This method does not harm the trees. Chronology and past climate can be traced by tree-ring crossdating . Database for tree rings from other parts of the world are available in NOAA s Paleoclimatology where tree-ring data sets of 2000 to 3000 years are maintained. Although growth rings are useful for tracing the past, not all tree-rings are suitable for dating. Specific limiting factors, both external and internal, affect the plant growth rings.
Internal factors are growth regulators, enzymes, and water.
These factors can be the result of external factors as well. Each ring is the result of both factors within a single year. Growth begins in spring, and ends in summer or early autumn. When one or more factors are limiting, distinct growth rings, or layers are formed. It is possible that no growth rings are formed under favorable conditions, or, one or more growth rings can be formed during an unfavorable year.