The University of Arizona

The Laboratory of Tree-Ring Research


LTRR logo
Dendrochronology is the dating and study of annual rings in trees:
  • ology: the study of
  • chronos: time, or more specifically events in past time
  • dendros: using trees, or more specifically the growth rings of trees
Conifer Tree Ring

  • Earlywood:
    • Cells: thin walls, large diameter
    • Appears light in color
  • Latewood:
    • Cells: thick walls, small diameter
    • Appears dark in color
conifer tree ring
Ring Porous Angiosperm Tree Ring

  • Earlywood:
    • Cells: large diameter vessels
  • Latewood:
    • Cells: small diameter vessels
conifer tree ring

In the image below, a confier tree-ring sample shows about thirty rings (every tenth ring is marked) grown from left to right. The rings display much variation:

tree-ring sample
  • Total ring width:
    a light and a dark band
  • Latewood width:
    just the dark bands
  • Latewood density:
    darkness of dark band

Variation in these rings is due to variation in environmental conditions when they were formed. Thus, studying this variation leads to improved understanding of past environmental conditions and is the basis for many research applications of dendrochronology.

A key distinction of dendrochronology is that all trees rings being analyzed are dated to their correct year of formation. At first glance, it appears easy to date tree rings by just counting them, but reality is often more complicated than that:

Locally Absent Rings:

wedging ring sample
  • Bottom part of this photo has 4 full rings
  • Top part of this photo has only 3 full rings
  • Wedging ring is "locally absent" from that part of the sample
  • This sample is crossdateable, but not by mere ring counting
False Rings:

false ring sample
  • This photo has 2 full rings -- right-most ring has a false band
  • The false band appears to go through a resin duct
  • This sample is crossdateable, but not by mere ring counting

Instead of merely counting rings, dendrochronologists crossdate tree rings :

  • Match ring-growth characteristics across many samples from a homogeneous area
  • Identify exact year of formation of each ring
  • Among other methods of crossdating, one is to "skeleton plot" samples:
    1. Plotting variation on graph paper
    2. Matching similar variation on graph strips
    3. Try crossdating by skeleton plotting for yourself on the web

Laboratory of Tree-Ring Research, The University of Arizona
Tucson, Arizona 85721 USA
Main Office: (520) 621-1608, Fax: (520) 621-8229
Comments to Paul Sheppard: