Tips for Studying Tree Rings
Everyone who cores trees or analyzes tree rings at some point has found a way to do things faster and do them more efficiently. So, I collected all these tips over the years from the "masters" themselves, and added a few of mine! Have fun!
Dealing with broken cores:
Broken or decayed cores and be difficult to get into a sample straw. Use a knife blade to slice the straw end to end, then slip it over the core while it is still on the extractor/spoon. Once the straw is in place, carefully pull out the extractor! (Thanks Russ Carlson!)
Multiple straws for long cores I: Paper:
You may find that some cores are too long for one straw and require you to use two straws, right? One way to deal with this is to carefully crimp one end of the paper straw, then place that inside the end of the other straw. No need to use tape to close as the two paper straws will form a very tight single straw when done right!
Multiple straws for long cores II: Plastic:
You may find that some cores are too long for one straw and require you to use two straws, right? Another way to deal with this is to use a sharp knife to cut a half-inch slice in the end of one straw, then place that inside the end of the other straw. This is smoother, and makes it easier to insert and remove the cores. (Thanks Russ Carlson!)
E-clip your handle:
Tired of the latch coming loose on the handle of your increment borer when it's supposed to clip onto the borer shaft? Head to an auto parts store and purchase several small e-clips, also called snap ring circlips. Take a borer with you to make sure you get the right size clip (ie, one with at tight fit). You can buy special pliers to get these on and off but regular pliers can work, too.
Treat your borer with respect:
Increment borers are expensive, yet take a lot of abuse when we core trees. Keep these in top condition at all times. Be sure to clean the outside of the shaft with fine-grade steel wool and WD-40 to remove excess resin. When storing your borer, clean it inside and out with a gun-cleaning kit and WD-40, and coat the shaft and extractor with WD-40 before placing in storage.
Gun cleaning kit:
Cleaning the inside of your increment borer can be difficult, but not if you use: (1) a 22-caliber gun cleaning kit, and (2) lots of WD-40. Any department store will carry such kits in their sporting goods section. Be sure to get the kits used to clean 22-caliber rifles as these will have the extensions needed for your longer borers.
Have trouble keeping the latch hooked on your increment borer? Often when backing the borer out of a tree, the latch can come loose, causing the handle to come off. Go to the hardware store and buy some 0.5 inch rubber O-rings used in sink faucets. Slide these down the handle and over the latch when the borer is being used. hair ties work great, too!
Are your cores "ragged" when you pull them out of your borer? If so, your borer needs sharpening! A sharpening kit can be purchased from a forestry supplier, and comes with various shaped stones. Learn how to sharpen your borer, and keep your borer sharp, always! Otherwise, your cores will be ragged and will be prone to jamming up inside your borer!
Cleaning your borer:
Do cores tend to jam inside your borer? If so, then your borer needs (1) sharpening, (2) cleaning, or (3) both! Always make sure you head to the field with a sharp borer. At the end of each day, you should clean your borer with a gun cleaning kit and lots of lubricant. Debris and resin left inside your borer for long periods will cause chemical reactions that ultimately will pit and damage the inside of your borer, causing cores to jam regularly.
Fixing the extractor:
Does the extractor (or spoon) on your borer fail to grab the core when you insert it? First, make sure your extractor is as sharp as possible. Use the cone-shaped sharpening stone that came with your sharpening kit. Second, you may want to "clench" the end of the spoon near the teeth. Place a nail that's slightly narrower than the extractor inside the tip, and clench the extractor in a vise, using the nail as a guide. Don't clench too much, though.
V-handles for your borer:
Sometimes the straight handles on increment borers prevent coring in tight places (such as archaeological logs in cabins). Create a V-handle by scoring the handle on either side, bending into a V-shape, then welding the score line closed. A cross-brace can also help strengthen the borer.
Gloves for coring:
After coring many trees a day, your hands and fingers can become very sore. Purchase some fingerless gloves like those used by bicyclists and weight lifters, making sure they have padded palms, and your hands and fingers will be much less sore!
Flag your extractor:
Don't lose your extractor in the grass or leaf litter around the tree you're coring! If you accidentally step on it, you may not have a borer to use. Tie some bright colored flagging through the end loop on the extractor handle, and you'll never lose it again.
Try not to place your extractor on the ground beside the tree as you can easily step on it and irreparably bend it. The ideal place? Wedge the extractor in some bark on the tree, if possible. If not, place it in your back pocket (my favorite), but be careful when you sit down!
Prevent jammed borers:
When coring, stop every few turns and insert the extractor until it reaches the core. Measure off the distance with your thumb on the end of the borer handle. Pull out the extractor and place it alongside the borer until the tip reaches the bark. If there is a discrepancy, your core is jamming!
Coring in tight places:
Sometimes the lower branches of trees (especially shrubby junipers) make coring difficult with those long handles. You do not have to use the handle that came with the borer -- the different lengths are interchangeable! So, you can core a tree with a 20 inch borer while turning the shaft with a 12 inch handle! Great when coring in tight places.
Stuck increment borer:
Sometimes our borers get stuck inside a tree. Be sure you have some parachute or heavy-duty cord with you. Tie a clove hitch around the shaft of the borer and wrap the other end of the cord around a nearby tree. Turn the handle counter-clockwise, thus tightening the rope. Be very careful, though, because the borer may come out of the tree with considerable force.
Extra borer leverage:
Sometimes coring a tree could be aided if you had additional leverage. Try this. Use a handle that comes from an increment borer one or two sizes larger than the one you're currently using. Be careful, though, because additional torque is applied to the auger by this longer handle.
Removing a jammed core:
If you do get a core stuck in your borer, check to see how much wood is compressed. If it's less than 2.5 cm (1 in), try this. Insert the extractor and turn the borer upside down, holding the extractor cap. Spin the borer with the other hand. After a while, you may remove enough wood to allow the extractor to slide beneath the jammed core.
Removing stuck cores:
If you jam your borer to the point it can't be unjammed in the field, take the auger back to a wood shop. Using a series of narrow to wider drill bits, use a table-mounted drill press to precision drill the jammed wood through the tip of the auger. Then clean out any residual wood with your gun cleaning kit.
"Pithing" a tree:
In some studies, pith (or near-pith) is required to accurately age the tree. (1) Be sure you pull the core as it was oriented in the tree. (2) Gauge by how far off you are (e.g., 1 cm) by looking at the curvature on innermost rings of your core. (3) Insert the extractor into the hole for a guide. (4) Take a second core, but offset the auger by the distance you are from pith. Keep it parallel to the extractor.
Cleaning your chains:
Are you sawing a lot of pines with your chain saw? If so, the chain can get gummed up with resin very quickly, thus reducing its cutting ability and performance. If you have any juniper logs nearby, run the chain through them. This will remove most of the resin on your chain, and rejuvenate your chain saw.
Sometimes you may need to wrap your fragile cross sections so that they will stay together until you get them back to the lab. Purchase some plastic wrapping in 5 inch wide rolls (12.5 cm) (see my Supplies web page). Alternatively, you can use 2.5 inch (5.25 cm) strapping tape.
Don't have enough pockets for all your supplies while coring trees? Invest in a fishing vest! These have multiple pockets and can store items such as straws, dbh tape, flagging, and sharpening kit, as well as first aid supplies. Larger pockets in the vest can also be used to carry small-sized cross sections!
Wooden golf tees:
Ever get a small section of wood stuck in the tip of your borer? Never ever use the metal tip of your extractor! Instead, purchase some wooden golf tees from a sporting goods store. These will not damage the tip of your borer as you push out the stuck piece of wood.
Next time you visit an Oriental restaurant, save those chopsticks! Why? They are great for removing small pieces of wood stuck in the tip of your increment borer, and they won't damage your borer. Carry one or two in your field vest. Remember, never ever use the metal tip of your extractor!
Coring height gauge:
Dendrochronologists regularly record their coring height on a tree. A quick and instant height measure can be made by simply marking the handle of your increment borer with a black felt tip pen, such as a Sharpie, at every cm. After coring, hold this up to the trunk of the tree and record your coring height!
GPS your trees:
Modern hand-held Global Positioning Systems can quickly document precise locations of your sampled trees to the nearest 1-3 meters, handy in case you need to return to the field to collect cores from the oldest tree in your study, for example! I've found that dense tree cover mostly is not a concern for obtaining coordinates, either.
Often, we have to sample while it's raining, and this can cause our field notes to become smudged and unreadable. Invest in some "Write-in-the Rain" brand field notebooks, available from Forestry Suppliers and other companies. They're low-cost and will save your field notes.
Pre-wrap those fragile cross-sections:
When collecting fragile samples for fire history analysis, I've found it very useful to wrap the sample tightly in-situ with plastic wrap prior to sawing with a chain saw. Make your top-cut first, wrap the sample, then make your bottom-cut. This will keep those fire scars from flying everywhere!
Check the top and bottom of the fire-scarred surface:
When collecting samples for fire history, don't assume the best sections will come from the middle of the scarred area. Often, the section containing the best scars will be located at the top and/or bottom of the scarred surface (also called a "catface"). If you can, collect sections from as many areas of the scarred area.
When conducting a complete inventory of all trees in a study plot for species composition and age structure analyses, mark trees that have been tallied using chalk markers available from most arts and crafts stores. These are the same types of markers used for writing "Just married" on the windshields of automobiles (thanks Elaine Kennedy Sutherland).
Mini dbh tapes:
When collecting tree information, dendrochronologists must carry a lot of supplies into the field. To save space, invest in the mini-sized diameter-at-breast-height ("dbh") tapes, capable of measuring trees up to two meters in diameter (but that's all). These are ultra-small and fit easily into a shirt pocket for easy access.
Portable hand drill and bit:
Sometimes we jam our borers in the field. To remove the jammed core, use a 6mm (0.25") drill bit that has been welded to a stock steel rod (any machine shop can do this). The final drill bit should be the length of your borer. You can use some duct tape wrapped around the end to hold the bit while you gently turn it inside the auger shaft (thanks Jeff Lukas).
This is nifty. When using a dry wood borer at an archaeological or historic site, the sawdust can accumulate around the core. Buy cans of compressed air at an office supply store (used for cleaning computer parts) and every 12-15 mm (0.5 inch) or so, stop coring and blow out the sawdust!
Insect Needles for Pinning
Dissecting needles can get bent, or may just be too wide for some things. Take a mechanical pencil for 0.5 mm lead, and insert an insect pin instead of the lead. You now have a replaceable needle for fine work. Caution: Use small pliers to hold the pin while inserting, to avoid piercing your fingers. (Thanks Russ Carlson!)
Save those flat cardboard trays that canned cat food and dog food come packed on because these make great trays for sorting and storing your cores while you're working on them in the lab! Have one tray marked for cores being processed and another tray for cores that have been processed (for example, already crossdated and measured).
Sometimes you need to estimate the age of a tree from cores that did not reach pith. Using graphics software, create templates of concentric circles (i.e., "ring") of various widths, e.g. every 1mm, 1.5mm, etc. Print these out on transparency film. To estimate the tree age, hold the template containing rings of the appropriate width over the innermost rings and age the tree.
Marking your rings:
I've seen that standard dissecting needles today are not very sharp. Try this. Rather than using a needle to pin-prick your rings once they're crossdated, use instead the lead on your mechanical pencil. This works only with softwoods, of course, and make sure you have thick lead (2H, 3B). In addition, you can sharpen your lead with fine-grade sandpaper (thanks Jeff Lukas).
Sharpen your dissecting needles:
We often use dissecting needles to put the final pin-pricks on decadal rings of crossdated pieces of wood. These tend to get dull and sometimes come shipped rather dull. Do this. Rub the tip of the needle back and forth across some fine-grade sandpaper, and then inspect the tip under a microscope until the desired sharpness is attained.
Clean your sanding belts:
Sanding belts are not cheap, so it's best to take care of them and make them last as long as possible. Few people realize you can clean the resin and debris off the belts using "belt cleaners." They come in various sizes, but the best are 25 cm long and 5 cm wide. For more information, check out my supplies page under "Sandpaper" at the bottom.
Need to polish up a surface on a core (or section)? Cut a strip of fine sandpaper or sanding film (>= 320 grit) 2.5 cm wide by 10 cm long, and wrap this around an artist's gummy eraser (available at all art supply stores or from my online supplies page). The eraser will conform to the contours of the core!
Beanbags for your cores:
Sometimes when you're measuring, you have to position the core and its mount at an angle to help see the rings, especially if the core was mounted slightly twisted. To help re-position the core, make some small beanbags partially filled with lead shot wrapped in some sturdy cover, such as heavy plastic or leather. Place these around the core to hold it at the appropriate angle while measuring!
It seems our favorite graph paper for creating skeleton plots is no longer made. On the "Supplies" page, click on "Laboratory supplies" and you'll see a link to a web site where you can download software for creating your very own green-tinted graph paper on your own color printer!
Scotch tape for core mounting:
This was a revelation when I learned this. I had been using masking tape for years, but Peter Brown taught me this trick! Once your core has been mounted in glue on your core mount, secure them tightly on the mount with a few strips of clear Scotch tape. And NO NEED to remove it before sanding! Just sand the core through the tape itself!
Once the tree rings in your wood are correctly crossdated, you should "prick" holes permanently into your rings: one hole = every 10th decade ring, two holes = 50th mid-century ring, three holes = century ring, and four holes = millennium ring). To do this, use dissecting needles, also called biological probes. High-quality metal needles are worth the extra money.
Stabilizing wet wood with PEG:
Sometimes we wish to preserve entire sections of wet wood for analysis. Use a low-molecular liquid such as polyethylenglycol (PEG) 200 or PEG 400 to soak the wood in a PEG-bath. Low viscosity PEG 400 enables the liquid to spread in the wet wood. After drying, PEG acts as dimensional stabilizing agent in relation to moisture (thanks Rupert Wimmer).
Stabilizing punky wood with Polycryl:
Preservation Solutions' Polycryl is a large molecular weight acrylic polymer that fortifies and stabilizes soft, punky, or spalted wood that you would like to sand. It is also water soluble and cleans up with soap and water. It can be brushed on or soaked in a Polycryl™ solution. All types of finishes and glues can be used once Polycryl dried into the wood (thanks Russ Carlson).
Pegboard sanding surface:
To create a sanding table that will allow you to sand cross sections of any size, nail down pegboard (available from your home improvement store) unto a sturdy table with a wooden top. Also, purchase the correct size wooden pegs. Hammer these into the pegboard around your irregularly shaped cross section for a firm fit!
Need a carrying case for your straws once you collect your cores? Go to a map store or mailing outlet (like Mailboxes Etc.) and buy those round mailing tubes in the length you require. I use one tube to store my unused straws and another to store my straws with the cores. Plastic works best, as paper tubes can become soggy if it rains.
Need to get excess resin off your cores to see your rings? Burnish the surface lightly with fine-grade steel wool! This will remove the excess resin and enhance the ring boundaries.
Need to get a flat surface on a cross section that has deep chain saw cuts? On large sections, use an electric hand planer to remove the saw cuts. On smaller sections, use a band saw to slice the section. Both techniques should result in a new, flatter surface on the section.
Are you working with cross sections from a tree species with rings difficult to see when sanded? Try this. Color half the section with black marker. Then spread baby powder over the colored half, rub in, and blow the remaining powder away. Rings (if any) should now be more prominent on the colored section. Compare this half with the original half.
Afraid of bringing home critters (ants, termites, and other critters) to your lab? This could be problematic if termites get into your wood collection. Take all pieces of wood to an herbarium or any place with a low temperature deep freezer. Place your sections in these overnight to ensure you don't have invasive insect problems.
Mold on your cores:
Does mold form inside your plastic straws on your valuable increment cores, thus masking your ring boundaries? As soon as possible, slit the plastic straws with a razor, thus allowing air in while allowing the moisture in the cores to wick away. This will prevent or reduce the amount of mold that forms on your increment cores.
Cardboard for mounting:
Running out of expensive plyboard to mount your fragile cross sections? Did you know that many cross sections can simply be mounted on sturdy corrugated cardboard, such as the cardboard found in boxes for shipping heavy items. I look for these on loading docks!
Fluorescent lighting for charcoal:
Tree rings on charcoal surfaces are difficult to see, often because of the reflection caused by regular incandescent lights found in standard microscope illuminators. Fluorescent lights (especially light rings) provide softer, cooler light that helps bring out tree-ring patterns on charcoal sections! And they are not that expensive.
"Crack" your charcoal:
The guys in the dendroarchaeology section of the tree-ring lab in Tucson taught me a neat trick to help bring out tree rings on charcoal pieces. Take the charcoal piece in both hands (if big enough) and carefully break the section in two along a transverse plane. If the piece is smaller, "flick" off a piece of charcoal from the surface with the edge of a razor blade. The rings should now stand out very nicely.
Document your cores:
When processing your valuable cores, the person responsible for each step in preparation should initial the bottom of the core mount. For example, "MS by GW" (mounted and sanded by GW), "XD by Joe H." (crossdated by Joe H.), and "ME by MS" (measured by MS). This technique ensures careful attention to these important steps by the technicians.
COFECHA Tip #1:
Be sure to check for "A" and "B" flags in your output. An "A" flag means COFECHA could not find an alternate dating position for a segment that correlates low with the other series. A "B" flag is more serious and means COFECHA found an alternate dating position. Systematic placements of flagged segments possibly indicates a misdated series.
COFECHA Tip #2:
Need help isolating a problem (missing or double) ring in a segment? Run COFECHA again a few times, decreasing the length of the segments being tested each time (e.g. 50 years, 40 years, then 30 years). Inspect the output and you'll notice you can zero in on the problem ring more efficiently. Then be sure to go to the wood and inspect that segment for the possible problem.
COFECHA Tip #3:
What constitutes a misdated segment or series in COFECHA? First, look for an r-value that's twice as high as that at the zero-shift position. Second, look for consecutive segments with the same suggested alternate placement, e.g. +1 or -1 (the two most common alternate placements). Third, look for an outlier ring listed by COFECHA at or around a known problem ring (most likely a missing or extremely narrow ring).
COFECHA Tip #4:
If you need to date some undated measurement series using already dated series, did you know you can save the master dating chronology created by COFECHA? In subsequent runs, enter the file name that contains the master chronology when COFECHA asks you for the "Crossdated tree-ring series." Then enter the file containing the undated series when prompted. The resulting output is much simpler to read and interpret!
COFECHA Tip #5:
See the graph with upper- and lower-case letters? This helps identify pointer years (extremely narrow or wide rings) as well as overall trends. The ampersand (@) symbol means a near average ring index, an upper-case letter means a year with overall wide rings, while a lower-case letter means a year with overall narrow rings. Each increment in the letter equals a 0.25 standard deviation unit!
COFECHA Tip #6:
If no reference chronology is handy, and you have many undated measurement series, first see if you have internal dating among them. These should all be measured beginning with year "0" or year "1." When asked to enter a dated series, hit return. Next, enter the name of the file containing the undated series, when prompted. COFECHA will then test each series against all others. Look for t-values at or above 3.5!
COFECHA Tip #7:
When attempting to date multiple undated series without a reference chronology or dated series, try not to overwhelm the analysis by analyzing too many series at once. Start with a few (8-12) of your measurement series with the clearest ring patterns, and enter these in COFECHA. As they become dated against each other, use one as the anchor and adjust all other relative dates accordingly.
COFECHA Tip #8:
Did you know you can use a reference index chronology as your dated series when attempting to date your undated measurement series? Simply enter the name of the file containing the index chronology when prompted for "Crossdated tree-ring series." COFECHA should recognize that this is an index chronology and not measurement series. If not, COFECHA will prompt you for the format. Simple!
COFECHA Tip #9:
Here's a tip that's sure to please. Sometimes you may want to use several index chronologies from a region to develop a single reference chronology to date some undated series. Place all index chronologies in one file (make sure they have the same format). Enter this file when prompted for "Crossdated tree-ring series." You may want to turn off detrending in COFECHA -- enter "-1" under the spline option.
COFECHA Tip #10:
Always archive your tree-ring measurements! In the Main Menu of COFECHA, you can choose the option that says "List Ring Measurements" and COFECHA will print out the measurements for each series in the output. Select this option when the measurements are completely and precisely dated, then place this output in a secure, permanent location!
COFECHA Tip #11:
If you're conducting many runs of COFECHA to diagnose the same data set, you don't have to print out the entire output produced by COFECHA. In the Main Menu, select option 8 and have COFECHA print out only those parts of the output you absolutely need, like the diagnostics in Part 6 or the results of dating an undated series in Part 8!
COFECHA Tip #12:
To help diagnose a possible location where a misdated segment may begin, carefully inspect Section C in Part 6 of the diagnostics. This section lists consecutive year-to-year changes that are very different from the mean change found in all other series. If consecutive years are listed (e.g. 1851 1852), this could be the location where a missing ring should be or a possible error in measurement.
COFECHA Tip #13:
So, what value of mean interseries correlation (first page in the box, and found in Part 7 at bottom) should you have? I consider a value of 0.40 the minimum a tree-ring data set should have. I've seen values much higher in the American Southwest (0.55 to 0.70) while data sets for eastern species may range from 0.45 to 0.60. Data sets with very long complacent series, however, may have values less than 0.40.
COFECHA Tip #14:
If you're developed a network of tree-ring chronologies in an area, you may want to check the final dating of the chronologies against each other, and to learn where the climate signal is the weakest. Did you know you can enter a series of chronologies from one file into COFECHA? Simply paste all the chronologies (Index or Compact format) one underneath another in one file!
COFECHA Tip #15:
Need help isolating a problem (missing or double) ring in a segment? Here's another tip. Run COFECHA again a few times, keeping the same segment length being tested (e.g., 50 years or 40 years), but decrease the amount of overlap in the segments. For example, I've found running COFECHA testing 40 year segments overlapped by 10 years (rather than the default 20 years) truly helps isolate problem areas!