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.