Ice Age Ice Storms

The ice storm that struck Augusta, Georgia 2 weeks ago showed how nature can drastically change the environment within a short period of time.  The weight of the ice busted trees in half, brought down tons of branches, and even felled large mature trees.  The constant crack and thunder of trees and limbs falling lasted all day and night.  In our modern world, humans will pick up and dispose of most of this debris, but before man tamed the wilderness, an ice storm such as this could have transformed a close canopied forest into an open woodland or even a savannah.

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My backyard after the Ice Storm. The black cherry tree and sand laurel oak on the right cracked in half under the ice.  The sand laurel oak on the left is bent over but has since bounced back.

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The weight of the ice made this tree tip over also.  Note how the roots are yanked from the ground.

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Many branches just broke off and fell.  This woody tissue will dry and become flammable.

A forest is defined as an environment with 80% canopy coverage; a woodland is an environment with 50%-80% canopy coverage; and a savannah is an environment with less than 50% canopy coverage.  A reduced canopy coverage will result in more sunlight reaching the ground, altering the plant species composition.  More grass, herbs, shrubs, and  shade intolerant tree saplings can then grow in the sunnier conditions.  This in turn influences faunal composition.  An ice storm by itself can reduce canopy coverage, but the flammable debris left behind can become an even greater factor that reduces canopy coverage.  A summertime drought following a winter ice storm can dry all the fallen wood littering the forest floor.  During droughts, weather fronts often produce disturbances I like to call “constipated thunderstorms” when there is a lot of lighting but little rain.  The lighting can ignite forest debris causing a fire that kills even more trees, leaving only the strongest specimens standing.  Fire resistant species such as oak and pine are favored in this kind of scenario.  The mature open woodlands of southeastern North America were always shaped by fire and ice, until man changed this natural pattern of landscaping.

Under our present climatic conditions, major ice storms strike the mid-south about once every 10 years.  During the Pleistocene, the frequency of ice storms likely varied but probably occurred during all climatic phases.  I hypothesize ice storms were most frequent during interstadials–the warm phases within Ice Ages.  Average temperatures then were slightly cooler than those of today, and glaciers were melting, allowing enough atmospheric moisture for ice storms to occur.  Average temperatures were even cooler during stadials, but there was less atmospheric moisture because glaciers were expanding and locking water in ice.  Stadials in the mid-south may have even had a lower frequency of ice storms than in the present climatic phase.  There were probably some climate phases when ice storms occurred on an annual basis in the mid-south, and this created more open environments that would have particularly favored grass-eating megafauna such as mammoths, bison, and horses.

The fallen woody debris from an ice storm provides habitat and foraging opportunities for wildlife.  Termites, beetles, and carpenter ants invade rotting wood.  Carpenter ants don’t actually eat the wood, but they tunnel into it and build nests.  (Carpenter ants mostly eat sugary aphid secretions, nectar, and dead insects they scavenge off the forest floor.)  Lizards and snakes lay their eggs in the rotting wood.  Woodpeckers attack the debris and prey upon the arthropods living in the piles of fallen wood.  Raccoons, possums, and bears feast on the high protein snacks they find in the fallen logs.  If a fire doesn’t incinerate this organic material, eventually it is consumed by microorganisms and transformed into soil.

The fallen wood from the ice storm will make abundant homes for colonies of carpenter ants (Camponotus pennsylvanicus).

The ice storm will provide a feeding bonanza for pileated woodpeckers (Drycopus pileatus) in a few years.  They can eat an entire colony of carpenter ants.  Here, one is probing for ants and beetles with its long tongue.

The Edgefield County Earthquake

A few days after the ice storm, I experienced an earthquake.  I heard a loud roar lasting for at least 15 seconds, and I felt the ground shake in alarming fashion.  At first I thought it was yet another tree falling under the weight of the ice but soon thereafter realized that it had been an earthquake, unrelated to the ice storm.  The fault is many miles deep, and the ice could not have influenced it.  Its occurrence was a coincidence.  The epicenter of the earthquake was Edgefield County, South Carolina, and I was staying in Evans, Georgia with my parents because our power was still out.  (It took Planters Electric 129 hours to restore our power.)  Evans is about 40 miles from Edgefield County.  I was able to correctly determine the direction of the earthquake from where I was sitting and watching television.

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