The Historical Database Known as Trees (and a new video)

Rob Diaz de Villegas WFSU-TV

IGOR chip- human appreciation 150I like the idea of hiking cross country, unimpeded, for miles at a time.  Trails are great- and usually safer- but the idea that you can have space to literally walk off the beaten path is appealing.  A couple of hundred years ago, you could travel across the entire southeastern coastal plain in this manner.  This was a road paved by fire.  On this blog, we’ve covered how fire creates the pine flatwoods ecosystem with its widely spaced trees, and how and why mankind has had to replicate a process that had happened naturally.  But how do we know how often to burn, and at what time of year?  It would be convenient if we could ask someone who was around before the area was settled.  As it turns out, we can.

Trees have the answers in their rings.  We get a glimpse of this towards the end of the video above, but I wanted to take a closer look at how Dr. Jean Huffman was able to interpret the data locked within trees.

The photo to the right is a detail of a longleaf pine stump cross-section.  In it you can see that the rings alternate in shading between light and dark.  The light wood is early wood.  This is from the beginning of the growing season, typically spring, when a tree usually grows the fastest.  The growth in the summer and fall is darker, and is called late wood.  Winter is the dormant season.  So one light and one dark ring equal one year of growth for the tree.  You may also notice that some rings are wider than others.  Wide rings indicate a higher rainfall, and especially narrow rings indicate drought.  Knowing this, we can start building a master chronology.

A master chronology is made by comparing the relative width of rings in a series of trees. In this way rings in each tree can be dated exactly, even if there are occasional missing rings or false rings in an individual tree. The master chronology can be used to exactly date the rings in individual stumps.  Since longleaf pine is such a long-lived species, there is potentially hundreds of years’ worth of climatological data in its rings.  When you have data for many trees, you can build a reliable chronology that goes back before people started keeping records.  This is a dendrochronology (dendro= tree, chronology= matching events to specific dates based on historical records).

fire scarFinally, you match years in your chronology to fire scars (that’s a scar to the left).  Longleaf pine are a fire resistant species, and it takes a lot to kill the cambium and create a scar.  Because of this, Jean only created fire histories for periods when she had at least three “recorder” trees- enough to establish a pattern.

She determined that there were frequent fires in the area- every one to three years.  That’s enough to keep oak and other woody plants from encroaching on ground cover plants, including the many rare plants of the SJB State Buffer Preserve.  It was strange to just trample over the grass and palmettos in the managed area, and all of the gems potentially hidden underneath them.  It doesn’t exactly adhere to the “Leave no Trace” ethos.  But the reality is that all of it will burn and go away, and then grow back again, and again, and again…

The video features music by Pitx and Airtone.  Thanks to Dr. Jean Huffman for reviewing my text for accuracy.
Next on EcoAdventures North Florida, we’re going to a place where large chunks of land get swallowed up by the earth, and where a river goes underground.  Of course we mean Aucilla Sinks (Wednesday April 11 at 7:30 PM/ ET on WFSU-TV’s dimensions).



About Rob

Rob Diaz de Villegas is a producer, editor, and director for WFSU-TV. He has produced and edited documentaries such as Keys & Hammers, Never the Same Way Twice, and Not Your Mother's Classical, and is also the co-creator of WFSU's music performance program, outloud. Over the last three years, Rob has collaborated with Dr. Randall Hughes and Dr. David Kimbro on In the Grass, On the Reef. View some of Rob's work here.