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B. H. Luckman1
and J.A.Boninsegna2
1 Department of Geography, University of
Western Ontario, London, Canada
luckman@uwo.ca
2Laboratorio de Dendrocronologia. IANIGLA-CONICET, Mendoza,
Argentina.
pbonin@lab.cricyt.edu.ar
Accepted for
PAGES 2002.
This is one of 14 Collaborative Research Networks
(CRN) funded by the Inter-American Institute for Global Change
Research. It was established in 1999 and involves 15 principal
investigators from 13 institutions in Canada, USA, Mexico, Bolivia,
Chile and Argentina. The primary goals of the project are (i ) to
develop a network of tree-ring chronologies from climatically-sensitive
treeline sites in the western American Cordillera and (ii) use these
data to reconstruct and compare regional climate variability along a
transect from Alaska to Tierra del Fuego (PEP-1) and define its
interannual-decadal scale modes of climate variability. The project
also focuses on enhancing the development and utilization of
dendrochronology for tropical mountain tree species and expanding
collaboration, training and application of dendrochronology and
paleoenvironmental science within Latin America to address the issues
of climate variability and change.
 The
existing chronology coverage of the American Cordillera is patchy (see
map) and the initial sampling has targeted significant geographical
gaps and key areas. We anticipate that the development of this more
comprehensive geographical coverage will allow the reconstruction of
global-scale spatial and temporal patterns of temperature and
precipitation along this transect over the last several hundred years.
Documentation of these changing spatial patterns is key to
understanding the atmospheric and oceanic controls of climate
variability. Several new chronology networks have been developed since
the inception of the project. In the Southern Canadian Cordillera
three new single species chronology networks have been developed for
temperature reconstructions at upper treeline sites. A complementary
network of 53 lower treeline moisture- sensitive sites has also been
assembled and is being used to derive maps showing annual
precipitation anomalies and to assess drought probabilities for the
region over the last 300 years. Extensive sampling is also planned for
temperature reconstructions from treeline sites across northern
British Columbia and the Yukon in the next few years. In Mexico the
new sampling programs have primarily targeted Douglas fir and
Montezuma baldcypress stands across central and Northern Mexico to
develop precipitation and drought reconstructions that have obvious
applications to agriculture and forestry in addition to their
paleoclimate significance. In South America, Nothofagus pumilo
(lenga) dominates treeline sites in the southern Andes of Chile and
Argentina. A network of over 90 lenga sites between 35 and 55°S has
been used to develop reconstructions of annual temperatures for
northwestern and southern Patagonia between AD 1630 and 1987.
Both reconstructions reveal the unusual nature of climate
conditions during the 20th century when compared with the
past 400 years. New chronologies have also been developed for
Austrocedrus chilensis in both Chile and Argentina with a maximum
length of over 1800 years that will yield long precipitation and ENSO
reconstructions. Tree growth in many of these tree-ring series is
strongly correlated with sea
 surface
temperatures (SST) in adjacent areas of the Pacific and Atlantic
Oceans. Reconstructing the spatial and temporal variability of Pacific
SSTs will provide a major component in enhancing our understanding of
the global climate system (e.g. in studies of el Niño, PDO and their
interrelationships). In conjunction with ongoing dendroclimate work,
several investigators are also using dendrochronology to date glacier
fluctuations of the last millennium in Canada, Chile and Argentina.
In addition to their value as paleorecords, these
tree-ring archives will also be applied to the study of a number of
economic, social or environmental issues. For example, recent drought
reconstructions indicate that the catastrophic
 cocoliztli
epidemics of the Mexican Highlands beginning in 1545 and 1576
coincided with the most severe drought in the last 500 years
(Acuna-Soto et al., 2000). Cocoliztli is now thought to be an
indigenous haemorrhagic fever, possibly transmitted by rodent hosts
and aggravated by drought conditions. It is hypothesized that drought
periods can concentrate and spread infection among the residual rodent
population. When climatic conditions ameliorate, the infected rodent
population may invade farms and homes to spread the disease agent.
Humans infected with cocoliztli often died painfully in as little as
3-4 days. Similar climate forcing was observed during the Hantavirus
outbreaks in the southwestern US in 1993, but cocoliztli probably was
not a Hantavirus and the true disease agent remains unknown.
Nevertheless, the 16th century epidemics do seem to have occurred
during one of the worst Mexican droughts in the past 500 years, and
the epidemics of 1545-8 and 1576-8 each reduced the population of the
Mexican Highlands by about 50%. Population recovery was slow and
numbers remained well below their 16th century levels until
the 20th century.
Reconstruction of climate variability in low
latitudes has been hampered by the lack of suitable annually-resolved
proxy climate records. This project will attempt to narrow the
"latitudinal gap" between the presently available tree-ring chronology
networks by (i) expanding existing chronology networks equatorwards
for those species known to have annual rings and (ii) by exploring the
potential of many new species to yield annual ring series. During the
last year we have developed chronologies from sites at the extreme
range of Douglas fir (Pseudotsuga menziesii) at 17° and 55°N in
Mexico and British Columbia, respectively. Chronologies have also been
developed from four new tropical species;
 Pinus
hartwegii growing at 3600-3700m on Nevado de Colima volcano,
Mexico (20°N): Polylepis tarapacana at 4800-4900m on Volcan
Sajama, Bolivia (18°S) and 4750m on Cerro Granados, Argentina (22°
32'S); Polylepis pepei in the Cordillera Tunari, Bolivia (17°S)
and Prosopis ferox at 3500m in the Humahuaca Valley, Argentina
(23°S). Although ring definition varies between these species they all
show promise for the reconstruction of temperatures (Polylepis)
or precipitation (Pinus and Prosopis) and living
specimens of Polylepis and Prosopis are known to reach
ca. 500 years of age. The two Bolivian chronologies are the highest
elevation tree-ring chronologies in the world.
Expanding scientific capacity, training and
exchanges are also major goals of the project. New laboratories have
been established for basic dendrochronological work in Durango, Mexico,
La Paz, Bolivia (both October 2000) and Piura, Peru (January 2001,
using IAI-PESCA funding). All will serve regions with little or no
prior expertise in tree-ring studies. Dedicated staff are associated
with each facility and have undertaken training at one of the
laboratories in the CRN (Mendoza, Tucson, Lamont or Arkansas). The CRN
has also encouraged and sponsored participation of latin american
students in the first dendroecological field courses to be held in
Latin America at San Martin de los Andes, Argentina (April 2000);
Saltillo, Mexico (August 2001) and in Valdivia, Chile (April 2001).
This project will run in its present form for 5
years and we are still in the initial stages. It will provide new
proxy records of local and regional climate variability and change,
many from regions that hitherto have been data-poor. It will also be
able to generate related datasets (e.g. drought and flow frequencies;
estimates of timber production) that may be usefully applied to impact
assessment or scenario development for environments undergoing
significant climate change. The combination of such regional data sets
with other, presently available, data (e.g. from the western United
States) will ultimately allow the development hemispheric-scale
datasets for the last 3-500 years. These data sets will be used to
document the large spatial and temporal variance that characterises
the tropical (ENSO) and high latitude (e.g. PDO) atmospheric
circulation features associated with interannual to decadal
variability of climate over the Americas and thereby achieve a better
understanding of its underlying patterns and causes. For example, the
recent ENSO reconstruction developed by Stahle et al. (1998) may be
significantly enhanced by the incorporation of data from drought-resistant
and el Niño sensitive tree-ring chronologies in Central Chile and
adjacent Argentina. Similarly the development and combination of data
sets to address low frequency climate variability (e.g. Villalba et
al, 2001) could significantly improve understanding of phenomena such
as the PDO and the relationship between PDO and ENSO phenomena. As the
project continues we hope to provide data that will address these
large scale issues.
The full membership of the CRN is J.A. Boninsegna,
F. A. Roig, R. Villalba (Mendoza, Argentina); J. Argollo (La Paz,
Bolivia), B.H.Luckman (London, Canada), D. J. Smith (Victoria, Canada),
J-C. Aravena
(Santiago, Chile), A. Lara (Valdivia, Chile), J.
Villanueva-Diaz (Durango, Mexico), F. Biondi (Reno, NV., USA), H. F.
Diaz (Boulder, CO., USA), M.K. Hughes (Tucson, AZ., USA), G. C. Jacoby
(New York, NY., USA), D.W. Stahle (Fayetteville, AK., USA) and L. G.
Thompson (Columbus, OH.,USA). The PESCA collaborators are R.
Rodríguez, A Mabres, L. Flores (Piura, Peru) and R. Woodman Lima, Peru)
Further information about participating scientists
and institutions, plus the first two annual reports of activity and
other information can be found on the project's web site at
http://www.cricyt.edu.ar/IAI/ or through
http://wdc.cricyt.edu.ar/
References
Acuna-Soto, R., L. Calderon Romero, and J.H.
McGuire, 2000. Large epidemics of hemorrhagic fevers in Mexico
1545-1815. American Journal of Tropical Medicine and Hygiene
62(6):733-739.
Acuna-Soto, R., D.W. Stahle, M.K. Cleaveland, M.D.
Therrell, in press. Megadrought and megadeath in 16th century Mexico.
Emerging Infectious Diseases.
Stahle, D.W., D’Arrigo, R.D., Krusic, P.J.,
Cleaveland, M.K., Cook, E.R., Allan, R.J., Cole, J.E., Dunbar, R.B.,Therrell,
M.D., Gay, D.A., Moore, M.D., Stokes,. M.A., Burns, B,T,, Villanueva-Diaz,
J. and Thompson, L.G., 1998. Experimental dendroclimatic
reconstruction of the southern oscillation. Bulletin of the American
Meteorological Society, 79(10): 2137-2152.
Villalba, R., D’Arrigo, R.D., Cook, E.R., Wiles, G,
and Jacoby G.C. 2001. Decadal-scale climatic variability along the
extratropical western coast of the Americas: Evidences from tree-ring
records. In: Inter-Hemispheric Climate Linkages, Vera Markgraf (ed.),
Academic Press. pp. 155-172.
Acknowledgements: We would like to thank R.
Villalba, M. Morales and D.W. Stahle for providing the information for
Figures 2-4, respectively.
Figure captions
Map of the Americas with prospective sampling areas
and location of participating tree-ring laboratories. (MM= Mexican
Monsoon; TPI= Trans-Polar Index; PDO= Pacific Decadal Oscillation)
Correlation fields between reconstructed temperatures in NW (above)
and Southern Patagonia ( below, based on lenga tree-ring width
chronologies) and SSTs across the South Pacific and South Atlantic.
Relationships between drought and disease in 16th
century Mexico (after Acuna-Soto et al., in press). The drawing is
reproduced from contemporaneous sources.
Annual rings in a specimen of Prosopis ferox, Argentina (ca.
23° S). The ring boundary is marked by a narrow band of terminal
parenchyma cells. The scale bar is 100m m
long.
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