Welcome to the Science of Tree Rings!

Eastern Hemlock

Latin name:
Tsuga canadensis

Extracted from a waterfront pier near Wilmington, Delaware, the tree used to make this portion of the pier
actually came from a forest located in central Pennsylvania. The outermost tree ring dates to the late 1830s.

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Giant Sequoia

Latin name:
Sequoiadendron giganteum

A close up of numerous fire scars on a giant sequoia cross section from Sequoia National Park in California, dating back well prior to A.D. 1000. Look closely! Can you find the sad bearded face cradled by his hands, as if he was crying?

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Douglas-fir

Latin name:
Pseudotsuga menziesii

This photo shows the tree rings from a beam extracted many years ago from a pueblo in northeastern Arizona. The section shows many false rings and many micro-rings, suggesting this tree may have been growing in a marginal environment.

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Ponderosa Pine

Latin name:
Pinus ponderosa

Close up of tree rings of a ponderosa pine collected at El Malpais National Monument in New Mexico, USA, showing tree rings centered around A.D. 1400. Notice the variability in ring widths indicative of sensitivity to year-to-year variation in precipitation.

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Douglas-fir

Latin name:
Pseudotsuga menziesii

Perhaps my most requested image of tree rings, obtained from a small Douglas-fir growing in the Zuni Mountains of west-central New Mexico by my colleagues Rex Adams and Chris Baisan. Not very old, but has some of the most beautiful rings of all my displays!

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White Oak

Latin name:
Quercus alba

Oak cores from the Hoskins House in Greensboro, North Carolina, site of a famous battle during the Revolutionary War. The house was built from trees cut in 1811 to 1813, not cut and built in the 1780s as the historical agency had hoped.

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Ponderosa Pine

Latin name:
Pinus ponderosa

This ponderosa pine once grew at El Morro National Monument in New Mexico, USA, and was cut many years ago. Once you get up close to the stump, you can see a very old scar from a fire many hundreds of years ago that scarred the tree when it only about 12 years old!

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Bahamian Pine

Latin name:
Pinus caribaea var. bahamensis

We collected many cross sections of Bahamian pines that had been cut for an industrial park on the island of Abaco, but the rings are very difficult to date! Many false rings, and the pine appears to terminate tree growth during the dry season.

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Longleaf Pine

Latin name:
Pinus palustris

This cross section was one of many that came from an old crib dam across a creek that was exposed after a modern dam broke in Hope Mills, North Carolina in 2003. Such sections from old-growth longleaf pines are very rare and provide information on climate back to AD 1500!

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White Oak

Latin name:
Quercus alba

Sometimes you don't have to look far to find beauty in wood, and sometimes it may not be a living tree! After an oak tree was cut a year or two before this section was obtained, decay fungi had already set in, beginning to break the wood down to its basic elements.

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Southwestern White Pine

Latin name:
Pinus strobiformis

I collected this fire-scarred pine on Mt. Graham in southern Arizona in fall 1991, and it remains one of the best examples of how we can determine the season of fire by looking at the position of the scar within the ring.

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Bristlecone Pine

Latin name:
Pinus longaeva

Bristlecone pines have become one of the best proxy records for those who study the history of volcanic eruptions because the cool temperatures caused by these eruptions create "frost rings" that form when the cells implode from the cold.

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Eastern Redcedar

Latin name:
Juniperus virginiana

Many well-preserved eastern redcedar sections have been recovered from prehistoric sites in eastern Tennessee, and they have more than enough rings to date, but we don't have a long enough living-tree reference chronology to overlap with them!

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Red Oak

Latin name:
Quercus rubra

Oak is by far the most common genus we find in the many historic structures we date using tree rings in the Southeastern U.S. The genus has good ring variability and rarely has problem rings. This section came from a historic tavern in Lexington, Virginia.

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Sugar Maple

Latin name:
Acer saccharum

Maple, birch, beech, and basswood are all examples of hardwood species that form diffuse porous wood, meaning that the ring contains many small-diameter vessels all through the ring. Identifying the ring boundary on this wood type is a challenge to tree-ring scientists.

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Live Oak

Latin name:
Quercus virginiana

Live oak is an example of an evergreen oak, which is not common within this genus. As such, the wood is semi-ring porous and the rings are very difficult to see and date. Ring growth is also very erratic, not forming the concentric around the tree that we require.

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Douglas-fir

Latin name:
Pseudotsuga menziesii

These cores were collected on Mt. Graham in southern Arizona and show a major suppression event beginning in 1685 when missing rings became evident, followed by many micro-rings. This suppression was caused by a major wildfire in 1685!

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Ponderosa Pine

Latin name:
Pinus ponderosa

I find it amazing what trees can record in their tree rings! Here we see a cross section of a pine that was damaged by a major flood in the year 1945 in the Chiricahua Mountains of southern Arizona. Notice the reaction wood that formed afterward.

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Pignut Hickory

Latin name:
Carya glabra

Sometimes gray-scale imagery helps define tree rings when measuring. Although classified as "ring porous" species, the rather ill-defined tree rings in hickory tree species form large earlywood vessels and smaller latewoood vessels.

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Subalpine Fir

Latin name:
Abies lasiocarpa

Decay has set in on the tree rings of this dead and downed subalpine fir that once grew on Apex Mountain in British Columbia, Canada, but the tree rings can still be measured and crossdated despite this!

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White Fir

Latin name:
Abies concolor

We found a beautiful fire scar on this white fir that was used to build a cabin in the Valles Caldera of New Mexico. Thought to have been built in the early 1900s, we instead found the cabin was built form white fir and Douglas-fir trees cut in 1941.

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Overcup Oak

Latin name:
Quercus lyrata

These oak cores were collected in northeastern Arkansas to investigate a change in the hydrologic regime of a wildlife refuge beginning in the 1990s. We found that trees at this site experienced a major disturbance event in the 1960s.

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Western Juniper

Latin name:
Juniperus occidentalis

Near Frederick Butte in central Oregon, we discovered an unusual stand of western junipers that had the most unusual lobate growth forms we had ever seen. This site yielded a drought-sensitive chronology dating back to the AD 800s!

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West Indies Pine

Latin name:
Pinus occidentalis

Above 3000 meters on the highest peak in the Carribean, we found an entire forest of these pines, many with fire scars, living on a steep rocky slope. The forest looked more like the dry ponderosa pine forests of the western U.S.

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Whitebark Pine

Latin name:
Pinus albicaulis

Whitebark pines growing in the northern Rockies of the western U.S. can grow to be over 1,000 years old, but the species is slowly being decimated by the introduced white pine blister rust. Many of these ancient trees are now dead with ghostly white trunks.

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Shagbark Hickory

Latin name:
Carya ovata

Curiously, tree-ring scientists rarely analyze some of the more common hardwood species in the eastern U.S., such as this hickory, perhaps because such forest interior trees may contain a weak climate signal necessary for crossdating.

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Virginia Pine

Latin name:
Pinus virginiana

Blue stain found in many sections of dead pines (both in the western and eastern U.S.) is caused by a fungus carried by a pine beetle. The fungus spreads into the phloem and sapwood of living and dead pines, sometimes creating stunning patterns!

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Pinyon Pine

Latin name:
Pinus edulis

Burned sections of pinyon pine are commonly found in archaeological sites in the southwestern U.S. These sections can be carefully broken or surfaced with a razor to reveal the ring structure inside to assist in dating the years of construction of the site.

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Red Spruce

Latin name:
Picea rubens

Conifers in the highest elevations of the Appalachians of the eastern U.S., such as this red spruce, don't experience wildfires very often, but when fires do occur, they can create numerous fire scars even in this fire-intolerant species. Notice the growth release!

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White Spruce

Latin name:
Picea glauca

This tree was located in the Canadian Rockies on the toe slope of an active avalanche path. The scar was created by a debris flow or snow avalanche which struck the tree, killing a section of the living tissue. The avalanche can therefore be dated to its exact year!

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Engelmann Spruce

Latin name:
Picea engelmannii

I worked considerably in the spruce-fir forests of southern Arizona in my earliest years in dendrochronology, and learned that trees with limited sensitivity can provide a vast amount of information on the history of these forests.

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Ponderosa Pine

Latin name:
Pinus ponderosa

The lava flows of El Malpais National Monument in New Mexico contain vast amounts of remnant wood, mostly ponderosa pines such as this sample, and the tree rings on these samples go back nearly 2000 years! Notice the year AD 1400 on this section.

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Chestnut Oak

Latin name:
Quercus montana

In the southeastern U.S., hardwood species are often scarred by wildfire. Most often, this also will cause considerable decay in the sample, but this oak had several well preserved fire scars, suggesting fire was common in these drier, lower elevation sites.

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Ponderosa Pine

Latin name:
Pinus ponderosa

I originally sampled this stump in 1991 for its fire scars, located in El Malpais National Monument of New Mexico. I found it again 20 years later and was happy you could still see the tree rings and fire scars clearly! It had originally been logged in the 1930s!

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Lodgepole Pine

Latin name:
Pinus contorta

This pine is found at higher elevations in the Rocky Mountains of the western U.S. At this site in Montana, we had thought we found fire scars on these pines, but it turns out that these are scars caused by bark beetles stripping away portions of the bark.

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Douglas-fir

Latin name:
Pseudotsuga menziesii

These cores illustrate the level of sensitivity to climate fluctuations in Douglas-fir trees growing in El Malpais National Monument in New Mexico. These rings show the common pattern of narrow marker rings between 1800 (on the left) and 1860 (on the right).

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Douglas-fir

Latin name:
Pseudotsuga menziesii

This photo shows a close-up of the rings in the previous image. The very wide tree ring is the year 1816, the "Year Without a Summer." Cooler temperatures meant more soil water for the malpais Douglas-firs, causing a wide ring for that year!

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Ponderosa Pine

Latin name:
Pinus ponderosa

Dating fire scars found in the annual rings is a major application of tree-ring dating. This photo shows two scars. Notice the wider rings that formed after the upper scar, perhaps caused by removal of competing vegetation or added nutrients.

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Longleaf Pine

Latin name:
Pinus palustris

Longleaf pines have the greatest ages of all the eastern pines. They grow slowly in sandy soils of the Atlantic Coastal Plain, and have proven ideal for learning about past climate and disturbance events, if old-growth stands can be located!

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Rocky Mountain Juniper

Latin name:
Juniperus scopulorum

The juniper species of the western U.S. have proven a challenge in tree-ring dating, but Rocky Mountain juniper has tree rings that are easily identified and can be crossdated. Just watch out for false rings and expanded latewood!

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Douglas-fir

Latin name:
Pseudotsuga menziesii

A close-up photo of tree rings in Douglas-fir reveals the individual wood cells that make up the xylem. These are called "tracheids." Notice the change in cell wall thickness from the earlywood cells to the latewood cells along a radial file of cells.

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Douglas-fir

Latin name:
Pseudotsuga menziesii

The best trees for learning about past climate will be those that grow to great ages and are particularly sensitive to year to year changes in climate. This Douglas-fir began growing around the year 200 BC and lived for nearly 1000 years!

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Mesquite

Latin name:
Prosopis glandulosa

Some desert species from the mid-latitudes do form annual rings, but these diffuse-porous species have rings that are difficult to see. You can use black marker and white chalk dust to help bring out the rings! The dust fills the small vessels and the rings appear!

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Norway Spruce

Latin name:
Picea abies

Spruce is the preferred genus for making high-quality wooden bodies on musical instruments. This photo shows the tree rings on the outer edge of the "Messiah" violin. Analysis of its tree rings helped show that the violin was contemporary with Stradivari!

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Black Locust

Latin name:
Robinia pseudoacacia

In the eastern U.S., this common hardwood species has beautiful tree rings that demonstrate the ring porous wood type. The tree species, however, has some of the densest wood found in North America and is extremely difficult to core!

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White Oak

Latin name:
Quercus alba

Oak is a major genus used to build log structures in the eastern U.S. Sometimes, however, we find that the individual trees experienced some major disturbances that caused very aberrant rings, making crossdating all but impossible.

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Palo Verde

Latin name:
Parkinsonia florida

A common tree species in the American Southwest, palo verde is a diffuse porous species that forms very indistinct tree rings. As a result, little tree-ring research has been performed on this genus. Best to use complete cross sections, when available.

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Ponderosa Pine

Latin name:
Pinus ponderosa

A major application of tree-ring research is learning about insect populations. For example, pandora moth defoliated the needles on this tree, causing some narrow rings to be produced. We can use this pattern to learn about insect populations over many centuries!

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Table Mountain Pine

Latin name:
Pinus pungens

The analysis of fire scars in tree rings can also be applied to pine species growing in the eastern U.S. Table Mountain pine has proven to be the best species in the Appalachian Mountains for learning about past wildfires!

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Subalpine Fir

Latin name:
Abies lasiocarpa

Subalpine fir grows in the highest elevations of the southern Rocky Mountains and forms fairly compacent ring series. Sometime between 1979 and 1980, this tree was stripped almost completely of its bark by a black bear, but it still survived in one small area!

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Florida Torreya

Latin name:
Torreya taxifolia

Perhaps the rarest conifer in the U.S., this species is on the brink of extinction because its habitat is facing mounting pressure from rapid changes in its native environment. It forms very nice tree rings, but few adult individuals are left to analyze.

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The Science of Tree Rings

Presented by
Henri D. Grissino-Mayer, Department of Geography, The University of Tennessee

The Science of Tree Rings

More than just counting ...

Welcome and thank you for visiting the Science of Tree Rings web pages, designed to be the ULTIMATE source for information on the science of Dendrochronology. I've designed these pages to be easily understood by people at all levels of education, from elementary school students to high school students, from first grade teachers to college professors. You won't find the fancy Flash-driven pages here anymore — I want these pages to be readable, enjoyable, and (most of all) educational for all, especially those with learning and physical disabilities.

My goal ...

My goal is to make available as much information about dendrochronology as I can possibly find on the Internet, from the basics of tree-ring dating, to reference and bibliographic information, to products and supplies, to books, and more! My mission was born from an overwhelming need among dendrochronologists for a permanent repository of information that was free to the public, easily understandable, and as comprehensive as humanly possible. Come back and visit from time to time to learn more about new or updated software, new educational tools, new institutions conducting tree-ring research, new publications, and more!

My philosophy ...

I believe that a scientific discipline is only as efficient and important to society as the information available to it. Too often, scientists are overwhelmed with a glut of information about a particular subject, making it difficult to read through and separate the significant material from the unimportant. Organization is key in science. In the Science of Tree Rings web site, I've organized all facets of dendrochronology into neat groups, each available by clicking on the links at the left or on the slide-out menus that follow.

Support this web site ...

Many people think that the Science of Tree Rings web site is supported completely by my university. Not at all. I do all the web page information searching, coding, and designing at home in my home office in my free time, which likely amounts so far to thousands of hours of personal time. I paid for the Microsoft Expression Web Pro and Dreamweaver CS5 software, my Macbook Pro laptop (also running Windows 7 via VMware), my Dropbox Pro account, high-speed Internet and home wireless, wireless printer, and all the "hidden" overhead (paper, cartridges, electricity), even the extra server space needed for the many files! Bottom line... all this adds up... over the years... like in the thousands of US dollars.

If you've found these pages useful, please consider making a small donation using the Paypal buttons at the top and bottom of this page. Any amount will be very much appreciated! Also, to further help offset costs of maintaining this web site, consider buying items from my online bookstore and online tree-ring supply store through Amazon.com. I receive a small percentage (4%) from each sale and all proceeds go towards helping keep these web pages going. In fact, if you buy anything after linking to Amazon through my stores, I still receive a small percentage. I'd like to keep these tree-ring web pages online for another 20 years! -- Henri

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Not sure where to find something? First, click on the "A to Z Index" button to the upper left for a comprehensive list of items available from these pages. Second, try searching for a particular keyword by using the Google search link at the bottom of this page or by clicking on Search Site in the top or bottom menus. A list of pages at this site will be provided with that keyword. Then find the item on that page by using the "Find in page" function of your browser. Finally, when all else fails, get in touch with me at the email address below and ask me your question. I promise I'll provide a timely answer as quickly as possible.

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