the study and dating of tree rings is called?
Hi,welcome to solsarin site,today we want to talk about“the study and dating of tree rings is called?”,
thank you for choosing us.
the study and dating of tree rings is called?
dendrochronology, also called tree-ring dating, the scientific discipline concerned with dating and interpreting past events, particularly paleoclimates and climatic trends, based on the analysis of tree rings. Samples are obtained by means of an increment borer, a simple metal tube of small diameter that can be driven into a tree to get a core extending from bark to centre. This core is split in the laboratory, the rings are counted and measured,
and the sequence of rings is correlated with sequences from other cores.
Dendrochronology is based on the fact that many species of trees produce growth rings during annual growing seasons. The width of the ring (i.e., the amount of growth) for each year is determined by various internal and external factors, but it tends to vary mainly in proportion to either the amount of available precipitation or the prevailing temperatures. The ring measurements taken from trees with overlapping ages can extend knowledge of climates back thousands of years. The bristlecone pines of California have proven to be particularly suitable for such chronologies, since some individual trees are more than 4,000 years old.
What is Dendrochronology?
Dendrochronology is the study of the growth of tree rings and we can learn much from their study. We can date organic archaeological material and create a chronological record against which artefacts can be dated . There is much we can learn about the past climate, how freak season-long weather conditions, or periods of climate change have affected tree growth and how it may affect our climate in future. American Astronomre A E Douglass, who had a strong interest in studying the climate, developed the method around 1900 .
He theorised that tree rings could be used as proxy data to extend climate study back further than had previously been permissible. He was right, and the more trees that were added to the record, the greater the size of the data could be extrapolated and the more complete picture we could build of our past climate. It was not until the 1970s that archaeologists saw the benefits of the use of tree ring data in their own field , even though Douglass himself had used his method to date many prehistoric North American artefacts and monuments that had previously not been satisfactorily placed into a definite chronology.
Dendrochronology
In each growth season, trees create a new ring that reflects the weather conditions of that growth season. On its own,
a single record can tell us only a little about the environmental conditions of the time in a specific year of the growth of the tree,
and of course the age of the tree at felling,
but when we put hundreds and thousands of tree-ring records together, it can tell us a lot more. Most importantly,
assuming there are no gaps in the record (and even if there are short gaps), it can tell us the precise year that a certain tree ring grew .
The potential then, even with these two simple sets of data that we may extrapolate from the tree ring data,
is enormous. It is an accurate and reliable dating method with a large number of uses in environmental studies,
archaeology and everything in between.
The method has gone from strength to strength and is now a vital method across multiple disciplines. From the 1980s,
several seminal studies began at the University of Arizona studying the bristlecone pine of California and hohenheim oak in Germany. Thanks to the work of these studies,
we now have an 8,600 year chronology for the bristlecone pine and in the region of 12,500 year chronology for the oak. This enormous and comprehensive data set is fundamental to both European and North American studies of the palaeoclimate and prehistory.
Origins
Andrew Ellicott Douglass, an astronomer at the University of Arizona in Tucson, is considered the father of tree-ring dating. He introduced the American public to the technique in a December 1929 article in National Geographic entitled “Talkative Tree-Rings and the Tales They Tell.” In that article, Douglass published construction dates for six cliff dwellings at Mesa Verde National Park (MVNP) in southwestern Colorado, including Balcony House, Cliff Palace, Oak Tree House, Spring House, Spruce Tree House, and Square Tower House.
Although the exact dates Douglass published have long since been refined,
his general dating has not changed: the vast majority of cliff dwellings were built and occupied in the mid-1200s. These dates came as a shock to many archaeologists who,
on the basis of little more than educated guesswork, thought that the cliff dwellings were much older.
In the 1930s archaeologist Earl Morris of the Carnegie Institution supplied Douglass with
numerous wood specimens from Johnson Canyon, Colorado, south of MVNP,
in an effort to extend his ability to date sites back to about 2,000 years ago. Also in the 1930s, Zeke Flora, an amateur archaeologist based in Durango,
sent wood and charcoal specimens to Douglass. Subsequent examination of the Flora collection in the 1960s led to
the discovery of the oldest tree-ring dated archaeological wood specimen in North America. From the Falls Creek rock shelters outside Durango, it dates to 272 BC.
Origins
A major expansion of visitor facilities at MVNP in the 1950s and 1960s led to huge improvements in archaeological tree-ring dating,
particularly in the dating of charcoal samples from pithouse sites on top of Wetherill Mesa,
in addition to dating cliff dwellings in the canyons between the mesas.
As we now know, the arid climate of southwestern Colorado makes it one of the best regions in the world for dating archaeological sites by tree-ring analysis. A recently completed database for the Four Corners region contains nearly 14,000 tree-ring dates from hundreds of archaeological sites; there are now over 4,300 tree-ring dates known from more than 140 archaeological sites in MVNP alone. As a result the earliest date is AD 255 from a pithouse at the Soda Canyon Campground Site; the latest date is AD 1281 from a loose log found in a ceremonial room at Spring House. These large datasets allow archaeologists to understand the occupation and abandonment of southwestern Colorado with unprecedented precision.
In another major contribution to science, Douglass used tree rings to infer that a “Great Drought” had occurred across the American Southwest from AD 1276 until 1299. The Great Drought was at least partially responsible for the migration of people away from southwestern Colorado in the late thirteenth century; archaeologists are still examining the social, political, religious, and environmental implications of this important event in pre-Columbian history.
Instructions
1. Finding Climate Sensitive Trees
Conducting tree-ring science isn’t as simple as it might first appear. The vast majority of trees we see on hikes or while driving will not have captured a good climate record over long periods of time. Dendrochronologists need to search for long-lived trees that grow in fairly harsh environments, making them very sensitive to the surrounding conditions, where their growth is slow— so slow that many years will be recorded in their lifetimes. One such tree is the bristlecone pine, which grows in Arizona, Colorado,
New Mexico, Utah, Nevada and eastern California, sometimes under very cold and dry conditions. The oldest known specimen is named Methuselah and is a 4,765 years old! You’ll have a chance to explore a bristlecone pine site in Part 2 of this lab.
2. Coring Trees
Now let’s learn how to obtain tree cores samples from a tree. People often ask if drilling into the tree to take a sample of its wood harms it. The core samples that scientists take from trees are actually quite small
(less than the diameter of a pencil) and non-destructive to the tree. The tree will heal itself fairly quickly, similar to when a spout is removed after tapping a tree for maple syrup. If there is concern for a particular group of trees,
scientists can dip their tree borers into alcohol to be sure they are not spreading any diseases from tree to tree. If forest managers are concerned for a particular forest,
they can deny scientists permission to core trees when they apply for a permit.
3. Processing the Cores
Scientists collect core samples from twenty or more trees at each of their sites. These samples need to be carefully contained and brought into a laboratory for analysis.moreover Cores taken from a tree need to be mounted in a special wooden holder, or core mount,
and then finely sanded to bring out the ring pattern clearly.
Dating and correlation
With the .txt document and data, we use a variety of computer programs from the Dendrochronology Program Library of the University of Arizona to correlate and date the tree rings. The first of these is COFECHA, which standardizes and normalizes the core and can correlate a single core’s ring widths to a master chronology (Holmes, 1983). If the master chronology was previously dated,
the ring widths can be matched to the corresponding years based on how well they correlate. moreover COFECHA gives us many possible correlations between the tree ring core and the master chronology,
but the best samples usually have consistent and statistically significant levels of correlation, which leads to a clear calendar date.
more work can be done in programs like ARSTAN ( for “autoregressive standardization”), which can be used to plot and transform data. EDRM — a program for data adjustments — can also shift the dates in the data easily once we have discovered a tree ring date that correlates significantly with the master chronology. For BI measurements,
we make use of CooRecorder — a program for measuring the amount of blue light in scans of cores.
