Texas Panhandle Junipers
Palo Duro Canyon

In June 2004 I did a quick look at the Juniper growth rates and  ages in the canyon.  According to the Park's Interpretive Center, these trees are One-seed Junipers.  I had studied Ashe Junipers in Comal County which gets 33 inches average annual rainfall.  Palo Duro Canyon's One-seed Junipers get 20 inches of average annual rainfall.

I found that in Comal County with its more frequent rains, the Ashe Junipers in the sun grew at about an inch of radial trunk diameter for each 13 to 22 years depending on soil depth.  In the Panhandle I cored nine One-seed Junipers in the sun and found they grew at rates of an inch radial diameter every  18 to 35 years, depending on the steepness of slope mostly.  Four of these were growing on soil underlain by Trujillo formation while 5 were on soil underlain by Ogallalla formation.  In these soils the growth rates averaged 28.35 and 28.9 years age per inch of radial growth respectively.  The soils around the cored trees would be considered shallow but at varying slopes.

Pictures of five of the cored trees with their associated ages can be seen here.

The purpose of the coring was to establish growth rates to be applied to much older looking trees which could not be cored effectively with a short small-diameter increment borer.  Older One-seed Junipers tend to loose the continuous protective bark layer around the trunks.  As they age and continue to grow in trunk size, they show mostly dead trunk with a few ribbons of live bark winding up the old trunk.  These trees usually provide poor increment cores and the wood is commonly too hard to core without breaking a bit anyway.  The trunk crossection with its discontinuous live bark becomes very contorted as the tree ages putting on discontinuous annual rings under the live bark ribbons..  Short of cutting the old trees down, an age estimate from established growth rates of younger trees seems best to determine the ages of the older trees in the canyon.

As in the Texas Hill Country, brush and woods, especially juniper, are taking over Palo Duro Canyon.  See this comparison of the tree cover in 1937 and 2004.

I found within a hundred yards of the car in a matter of an hour many trees which I believe are between 200 and 450 years old, based on the growth rates of  the cored trees in the vicinity.  Click here to see a few of these trees and their estimated ages.

Can growth rates of 100 to 150 year old trees be used for estimating tree growth of the period from 150 to 500 years back?  Probably only if the climate was consistent.  Perhaps it will be necessary to get a core of the inner part of the large-trunked old trees to see if the younger trees are adequate for growth rate estimation centuries back.