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

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.

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Pleistocene Fossil Canid Ratios Recorded in the University of Florida Database

The abundance of Pleistocene fossil sites in Florida has allowed the university in Gainesville to become a center of information for other scientists.  Scientists excavating new fossil sites use existing fossils at the University of Florida Museum of Natural History to help identify the new specimens they pull from the earth.  It’s not always easy to differentiate closely related species–the subject of this blog entry, the canids, are notoriously difficult to distinguish.  Vertebrate zoologists and paleontologists measure and describe every part of every bone and tooth when examining new specimens.  They publish this information in scientific journals and accumulate knowledge of the size limits and shape variations of a particular species’ anatomy.  If a newly discovered fossil tooth for example doesn’t fit any known pattern of shape or size, than scientists suspect they may have discovered a new species.  The more data scientists have, the better able they are to identify new species and spot evolutionary trends over time within a species.

Fossil collecting is popular in Florida, thanks to all the sinkhole lakes and caves with basal chemistry in the soil that preserves bones.  Amateur fossil collectors have many more fossils in their collections than the University of Florida’s Natural History Museum..  Many are for sale as well.  It would be a great benefit to science, if collectors made arrangements to donate their collections to the museum upon their deaths.  Many valuable specimens have been lost when their owners die and family members, not interested in the subject, lose track of where they put the old bones.

My little study is limited to canid fossils listed on the University of Florida database and leaves out the great many more in the hands of amateur fossil collectors.  I also limited this survey to the Rancholabrean Land Mammal Age (300,000 BP-11,000 BP), leaving out Armbruster’s wolf which dominated the middle Pleistocene before being replaced by dire wolves.  Nevertheless, I think there’s enough information to suggest relative canid species abundance during the late Pleistocene.  Keep in mind, I was counting on a computer screen while scrolling down, so my numbers may be off slightly.

Listed on the Florida Museum of Natural History’s database, I counted 64 dire wolf (Canis dirus) specimens, 34 coyote (Canis latrans) specimens, 1 red wolf (Canis niger) specimen, 9 domestic dog (Canis familiaris) specimens, 0 dhole (Cuon alpinus) specimens, and 55 gray fox (Urocyon cineorgenteus) specimens.

The fossil record strongly suggests that from 300,000 BP to about 11,000 BP dire wolves were by far the most common large canid being about twice as abundant as coyotes.  Red wolves were rare but present.  Gray foxes were just as common during the Pleistocene as they are today.  These neat little foxes have the ability to climb trees, a skill that saves them from their larger relatives.  There is no evidence of dholes but as I wrote in a previous blog entry http://markgelbart.wordpress.com/2011/06/01/did-the-dhole-cuon-alpinus-range-into-southeastern-north-america-during-the-pleistocene/ , I suspect they may have periodically colonized parts of the southeast but in numbers too low to leave fossil evidence.

Dire wolves were the dominant large canid in the southeast (and all across North America south of the Ice Sheets) during the late Pleistocene.

Coyotes probably occupied a niche similar to African jackals.

Gray foxes thrived in areas where they had access to trees and could escape larger predators.

The presence of domesticated dogs in the Pleistocene fossil record puzzled and surprised me.  I almost didn’t even do a database search for Canis familiaris and only did so as an afterthought.  Most anthropologists don’t think humans domesticated dogs until after the Pleistocene about 10,000 years ago, but the fossil evidence contradicts this.  In fact scientists recently discovered the skull of a domesticated dog in a Siberian cave that dates to 33,000 BP.  They determined  this particular domesticated dog was not the ancestor of the lineage that led to today’s dogs but instead its descendents died out.  It’s probable that there were many early lineages of domesticated dogs that ceased to exist for various reasons.  Perhaps that group of people died out or stopped keeping dogs.  The popular idea that people domesticated dogs by kidnapping and raising wolf pups is a misconception.  Scientists think it’s the other way around–dogs adopted us.  Dogs are descended from the wolves which had the least flight response.  Wolves that hung closely around human campsites for access to leftovers gave birth to pups with floppy ears, multi-colored coats, and other dog traits that differentiate them from other wolves.  The gene for tameness shares a pathway with the gene for these physical characteristics.  So it’s likely that dogs adopted people in many different geographic locations wherever wolves (Canis lupus) began occupying areas adjacent to human campsites.  Obviously, dogs either followed or were brought to Florida by the Paleo-Indians.

The authors of a chapter in the book The First Floridians and the Last Mastodons suggest that all the coyote fossils found in Florida are actually domesticated dog fossils, but they only knew of a handful of coyote fossils.  Apparently, they didn’t know 34 specimens had been found.  I doubt scientists made that many misidentifications.

Dire wolves succeeded in becoming one of the dominant predators in the environments of southeastern North America where they found a wealth of prey roaming the open woodlands and savannahs.  Everything from bison and horses to deer and rabbits sustained them, and a mammoth or mastodon that died of natural causes provided a feast.  Coyotes successfully co-existed with dire wolves by scavenging large predator kills and by hunting rodents.  Red wolves must have been restricted to islands and perhaps deeply wooded swamps where they could survive on deer and small game.  Their niche must have been areas with lower densities of prey as opposed to grasslands that hosted large herds of ungulates.  Following the extinction of the megafauna and dire wolves, forests replaced grasslands and red wolves increased in number and drove coyotes completely out of the south.  But after European settlers wiped out the red wolves, coyotes returned.

References:

Ovodov, Nikolai, et. al.

“A 33,000 Year Old Incipient Dog from the Altai Mountains of Siberia: Evidence of the Earliest Domestication Disrupted by the Last Glacial Maximum”

Plos One 6 (7) 2011

http://www.flmnh.ufl.edu/databases/vp/intro.htm

The Dunwoody Nature Center

I attended my nephew’s bar mitzvah in Dunwoody, Georgia last weekend.  Dunwoody consists of dozens of subdivisions and plenty of shopping centers and absolutely no rural farmland.  I didn’t hold out much hope for a nice nature walk here–the traffic is terrible.  But at least the developers left a lot of trees standing.  I decided to walk from my sister’s house to a little park known as the Dunwoody Nature Center and I discovered a surprising gem.

This white oak was about 4 feet in diameter.  White oak is a common tree in Dunwoody.

From the composition of the trees left standing most of Dunwoody must have once hosted a pretty nice dry upland forest.  Too bad developers converted it into a crowded suburb.  Today, white oaks, black oaks, southern red oaks, shortleaf pines, and loblolly pines are the dominant trees.  The Dunwoody Nature Center slopes sharply down toward Wildcat Creek, the name of which is a relic to its former status as a wilderness.  The woods here are dominated by beech, white oak, sweetgum, river birch, and loblolly pine.  I was stunned to see a woodlot of mostly beech trees in central Georgia.

A mature beech tree growing on the edge of a rocky creek.  It’s surrounded by many immature beech saplings.

Fossil pollen studies show beech was a common tree in the south during the end of the Ice Age when the Laurentide glacier began melting and releasing more moisture in the atmosphere creating a climate that was still cool but more rainy than it was during the height of the Ice Age.  The presence of abundant beech in the fossil record is indirect evidence of massive flocks of passenger pigeons.  Passenger pigeons fed on acorns–in some places completely eliminating the oak seed crop…and the beech’s competition.  Although beech trees produce an edible nut, they can also spread from roots and could survive their seed being consumed by passenger pigeon flocks.  Since the passenger pigeon’s demise, oak forests have been replacing beech forests in many areas.  So I was delighted to see this remnant beech forest in central Georgia.

Wildcat Creek flows through a granite outcropping.  Here is a miniature waterfall.

Two little league baseball fields take up about half the space of the park.  The park is heavily used by dog and toddler walkers.  It’s popularity shows that the planning commission in charge of developing Dunwoody should have arranged for the purchase of more land for more parks.

The Congaree National Park, Home of the Giants

The Congaree National Park in South Carolina still held some surprises for me, even though I traversed this biggest last stand of bottomland forest in 1988.  Then, it was just a National Monument but in 2003 was upgraded to National Park status.  The park hosts 17 national and/or state record trees, including an 156 foot tall loblolly pine; and record shumard, southern red, and overcup oaks; as well as champion water hickory, Carolina ash, holly, box elder, persimmon, and paw paw.

Loblolly Pine–Pinus taeda

Loblolly pine.  The state record tree located in this park has a circumference of 16 feet.  This one looks to be at about 9 or 10.

The tree on the right is the loblolly pine from the previous photo.  The tree to the left is a red maple.  Some of the stands of loblolly pine in the park were found to be 227 years old.  The same study found that this species sprouts following hurricanes which open up the forest canopy.  The ages of stands corresponded with the history of hurricanes. (I took all the photos for this blog entry.)

This species is also known as old field pine because it reseeds so easily in lots devoid of other trees.  It has become a dominant tree throughout the southeast since much of the cotton and corn fields and horse pastures, which 100 years ago made up the face of the southern lands, were abandoned and went fallow.  Before European settlement it was merely a common component, but today it grows in pure stands as well as mixed with other species.  Therefore, it’s sometimes given the name bull pine due to its predominance.  Not only does it grow in upland locations, but it reaches prodigious size in wet areas from whence it gets its name, loblolly, which means mud puddle.  In the Congaree they grow in wet mud.

Sweetgum–Liquidamber styraciflua

Forked sweetgum trunk.

Another surprise for me.  I didn’t know this species could grow with its root system submerged in water, but I saw plenty of individuals in the Congaree growing in 6-12 inches of water.  Some had roots spread in structures similar to those of cypress and tupelo, enabling them to balance without tipping over in muddy soils.  Sweetgums, like loblolly pines, reseed readily in fields and are a common tree in upland sites.  But they’re adaptible enough to thrive in low muddy land as well.

Cypress–Taxodium distichum and Tupelo– Nyssa sp.

Cypress tree trunk.

Look at all of these cypress knees.  Scientists are unsure whether the cypress knees, which are part of the root system, grow for respiration or balance.

Up close view of a cypress knee.  Cypress trees are closely related to California red woods.

There are a lot of interesting microhabitats within a cypress-tupelo swamp.  Areas flooded in shallow water provide homes for fish, reptiles, amphibians, crayfish, and aquatic insects and spiders.

Flooded land in the cypress-tupelo swamp.

Fallen hollow logs and standing snags provide dens from everything from bats and possums to snakes and birds.

This hollow log is a possum mansion.

This standing snag could be hiding bats or flying squirrels.

When the water recedes lush grass and bamboo cane grow.  I can just imagine such Pleistocene mammals as long-horned bison, horses, and mammoths feeding in these grassy glades which often come about when a mighty old tree topples over allowing more light to reach the forest floor.

Note the grassy glade in the background.  There is plenty of grass and cane for a small population of bison and horses in the Congaree.  Too bad they’ve been extirpated.  The only big game left is deer and feral hogs.

A stand of cane.

When the mighty behemonths do topple over, their roots rip caverns in the forest floor.  Those often fill with water forming deep pools that are free of fish.  Amphibians can breed here without fish preying on their eggs and tadpoles.

Upturned tree root.

Pool formed in a hole from where a tree toppled over.

Beech–Fagus grandifolia

Beech tree canopy

Beech grows on sites that are near water but normally stay high and dry.  I love beech, and I wish I lived in a forest of these beautiful trees.  Their bark is white, the leaves turn a lovely yellow in fall, and they produce delicious little nuts.  Beech trees were common in the south during certain climatic stages of the Pleistocene, and as I mentioned in my blog entry “Pleistocene Passenger Pigeon Populations,” I think it’s a clue that passenger pigeon populations skyrocketed when beech was common because beech can grow and spread from sprouts.  The absence of passenger pigeons feeding allows more oak acorns to survive, and oaks outcompete beech.

The Congaree Swamp is probably as old as the Okefenokee Swamp

No studies on the age of the Congaree Swamp have been conducted as far as I know, but I assume it formed about the same time as the Okefenokee which became a swamp between 7,000-8,000 years ago following the final dissolution of the Canadian glacial Lake Agassiz when the water table rose all across the continent.  Throughout much of the Pleistocene, the region around the Congaree River was likely a mixture of upland oak and pine forests and savannahs with only scattered marshes perhaps near creeks and beaver ponds.  Particularly dry climatic stages even hosted oak scrub and sand dune environments.  It’s possible this region has repeatedly converted and re-converted to swamps with every full blown interglacial.

A comparison between my 1988 trip to the Congaree with my experience in 2011

The park system has considerably upgraded the facilities since I was here last in 1988.  Then, there was a gravel parking lot, and nothing else other than some gray paint marks on trees to demarcate the trails.  I hiked by myself in late July and was impressed with the giant trees.  This was before 1989 when Hurricane Hugo flattened many of the trees, but even then there were quite a few felled trees.  I saw a deer resting on a log, a scarlet king snake, and about a billion orb-weaving spiders that built webs across the entire trail at about 1 foot intervals.  After about 5 hours of enjoying nature, I became paranoid that I didn’t know what trail I was on, and I began jogging because I didn’t want to get lost in the park after dark–I feared the potential threat from feral hogs and rabid raccoons.  I didn’t see a single person while I was there until I got back to my car and met a park ranger.

Today, the Harry Hampton Visitor center is located at the entrance of the park.  It’s an air conditioned haven with clean lavatories.  Though the park is still not crowded, we did cross paths with many people.  Moreover, there is a pleasant 2.4 mile boardwalk which made the park accessible for us because my wife is wheelchair bound.

The lower boardwalk goes through a cypress-tupelo swamp.  The upper boardwalk goes through a bottomland forest dominated by sweetgum, loblolly pine, red maple, river birch, and ash.  I only saw a few oaks here–water, swamp chestnut, and willow; though in other areas of the park they’re more common.  Holly trees are common in the understory, and there are occasional patches of palmetto.  I saw no paw paw trees here, but I remember there were many on the trails.

The trails are now color coded, so there is little danger of becoming confused as to which trail one is on as I did 23 years ago.  The paint marks are on trees for the hiker to follow.