Posts Tagged ‘magnolia’

Beech-Magnolia Climax Forests–Another Relic Environment of the Pleistocene?

March 15, 2012

In the piedmont and coastal plain of Georgia and other southern states, bluff forests of northern affinities and bluff and slope forests both occur as relics in areas that are too steep to cultivate and too moist to burn.  The species composition of both  forest types would probably be more widespread, if not for the influence of man.  It is a safe assumption that both forest types were common across Pleistocene landscapes, especially during interglacials, interstadials, and even the weak stadials that preceded the Last Glacial Maximum, though during stadials, prairie and coniferous woods were more predominant.

I’m lumping bluff forests of northern affinities together with bluff and slope forests because they are so similar–the only distinction is that the former holds a greater variety of northern species of plants, including disjunct populations of some.  The dominant plants in a bluff forest consist of tulip, hickory, black walnut, beech, sweetgum, basswood, oaks (swamp chestnut, red, black, cherrybark), southern sugar maple, cottonwood, umbrella magnolia, red buckeye, mulberry, pawpaw, hornbeam, mayapple, maidenhair fern, Canadian ginger, and bluebell.

Bluebells (Canpanula americana) blooming in the forest undergrowth.  Disjunct populations of bluebells occur in bluff forests of northern affinities in the deep south.  The southern Pleistocene landscapes must have included scenes like this during phases of  equible climates.

Surprisingly, mountain laurel grows as far south as the piedmont in bluff forests with northern affinities.

These lush forests consisting of cool climate species such as beech and warm climate species such as magnolia were probably the most common climax forests during much of the Pleistocene, particularly when climate phases were more equible than they are today with much cooler summers, but only slightly cooler winters.  The only important missing floral component of this type of forest that was prevalent during the Pleistocene was the extinct Critchfield’s spruce.

Today, both types of bluff forests now only occur on land that slopes toward a river and faces north.  These conditions create a cool microclimate.  Moreover, feeder creeks and seepage springs protect the mature woods from frequent fire.  Before Indians began their annual burning of forests to improve conditions for game, beech-magnolia climax woods probably  occupied land that was eventually transformed into open pine savannah.  Pollen records show that early in the Holocene about 10,000 calender years BP, hardwoods were more prevalent than pine, even in south Georgia.  After the Last Glacial Maximum and into the early Holocene (~15,000 BP-~10,000 BP) beech was much more common in the south than it is today.  So for much of the Pleistocene prior to man, primeval forests on moist sites resembled the bluff forests that now can only be found in a few sites along the Savannah, Altamaha, Chattahoochee, and Appalachiacola Rivers.  Bluff forests at the latter river hold the southernmost population of American beech which grows alongside southern species such as magnolia, cypress, and palm trees.  Other examples of piedmont and coastal plain bluff forests are Magnolia Bluff in Camden County, the Alapaha Bluff, Springhill Plantation, William Bluff Preserve, Altamaha Bluff, and Shell Bluff in Burke County.

Beech-Magnolia climax forest at the Tall Timbers Research Station near Tallahassee, Florida.  Reportedly, this tract is adjacent to long-leaf pine savannahs.

Though the biomass of large mammal species in Beech-Magnolia climax forests of the Pleistocene wasn’t as great as that of Ice Age grasslands in the south, diversity was high.  Ice Age grasslands, which probably occurred adjacent to hardwood hammocks, held large herds of mammoths, bison, horses, llamas, and elk.  But during interglacials and interstadials  when primeval climax forests were more widespread than grasslands, gaps within them supported smaller herds of grazers as well as the beasts of the forest.  White-tailed deer, long-nosed peccary, tapirs, Jefferson’s ground sloth, mastodons, and bears all lived in these truly virgin forests where the mast from giant mature trees must have been exceedingly abundant.  The forests were the haunt of saber-tooth, jaguar, and dire wolf.  The birdlife of today’s world is likely the tiniest of remnants compared to that of the original unspoiled environments because every species living had taken millions of years adapting to it.  American birds have only had a few thousand years to evolve to survive in anthropogenic environments, and recent environmental change is occurring at an even more accelerated rate.

Common mammal species in South American forests.  A similar composition of animals probably occurred in Pleistocene beech-magnolia forests, though the species differed–long-nosed peccary instead of collared, white-tailed deer instead of brocket, Vero tapir instead of the extant South American species.  There were no pacas and agoutis but other unusual species such as Jefferson’s ground sloth and mastodons lived there.

The closest bluff forest near my house is Shell Bluff, named for the Eocene-age fossil oyster shells found there.  Access to Shell Bluff is either a long hike through private property or a boat ride down the river.  I didn’t think a trip to see it was feasible for me.  However, Dr. Charles Wharton wrote that nearby Griffin’s Landing is an even better example of a bluff forest.  I almost explored this area last summer, but it is next to a nuclear plant, and guards from Plant Vogtle close the gate to Griffin’s Landing at dark. I didn’t want to get stuck overnight behind the gate, but now that I know a bluff forest exists there along with fossil oysters, it may be worth a day trip later this year.