Ring-Growth Anomalies

Question: If one tree ring is grown each year ("annual rings"), why not just count the rings?
Answer: Ring growth is not always annual:

Occasionally, a ring isn't grown during a year -- called "locally absent" or "missing" for that year
Occasionally, more than one ring is grown during a year -- called "false" for that year

Single Locally Absent Ring: 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	Photo provided by P.R. Sheppard

Many Locally Absent Rings: This photo of a coast redwood sample has many rings that are wedging out This sample probably is not crossdateable Important Point: Not all tree-ring samples are crossdateable	Photo provided by H.C. Fritts

Easy False Ring Example: This photo has 2 full rings -- left-most ring has a false band The false band of dark latewood cells fades back to earlywood This sample is crossdateable, but not by mere ring counting	Photo provided by C.H. Baisan

Difficult False Ring Example: This photo has 2 full rings -- right-most ring has a false band The false band appears to go through the resin duct This sample is crossdateable, but not by mere ring counting	Photo provided by C.H. Baisan

Paul R. Sheppard
Laboratory of Tree-Ring Research, The University of Arizona
Tucson, Arizona 85721 USA
office: (520) 621-6474, fax: (520) 621-8229
Comments to: sheppard@ltrr.arizona.edu