Message #185
From: AzTeC SW Archaeology SIG
To:   "'Matthias Giessler'" 

[ AzTeC / SWA SASIG ] :

Date: Mon, 08 Jun 1998 19:22:06
Subject:	Dendrochronologist Gets Date With
		Extended Woody History


http://www.unisci.com/news3.htm

Arizona Tree Alive Since 1300s Helps Explain
Environment

Learning how climate changes over time -- decades
and centuries -- is important to anyone concerned
with water supply, agriculture, forestry, energy
and ecology. One approach is for dendrochronologists
to develop a tree-ring chronology.

Now tree-ring scientists from The University of
Arizona in Tucson have discovered living Douglas-
fir trees that have been growing since the 1300s
on rugged slopes near the Reef of Rocks in the
Santa Catalina Mountains north of the city.

Until two weeks ago, the oldest living tree ever
found in the Catalinas was a Ponderosa pine with
an inner date of A.D.1412 growing on Green
Mountain. That tree died during the drought of
1989, the tree-ring scientists said. 

The oldest of the newly discovered Douglas-firs
has been growing at least since A.D. 1320, said
Ed Wright, a graduate research associate with the
UA Laboratory of Tree Ring Research, who found the
sites. 

Few might believe a 678-year-old fir grows so
close to Tucson. It began life at the height of
the Hohokam Classic Period, when people in central
and southern Arizona built ceremonial platform
mounds, hunted desert bighorn sheep and other game,
and farmed with the largest prehistoric system of
irrigation canals north of Peru. 

Wright has been spending his free weekends for the
past 15 months scouting sites for very old living
trees and remnant wood. He recently secured the
necessary permits through the U.S. Forest Service
for coring living trees and sampling dead wood in
the Reef of Rocks and Wilderness of Rocks areas. 

His aim has been to push the known tree ring
chronology of the Santa Catalina range farther
into the past for more information on climate. His
particular research focus is to find old remnant
wood with wide rings and other features that can
be used to extend the stable isotope chronology
back in time. 

Scientists have discovered that stable isotopes
ratios (ratios of non-radioactive forms of such
elements as oxygen) are sensitive to some aspects
of the environment and can be used to help
reconstruct environmental history. 

Recently, Wright, joined by Rex Adams, a senior
research specialist, and David Street, research
technician, took pencil-thin tree cores from what
they suspected might be the oldest trees at sites
near the Reef of Rocks. The trees grow at 8,400-
foot and 8,600-foot elevations.

(Coring does not damage a tree. Conifers
immediately start making chemicals in response to
any wound. These chemicals prevent molds, fungus
and insects from using a wound as a pathway into a
tree. An evergreen also quickly caps any core hole
with resin.) 

Wright compared ring-width patterns from the
Catalinas trees to ring-width patterns in the
longer tree-ring chronology from the Pinalenos
Mountains in eastern Arizona, a technique called
cross-dating.

The pattern of wide and narrow rings in the old
Catalinas trees and the ring-width pattern in known
Pinalenos chronology were a close match: Wright
and his collegues had effectively extended the
Catalina tree chronology back to the early 14th
century overnight. 

The Green Mountain chronology is complete only to
1457. In addition to the 1320 tree, two sampled
trees have been growing since before 1397 and
another tree has been growing since before 1393. 

The 1390s trees grow on such steep cliffs that it
is dangerous to core low enough on the trunks to
reach the first-year pith dates. Wright said he
will go back for cores nearer the base of the
trees. A core from lower on the 1393 tree, for
example, will probably yield a mid-14th century
pith date, he added. 

Until this decade, scientists fruitlessly searched
the southern Arizona mountains for trees older
than early 15th century. For decades, the oldest
known living southern Arizona trees were Douglas-
firs growing in the Santa Rita Mountains south of
Tucson. 

The firs, which included a living 1414 tree, were
discovered in the 1940s by a distinguished UA
tree-ring scientist, the late Edmund Schulman. The
1412 Green Mountain tree, discovered after
Schulman's death, was among only a few 15th
century southern Arizona trees found since. 

But in 1991, Henri Grissino-Mayer, then a research
associate with the Tree Ring Lab, and senior
research specialist Christopher Baisan
significantly lengthened the Mount Graham
chronology by finding trees that included two
living Douglas-firs dating to A.D. 1257 and 1270.
The 1257 tree appeared to be dying after the May
1996 Clark Peak fire, although the 1270 tree
survived. 

Baisan has since located several other trees in
the Pinalenos which date to the late 1200s and
early 1300s. Beyond southern Arizona, the oldest
living trees in the state are bristlecone pine
that grow in the San Francisco Peaks area of
Flagstaff. Several of these pines date to the
1200s, said Matthew Salzer, graduate research
associate with the Tree Ring Lab. The oldest
living bristlecone he has found in this area was
growing before A.D. 658. 

UA tree-ring scientists have developed 80 tree-ring
chronologies of at least 1,000 years long for the
western United States. This millennium-plus,
climate-sensitive, regional tree-ring record is
unique. It is key for researchers studying long-term
climate change and the history of human occupation
in the Southwest. 

If dendrochronologists can develop a long tree-ring
chronology for the Catalinas, it eventually may be
possible to get absolute dates on archaeological
sites in the Tucson area and surrounding basins, to
date fire-scarred remnant wood for an extended
record of Tucson area forest fire, and to
reconstruct a long history of Tucson precipitation,
Wright said.