Big Creek Soils   Will Blozan
  Jan 18, 2004 09:30 PST 

Me neither!

Currently, the GRSM Rucker Index is 163.07, and 8 of the trees are in NC, 7
in Cataloochee or Big Creek (same NPS district of Cataloochee). Big Creek is
quickly redefining conventional thoughts about hardwood development! Sounds
like a study site!!

What is curious to me, and must be indicative of the soils, is the dominance
of traditional floodplain or riparian species on south facing boulder fields
and slopes well away from "typical" conditions. Green ash, American elm,
sycamore, bitternut, etc. growing like nuts in an upland situation! In the
spring it would be fascinating to see the wildflower component of the site.

Big Creek Soils   Colby Rucker
  Jan 20, 2004 11:10 PST 


Your observations regarding the presence of floodplain species on slopes,
and greater height on south-facing slopes is interesting, in that both
conditions seem contradictory to our generally accepted viewpoints. I'll
attack this situation by starting with several well-separated observations,
and then see what that leaves in the center.

Although we associate the rich silty alluvium of floodplains with high
fertility, spawning the Egyptian civilization, maybe floodplains aren't
altogether perfect. The dense wet soil deposits exclude air, and tree
species that are present are noted for their shallow, much-divided root
systems, to the delight of nurserymen, being easily transplanted. So,
floodplains are a problem environment, being rather two-dimensional, and
windthrow usually overtakes tuliptree and deeper-rooted species that venture

Tuliptree has rather tender roots. As a result, the crown will deviate from
the vertical, with multiple arching on sites affected by mid-summer dryness.
The greater annual rainfall in the Southern Appalachians moderates this
effect, while on the coastal plain the tallest trees are likely to be found
on north facing slopes in those few deep ravines where the sun seldom
ventures. The best sites seem to coincide with the presence of glade fern
and maidenhair fern.

At Chase Creek, sandy loams on south-facing slopes, especially those toward
the southwest, are often unusually dry, resulting in an absence of tuliptree
or northern red oak, being dominated by chestnut oak, black oak, virginia
pine, and some post oak. These species are deep-rooted in the loose soil,
which is nearly devoid of herbaceous vegetation.

Where subsoils are nearly impermeable clays, typical floodplain species are
often found on hilltop terraces. Excess soil moisture drains slowly, moving
down slopes, unseen, but creating a more shallow soil than ideal for
chestnut oak, often resulting in windthrow or shoestring fungus problems as
these trees age. The moisture flows ever-deeper beneath sandy lower
terraces that are actually relic sandbars, uplifted over the past million
years or so. New York fern and clethra may occur at the upper end of these
terraces, and sour gums thrive on these dry sites by extending their root
systems down to the constant source of water. Sour gum is a most valuable
indicator species, outlining wetlands of all types like a row of fence
posts, but not venturing onto saturated soils or ravine bottoms.

At Mohawk Trail, the best white ash sites were somewhat similar to the
coastal plain lower terraces, being deep loose soils overlying an
impermeable rocky slope below a concave "collector" extending upslope. The
white ash benefitted by a deep loose soil, but did not experience a shortage
of available moisture. If the steep upper slope had been south-facing, not
north, it is uncertain if the moisture supply would have been so reliable.

The woods behind my house is south-facing, and the slopes have some chestnut
oak, black oak, beech and sour gum to the southwest, but phase to
tuliptree-northern red, with a good bit of pignut, pawpaw, redbud, blackhaw,
flowering dogwood, American holly, and red mulberry to the south. Similar
sites include black walnut, sycamore and slippery elm, phasing to a bit of
sweet gum and basket oak, which are more southern species. Mayapple and
other herbaceous plants occur, showing the slopes to be quite different than
the chestnut oak - post oak sites.

One difference seems to be whether the slope is concave or convex, the more
sheltered coves escaping the drying influence of prevailing winds. This
influence can be seen by comparing ravines that run eastward versus those
that are west-facing funnels capturing the typical winds from that

Enough! Let's get back to Big Creek, and ask whether south-facing slopes
offer deeper soils than the lowlands, whether the rocky substrates conduct a
reliable source of moisture downslope throughout the seasons, and if, thus
enjoining a deeper and warmer soil environment, tree height is equal to, or
greater than the moist, but colder, north-facing sites.

In many ways, it appears that the heavy alluvial floodplain environment is
not so advantageous as we suppose, and only certain tree species are adapted
to venture there. Many steep slopes are too dry for the taller species,
some terraces are too dry, some are too wet. Some exposures conserve
moisture, but growth is limited by lower temperatures. So, how do we come
up with the ideal compromise, in a locale where annual rainfall is high, the
decay of hard rock adds minerals, and both steep terrain and second-growth
increase competition?

Big Creek seems to offer such advantages. The boulder fields may act as
dams slowing the downslope movement of soil moisture, or simply break the
upward wick action of surface evaporation. What seems to be the limiting
factor is the age of the second growth stand. One might assume that older
specimens might be taller, although windthrow collapse of such slender
verticality seems likely to overtake these stands, overall. That would
leave specimens with larger crowns, which would build upward more slowly, by
multiple arching.

So, Big Creek probably mimics ideal habitat, but, without ultimate age
development, it's difficult to point to such sites as having the most nearly
perfect combination of advantages - or should we say, compromises.