Thaw

A March thaw at Ryerson Woods.

Snow melt at Ryerson Woods.

by Luke Buckardt

Although it seems that we may never escape this winter’s grasp, spring is near.  This transition into a warmer season is driven by a lengthening day and more direct sunlight.  Every year, spring brings about a plethora of changes to our local environment.  We think of ephemeral flowers and migrating songbirds, but what happens to the environment during the early stages of the transition?  The impending thaw is something we can look forward to, but it also brings many necessary changes to Ryerson Woods.

When the first thaw occurs, the ground is usually still frozen on the surface, which creates an impermeable surface.  The water needs somewhere to go, so it acts as it would during a heavy rain.  Water is affected by gravity, and it will go to the lowest point possible.  In many areas, including our own corner of Lake County, this is in a river or stream.

The Des Plaines River overflowed its banks last spring.

The Des Plaines River overflowed its banks last spring.

The Des Plaines River breaks out of its banks and causes flooding, which varies from year to year depending on many factors.  These include snow totals, the speed of the melt, and any additional precipitation that occurs during a thaw.  Flooding is considered a nuisance for many reasons.  It affects homeowners along the river and can close streets.  However, the annual spring flood plays an essential part in developing and sustaining a healthy ecosystem.  Each year, the flood alters the river landscape, rearranging downed trees and other debris.  This constant change keeps habitat available for many species.  This extra material can accumulate in the river, making necessary habitat for native fish and invertebrate species.  It can also pile up along the river, creating protection for other native fauna.   Debris carried by floods can alter the entire hydrology of a river or stream.

Snow melt and river flooding creates vernal pools at Ryerson Woods.

Snow melt and river flooding creates vernal pools at Ryerson Woods.

Floodwaters often creep into the riparian areas alongside the river, which adds many benefits to a habitat.  When the water is out of its banks, it often slows down due to increased vegetation and a less channeled path.  When the water slows, it deposits the suspended sediments.  These are often very nutrient-rich.  Once the water recedes, the sediment is left along the banks and regenerates the nutrient levels along the river.  This leads to an increase in productivity for both plants and animals that are found within a riparian zone.

Finally, flooding benefits the diversification of plants along a river.  The floods transport seeds down river.  This increases diversity within a plant community, but it also perpetuates the success of many species.  The river can carry seeds or pollen to new areas where they have not been previously.  This aids in the genetic diversification of a plant species, which ultimately strengthens that plants ability to survive.

Blue-spotted salamander.  © Scott Albert; www.ilherps.com

Blue-spotted salamander.
© Scott Albert; http://www.ilherps.com

Once the thaw begins, it also creates another important habitat for many species in Lake County.  When water cannot travel to a stream or river, it pools in low-lying areas.  These temporary vernal pools are an extremely important wetland for many plant and animal species.  Because they are often void of predators, these ponds attract many species of amphibian.  Frogs and salamanders live close to vernal ponds year round, but during the spring thaw, they flock to the area for mating purposes.  They attract mating partners in the water, mate, and lay eggs.  Because these areas are void of constant aquatic predation, they are perfect for perpetuating a species.  Chorus frogs, spring peepers, and wood frogs all use these vernal ponds for mating.   The blue-spotted salamander frequents vernal ponds of Lake County in order to mate and lay eggs.  These habitats are necessary for some of the county’s most endangered species, particularly the tiger salamander.  For just a few weeks out of the year, these pools become extremely busy areas in the forest.

wood frog by Luke Buckardt

Spring peepers, a tiny species of frog, are often referred to as the “harbinger of spring.” As soon as things thaw in the spring, they leave the trees to converge upon vernal pools where they sing to attract a mate and breed. Photo by Luke Buckardt.

The spring thaw is a wonderful thing for all the inhabitants of Lake County.  Although it can cause some temporary issues for people, the thaw is essential in the perpetuation of many species of plants and animals.  Now all we can do is wait and enjoy the thaw when it comes.  It is just the first step in a very exciting transitional time for the local environment.

This blog post was written by Luke Buckardt, who assists Brushwood Center with social media.  Luke graduated from Northland College in 2012 with a degree in biology.  He grew up in Riverwoods and has roamed Ryerson Woods since he was young, knowing the preserve intimately.

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About Brushwood Center at Ryerson Woods

http://www.brushwoodcenter.org
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