Lessons from the Earth’s Largest Living Organism

We regularly see in newspapers and magazines a general interest filler piece featuring the world’s largest single organism named Pando.  It lives in the mountains of Utah and consists of a giant aspen grove connected by a network of underground roots: covering 106 acres, weighing an estimated 13 million pounds, and consisting of 40,000 individual trees.  Pando is always photographed from the air above as the only practical way of giving a sense of its sheer size.  Here I am reminded of the description of Hinduism as a faith that features thousands of different deities all of whom are the same god.  In Pando, each individual tree has its own avatar, but they are all part of the same biological entity.  The concept of entire groves of trees and shrubs that are separate yet the same – and otherwise genetically identical – is a theme that is repeatedly invoked in the science of forest ecology.  There are many specific examples we can cite in the Ozarks.  But the connection between stands of trees expanding by stems sprouting at a distance from their roots has been an important part of my own personal studies in forest ecology both here and in previous locations during my career. 

    A great local example was given in an earlier Pack and Paddle issue where I described an unusual grove of mature sassafras trees along the Ozark Highlands Trail in a saddle on a ridge just west of where the trail reaches the summit of Hare Mountain.  Since that tree’s leaf and fruit has been made the trademark of our society, I proposed that we could designate this impressive stand as our own sacred grove – like those of ancient Greek philosophers or druid princes.  These trees were all nearly identical, with tall and stately trunks rising to their canopy of characteristically tangled branches.  Each trunk was nearly a foot in diameter with the medium brown, deeply-ridged bark typical of sassafras.

    I passed through this grove in late fall when the ground was carpeted with the bright red and orange mitten-shaped foliage recently shed from above. This place seemed a great site in which to celebrate the Ozark Society trademark in all its glory.  I then went on to speculate that this grove had originated by the spread of a pioneer tree that established in an abandoned pasture and progressed outward by sprouting from an expanding root system.  The colorful carpet of leaves at that time was an indication that all the seemingly separate trees had exactly the same type of fall coloring and had shed their leaves at the same time, suggesting that they were all genetically identical (a trick I had used in previous studies as described below).  You don’t have to take the vigorous hike on the OHT from Cherry Bend to see such a sassafras grove as they are found all over our area.  One of the best places to see sassafras clones right from your vehicle is at stop number 4 along the one-way Pea Ridge Battlefield Park scenic drive.  There is a small parking lot where you can look off to the northwest over open fields.  If you look to the right, the edge of the field is filled with an extensive stand of sassafras trees all looking about the same size and shape.  In the winter it’s obvious that all of them have exactly the same branching pattern and bark ridges.  In the fall they will have exactly the same timing and coloration as they shed their leaves.  Thus, a perfect example of how a grove of many trees can come in the form of a single organism.

I first used the concept of trees and shrubs expanding by root sprouting in my observations near my home in Colorado’s Front Range.  The rocky foothills on the east side of the range had open stands of ponderosa pine and juniper with intervening areas of Gambel oak scrub and aspen groves.  Both of those deciduous trees consist of extensive clones that had spread from an initial pioneer by expanding root systems producing stems of genetically identical copies.  In summer and winter these trees all looked about the same, but their autumn foliage showed a mosaic of patches of varying color and rate of leaf drop.  Often, aspen groves of up to several acres were clearly turning autumn colors of the same exact shade of yellow at the same time as if acting in unison.  In contrast, the oak showed a regular patchwork of clones varying from about 20 to 30 feet in diameter. 

This provided an idea of the previous history of conditions in the local landscape.  This also prompted me to start using color added to my line diagrams of the scenery I was recording in my field notes to document these observations.

    In a more serious line of investigation, I had been interested in the repeatedly documented persistence of American chestnut saplings in the forests of New England long after the seed source had been completely eradicated by the arrival of chestnut blight as it spread across the area before 1920.   After more than six decades the small chestnut saplings could not have been recently-established seedlings and must represent some kind of repeated root sprouting.  During a 1982 sabbatical stay in the Boston area, I began to map the spatial distribution of these saplings on representative sites.  The results showed as many as 100 such saplings on an acre, a number less than the number of mature oaks and other trees on such sites.  This seemed to indicate a process of multiplication from the roots of former blighted trees by means of root sprouting.  Yet the details did not match that theory.  First of all, the rot-resistant stumps of the original chestnut trees were still easy to see, and their distribution did not seem at all related to the living saplings.  This could be checked by examining chestnut saplings located near each other.  I had seen that the spring leaf break varied greatly among saplings.  Some had nearly fully developed leaves in late April while others were just breaking bud.  It became clear that chestnut saplings were each an individual genetic package and not part of extended root clones.  This kind of evidence lead me to conclude that these saplings were all seedlings established before blight cut off the seed source and indicated a remarkable ability of chestnut seedlings to persist in the forest understory.  An amazing feat of what ecologists call shade tolerance, and worthy of a nice publication in the literature to make that known to scientists concerned with re-introducing blight-free chestnut in the future.

    This line of work was continued here in the Ozarks by mapping the distribution of living Ozark chinquapin saplings starting in 2010, fifty years after chestnut blight.  In this case the issue was the abundance of chinquapin sprout saplings so long after my identification of 1957 as the year chestnut blight arrived in NW Arkansas.  It was soon evident that Ozark chinquapin saplings had the same extreme shade tolerance I had inferred for chestnut.  The living saplings were not found where they could have sprung from the roots of former trees – except in a few cases where they were recognized as stump sprouts from the base of the old trees.  But there was one important difference.  The surviving chestnut seedlings only produced new stems from the base when injured while chinquapin bud break showed root sprouting at a distance of up to several feet –- an important difference from closely related American chestnut with important implications for the propagation of blight-resistant varieties whenever they are developed. 

    One practical instance of tree clones and root sprouting of local interest is the case of the pawpaw.  There is a growing interest in the pawpaw as a traditional Ozark fruit.  You can even find pawpaw ice cream and pawpaw beer if you look online.  However, many of us are disappointed to know of extensive groves of pawpaw in the understory of mature forests that hardly ever seem to produce fruit.  This is because pawpaw is a species like some cherries and plums that require cross-pollination to set fruit.  Because pawpaw propagates by rampant root sprouting, some groves may be essentially the same tree and so cannot self-pollinate.   As in the case of chinquapin, pawpaw bud break and early spring flowering varies between clones, so that the clonal identity can be established by observing whether there is any variation between the exact extent of leaf or flower expansion within a pawpaw population.  Otherwise, being aware of how common root-sprouting is among trees and shrubs can provide insights to contribute to understanding of the diverse patches of vegetation you see during outings in our own Ozark forests.