracts - Mendoza, March 2000 (abstr.).

Leavitt, S.W., Wright, W.E. and Long, A., 2000. Seasonal water status in carbon-13/carbon-12 ratios of ponderosa pine tree rings from S. Arizona and New Mexico. AGU Fall Meeting, 15-19 December 2000, San Francisco, CA. (Eos, Transactions of the American Geophysical Union, v. 80, n. 48, p. F460 (abstr.)).

Leavitt, S.W., Wright, W.E. and Long, A., 2001. Stable isotopes, tree rings and the southwestern Monsoon. 18th Pacific Climate Workshop, Asilomar Conference Center, Pacific Grove, CA, 18-21 March (abstr.).

Leavitt, S.W., Wright, W.E., Long, A. 2002. Spatial expression of ENSO, drought and summer monsoon in seasonal d¹³C of ponderosa pine tree rings in southern Arizona and New Mexico. Journal of Geophysical Research 107(D18) 4349, doi:10.1029/2001JD001312. (Link to Data)

Leavitt, S.W., Wright, W.E., Long, A. and Fritts, H., 2001. A century-length tree-ring d¹³C chronology from southeastern Arizona. Proceedings of 17th Annual Pacific Climate (PACLIM) Workshop, 22-25 May 2000, Two Harbors, Santa Catalina Island. Eds. West, G.J. and Buffaloe, L.D., Technical Report #67 of the Interagency Ecological Program for the San Francisco Estuary, pp. 11-18, March 2001.

Wright, W.E. 2001. D and 18O in Mixed Conifer Systems in the United States Southwest: The Potential of d¹⁸O in Pinus ponderosa tree rings as a natural environmental recorder. Ph.D. Dissertation, University of Arizona, Tucson, AZ. 329 pp.

Wright, W.E., Long, A., Comrie, A., Leavitt, S., Cavazos, T. (1999) The North American Monsoon: Eastern Pacific Atmospheric Circulation, Sea Surface Temperatures and 18O in Terrestrial Precipitation. American Geophysical Union. Abstracts - San Francisco, December 1999 (abstr.).

Wright, W.E., Leavitt, S.W., 2001. The potential of tree-ring 18O as a proxy for mean northward moisture transport during and immediately following the North American Monsoon. NOAA 26th Annual Climate Diagnostics and Prediction Workshop, Scripps Institution of Oceanography, La Jolla, California, 22-26 October.

Wright,W.E., Leavitt, S.W., 2002. d¹⁸O Variation in Pinus ponderosa needle subdivisions from two growing seasons. Ecological Society of America Annual Meeting, 4-9 August, Tucson.

Wright,W.E., Leavitt, S.W. 2002. Specific humidity reconstruction in the semi-arid southwestern United States using cellulose oxygen isotope ratios. 6th International Conference on Dendrochronology, Quebec City, Canada, 22-27 August.

Wright, W.E. and Leavitt, S.W. 2006, Needle cell elongation and maturation timing derived from pine needle cellulose d¹⁸O. Plant, Cell and Environment 29: 1-15.

Wright, W.E. and Leavitt, S.W. 2006. Seasonal humidity reconstructed from a tree-cellulose d¹⁸O time series. Journal of Geophysical Research 111: D18105, doi:10.1029/2005JD006806.

Wright, W.E., Leavitt, S.W. and Long, A., 1997. Intra-annual measurements of d¹⁸O compared with d¹³C in tree cellulose: A unique record reflecting either physiological responses or challenging fundamental assumptions. 7th Annual V.M. Goldschmidt Conference, 2-6 June, Tucson. LPI Contribution No. 921, Lunar and Planetary Institute, Houston, pp. 221-222.

Wright, W.E., Leavitt, S.W., Long, A. 1999. ENSO Teleconnections: Eastern Pacific Sea Surface Temperature Correlations with d¹⁸O in Southeastern Arizona Precipitation and Tree Cellulose. Proceedings of the 15th Pacific Climate (PACLIM) Workshop, 27-30 April 1998, Two Harbors, Santa Catalina Island. Eds. Wilson, R. and Buffaloe, L.D., Technical Report #64 of the Interagency Ecological Program for the Sacramento-San Francisco Estuary, pp. 97-109, April 1999.

Wright, W., Leavitt, S., Long, A., Comrie, A., Cavazos, T., Eastoe, C. (2000) Can Stable Isotopes in Precipitation and Post-false Latewood Tree Ring Cellulose Indicate Inter-annual Changes in North American Monsoonal Circulation? International Conference on Dendrochronology. Abstracts - Mendoza, March 2000 (abstr.).

Wright, W.E., Long, A., Comrie, A.C., Leavitt, S.W., Cavazos, T., Eastoe, C. 2001. North American Monsoonal Moisture Sources and Climatic Teleconnections Revealed Using Precipitation Stable Isotope Timeseries. 12th Symposium on Global Change Studies and Climate Variations, Session 9: North American Monsoon. 13-18 January, Albuquerque, NM.

Wright, W.E., Long, A., Comrie, A.C., Leavitt, S.W., Cavazos, T., Eastoe, C. 2001. Monsoonal Moisture Sources Revealed Using Temperature, Precipitation, and Precipitation Stable Isotope Timeseries. Geophysical Research Letters 28(5): 787-790.