Friday, January 16, 2015

Fallen Trees to Soil

Winter is a wonderful time to assess the condition of a woodland.  While the trees are in a leafless condition, it’s easy to get a quick idea of tree density, species composition, trunk size and general condition.  Viewing a winter woodland reminds me of visiting a home stripped of furniture and fixtures.  The basic foundation is laid bare to be appreciated.  What we see during the winter is the infrastructure upon which the diversity of summer life will depend.

I think the best way to describe the Blue Jay Barrens woodland is to say that it is recovering.  1938 aerial photographs show the area to have been woodland then and it has remained in that condition since.  I doubt that this area avoided the deforestation that resulted from timber harvest to create charcoal for the Iron Furnace industry in the early 1800’s.  Since that initial clearcutting, I suspect that the area has remained woodland, so except for that small break, the influence of a closed canopy environment has been at work here for centuries.  Timber harvests have taken place during the past 150 years, but they have been selective cuts that left much of the canopy in place.  Each harvest took the best timber and left the remaining trees standing.  That long term strategy has left its mark.  Most of the large trees display damage or deformities that would have made them of low value during the last harvest.  Add to that the damage that occurred to tree roots from cattle grazing in the woods and you have a stand of trees that is in far from prime condition.  The woodland as a whole is slowly improving, but recovery is a long process that is still working through some ugly times.

Most of the woodland is located along a series of east-west oriented ridgetops.  The ridgetops are quite narrow and drop off steeply on each side.  This topography is probably what kept the area from being plowed for crop production.  Soil is extremely shallow to bedrock on these ridgetops, which would have also made them unsuitable as cropland.

Part of the woodland recovery process is the loss of trees that were weakened by past abuses.  A few trees have traditionally fallen each year.  This process creates pockets of light that allow younger trees to grow.  The result is a diversity of tree size within the woodland itself.  The 2012 derecho accelerated the process by simultaneously bringing down multiple trees in several different areas.

A common monument to a wind thrown tree is the mass of newly exposed roots.  Healthy trees can survive some awfully strong winds.  The problem is that so many trees suffer from multiple environmental factors.  This particular tree had several trunk deformities as the result damage inflicted early in the tree’s life.  Cattle in the woods would have stressed the tree through soil compaction and physical damage to the roots.  Shallow, droughty soil provided harsh growing conditions throughout the life of the tree.  When you add to that the stresses put on most trees by general air and rainfall quality factors, the result is a tree that is extremely vulnerable to a wide range of hazardous conditions.

The root masses can be quite impressive.  This one measures about seven feet from the ground to the top of the soil ball.  Broken roots project upward another couple of feet.  Typical of most of these trees, there are no particularly large lateral roots present.

As the tree fell, chunks of bedrock were scattered about.  The presence of a solid bedrock layer just below the soil surface prohibited the tree from developing any sort of tap root.  With such a tenuous hold on the earth, it’s surprising that the tree remained upright as long as it did.

The bottom of the root mass mirrors the solid rock layer that blocked all root penetration.

The smaller roots, responsible for drawing water and necessary elements from the soil, were restricted to an inches thick layer above the bedrock.  Annual drought stress would have come early to this tree.

In addition to changing the composition of the woodland overstory, fallen trees modify and diversify the woodland floor.  The root mass will eventually decompose through a series of roughly predictable stages.  During the first few years, soil particles will detach from the roots and drop down to form a mound.  Next, the smaller roots will begin to decompose.  This material, along with small rocks, will be deposited on top of the soil mound.  The larger roots and stump will be the last to decompose.  As this material breaks down, the large rocks will be released to take their place atop the soil mound.  Decades from now, an area of slightly deeper soil beneath a mound of loose rock will provide an interesting microhabitat for plants and animals.  It might also cause some people to wonder how that pile of rock came into existence.

Another habitat changer is the tree trunk itself.  Like the tree stump, the trunk will eventually decompose and disappear from sight.  What it will leave behind is a strip of slightly deeper soil with an organic matter content that will allow it to hold slightly more moisture than the surrounding area.  These soil conditions would most likely support a greater concentration of plant growth and produce a noticeable swath of plant life across the future woodland floor.

Prior to my arrival on the property, the fallen trees were regularly cut and used as firewood.  As a result, I have few old logs that have had time to completely disappear.  I do have many that have come a long way on their return journey to the soil.

Subtle differences in available moisture, soil depth, soil composition, sunlight exposure, temperature and other environmental factors create a diversity of micro habitats that allow for a diversity of plant and animal life in a given area.  Each tree that falls and processes back into the soil, increases that diversity and that matches well with my property management goals.

When I see a fallen tree, I often contemplate what that will mean to the health of the woodland environment 50 or 100 years from now, but I don’t forget the immediate changes that occur.  A downed tree, whether or not it has actually completed its journey to the ground, provides an instant source of food and shelter to animals and plants that could not have utilized that resource while in its vertical position. 

The woodland at Blue Jay Barrens is certainly an odd looking creation.  I won’t be around to see this woodland graduated from its recovering status to that of healthy, but I’m confident that it is moving in that direction.


  1. Sounds much like many wood lots in eastern North America, certainly around here. I'm so glad I learned to identify trees by their bark many years ago.

  2. Hi, Furry Gnome. Tree identification by bark is a handy skill. I once worked with a surveyor who only knew trees by their leaves. His default for any tree he couldn't identify was Hackberry, so his survey notes taken during the winter were filled with references to Hackberry trees.