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Autumn
As summer gives way to autumn, the natural
world undergoes many changes which are triggered by changes in
temperature, humidity, and/or photoperiod (the length of daylight
in each twenty four hour period).
I always look forward to the cooler temperatures of autumn, particularly
after the heat and insects of summer! As our days shorten and
the temperatures drop, the southern Appalachian Mountains undergo
a transformation that provides great beauty for us to appreciate,
but the true function of which is to prepare the natural world
for the winter to come.
Probably the most familiar change is that of the leaf color.
While we all enjoy the amazing variety of colors; red for the
maples and sourwoods, yellows for the hickories and birches,
and maroons and browns for the oaks and beeches, how many of
us understand what is happening and why?
As the trees detect the approach of winter, probably from the
decreasing photoperiod, physiological changes take place to ensure
the tree's best chance of surviving the approaching weather.
One of the first changes in the tree's physiology is that photosynthesis,
the process by which plants use the energy of sunlight to convert
water and Carbon Dioxide into sugars and starches, stops. As
this happens the specialized photosynthetic organ in the leaf,
the chloroplast, shuts down and no more "food" is produced.
From this time, until the following spring, the plant will survive
on resources stored in its root system.
When the chloroplast shuts down the light which is reflected
from the leaf no longer seems green to our eyes - this is the
autumn color for which this region is noted. What most of us
don't realize is that the colors we see at this time of year
are really there all year long - the green of the chloroplast
has simply masked the leaf's true color during the spring and
summer!
Additionally, the vascular transport system connecting the leaves
to the tree seals itself shut, and the leaves eventually drop
off the tree. Trees lose water through minute openings in the
bottom of the leaves, the stomata. Since the winter ground may
be frozen and the uptake of water difficult at best, sealing
off the leaves and then shedding them helps ensure the tree doesn't
suffer dehydration during the winter.
Another fascinating change that takes place at this time of year
is the migration of various species to their winter territories.
Ruby-throated
Hummingbirds will be leaving the region starting in mid-September,
and most will be gone by mid-October. Banding studies have indicated
that individual birds are very loyal to their migratory route,
to the extent that many are observed at the same site on the
same date each year. These beautiful little birds will travel
south, stopping on the gulf coasts of Texas and Louisiana to
rest and feed. Studies have shown that these birds can increase
their fat reserves and double their body weight in roughly ten
days. This weight/fuel gain will soon be vital to them as at
some unknown signal they will take off and fly as much as 600
miles, non-stop, across the Gulf of Mexico to their wintering
sites. Those that successfully complete the trip will return
to the same nest sites and feeders, year after year. In the Asheville
area, the first males are usually seen during the first week
in April. The males precede the females by a week or two and
spend that time establishing, and fiercely defending, their territories
against any and all threats.
A more obvious migration is that of the Broad-winged
Hawk. These are common summer residents here in the mountains
of North Carolina, but are much rarer as you near the coastal
plain. After spending spring and summer here these large birds
migrate to tropical South America for the winter. During late
September and early October the Broad-wings migrate southwards
in large groups known as "kettles". At this time of
year I look forward to cold fronts moving south, as these are
usually followed by the hawks. To see the "Broadies"
I like to go to the Standing Indian area near Franklin, NC. Pickens
Nose Ridge is a good spot to see them, and, on a good day, it
is not unusual to see several kettles with 40 or 50 birds in
each. Closer to Asheville is the Craggy Pinnacle which is just
north of the Craggy Visitors Center on the Blue Ridge Parkway.
Their mode of travel is one I think I would like. These birds
locate uprisings of air created in one of two ways. On overcast
days or early in the mornings they find uprisings where the winds
are deflected upwards against the sides of mountains. On sunnier
days, usually in the afternoon when the ground has been heated
by the sun, they find rising columns of hot air known as thermals.
In either case the birds circle upwards, rarely flapping their
wings, until they run out of lift. At this point they leave the
thermal, gliding southwards and looking for another thermal or
deflective uprising to repeat the process. They can cover hundreds
of miles in a single day, and by "surfing" the air
can do it with hardly any effort.
I've met folks who have gone out into the woods hoping to see
a particular flower or bird, and when they didn't see that one
thing they considered the day a waste. Don't become so focused
on seeing one thing that you don't see the countless other things
that are there! Whether it is trees showing their autumn colors,
or birds flying south to escape the winter's chill, nature's
preparations are both awe-inspiring and lovely.
This article was originally
published in Travel Host magazine, October/November 2003. |
