The Pros

Most of my work this month has been in live ponderosa pine on the Kaibab Plateau.  On Friday, though, I was back in Utah, in the Pavant Range, sampling from among the dead and the down.  A couple of colleagues are building a climate chronology for southern Utah using dead wood, and I invited myself to help with data collection.  Being, as I have mentioned, a very amateur dendrochronologist, it was good for me to spend a day with the pros.  I learned a lot.

First, while live trees are useful for telling us about the past 100 years, the dead can tell us about the past 1000 years.  We did collect cores from large, live ponderosa in the canyon, but the real hunt was for material that had been dead for 500 years.  This was a surprise to me.  I knew that wood decay rates were slow on arid, south-facing, mid-elevation slopes, but I didn't think they were that slow.  In fact, they are:  Because of the architecture of these trees and their location in rocky canyons, they can often wind up dead, but suspended above the ground by a thick lower branch wedged against a rock.  There the stems can remain, essentially forever, without decaying.

The second thing that is really useful to the professionals is to sample from trees that can live a long time.  If you have a sample that has been dead for 500 years, but before that it was alive for 1000 years, then you have information from 1500 years ago.  Everybody knows what lives a thousand years, right?  Yep.  Great basin bristlecone.  Actually, many long-lived, and slow growing species are found in these arid south-facing canyons.  We sampled from Douglas fir (pictured), ponderosa pine, pinyon pine, and rocky mountain juniper, but the holy grail was bristlecone.

Which brings us to the question:  If you are sampling from a long-dead, gray stob lying on a rock, how do you know what species it is?  It is a good question, but I found that—like anything—the more you work with dead wood, the more obvious it becomes.  Tree architecture is one clue, sometimes there is a very old flake of bark, or maybe a deformity that is unique to a particular species, but eventually you start to recognize species by the cross section alone:  By the color, by the weight, and, especially, by the smell.