Pit and Mound Topography   Edward Frank
  Feb 24, 2007 19:49 PST 


I have been thinking (again) about characteristics of old-growth
forests. One in particular has been bothering me:
"PITS AND MOUNDS Pits and mounds are formed when large trees are
uprooted. The pits form when the roots and clinging soil are pulled from
the ground. The mounds form as the roots decay. Together, the pits and
the mounds give the forest floor a rugged appearance and provide a great
diversity of drier and wetter habitats. The exposed mineral soil in the
pits provides the dry conditions that red oaks, white pines and
basswoods need to germinate. The moist mounds of decaying matter and
rich soil are home to fungi, lichen, bacteria, invertebrates, amphibians
and plants. Settlers leveled the pit-and-mound topography when they
cultivated the land."

The process described seems reasonable, and you can see it in action
when a tree falls and uproots its base. But is it a defining
characteristic of Old-growth. At Cook Forest and at many other sites
with old-growth is topography that has been described as pit and mound.
The problem is that it really isn't and has been misidentified. At Cook
Forest for example the ridgetops are capped with a thickly bedded
sandstone unit. As the hillside erodes pieces of sandstone break off
the edge of the caprock and start sliding down the hill. They are
heavier than the soil, but do not sink the entirely underground.
Freeze-thaw and other mechanical processes cause the rocks to "float" as
they move down the hillside. If the motion is slow they will be
partially buried. Faster motion and they are exposed. At Cook these
float blocks (That is the real term) are often partially buried and may
be covered by thick mats of moss, ferns and the like. They collect
light-weight detritus and debris. These may look like they are earth
mounds, but in fact they are simply rock float blocks covered by mostly
organic material.

I have seen these same features at many sites and I have read of these
being called Pits and Mound topography. Pits and mounds do occur from
fallen trees. In an area with even a small slope these features as a
topographic element are short-lived. I don't see them as being a
persistent feature to characterize old-growth. I don't see them as
being more common in old-growth than they are in younger forests. Is
this an erroneous impression on my part? Do others have thoughts on
this matter?

Ed Frank
Re: Pit and Mound Topography   Lee Frelich
  Feb 25, 2007 07:56 PST 


Pit and mound topography often occurs in old growth forest. But it also
occurs in second growth that was clearcut but not plowed, in which case the
mounds may persist as second growth develops.

Some true old growth forests do not have pit and mound topography. For
example, floodplain forests where mounds may form but are obliterated by
floods, pine forests on sandy soils where trees mostly die standing up and
become snags, and even if mounds do form, the sand flows back down pretty
quickly, and some hemlock forests where all the trees get heart rot at the
base of the trunk and snap off rather than uproot.

So, no pit and mound topography is not diagnostic of old growth, even
though there is an association between the two.

Re: Pit and Mound Topography   Fores-@aol.com
  Feb 25, 2007 08:38 PST 

I had an awful lot of exposure to the pit and mound formations in my years
working in New England. In most cases the pits and mounds could be traced to
some specific severe weather event in the past like a severe hurricane.

It is amazing in many parts of the Connecticut valley in southern Vermont
and New Hampshire where you can still see where the wind came from in 1938...in
some places the stems of the blown down trees are still rotting but in others
everything except the holes are gone.

In WV where many of the slopes are very steep and can exceed 70% pits from
old fallen giants can be the only level place to even stand on a mountainside.
If you have been walking side hill for several hours the little flats that
pockmark otherwise steep slopes can save your ankles.   The size of some of
the flat areas can be small, less than 10 square feet while some of the very
large ones can leave a flat more that 25 feet across the hillside and ten feet
into the hillside. Most of our tip up mounds result from trees falling 90
degrees to the direction of the slope and seem to be the result of heavy grape
vine infestation or ice storms.

The largest difference between mounds in NE and WV is that in NE most places
the mounds are oriented as the wind came through and blew everything
over...usually pointing to the north or east. In WV the wind that can cause such
events can result in trees pointing in any direction but generally down hill.