Definition - (vernal pool )
Vernal pools are seasonal depressional wetlands that occur under Mediterranean climate
conditions. They are covered by shallow water for variable periods
from winter to spring, but may be completely dry for most of the
summer and fall. These wetlands range in size from small puddles to
shallow lakes and are usually found in a gently sloping plain of
grassland. Although generally isolated, they are sometimes connected
to each other by small drainages known as vernal swales. Beneath
vernal pools lies either bedrock or a hard clay layer in the soil
that helps keep water in the pool.
Vernal Pools are vital to our environment.
Without them there would be no grasses, no trees, no nutrients in
the soil. Without these wetlands our planet would be reduced to a
gigantic desert of sand-like covering and rock, not unlike Mars, unable to sustain life as we know
it and our world would be silent.
Where would we be if we did not have the
songs of the frogs, toads and and other amphibians that make the
on-coming evening and night so palatable. They sing their mating
songs from the pools where they have laid their eggs and where their
young grow and continue life's cycle. This would be lost to us if we
did not have the Vernal Pools.
Climatic changes associated with each
season cause dramatic changes in the appearance of vernal pools. The
pools collect water during winter and spring rains, changing in
volume in response to varying weather patterns. During a single
season, pools may fill and dry several times. In years of drought,
some pools may not fill at all.
In the spring, wildflowers often bloom in
brilliant circles of color that follow the receding shoreline of the
pools. By early summer, the water has evaporated, and the clay pools
appear brown, barren, and cracked.
The term vernal pool originally referred
only to small, intermittently filled wetlands found in the
Mediterranean-type climate of the western United States. Today it is
used more broadly to include other small ephemeral wetlands found
country-wide in both United States and Canada.
Vernal pools are
unique, specialized habitats that are frequently overlooked because of
their size and appearance.
Vernal pools, or ephemeral wetlands are landform
depressions that temporarily fill with water following heavy rainfalls,
the snowmelt in the spring, or as a result of a high water table.
Vernal pools vary in their size, shape, depth,
timing and duration of flooding, and the types of species that are able to
use them. A defining feature of vernal pools is that they usually dry up
by the middle of the summer; however, some vernal pools may only dry up
every couple of years.
Some animals have adapted and thrive because of
the wet-dry cycles of the vernal pool. The ephemeral nature of these
wetlands ensures that fish cannot exist in these pools. The lack of fish
in these pools is essential to the vitality of frogs, salamanders, and
invertebrates that would otherwise be preyed upon by the fish. Many of the
species found in vernal pools are dependant on the water of vernal pools
for reproduction and other stages of their life cycle.
To properly understand and conserve vernal pools
we must examine these life cycles and the creatures themselves. On our
Creature Pages we will examine those species we have identified in and around
the pools contained within Heartland Forest, our subject forest.
