W. Stahle is a professor of Physical Geography and the
Conservation of Natural Resources at the University
of Arkansas. He received his B.A. in Anthropology from
the University of Arizona in 1973, his M.A. in Archaeology
from the University of Arkansas in 1978, and his Ph.D.
in Geography from Arizona State University in 1990.
research interests include all aspects of dendrochronology
(the study of tree rings), particularly climate change
and the proxy evidence for past variation in the El
Nino/Southern Oscillation and other large scale atmospheric
circulations. He has developed GIS-based predictive
models for the location of ancient forests, and is conducting
active research in the United States, Mexico and Africa.
Stahle's research is funded by NOAA, NSF, NPS and the
USGS and he has published in a variety of journals including,
Science, Nature, Journal of Climate and Bulletin of
the American Meteorological Society.
links to David Stahle's home page and other related infomation
please see our resources
What are the future global weather effects of the national
timber industry cutting down "old growth" trees?
are many sound arguments against the logging of our
last remaining old-growth forests in the USA, but the
threat of global climate change is probably not the
strongest. The remaining old-growth forests constitute
just a small fraction of the country, and the USA constitutes
just a small fraction of the land area of earth. So
logging what's left of old growth in the USA, bad though
that would be, probably would not have a big impact
on global climate, particularly if these ancient forest
sites were allowed to regenerate into some kind of forest
cover. It should be acknowledged, however, that net
deforestation worldwide is a different matter. Climate
simulations have indicated that replacing the triple
canopy virgin rainforest in Amazonia with cattle pasture
would probably indeed have a drastic impact on the regional
climate, and these changes would surely alter the global
atmospheric circulation as well.
What are some other mysteries of history that natural
records like tree rings have been able to solve?
rings are shedding new light on several historical mysteries.
White spruce trees from Alaska indicate that the coldest
summer in 400 years occurred in 1783. This unusual cold
was probably brought on by the 1783 eruption of the
Laki volcano in Iceland, and appears to have been responsible
for widespread starvation and population decline among
the Inuit during the "Time summer Did Not Come" (Gordon
Jacoby and others, Quaternary Science Reviews, 1999).
16th century "megadrought" across North America (roughly
extending from 1540-1590) has been linked with the disappearance
of the English Lost Colony of Roanoke Island (1587),
the abandonment of the Spanish colony of Santa Elena
at Parris Island, South Carolina (1587), the abandonment
of Tewa, Keres, and other Puebloan villages in New Mexico
(mid-16th century), and with two of the greatest human
mortality events in New World history....the cocoliztli
epidemics of 1545 and 1576 in Mexico when millions died
from hemorrhagic fevers possibly associated with a rodent
vector leveraged by extreme drought conditions (Stahle
and others, Eos, Transactions of the American Geophysical
Union, March 21, 2000).
Mike Baille describes tree ring and other evidence for
a climatic catastrophe in AD 536, which he postulates
might have been due to a comet impact with earth (Exodus
to Arthur: Catastrophic Encounters with Comets, Batsford
Ltd., London, 1999). The evidence for a 536 climate
extreme is impressive and includes record or near-record
narrow tree rings in Fennoscandia, Ireland, North America,
Chile, and Mongolia, frost rings in Mongolia, historical
evidence for dry fogs, unusual cold, crop failure, and
famine over Europe and the Middle East, and Chinese
records of dim sun, frost damage to crops and famine.
A cataclysmic volcanic eruption might also explain these
global scale climate anomalies of 536, but undisputed
ice core evidence for a major eruption at 536 or shortly
before has yet to be produced.
LaMarche (deceased) and Katie Hirschboeck describe tree-ring
evidence for a massive volcanic eruption in 1627B.C.,
which is believed by many analysts (but by no means
all) to have been the catastrophic explosion of Santorini
on the island of Thera, which may have played a role
in the collapse of the Minoan Civilization.
rings and other annually-resolved paleoclimatic proxies
such as glacial ice layers and coral bands record detailed
environmental histories and will no doubt provide many
interesting new insights into history and prehistory.
I know carbon dating is sometimes controversial. Can comparing
carbon dating data with tree-ring data help resolve debates?
How far back can tree rings help you date something? What
other natural time-keepers are there?
dating is an outstanding method for age determination
covering the late glacial and post-glacial period. In
any dating problem, it is always preferable to have
multiple dating methods providing concordant results.
But there is a special relationship between dendrochronology
and radiocarbon dating, because wood samples that have
been exactly dated to the calendar year by dendrochronology
have then been analyzed for radiocarbon content. It
was found early on in the development of radiocarbon
dating that carbon dates systematically deviated from
true calendar age determined from tree rings. This systematic
deviation is due to long-period variations in the solar
magnetic field that would alternately shield the earth
from incoming cosmic radiation and thereby alter the
production rate of atmospheric radiocarbon. This systematic
error in carbon dating is now well recognized and routinely
corrected. So it is entirely true to say that dendrochronology
has helped improve the accuracy of radiocarbon dating
over the last 10,000 years or so during which we have
continuous tree-ring chronologies.
dating is the most accurate and precise dating method
in geochronology, capable of dating determinations to
the season of a specific calendar year. However, the
oldest known trees on earth are just a shade less than
5000 years old, so tree-ring dating is really only possible
during the post-glacial period. Dendrochronologists
have been able to extend exact tree-ring chronologies
back to 10,000 years in rare circumstances by including
older wood found in archaeological or subfossil deposits,
but most tree-ring chronologies are less than 1000 years
are many other natural timekeepers. The horizontal sedimentary
rock strata seen in the sidewalls of the Grand Canyon
of the Colorado River have to be among the most famous
pages of earth history, recording deep geological time
with the evolutionary changes in life witnessed in the
beautiful rock strata of western North America. But
there are also many excellent natural archives that
record annual changes, and my personal favorites include
annually banded corals (the dating of which is referred
to as sclerochronology), varved sediments found at the
bottom of proglacial lakes and in a few other lacustrine
and marine settings, and annually banded ice found in
some glaciers worldwide.
I read your web feature "Lessons From the Past," What's
being done to protect these natural records of the climate
of the past? What is the most endangered natural record?
my opinion, we are not doing enough to protect ancient
climate sensitive forest trees, banded coral heads of
the tropical oceans, or even the annually layered ice
found in tropical glaciers such as Quelccaya in Peru
or Kilimanjaro in East Africa. Coral reefs need more
serious protection from overfishing and water pollution.
And it may be ironic, but coral reefs in the tropical
oceans and ice sheets at the summits of tropical mountains
are both threatened by global warming, and yet many
political leaders are in denial about our wasteful overconsumption
of fossil fuels and the harmful consequences of that
waste to our environment, economy, and even national
forests with giant trees get a good deal of press, deservedly
so, but not the dwarfed, gnarly, old-growth trees found
on harsh sites throughout the United States and really
around the world. Our public vision of old growth tends
to perceive redwoods or other huge trees of temperate
rainforests, and not the stubby, stunted, and most ancient
of trees such as the bristlecone pine, the blue oaks
of the California foothills, or the craggy chestnut
oak still found along exposed positions of the Blue
Ridge Parkway. Out of ignorance for the true antiquity
of these sorts of super senescent trees, they continue
to be destroyed for very mundane reasons. You can see
an example of this type of low-stature noncommercial
woodland at our website on the Ancient Cross Timbers
in the south-central USA (http://www.uark.edu/xtimber).
I believe that if people realized that many trees in
noncommercial woodlands were old at the birth of American
democracy, then they might very well have a higher opinion
of these austere survivors and the intricate natural
histories they preserve in their centuries-long tree-ring
series. If we realized that these ancient woodlands
on stressful sites scattered throughout the United States
were indeed one part of the complex vegetation mosaic
that made up the presettlement natural landscape, then
we might think twice about scraping away these authentic
Americans for chip mills, parking lots, or new homes
landscaped with still more Bermuda grass and ornamental
pear trees. --