Canebrakes are Forlorn Landscapes

200 years ago, landscapes in southeastern North America looked nothing like they do now.  When William Bartram traveled through the piedmont region of the south (circa 1775), the path he followed mostly stayed on the high ground because impenetrable thickets of bamboo cane (Arundinerea gigantea) grew alongside creeks and river bottoms.  His party was always in sight of canebrakes as they traveled through the open woodlands on the high ground.  Canebrakes covered tracts that were hundreds of square miles in extent.  Today, canebrakes are nearly an extinct type of environment.

I looked for this photo on google images and couldn’t find it.  I did find it within a pdf document but I couldn’t link the photo directly. So I scanned it from the book Forgotten Grasslands of the South by Reed Noss.  Click to enlarge.  It’s of a man on a horseback dwarfed by a stand of 40 foot tall cane in 1906.  This was probably one of the last stands of a primeval canebrake.

I found this stand of bamboo cane growing behind a Burger King in Madison, Georgia.  Cane is planted as an ornamental.  It’s probably not even American bamboo, but rather Asian bamboo.

Canebrakes are an ancient environment, dating back to at least the Miocene (25 million-5 million years BP).  It’s a species of grass.  Grasses began to become abundant during the Oligocene (33 million-25 million years BP).  Scientists unearthed ~5 million year old fossil bamboo from the Gray Fossil Site in Tennessee along with the bones of an extinct species of red panda (Pristinailurus bristoli) that fed upon it.  American bamboo likely shares an ancestry with Asian bamboo back when both continents were composed of a continous mosaic of tropical environments.  ( https://markgelbart.wordpress.com/2012/12/05/the-gray-fossil-site-in-washington-county-tennessee/)  Scientists disagree over whether giant gane (Arundinerea gigantea) is the same species as switch cane  (A. tecta).  Some botanists argue a structure inside switch cane makes it a different species, but others don’t think the difference is significant enough.  In any case cane grew in dense stands on rich soils, either by itself in pure stands or with an occasional tree in a savannah-like landscape.  Cane is shade intolerant and today seems to be restricted to wooded swamp edges.

Canebrakes require a complicated combination of forcing events to exist.  Formerly, floods, flocks of passenger pigeons, windstorms, or ice storms destroyed great tracts of forest.  Passenger pigeons (Ectopistes migratorius) used to roost in flocks estimated to be in the billions.  Witnesses described their roosting areas as resembling tornado damage.  Great limbs and even whole trees broke in half under the weight of the birds, and the pigeon dung killed the trees via overfertilization.  (See also https://markgelbart.wordpress.com/2010/08/27/pleistocene-passenger-pigeon-populations/) The New Madrid earthquakes in 1811 also caused the creation of large tracts of canebrakes.  Following these natural disturbances of the forest, a great amount of flammable dead wood covered the forest floor.  Lightning or human set fires burned through the woody refuse, creating vast sunny areas that allowed shade-intolerant bamboo cane to colonize large tracts of land.  Cane growing in small sunny patches within the forest could take advantage of these disturbances by spreading clonally from root rhizomes into the newly suitable habitat.  As long as fire occurred at least once a decade, canebrakes could be maintained indefinitely.  Dr. Noss suggests canebrakes were an alternate climax stage with bottomland forests near rivers and streams.  Without disturbances these areas succeeded to bottomland forests, but disturbances were so common that canebrakes may have covered an equal amount of territory.

Modern studies show that fire and windstorm double the growth of cane which can grow as fast as 20 feet annually.  Cane formerly reached heights of 40 feet, perhaps because they were enriched with pigeon dung.  Today, the tallest cane known grows in Louisiana and reaches just 30 feet in height.  It depends mostly on clonal growth and only flowers and produces seed once every 40-50 years.  It prefers rich river bottomland soils where it can become dominant.  Surprisingly, rich soils have less species diversity than poor soils.  On poor soils no one species can become dominant due to more difficult growing conditions.

Canebrakes were undoubtedly a widespread environment during the Pleistocene before man colonized North America.  There are many endemic species of animals that depend exclusively upon canebrake habitats, and it’s unlikely they evolved that dependence within the last 15,000 years.  However, canebrakes likely enjoyed a heyday during the 18th century when Native American populations collapsed.  Indians preferred to grow their crops on rich river bottomland soils and when they abandoned their fields cane rapidly colonized the land.

Modern anthropogenic changes in land use have nearly eliminated canebrakes.  Humans built levees and dams to prevent flooding.  People suppress fires.  People exterminated passenger pigeons.  These activities ended ancient patterns of disturbances that bamboo cane requires to form vast monotypical stands.  Moreover, cane grew on rich soils that farmers coveted for field crops, and the farmers let their livestock overgraze cane growing on any land left unplanted.  Today, river bottomlands left undeveloped are dominated by trees that shade out cane.  Canebrakes are a forlorn landscape and will be difficult to re-establish.

Canebrakes were a rich habitat utilized by many species of animals.  Cane is a high quality forage that formerly provided food for grazers such as mammoths, horses, and bison.  Bears and big cats liked to den inside the thickets where they could hide their cubs.  Swamp rabbits (Sylvilagus aquaticus) are also known as canecutters because they feed upon cane by gnawing through the stem to fell the tall grass so they can get at the leaves.  If it’s not extinct, Bachman’s warbler (Vermivora bachmanii) and Swainson’s warbler (Limnothlypis swainsonii) depend upon canebrake habitat.  Eastern diamondback rattlesnakes (Crotalus adamteus), also known as canebrake rattlesnakes, hunt swamp rabbits in the thickets.  6 species of butterfly depend entirely upon bamboo cane as part of their life history.

Swamp rabbits are also called canecutters.  They’re much larger than cottontails.

Bachman’s warbler.  This bird is probably extinct.  They formerly summered in canebrakes.  They built their nests in the cane thickets and foraged for insects on the ground in the fallen cane leaves.  They wintered in Cuba.  They became extinct (probably) because canebrakes are gone.  None have been seen since 1988.

A man holding an eastern diamondback rattlesnake.  They are big serpents growing to 8 feet long and weighing 35 pounds.

Southern pearly eye (Enodia portlandia).  5 other species of butterfly depend upon canebrakes for at least part of their life cycle including Creole pearly eye (E. creota), southern swamp skipper (Poanes yehl), cobweb little skipper (Amblyscertes aesolypia), cane little skipper (A.reversa), and yellow little skipper (A. carolina).  These endemic species are evidence canebrakes predate anthropogenic influences on the environment.

Native Americans also used to rely on bamboo cane.  They used to mix mud with strips of cane to build houses, and they covered the floors inside with mats made of cane.  They made baskets and fish traps and coffins from cane.  Weapons fashioned out of bamboo cane included spears, knives, body armor, and blowguns.  Indians incorporated cane into the structures of their famous mounds.  Cane even provided food.  Bamboo shoots are a tasty vegetable, and the seeds could be ground into a flour that was reputed to be almost as good as wheat flour.

References:

Ellsworth, J.W.; and B.C. McComb

“Potential Effects of Passenger Pigeon Flocks on the Structure and Composition of Presettlement Forests of Eastern North America”

Conservation Biology 17: 1548-1558 2003

Gagnon, P.R.; and W.J Platt

“Multiple disturbances accelerate clonal growth in potentially monodominant bamboo”

Ecology 89: 612-618 2008

Platt, W.J.; and C.J. Brantley

“Canebrakes: An Ecological and Historical Perspective”

Castanea 62: 8-21 1997

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CSI: Pleistocene Alaska

“Science” programs on cable networks are often idiotic.  I suppose the television producers want to boost ratings and make their presentation dramatic for entertainment value.  But for those of us who know a good bit more about the subject than the average couch potato, these programs are laughable.  I think it was the History Channel that featured a special about the Pleistocene megafauna that concluded the beasts became extinct because of global warming.  The imbecilic producers actually showed computer images of the beasts dropping dead due to a heat wave.  They made no mention of overhunting by humans which is a much more plausible cause of extinction.  Instead, they wanted to jump on the bandwagon of global warming phobia, unware that all of these “Ice Age” species survived the Sangamonian Interglacial which was on average warmer than present day temperatures.

Another program about megafauna extinction (either on Discovery or PBS) did give equal time to overkill, climate change, hyperdisease, and comet impact.  The latter two, in my opinion, are crackpot theories.  While it is clear that an extraterrestrial impact probably led to the extinction of the dinosaurs, the evidence that a comet caused the recent megafauna extinction event is not at all convincing.  Supposedly, the comet hit a glacier–explaining why there’s no impact crater.  The theory is on shaky legs to start, if it’s proponents have to make an excuse for the lack of a smoking gun.  Other independent scientists have been unable to replicate their findings, perhaps relegating the comet impact theory to the trash can of illogical ideas.  When interviewed for the above mentioned program, one of the comet impact proponents made an astoundingly illogical comment.  He stated that the overkill theory didn’t make sense to him because he couldn’t believe humans could kill every last individual of a species.

His statement demonstrates a remarkable ignorance of basic ecology.  Humans would not have to kill every last individual of a species to render it extinct.  All wild species of animals already have high rates of natural mortality.  Let’s take the mastodon for example.  Mastodons had a long lifespan and low birthrate.  Saber-tooths and scimitar-toothed cats caused a certain amount of mortality.  Diseases, such as tuberculosis, took a percentage more.  Accidents (falling into quagmires, males killing each other in battles for mates, etc.) took a toll as well.  But this was mortality the mastodon birthrate could keep up with, and they maintained their existence for millions of years.  However, the addition of human hunting was a variable that increased a mortality rate that exceeded their birthrate.   So man + natural mortality = extinction.  Remove man from the equation and it would be natural mortality = a still extant species.

In my opinion overhunting by man is the only cause of the demise of the Pleistocene megafauna.  There is no other logical solution to this mystery. But I don’t agree with Paul Martin’s blitzkrieg model of extinction.  I believe the process took thousands of years rather than hundreds.  A recent study supports my belief in a protracted overkill scenario.

Researchers taking cores of permafrost in Alaska’s north slope.  There is forensic evidence of extinct Pleistocene megafauna in some of these cores.  This forensic evidence dates thousands of years later than the most recent dated fossil evidence of these species.  That means these animals lived more recently than previously thought.  Photo from google images.

A group of scientists led by James Halle examined cores of permafrost found in Alaska.  They were looking for megafauna DNA.    The cores were dated using carbon dating and optically stimulated luminescence (see  http://crustal.usgs.gov/laboratories/luminescence_dating/technique.htmlxplanation for an explanation of OSL dating).  The dates of the cores with the megafauna DNA ranged from 11,000 to 8,000 years old.  This sediment is more recent than the youngest known dated megafauna fossils from the interior of Alaska.  (A population of dwarf mammoths is known to have survived on the Pribiloff Islands until ~4000 BP.)  These cores harbored DNA from mammoth, horse, bison, moose, and snowshoe hare.  This DNA is referred to as sedaDNA and comes from hair, feces, and urine.  It proves the existence of these species in the environment, even though they left no fossil evidence from this time period.  The mammoth DNA is 2600 years younger than the youngest known mammoth fossil from the interior of Alaska; the horse DNA is 3700 years younger than the youngest known horse fossil from this region.  Using sedaDNA is uniquely possible in Alaska, thanks to permafrost conditions, and it’s a technique probably not possible anywhere else. 

The scientists concluded that the continued existence of megafauna until ~7500 BP rules out climate change, the blitzkrieg model of overhunting, comet impact, and hyperdisease as the ultimate causes of megafauna extinction, though they do concede that anyone of these factors could’ve caused an initial population collapse.  Curiously, they made no mention of a protracted overkill model of extinction, which in my opinion this study strongly supports.

It occurs to me that previously disregarded recent dates of megafauna fossils my not be in error.  For example the Devil’s Den fossil site in Levy County, Florida yields remains of Jefferson’s ground sloth, dire wolf, Florida spectacled bear, southeastern lemming, saber-tooth cat, mastodon, horse, and flat headed peccary.  The fossils from this site were radiocarbon dated to be 7,000-8,000 years old–several thousand years later than when scientists believe these species became extinct.  Therefore, scientists disregard these dates as inaccurate due to some kind of contamination or obsolete carbon dating techniques.  I suggest scientists redate these fossils, as well as those from other sites with unusually young dates, using the more updated and improved methods of carbon dating.  It seems likely the Pleistocene megafauna may have survived in southeastern North America for several thousand years longer than previously thought.

References

Halle, James et. al.

“Ancient DNA reveals late survival of mammoth and horse in interior Alaska”

http://www.pnas.org/content/early/2009/12/16/0912510106.full.pdf

www.devilsden.com/