Cliff Dwellers
If you plan to only walk one trail on Sugar
Hill, the Cliff Trail should be the one, and not just because of the maturity of the forest.
Rock outcrops along the trail drip with mosses, ferns, and flowers in a
perfect example of the wet limestone cliff community, while dense
jumbles of boulders beneath the cliffs showcase the boulderfield forest
community. Both of these plant communities are all about rocks
that began as living beings --- limestone.
Limestone is
not a typical rock. Instead of forming from sand, silt, or molten
lava, limestone can be traced back to tiny critters living in an
ancient ocean. Many of these ocean animals extract a mineral
called calcium carbonate out of the water and use it to form hard
shells like the ones you see washed up on ocean beaches. When the
shell-encased animals die, a few of their shells do end up on beaches
but most instead drift down to the ocean floor where they are ground up
by wave action and eventually compacted into layers of rock called
limestone. Over millions of years, the limestone on the ocean
floor may be lifted up into mountains, leaving behind the remains of
ocean critters in places like Sugar Hill.
Eventually, all
rocks begin to weather into dirt, but the soil produced on top of
limestone is very different from the soil produced by other
rocks. Sandstone, for example, breaks down into sandy soil that
tends to be acidic, while limestone breaks down into alkaline
soil. Acidity and alkalinity are measures of pH --- even if you
have not heard of pH, you have certainly experienced the sour acidity
of lemons and the slippery alkalinity of bleach.
Just as we can
taste or feel the difference between acidic and alkaline foods, plants
can tell the difference between acidic and alkaline soil, and most
plants prefer one over the other. Many of the flowers you will
find growing along the cliffs on Sugar Hill would not be caught dead
growing on acidic sandstone. These limestone-lovers include
several of the ferns
discussed in an earlier chapter as well as plants like Red Columbine
and Smooth Sicklepod.
Other plants
are found on the limestone cliffs because they are able to thrive in
desert-like conditions. Although the shaded hillside along the
Cliff Trail stays moist for much of the year, the lack of soil on the
cliff face means that plants go for long periods without being able to
soak up water through their roots. Three-leaved Stonecrop is
perfectly adapted to surviving droughts --- the plant’s thick,
succulent leaves fill up with water during rainy spells, storing
moisture for the stonecrop to use during dry, sunny days between
storms. Wild Hydrangeas also seem to do well in rocky areas with
only pockets of soil, and I often see them clinging to the side of
cliff faces. Pete’s Rock --- on the sunnier side of Sugar Hill
--- is home to even more of these desert-adapted cliff plants.
One more niche
is worth looking for along the Cliff Trail --- the boulderfield
community. Talus heaps of boulders are often found at the bases
of cliffs, where winter’s freezing and thawing cracks blocks of stone
loose to roll down and collect in a pile beneath the cliff. For
plants, boulderfields are even more difficult to colonize than cliffs
are --- as the saying goes, a rolling stone gathers no moss, and stones
in the talus heap do slowly move and roll as boulders knock into them
from above. Trees can seldom find a safe foothold in the
boulderfield, but mosses and lichens manage to cling onto the more
stable rocks. Without even the tiny pockets of soil that collect
in crannies in the cliff-face, lichens on boulders have to create their
own dirt. The lichens secrete acids that hasten the breakdown of
the rock surface, forming little clumps of dirt into which mosses and
eventually larger plants can grow. Here in the boulderfields
along the Cliff Trail, you can see the true beginnings of forest
succession as bare rock slowly dissolves into soil and provides a home
to lichens, mosses, and finally flowers and ferns.
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