Tree Species Unsuitable for Tree-Ring Dating

Saguaro Most temperate forest tree species (those growing between 25 and 65 degrees latitude), produce tree rings. Therefore, the majority of dendrochronological research occurs in these latitudes. Some species, however, are not suitable for tree-ring dating, and it is important to know and recognize which species to avoid.

On the right is an image of woody tissue from a saguaro (Carnegeia giganteum), the large (sometimes up to 50 feet tall) cactuses with many arms that characterize the American Southwest. Three "ribs" of the cactus are depicted here, emanating from the center of the cactus (a the top of the image). Although dendrochronologists receive many inquiries into the age of these spectacular plants, saguaros do not produce annual rings.

Fan Palm

Here is a partial cross section from a fan palm, a monocotolydon (the same type of plant as grasses), which also does not form annual rings. The inside of a plam tree is basically all primary xylem (woody) tissue - to form annual rings, plants must form secondary xylem tissue radially, from the inside to the outside. Have you ever noticed that palm trees never grow wider around the trunk? This is why.


Some desert species do form annual rings, but the ring structure is very difficult to discern. To the right is a cross section of a mesquite (Prosopis glandulosa) which shows very faint rings, and is usually undatable. To enhance the ring structure, and to perhaps help date this desert species, the darker half was colored with black marker, then covered with chalk dust. The small vessels then fill up with chalk to highlight the rings. Mesquite is a type of ring-porous angiosperm.

All graphics and text on these pages © 1996 by Lori Martinez, Laboratory of Tree-Ring Research, and The University of Arizona. Last updated 18 December, 1996. All rights reserved.