Dendrochronology: Death and Double Counting

Death and Double Counting
Dendrochronology is stuck in a curious philosophical time warp because it believes “the present is the key to the past”.

Principles of Dendrochronology – The Uniformitarian Principle
This principle states that physical and biological processes that link current environmental processes with current patterns of tree growth must have been in operation in the past.

In other words, “the present is the key to the past,” originally stated by James Hutton in 1785.

Constructed with much sweat by Dr. Henri D. Grissino-Mayer,
Department of Geography, The University of Tennessee, Knoxville, Tennessee

Therefore, dendrochronologists believe that the present behaviour of trees determines how trees grew in the past even though the tree-ring evidence shows they behaved differently in the past.

A reconstruction of the climate in northern Europe over the last 2,000 years

An international team including scientists from Johannes Gutenberg University Mainz (JGU) has published a reconstruction of the climate in northern Europe over the last 2,000 years based on the information provided by tree-rings.

Professor Dr. Jan Esper’s group at the Institute of Geography at JGU used tree-ring density measurements from sub-fossil pine trees originating from Finnish Lapland to produce a reconstruction reaching back to 138 BC.

Growth-Ring Response

In other words: Dendrochronology provides input to Climatology but dendrochronology does not accept input [aka feedback] from Climatology.

However, dendrochronology then performs a curious form of post-normal mental gymnastics [aka adds a new “twist”] by accepting that the Climatology of “the past is the key to the future”.

However, dendrochronology adds a new “twist” to this principle: “the past is the key to the future.

In other words, by knowing environmental conditions that operated in the past (by analyzing such conditions in tree rings), we can better predict and/or manage such environmental conditions in the future.

Hence, by knowing what the climate-tree growth relationship is in the 20th century, we can reconstruct climate from tree rings well before weather records were ever kept.

Long-term precipitation reconstruction for northern New Mexico

For example, the graph above shows a long-term precipitation reconstruction for northern New Mexico based on tree rings.

The reconstruction was developed by calibrating the widths of tree rings from the 1900s with rainfall records from the 1900s.

Because we assume that conditions must have been similar in the past, we can then use the widths of tree rings as a proxy (or substitute) for actual rainfall amounts prior to the historical record.

Constructed with much sweat by Dr. Henri D. Grissino-Mayer,
Department of Geography, The University of Tennessee, Knoxville, Tennessee

Understanding the philosophy and semantics employed by dendrochronologists is central to understanding another bizarre “twist” in the bristlecone pine saga.

The saga begins when the father of dendrochronology, A E Douglass, hypothesised in 1909 that the tree rings of the yellow pine (Pinus ponderosa) “are likely to form a measure of the precipitation” and that “individual rings of the trees are extremely well marked and leave no doubt whatever as to their purely annual or seasonal character”.

Climatically Arizona is divided into two parts, the northern, a great plateau at an average elevation of 6,000 feet, and the southern, a broken country consisting of scattered mountain ranges separated by broad level valleys averaging some 2,000 thousand feet above the sea.

The higher, elevations, culminating in the San Francisco Peaks near Flagstaff, are covered with great forests of yellow pine (Pinus ponderosa), a fine timber tree with heavy cylindrical trunk and a rather bushy top.

The trees are scattered gracefully over the plains and hills and, with the remarkable absence of undergrowth, render travel through their shady midst attractive and delightful.

Contrary to Arizona’s reputation, northern Arizona has really a cold climate.

Several feet of snow lie on the ground during winter, and the summer evenings are rarely warm enough for one to sit outdoors.

For centuries these magnificent pines have stood there enduring all the vicissitudes of heat and cold, flood and drought.

They should contain some record of such alternations.

Other studies of weather variations have been made upon records extending back from twenty to fifty years.

These trees, if they prove to convey such information at all, will yield data covering two to five centuries.

The working hypothesis which in 1901 and before gave a beginning to the collection of material along these lines was as follows:
(1) The rings of a tree measure its food supply;
(2) Food supply depends largely upon the amount of moisture, especially where the quantity of moisture is limited and the life struggle of the tree is against drought rather than against competing vegetation;
(3) In such countries, therefore, the rings are likely to form a measure of the precipitation.

Weather Cycles in the Growth of Big Trees

One Ring to a Year
In comparing rings and the rainfall over long periods of years, a preliminary condition is that the time of formation of any individual ring shall be subject to identification.

As a rule the individual rings of the trees are extremely well marked and leave no doubt whatever as to their purely annual or seasonal character.

However, doubtful cases occasionally appear, with greater frequency near the center of the tree.

For the last two hundred years, I estimate that 2 per cent is the average number of doubtful cases.

The arguments bearing upon this subject are as follows:
(1) The agreement shown in fig. 3 between tree growth and rainfall in individual years shows the yearly character of the rings;
(2) At the 7,000 feet of elevation at which these trees grew, the seasons are very sharply defined; the mean temperature for January is 29° F., and for July is 65° F.; frost, therefore, gives a sharply seasonal character to the growth;
(3) The examination of stumps and logs at different seasons during several years showed entire consistency in the formation of a narrow red ring in autumn and winter and a broad, soft white ring in summer;
(4) In the investigation of uncertain cases, it is a great help to trace the doubtful ring around different portions of the tree. In some other part, the ring’s claim to individuality is often clearly settled.

Weather Cycles in the Growth of Big Trees – A. E. Douglass
Monthly Weather Review – June 1909

Pinus ponderosa

Like most western pines, the ponderosa generally is associated with mountainous topography but not always. In Nebraska it is found on breaks of the Niobrara River. Scattered stands occur in the Willamette Valley of Oregon and in both Washington’s Puget Sound area and Okanagan Valley. It is found on the Black Hills; on foothills and mid-height peaks of the northern, central, and southern Rocky Mountains; in the Cascade Range; in the Sierra Nevada; and in the maritime-influenced Coast Range. In Arizona it predominates on the Mogollon Rim and is scattered on the Mogollon Plateau and on mid-height peaks in Arizona and New Mexico. It does not extend into Mexico.

Ten years later, in 1919, A. E. Douglass stated that “in wet regions the rings show a very evident relation to solar radiation through sun-spot numbers” and emphasised that “in dry regions the rainfall is a much more obvious cause of variations in the rings of trees”.

The rings of the yellow pine in northern Arizona show varying thickness in marked correlation with rainfall.

The sequoias of California show similar characteristics.

In less degree climatic effects may also be detected by finding similarity in ring growth of trees over large areas.

Prof. H. J. Cox had noted a waxy deposit on the leaves of trees in Montana during a drought, and asked if this was the case in Arizona.

Prof. Douglass replied that this is a general characteristic of vegetation in the Southwest.

Prof. W. J. Humphreys asked if the cliff dwellings in Arizona can be dated by getting the age of the timber used in them.

Prof. Douglass answered that this probably could be done.
He called attention to the fact, that in wet regions the rings show a very evident relation to solar radiation through sun-spot numbers, but that in dry regions the rainfall is a much more obvious cause of variations in the rings of trees.

Evidence of Climatic Effect in the Annual Rings of Trees – A. E. Douglass
Monthly Weather Review – December 1919

Click to access trb-32-019-033.pdf

Rings of growth in Ponderosa Pine

The saga then jumps forward 46 years to 1965 [three years after the death of A. E. Douglass] to a Ponderosa Pine reanalysis which revealed:
a) Double (false or intra-annual) rings occur frequently [10% to 50%].
b) Locally absent (partial rings) are directly related to water stress [0% to 8%].

Tree-ring characteristics are studied within and among stems of four Pinus ponderosa Laws located at several semiarid sites in northern Arizona.

Analyses are made of changes associated with certain physiological, height, and age gradients within the tree.

Rings are grouped into twenty or forty year intervals, are classified in four different arrangements, and the characteristics for the intervals are averaged and plotted to represent the gradients within the tree stem.

Tree-rings are widest near the base and central portions of the stem.

Ring width decreases with increasing age of the cambium, with increasing height within the young stem, with decreasing terminal growth, and with increasing environmental stress.

Double (false or intra- annual) rings occur most frequently in the wide rings near the base and in the younger portions of the stem, or in the upper stem and branches of older trees.

The frequency of rings which are locally absent (partial rings) is inversely related to ring width, and directly related to the potentiality for water stress conditions in the site or within the tree.

Correlations among the year-to-year ring-width patterns throughout the tree generally increase with increasing tree age and frequency of water stress.

First order serial correlation is frequently highest in older trees on semiarid sites.

Many of these changes in ring characteristics within the tree are attributed to specific gradients or changes in auxin, food, and water supplies.

A wide sampling of annual rings from the base of many semiarid site trees appears more appropriate for evaluating past fluctuations in climatic factors than an intensive sampling of rings at several heights in only a few trees.

The Variability of Ring Characteristics

The Variability of Ring Characteristics within Trees as shown by a Reanalysis of Four Ponderosa Pine – Harold C. Fritts, David G. Smith, Carl A. Budelsky, and John W. Cardis
Tree-Ring Bulletin – Volume 27 – November 1965

The occurrence of “double (false or intra- annual) rings” and “locally absent (partial rings)” in the Ponderosa Pine [“associated with mountainous topography” and “mid-height peaks in Arizona and New Mexico”] is primarily controlled by the availability of water.

Therefore, the next step in this saga requires an understanding of the annual weather pattern that the Ponderosa Pine might experience in a “mountainous” region.

Thankfully, the US National Park Service provides a rough guide by supplying a monthly breakdown of the weather for Yosemite Valley at an altitude of 1,220 metres.

Yosemite Valley

The weather in the Yosemite Valley has some very notable features:

1) The winter months are cold and precipitation is primarily in the form of snow
2) The spring melt season provides plenty of water for a tree-ring growth.
3) The summer months are cool and there is virtually no precipitation and no growth.
4) The autumn rains provide water for tree-ring growth provided there is no early snow.

Yosemite Valley at 1220 metres

Having the basics covered for the Ponderosa Pine it’s time to move on to the Bristlecone Pine.

Wikipedia provides a fairly good overview of the Bristlecone Pine but it important to note:
a) It has “shallow roots with a few large, branching roots provide structural support” which means it is very dependent upon precipitation and surface water.
b) It grows at a higher altitude than the Ponderosa Pine and experiences a more severe climate.

There are three closely related species of bristlecone pine:

Rocky Mountains bristlecone pine Pinus aristata in Colorado, New Mexico and Arizona
Great Basin bristlecone pine Pinus longaeva in Utah, Nevada and eastern California
Foxtail pine Pinus balfouriana in California and one isolated population in southern Oregon.

Bristlecone pines grow in isolated groves just below the tree line, between 1,700 and 3,400 m elevation on dolomitic soils.

The trees grow in soils that are shallow lithosols, usually derived from dolomite and sometimes limestone, and occasionally sandstone or quartzite soils. Dolomite soils are alkaline, high in calcium and magnesium, and low in phosphorus.

Those factors tend to exclude other plant species, allowing bristlecones to thrive.

Because of cold temperatures, dry soils, high winds, and short growing seasons, the trees grow very slowly.

Even the tree’s needles, which grow in bunches of five, can remain on the tree for forty years, which gives the tree’s terminal branches the unique appearance of a long bottle brush.

The bristlecone pine’s root system is mostly composed of highly branched, shallow roots with a few large, branching roots provide structural support.

The bristlecone pine is extremely drought tolerant, due to its branched shallow root system and its waxy needles, and thick needle cuticles that aid in water retention.

The wood is very dense and resinous, and thus resistant to invasion by insects, fungi, and other potential pests.

The tree’s longevity is due in part to the wood’s extreme durability.

While other species of trees that grow nearby suffer rot, bare bristlecone pines can endure, even after death, often still standing on their roots, for many centuries.

Rather than rot, exposed wood, on living and dead trees, erodes like stone due to wind, rain, and freezing, which creates unusual forms and shapes.

The bristlecone pine has an intrinsically low rate of reproduction and regeneration, and it is thought that under present climatic and environmental conditions the rate of regeneration may be insufficient to sustain its population.

However, when Wikipedia talks about:
i) The “tree’s longevity” what it really means to say is that the tree is very resilient and that it can take a very long time to die [important difference].
ii) “Allowing bristlecones to thrive” what it really means to say is that “under present climatic and environmental conditions the rate of regeneration may be insufficient to sustain its population”.
iii) “Bristlecone pines grow in isolated groves just below the tree line” what it really means to say is that the many bristlecone pines are stranded [and slowly dying] above the tree line which has retreated by about 100 metres due to a naturally changing climate – see below.

Tree Line

Pollen evidence from central Colorado indicates that between 7000 and 4000 yr B.P. “the Engelmann spruce-subalpine fir forest [“subalpine zone”] covered a broader elevational range than it does today.

The subalpine forest expanded at least 100 m lower in elevation in response to greater available soil moisture.

The upper limits of the subalpine forest also expanded during this period…
In effect, the middle Holocene…was both warmer and wetter than today”.
(Fall, 1985; figure modified from that report).

Past Climate and Vegetation Changes in the Southwestern United States
Robert S. Thompson – U.S. Geological Survey and
Katherine H. Anderson – INSTAAR, University of Colorado

The next step in the saga is to focus upon the Rocky Mountains bristlecone pine [Pinus Aristata].

Pinus Aristata, the Rocky Mountain bristlecone pine, is a species of pine native to the United States.

It appears in the Rocky Mountains in Colorado and northern New Mexico, with an isolated population in the San Francisco Peaks in Arizona.

It is usually found at very high altitudes, from 2500–3700 m, in cold, dry subalpine climate conditions, often at the tree line, although it also forms extensive closed-canopy stands at somewhat lower elevations.

We don’t have climate data for other locations in Yosemite.
For Yosemite’s higher elevations (e.g., Tuolumne Meadows), subtract about 10 to 20 Fahrenheit degrees (6 to 11 Celsius degrees) from the average temperatures above.

Pinus aristata

The sub-alpine climate at 3,000 metres is about 11°C lower than the figures quoted for Yosemite Valley by the US National Park Service.

Therefore, the two growing seasons [spring and autumn] for Pinus Aristata will be shorter [compared to 1,220 metres] with an increased risk of missed rings due to early snow.

Yosemite Valley at 3000 metres

Wikipedia provides the following description for the Rocky Mountain sub-alpine zone.

The Rocky Mountains subalpine zone is the biotic zone immediately below tree line in the Rocky Mountains of North America.

In Colorado, the subalpine zone occupies elevations approximately from 9,000 to 12,000 feet (2,700 to 3,700 m); while in northern Alberta, the subalpine zone extends from 1,350 to 2,300 metres (4,400 to 7,500 ft).

The climate of the Rocky Mountains subalpine zone is never warm, with summer highs reaching 75 °F (24 °C) on only the warmest days near the montane zone, and commonly failing to reach 60 °F (16 °C) near tree line; Frost may occur any day of the year.

Although winter low temperatures may be warmer than those in nearby lower valleys, typically staying above −10 °F (−23 °C), prodigious snows blanket the region well into spring.

Some drifts may linger into summer.

Convectional precipitation, typically thunderstorms, often forms rapidly and frequently drop graupel or hail.

Although uncommon, hurricane-force winds may develop and cause massive destruction such as the Routt Divide Blowdown.

Wikipedia also provides a description of plant adaptation in Sierra Nevada sub-alpine zone.

The most ubiquitous adaptation of subalpine plants is the ability to perform metabolic activities at extremely low temperatures.

Again, without this trait, the growing season would not be long enough to support sustained life. A side effect of this trait is slow growth, even when conditions are good, which may be a major factor in setting the lower limits of subalpine zones.

Because subalpine tree species have such slow growth, they are out-competed at lower elevations by trees capable of more rigorous growth, such as red fir.

Slow growth, however, may be an adaptation in and of itself in extremely harsh environments as it leads to very long-lived individuals.

Many of the tree species in Sierran subalpine are capable of living over 500 years.

Whitebark pine has been found to live as long as 800 years, and foxtail pine, which is closely related to bristlecone pine (Pinus longaevis) has been estimated to live 2500–3000 years.

Seedling establishment in the harsh subalpine environment is difficult, so evolution has instead favored long-lived individuals that are reproductively active for tens or hundreds of years.

The Rocky Mountains bristlecone pine [Pinus Aristata] was only discovered by dendrochronology in the 1950s and research only really started in earnest in 1961.

When, in 1950, Willard Libby and his coworkers obtained their first radiocarbon (14C) dates, C. W. Ferguson at the University of Arizona Tree Ring Laboratory was working on establishing a continuous tree ring series for the newly discovered bristlecone pine Pinus aristata.

The 14C Record in Bristlecone Pine Wood of the past 8000 Years Based on the Dendrochronology of the Late C. W. Ferguson – H. E. Suess, T. W. Linick Philosophical Transactions of the Royal Society of London.
Series A, Mathematical and Physical Sciences, Volume 330, Issue 1615, pp. 403-412

Interest was drawn to the bristlecone pine in 1953 when Edmund Schulman began tree-ring studies of species of the upper timberline in a search for evidence of climatic change.

In 1954 and 1955, a widespread search through the western United States resulted in the discovery of three bristlecone pines more than 4000 years old and six others more than 3000 years old (Schulman and Ferguson 1956).

One, a 3100 -year -old specimen, was in the Schell Creek Range, east of Ely, Nevada.

All the others were in the White Mountains of east-central California, and this fact caused Schulman to focus his attention on that district of the Inyo National Forest.

Collections by Schulman and Ferguson in 1956 and by Schulman and Cooley in 1957 were reported in National Geographic (Schulman 1958), in an issue that went to press just before Schulman’s death on 8 January, 1958.

With Schulman’s death, however, study of the bristlecone pine lapsed until 1961, when the Laboratory of Tree-Ring Research gained support for further research.

A 7104 Year Annual Tree Ring Chronology for Bristlecone Pine, Pinus Aristata, from the White Mountains, California – C. W. Ferguson – Tree-Ring Bulletin, Volume 29 (1969)

Click to access trb-29-03-04-003-029.pdf

Surprisingly, a mere eight years later dendrochronology produced a 7,104 year tree-ring chronology based upon Pinus Aristata samples collected in the White Mountains, California [which are far more arid than the Yosemite Valley].

… we confined our research primarily to the White Mountains because we knew old trees were there and such factors as accessibility, research facilities, and climate were favorable.

As Pacific storms move inland, moisture falls on the Sierra Nevada, leaving the White Mountains and the intervening Owens Valley in a rain shadow.

Thus, even though conifers in the White Mountains grow at elevations of 3000 to 3350 meters (10,000 to 11,000 feet) above sea level, they are in a relatively arid environment with an average annual rainfall of 305 to 330 millimeters (12 to 13 inches) (D’Ooge 1955; Wright and Mooney 1965).

A 7104 Year Annual Tree Ring Chronology for Bristlecone Pine, Pinus Aristata, from the White Mountains, California – C. W. Ferguson – Tree-Ring Bulletin, Volume 29 (1969)

Click to access trb-29-03-04-003-029.pdf

White Mountains

However, the 64 million dollar question is:
Does Pinus Aristata produce two growth rings per year?

The 1969 paper acknowledges it occurs in other species and quotes three sources.

In certain species of conifers, especially those at lower elevation or in southern latitudes, one season’s growth increment may be composed of two or more flushes of growth, each of which may strongly resemble an annual ring (Glock, et al. 1960; Glock, et al. 1963; Fritts, et al. 1965).

A 7104 Year Annual Tree Ring Chronology for Bristlecone Pine, Pinus Aristata, from the White Mountains, California – C. W. Ferguson – Tree-Ring Bulletin, Volume 29 (1969)

Click to access trb-29-03-04-003-029.pdf

But when it comes to Pinus Aristata the author of the 1969 simply provides his opinion that “multiple growth rings are extremely rare” based upon his short experience in dealing with this “new dendrochronological species, in a new area, and (increasingly) in a new time period”.

Such multiple growth rings are extremely rare in bristlecone pine, however, and they are especially infrequent at the elevation and latitude (37 °23’N) of the sites being studied.

In the growth-ring analyses of approximately 1000 trees in the White Mountains, we have, in fact, found no more than three or four specimens with even incipient multiple growth layers.

A 7104 Year Annual Tree Ring Chronology for Bristlecone Pine, Pinus Aristata, from the White Mountains, California – C. W. Ferguson – Tree-Ring Bulletin, Volume 29 (1969)

Click to access trb-29-03-04-003-029.pdf

However, the author does admit to having a problem with “missing” rings which is more suggestive of a lack of autumnal rain [i.e. no autumnal growth] than missing growth for a whole year.

In bristlecone pine, problems of crossdating are caused by so-called “missing” rings associated with the extremely slow growth rate of this species on arid sites.

One specimen, for example, contains more than 1100 annual rings in 12.7 centimeters of radius.

Such slow-growing wood, with an average ring width of only a few hundredths of a millimeter, frequently lacks evidence of growth in a large portion of the circuit during a year of environmental stress.

In some instances, 5 percent or more of the annual rings may be missing along a given radius that spans many centuries.

The location of such “missing” rings in a specimen is verified by crossdating its ring pattern with the ring pattern of other trees in which the “missing” ring is present, or by checking against the ring record of the occasional specimen that contains every ring in a span of over 2000 years.

A 7104 Year Annual Tree Ring Chronology for Bristlecone Pine, Pinus Aristata, from the White Mountains, California – C. W. Ferguson – Tree-Ring Bulletin, Volume 29 (1969)

Click to access trb-29-03-04-003-029.pdf

Additionally, even if the unsubstantiated claim that “multiple growth rings are extremely rare” today it does not mean that they were rare in the past when the climate was “both warmer and wetter than today” and the sub-alpine tree line was higher than today.

Obviously, classifying spring and autumn growth rings as annual rings [potentially] doubles the status [and prowess] of the dendrochronologist whilst doubling the length of the chronology.

Clearly, this would be one giant leap for dendrochronology in the same year that NASA enabled Neil Armstrong to make one giant leap for mankind.

Therefore, in the interests of science, it’s worth examining the robustness of this 7,104 year Pinus Aristata chronology.

Firstly, it’s worth noting that this chronology was extending two existing chronologies that were anchored to [in total] 23 living trees.

The first chronology unit is made up of paired cores from nine trees in Methuselah Walk. These specimens comprise the second half (those with the most missing rings, and generally higher mean sensitivity and lower serial correlation) of the data in Table 1 (Ferguson 1968, Table 1).

The second unit is the Schulman Master, composed of 14 trees, which extends from A.D. 800 to 1954. It incorporates specimens from four sites in the White Mountains…

A 7104 Year Annual Tree Ring Chronology for Bristlecone Pine, Pinus Aristata, from the White Mountains, California – C. W. Ferguson – Tree-Ring Bulletin, Volume 29 (1969)

Click to access trb-29-03-04-003-029.pdf

Secondly, they started collecting “additional specimens” in 1963.

The chronology was extended backward in time by incorporating tree-ring series from living trees up to 4600 years old, as well as from standing snags, fallen trees, large remnants, and eroded fragments.

To secure additional specimens and improve the quality of the chronology in the earlier periods, especially beyond the maximum age of living trees, we began, in 1963, to collect material of two types:
(i) cores extracted either from the original central portion of standing or fallen snags or from large, eroded remnants of trees, and
(ii) entire smaller remnants having the appearance of age and without specific known origin in relation to any tree, living or dead.

A 7104 Year Annual Tree Ring Chronology for Bristlecone Pine, Pinus Aristata, from the White Mountains, California – C. W. Ferguson – Tree-Ring Bulletin, Volume 29 (1969)

Click to access trb-29-03-04-003-029.pdf

Thirdly, the final chronology included only 17 new specimens [after “growth-ring analyses” had been performed on “approximately 1000 trees”] that were collected between 1961 and 1968.

7104 Components

A 7104 Year Annual Tree Ring Chronology for Bristlecone Pine, Pinus Aristata, from the White Mountains, California – C. W. Ferguson – Tree-Ring Bulletin, Volume 29 (1969)

Click to access trb-29-03-04-003-029.pdf

Fourthly, the crossmatching of the chronology incorporated two tenuous bridges and four very suspect short inserts.


A 7104 Year Annual Tree Ring Chronology for Bristlecone Pine, Pinus Aristata, from the White Mountains, California – C. W. Ferguson – Tree-Ring Bulletin, Volume 29 (1969)

Click to access trb-29-03-04-003-029.pdf

Finally, English Heritage reports that the crossmatching was performed by just matching the “incidence of particularly narrow rings”.

The science of dendrochronology was pioneered by A E Douglass, an American astronomer, early in the twentieth century. He used tree-rings as proxy climatic records to extend his climate data back in time further than written records. His major breakthrough came when he extended his tree-ring data from living trees by crossmatching them with a ring sequence from archaeological timbers, thus placing many previously undated prehistoric structures precisely in time.

He and his successors at the Tree-Ring Laboratory in Tucson, Arizona, went on to construct long chronologies, including the 8200-year sequence from the long-lived bristlecone pines, which was used as the first radiocarbon calibration standard.

Much of the crossmatching was done, not by measuring the absolute ring widths, but by comparing signature plots, which mapped the incidence of particularly narrow rings.

Dendrochronology – Guidelines on producing and interpreting dendrochronological dates
English Heritage – 2004

Click to access dendrochronology.pdf

We began to rely upon a new ring – growth characteristic, that of a skewed ring-width distribution (Ferguson 1968).

In this, we found the desired feature for relatively rapid chronology building in ring series with a large dependable ring width, but only a few very diagnostic rings per century.

A 7104 Year Annual Tree Ring Chronology for Bristlecone Pine, Pinus Aristata, from the White Mountains, California – C. W. Ferguson – Tree-Ring Bulletin, Volume 29 (1969)

Click to access trb-29-03-04-003-029.pdf

Obviously, these very long tree-ring chronologies are very useful for radiocarbon dating, climatology and the odd Guinness World Record.

The current record-holders for individual, non-clonal trees are the Great Basin bristlecone pine trees from California and Nevada, in the United States. Through tree-ring cross-referencing, they have been shown to be more than 5,000 years old.

Whether they are accurate is another matter altogether.

UPDATE 30th August 2014
The following study of the omission and doubling of tree-rings in Pinus Ponderosa [by A E Douglass – 1919] highlights the effects of precipitation and drought during the growing season.

Clearly, it was foolhardy to construct a Bristlecone Pine chronology without a detailed knowledge of the effects of spring and autumn droughts.

Page 9
It is entirely natural that the yellow pine, Pinus ponderosa, common on the western Rockies, should have been the first tree studied, since it was an intimate and extensive acquaintance with the forest and with the climate of northern Arizona that led the writer to the thought of possible relation between the two.

Page 15
Superficial counting of rings is subject to errors due to omission and doubling of rings.

In the first investigation of trees at Flagstaff it was supposed that the results were subject to an error of 2 per cent, most of which arose from double rings near the center of the tree.

But the discovery and application of the method of cross-identification revolutionized the process of ring identification, and it was proved that the error of unchecked counting in the Arizona pines was 4 per cent and lay almost entirely in the recent years.

It was due to the omission of rings or the fusion of several together.

The effect of the undetected omission or the doubling of the rings in individual trees is to lessen the intensity of the variations in the curve of growth obtained by the averaging of many trees.

Page 16
The value and accuracy of cross-identification was first observed in 191 1 in connection with the Prescott trees.

After measuring the first 18 sections, it became apparent that much the same succession of rings was occurring in each ; therefore the other sections were examined and the appearance of some 60 or 70 rings memorized.

All the sections were then reviewed and pinpricks placed in each against certain rings which had characteristics common to all.

For example, the red ring of 1896 was nearly always double, while the rings of 1884 and 1885 were wider than their neighbors.

Page 18
Among the problems connected with the relation of the growth of trees and the amount of rainfall, one of the most interesting was suggested by Director R. H. Forbes, formerly of the Arizona Experiment Station.

This was to determine the time of formation of the red or autumn portion of the rings and the causes for the formation of double rings, which were very numerous in the Prescott group.

It seems evident at once that the growth of red cells is related to the decreased absorption of moisture as winter approaches.

A number of tests were made on the Prescott group.

The first was designed to determine the character of the rainfall in the years producing double rings.

The half-dozen most persistent cases were selected and in each of these the red ring was found double in the following number of cases: 4 out of 10 in 1896; 5 out of 10 in 1891; 7 out of 10 in 1881; 4 out of 10 in 1878, 1872, and 1871.

The average width of all the rings was 1.55 mm.

The mean rainfall by months for the years above selected was found and is plotted in the solid line of the upper diagram of figure 1.

Six other rings showing one double in 10 trees in 1898, but no doubles in 1897, 1885, 1884, 1876, and 1874, and averaging 1.54 mm. in thickness, were then selected and the curve of rainfall by months for the year during which they grew has been plotted as the upper dotted line in figure 1.

In each curve the 6 months preceding and the 2 months following the year are included.

The curves seem to indicate clearly that the chief cause of doubling is a deficiency of snowfall in the winter months, December to March.

This appears to mean that if the winter precipitation is sufficient to bridge over the usual spring drought, the growth continues through the season, giving a large single ring which ends only in the usual red growth as the severity of winter comes on.

If, however, the preceding winter precipitation has not been entirely adequate, the spring drought taxes the resources of the tree and some red tissue is formed because of efficient absorption in the early summer before the rains begin.

When these rains come the tree continues its growth.

It appears further that if not only the winter snows are lacking, but the spring rains are unusually scanty, then the tree may close up shop for the year and produce its final red tissue in midsummer, gaining no immediate benefit from the summer rains.

This appears to be the interpretation of the lower diagram of figure 1.

Here the same 6 big doubles mentioned above are plotted, together with a selected list of 6 small singles particularly deficient in red tissues.

They are, 1904 double once in 10, 1902 double once in 10, 1899 single, 1895 single, 1894 single and 1880 double once in 10.

In these it is evident that drought in the spring stops the growth of the tree.

The double ring, therefore, seems to be an intermediate form between the large normal single ring, growing through the warm parts of the year, and the small, deficient ring, ending its growth by midsummer.

This occasional failure to benefit by the summer rains probably explains why the Prescott trees do not show an agreement of more than about 70 per cent between growth and rainfall.

It suggests also that the Flagstaff trees, which grow under conditions of more rainfall and have very few double rings, give a more accurate record than those of Prescott.

Effect of monthly distribution of precipitation

Consistent with this view of the doubling is the condition of the outer ring in the Prescott sections collected by Mr. Hinderer.

These trees were cut during various months from May to November.

Naturally, those cut in May are in the midst of their most rapid growth, while those cut in summer may or may not show the double ring just forming.

The conditions are shown in table 2.

Table 2

By reference to figure 1, showing the curves of monthly rainfall for 1909 and 1910, it will be seen that 1910 would be likely to carry its growth through the year and produce a single line, as in group 3 above.

The year 1909 is of intermediate character, having heavy winter precipitation and a severe spring drought of 3 months.

In the groups cut at this time 33 out of 43 show a red ring forming in July, August, or September, doubtless the preliminary ring of a double.

This lesser red ring is due to the spring drought, and its appearance at this time indicates a lag of a couple of months, more or less, in the response of the tree to rain.

The whole matter of the relative thickness of the red and white portions of the rings is illustrated in figure 2.

The heavy sinuous fine shows the rainfall month by month at Prescott throughout the 43 years under consideration.

The total rainfall for the year is indicated by the dotted rectangles while the size and character of the, rings is shown in the solid rectangles.

In these the white portion indicates the white tissue and the shaded portion indicates red tissue.

Monthly and yearly precipitation at Prescott

Significance of subdivisions in rings
The normal ring consists of a soft, light-colored tissue which forms in the spring, merging into a harder reddish portion which abruptly ends as the tree ceases growth for the year.

The present subject (namely, the time of year of ring formation) indicates that the red tissue appears as the tree feels lack of sufficient moisture.

Therefore, the great diversity in relative size of the red tissue and the occasional appearance of false rings undoubtedly has a real significance as to distribution of precipitation during the growing-season.

This subject is a very promising one, but has received little attention in the present work.

The trees of the Prescott group offer a few interesting examples of two or three false red rings in one year; they also have exceptionally many cases of omitted rings; both of these peculiarities are explained by the fact that these trees are close to the lowest elevation at which the climate permits them to live; they are therefore greatly affected by rainfall distribution and probably exaggerate its changes.

Climatic cycles and tree-growth – 1919 – A E Douglass

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6 Responses to Dendrochronology: Death and Double Counting

  1. Louis Hissink says:

    Interesting – I wonder what tree rings might mean for a tree growing in an environment that had no climate seasons. I wonder if lumps of carboniferous era woods had tree rings? I wonder if anyone noticed, for if the past climate was not identified as seasonal, no winter, no summer etc, then tree rings might be only a recent phenomenon. And how would you recognise a pre 930 AD tree for that matter – not by radio carbon dating. There are Wollombi palms in Australia that are extremely old – I wonder if those have rings.

  2. malagabay says:

    Posting updated with the study of missing and doubled tree-rings in Pinus Ponderosa [by A E Douglass – 1919] which highlights the impact of drought during the growing season.

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  6. Revelation can be sooo disappointing

    Under investment. What of China? Some travellers say they have trees….. but do they have scholars?

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