14, 2002 1:54 PM
Another day in the mid-nineties with no rain in sight. Did
Kermit the frog
say, "It's not easy being green?" The same goes for
Maryland springtimes promote a exuberance of new growth, our
often cruel, seemingly bent on reclaiming what has been
Of course, there are a few deep coves where the sun hardly
drying winds are broken, and the multiple canopies conserve the
fragrant air, and fresh green moss hangs in strips from old
trunks of tuliptrees rise straight from these havens, their tops
supported by strong fibers and non-compressible water.
Elsewhere, the tuliptrees will begin dropping yellowed leaves.
retain all their foliage, inviting scorch and even the fatal
all available moisture from the entire structure, tuliptrees are
By shedding excess leaves, less precious water is expended, and
remaining leaves continue to function.
More importantly, the tuliptree prevents its woody structure
killing effects of drought. Still, drought has an effect on the
architecture of trees. Although we say, "as the tree is
bent, so grow the
tree," the structural evolution of each tree is more
complex, and drought is
but one of many influences that creates the structural identity
A straight line being the shortest distance between two points,
become straighter with time. The black locust has no terminal
young stems are usually somewhat crooked. As the trunk thickens,
most rapid along concave curves, that being the shortest path
and roots. A locust post split to butterfly the curve is flat,
split at right angles is irregular. Concave curves of the limbs
sassafras, basswood and some junipers can fill rapidly,
cross-sections, not unlike the flaring buttress root formations
Of course, as trunks thicken, forks are raised, and limbs leave
the bark, like the wake of a boat, each spreading at precise
according to the angle of the limb and growth rate of the trunk.
concave surfaces must be shortened, and crumples, slowly forming
surfaces, the attached cambium so influencing the contour of the
beneath. Roots increase in diameter, easily elevating the turf,
and adding most of their diameter on the upper surfaces.
Competition for sunlight constantly changes the structure of
course, lower and inner branches die as essential sunlight is
new growth of the expanding crown, but other changes take place.
produce numerous limbs growing upward at a considerable angle.
competition, most do not greatly increase in diameter, but they
and gravity bends them downward. This bending is beneficial to
individual limb, causing it to move outwards, access more
thereby thicken and stabilize. As gravity brings the most
below horizontal, they lose sunlight and die.
Resistance to bending is the result of the tensile strength of
the compressive strength of cell walls. These forces are often
white mulberry branches, where snow loads cause the wood to
the two forces, the lower half buckling downward, leaving a
enough to put your hand into. Sections of wood exposed by a
split fork are
flat in cross-section, and easily broken, like a ruler, because
forces are close together. Hollow trees are strong, but fail
or when the sides are forced outwards, allowing tensile and
forces to move closer together.
Heavy woods are hard to compress, but lighter woods, such as
strengthened by non-compressible water, and weakened when that
reduced by drought. The multiple-arched structure of tuliptrees
influenced by several factors. Fast growing vertical branches
may be bent
by the load of precipitation on the broad leaves. This also
sycamore and sweet gum, and is most likely after a drought. This
moves a lateral branch upward, and it becomes the new leader. In
series of leaders so produced bend, the lower portions die from
sunlight, and a multiple-arched structure is created.
Although the intolerance of tuliptree leaves causes new growth
outward, gravity is a constant factor, causing large structural
bend over the years. The development of a tuliptree crown
structure where members move from one another, more than simply
from a central point. In winter, the outline usually shows
the upper crown arranged in a given direction, allowing one to
tree as being "left-handed" or
On dry-mesic soils with mixed hardwoods, tuliptrees grow more
there is no abundance of available moisture, the supply may be
through the seasons, producing trees of excellent quality. The
light in weight, with a distinct yellow heartwood. Poplar
growing on wet
soils, especially old-field sites, produces much heavier logs
heartwood, which is somewhat greenish. Often called "blue
"yellow poplar," the lumber is more prone to warp and
Tuliptrees are noted for their straight trunks. The tallest
trees are those
that maintain a vertical stem completely to the top. Such trees
and usually occur in the deepest, coolest coves, protected from
of climate, especially during drought. A handsome grove of eight
trees in a deep ravine near here has several trees nearly 150
height, and the trunks are straight and devoid of branches to
height, 98 feet in one case. These vertical lines terminate
several divergent and crooked leaders forming the upper fifty
appears these trees were released by logging nearly 100 years
stimulated faster top growth on slender stems prone to bending,
logging allowed the once-sheltered cove to dry out, resulting in
awkward subsequent top structures.
Very old tuliptrees growing on dry-mesic sites with little
develop large crowns with numerous growing tips, none having a
advantage. Such trees are usually about 114 feet tall, and
arching down to the twig level. At this stage, it seems that
growth does little more than offset the influence of gravity in
larger non-vertical structures.
So, we have another drought, and plants will suffer, but the
endure, though constantly changing their structure, adding
to our natural world.