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Paleo Slide Set: Tree Rings: Ancient Chronicles of Environmental Change
False rings in Mexican cypress (Cupressus lusitanica).
Under certain climatic conditions, some species will form intra-annual or false rings . If climatic conditions are unfavorable to growth during the growing season, the tree may mistakenly sense that the end of the season is near, and produce dark, thick-walled latewood cells. Improved conditions will cause the tree to produce lighter, thinner-walled cells once again, until the true end of the season. The resulting annual ring looks like two rings, but when this first ring is closely inspected it can be identified as false because the latewood boundary grades back into the earlywood. False rings occur in a number of species such as the Mexican cypress pictured here. Young ponderosa pines in southeastern Arizona commonly contain false rings as well. In this region, winter and early spring rains provide moisture to trees in the early part of the growing season. By May and June, the driest part of the year, trees have used up the available moisture and, if stressed enough, will begin to produce latewood cells. However, monsoon moisture usually begins to fall in July, and with this moisture, trees will again produce earlywood cells.

Photo Credits:
Peter Brown
Rocky Mountain Tree-Ring Research, Ft. Collins, CO
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Last Modified: 12 October 2001

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