Southeastern Grasslands are of Great Antiquity

I enjoy watching a summer thunderstorm.  Lightning strikes offer a natural fireworks show that sometimes surpasses the manmade kind.  The furious wind and roaring thunder show the excited side of mother nature.  It’s the dangerous side of nature–a human could be vacuumed into the sky by a tornado, electrocuted by lightning, or clobbered by a hailstone or wind-strewn debris.  Nobody, not a king nor a baby, is immune to these hazards.

Natural fireworks.

Some anthropologists and a few old school ecologists wrongly believe most of the grasslands that occurred in southeastern North America when Columbus accidentally sailed into the Caribbean were the result of manmade fires.  Reed Noss dispels this notion in his book, Forgotten Grasslands of the South. The map below shows the frequency of lightning strikes in North America.  The south, and especially Florida, has more lightning strikes than any other region of the continent.  Dr. Noss believes the high frequency of lightning strikes can spark enough wild fires to maintain abundant grasslands without any human activity.

Map of average annual lighting strikes in North America between 1989-1999.  Lighting strikes were naturally common enough to have sparked grassland-creating wild fires long before humans arrived in North America.

Long Distance Controlled Burn

A longleaf pine savannah on fire.  Longleaf pines are one of the few species of tree whose seedlings can survive fire.

Several lines of evidence support Dr. Noss’s conclusion that anthropogenic activity was not necessary to maintain grasslands.  Formerly, longleaf pine savannah covered most of the coastal plain region of the south.  There were even patches of pine savannah in the piedmont region, though oak and hickory dominated that area.  There are over 900 species of plants endemic (meaning they live nowhere else) to longleaf pine savannah compared to just 80 endemic species found on the grasslands of the Great Plains.  A high number of endemic species suggests an ecosystem of great antiquity and stability.  Because evolution is usually a slow process, it’s not likely that all of these endemic fire-dependent species could have evolved in just the last 12,000 years.  Longleaf pines require fire intervals of 1-10 years or hardwoods will crowd them out.  Longleaf pines grow slowly, taking decades to reach reproductive age.  A species that reproduces this slowly would have never been able to adapt quickly enough to survive a sudden change in fire regime caused by man.  These fire dependent species must have already been present before man colonized the region.

Many species of animals are also endemic to pine savannahs.  The gopher tortoise and the red cockaded woodpecker are perhaps the 2 most well known vertebrates dependent on this fire-influenced environment. Gopher tortoise fossils have been found that date to millions of years ago, while red cockaded woodpecker fossils come from deposits in the vicinity of 200,000 years old.  The presence of these species and many others in the fossil record long predate man’s entrance into the region.  This is obvious evidence that southern grasslands preceded man.

There was a lower frequency of lightning strikes during the coldest stages of the Ice Ages.  Evidence from most fossil sedimentary sites show little, if any charcoal, indicating reduced fire activity.  However, less precipitation combined with megafaunal grazing created grasslands during the colder climatic phases.  Following the megafaunal extinctions, fire activity spiked because so much vegetation was no longer being eaten and instead it became dry tinder.

During the Last Glacial Maximum, longleaf pine savannahs still occurred in refugium located in Florida, Louisiana, Texas, and probably along the continental shelf where sea levels regressed.  Paradoxically, these areas were warmer and wetter during Ice Ages because the Gulf Stream shut down and warm water that normally circulated north pooled around these lower latitudes.  Oak scrub and prairie, the result of aridity and megafauna foraging, predominated in the upper coastal plain.  Longleaf pine savannah didn’t recolonize the upper coastal plain until about 6,000 years ago, but the pollen record suggests this type of environment has waxed and waned cyclically for millions of years, becoming common and widespread during warm and wet climatic phases.

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