How Widespread were Open Pine Savannahs During the Pleistocene?

Photo of an open pine savannah from the Summer 2010 issue of the Nature Conservancy Magazine.  The photo was taken by Beth Young.

Modern day ecologists are attempting to protect and restore the last remnants of open pine savannahs in the southeast.  Open pine savannahs were the most common type of ecosystem in the coastal plain of southeastern North America when Europeans first colonized the continent.  They are rich unique landscapes dependent upon frequent light fires that incinerate brush and saplings, creating an environment where pine trees grow far enough apart for grassy glades to exist between the widely spaced conifers.  Typically, pine needles slough off the trees, falling on top of tufts of wiregrass.  Droughts dry this combustible material which later is ignited by lightning or humans.  The fires kill hardwood saplings, but longleaf pines have fire resistant bark, and the grass roots survive underground, thus explaining how the environment becomes dominated by pine and grass.  Scientists consider the sloughing off of combustible pine needles as an active evolutionary adaptation by longleaf pines to maintain the type of environment they need to survive–it prevents them from being shaded out in the closed canopy forests that would grow without fire.

Another name for this ecotype is the pine barrens, but this is misleading.  On first glance these savannahs may seem monotonous, but they’re quite diverse–over 100 species of plants have been surveyed in as little as 1/4 acre.  This is a higher diversity than any other ecosystem in North America.  Wiregrass is the most common grass.  It co-occurs with many species of grass in the Poaceae family, as well as species of legumes (Faboceae), and flowering asters (Asteraceae).  Low bush blueberries love to sprout and colonize fire-prone savannahs, and they abound here.  Bird diversity is high too, and one species occuring only here includes the endangered red cockaded woodpecker.

There are different kinds of pine savannahs as well–the types of plants and animals living on them vary according to how well drained the soil is.  On the driest sandy sites, where there isn’t enough tinder for even light fires, scrubby oaks predominate.  On well drained sites with good soils tall longleaf pines and wiregrass dominate the vegetation, and gopher tortoises and gophers can be found digging their burrows.  On poorly drained sites wet pine savannahs are home to sphagnum moss and chimney hill crayfish.  And there are areas grading between wet and dry savannah.  Rivers, streams, and Carolina Bays are watery barriers that protect some sites from fire, allowing cypress swamps and hardwood forests to grow.

In the 19th century man began the destruction of this ecosystem.  Workers harvested resin to manufacture naval stores (turpentine and tar).  This killed many trees and degraded the environment.  Later, lumbermen and farmers cleared the land and planted horizon-to-horizon field crops such as cotton and peanuts.  Fires were suppressed to protect lumber, and loblolly pine replaced longleaf pine as the dominant tree in now closed canopy forests.  So today’s coastal plain landscape bares no resemblance whatsoever to the original.  Thankfully, at least a few pitiful remnants still exist on military bases, and on lands belonging to hunting clubs specializing in quail which thrive in this type of enviroment.  Organizations such as the Nature Conservancy are working to protect these areas.

I don’t think scientists currently studying open pine savannahs are aware that Frances Harper extensively surveyed this ecosystem on the uplands surrounding the Okefenokee while researching his 1927 book, Mammals of the Okefenokee Swamp.  They never reference it.  Though many areas of the savannah were already damaged from naval store activity, he was able to study them before their final destruction at the hands of clear cutters and agriculturalists.  Here’s his list of plant and animal abundance by species, listed from most abundant to least.

TREES

Longleaf pine

Slash Pine

Black-jack oak

Live oak

Pond pine

SHRUBS

Saw palmetto

Blueberry

Calico bush

Gallberry–a type of holly

Oak runner

Poor grub–Xolisma fruticosa

Dwarf myrtle

St. John’s wort

Chinquapin–a dwarf chestnut bush that used to be common but is now rare.  Saplings are available for transplant at www.willisorchards.com

Huckleberry

Persimmon

Lather bush–Clethra alnifolia

Possum haw

Cyrilla racemiflora

Parkerberry bush

Laurel–Osmanthus americana

HERBS

Wiregrass–Aristida stricta

Andropogen sp.–Includes broom grass and prairie grasses like bluestem

Xyris flexuosa

Aster Squarrosus–a flowering aster

Rhexia alfifanus–deer grass

Polygala lutea

Ericaulon decangulare

Sporobolus curtissii

Sphagnum

Linodorum tuberosum

Trilisa odoratissima

Habeneria nivea

Rhexia cilisoa

Asclepia cinerea–milk weed

Eleocharis baldwinii–road grass

Sabbatia decandra

Pterididum aquilinum–bracken fern

Baptisa lanceolata–gopher grass

Sarraceania minor–trumpet pitcher plant

Sarracenai flava–pitcher plant

Pogonia divericata–an orchid

Lilium catesbaei

Rynochospora filifolia–beak rush

Stillingia sylvatica

Sophronanthe hispida

Lycopodium alapecuroides

Galactiea Elliotii

Chrysopsis graminifolia–silver grass

Opuntia–prickly pear cactus

Aristida spiciformis

Servicarpus bifoliatus

Carphenophorus corymbosus

Cyperus cylindricus–sedge

Scleria glabra–nut rush

Hiercium

Lycopodium adpresum

Cladonia–lichen

MAMMALS

Cotton rat

Cotton mouse

Rafinesque’s bat

Seminole bat

Pipistrelle bat

Cottontail rabbit

Red bat

Southern flying squirrel

Eastern mole

Pocket gophers

Short tailed shrew

raccoon

fox squirrel–less common today because they like open forests. 

marsh rabbit

opossum

Striped skunk

Gray squirrel–more common today because they like closed canopy forests

Bobcat

Gray Fox

white-tail deer

weasel

Black Bear

Cougar

Red wolf

Frances Harper was 12,000 years too late to record the animals that would’ve thrived on open pine savannahs during the Pleistocene.  Here’s my additions.  The order of abundance is, of course, unknown.

PLEISTOCENE MAMMALS THAT WOULD HAVE OCCURRED ON OPEN PINE SAVANNAS

Columbian mammoth

Mastodon

Long-horned bison

Horses

Donkeys

Llamas–two kinds

Peccaries–two kinds.  The flat-headed peccary is thought to have preferred scrubby forests that would’ve been common during dry glacial climate phases.

Beautiful Armadillo

Harlan’s Ground Sloth

Jefferson’s Ground Sloth

13-lined ground squirrels

Jackrabbits?

Dire Wolves

Giant Short-faced bears

Saber-tooth cats

Scimitar tooth cats

Giant Panthers

Jaguars

I believe open pine savannahs are a very old ecosystem descended from the first grasslands that evolved during the Oligocene or Miocene.  It’s true that Indian-set fires facilitated the extent of these grasslands, but savannahs must have existed prior to the advent of man here.  Ironically, pine savannahs were probably more widespread during wetter climate phases because lightning from more frequent thunderstorms would’ve ignited more fires.  During cold arid glacial stages, scrubby oak thickets expanded at the expense of pine savannahs due to lessened incidence of lightning-induced fires in an environment so dry that eolian sand dunes rolled across the landscape.

The Pleistocene climate fluctuated between wet and dry climate phases, depending on whether the Laurentide glacier to the north was in a melting or expanding phase.   The ratio of pine savannah to oak scrub habitat corresponded to these climate phases–the pine savannah expanding with melt water wet phases; the oak scrub/desert expanding with dry cool expansion phases.  But neither habitat was completely eliminated during the climate fluctuations unfavorbable to them.  Many pollen studies show these alternating dry and wet climate phases still occur, though they’re not as drastic as the Ice Age fluctuations.  Today, we’re in a wetter phase, but 5,000 years ago the climate was much drier.

The bigggest influence on open pine savannahs during the Pleistocene, besides climate, was the megafauna.  Cooler climate and megafauna grazing, trampling, and dung-depositing probably caused the savannahs to vary more in composition than they do today, but their basic structure was likely similar, and they were just as widespread as they were when white men invaded the continent.

Especially wet interstadials, however, increased the quantity and size of wetlands which made for barriers that stopped fires, allowing chestnut, oak, and beech forests to occur as far south as what today is Florida.  The dry cycles of climate of the LGM restricted the occurrence of these rich hardwood forests on the coastal plain to river sides and springs that didn’t completely dry up, following extended droughts and the dramatic drop in the water table.

The terrain of the piedmont and mountains localized fires and created patchy environments of mixed forests and meadows quite different from those of the coastal plain.

 

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Wild Cranberry Bogs–A Relic Ice Age Landscape of the Upper South

The Nature Conservancy is successfully protecting habitat in Shady Grove, Tennessee for the federally threatened bog turtle (Clemmys muhlenbergii), a species small enough to fit in the palm of the hand.  In fact, it’s America’s smallest turtle species.  The bog turtle, as the name would suggest, is dependent on bog habitats, particularly the kind where wild cranberries grow.  Bogs are wetlands that differ from swamps in that they’re poorly drained, whereas swamps may appear stagnant but actually consist of slowly moving water.  Bogs are also more associated with cooler climates.

Range map for the bog turtle.  Part of its present range was under glacial ice during the ice age.  This map isn’t entirely accurate because one of the areas the Nature Conservancy has protected for this species is in Tennessee, which according to this map is outside its range.  During the Ice Age, this species probably had a more continous range and wild cranberry bogs were more common due to differences in climate.

There exists two distinct populations of bog turtles–one in northeastern states, and the other in high elevations of the southern Appalachians.  During the last Ice Age these ranges were likely continuous.  The southern population is threatened by agricultural practices, including the drainage of bogs to increase land for cultivation.  To protect the present day habitat of the bog turtle, The Nature Conservancy, over the past few decades, has purchased small parcels of remaining habitat–the last of the southeast’s wild cranberry bogs, a landscape that was probably more widespread in the upper south during the Ice Age when cool, rainy climate prevailed.  Now, the Conservancy is restoring cranberry bogs by building berms to stop drainage.

The Conservancy leases the land around these bogs to farmers because livestock grazing improves habitat for bog turtles which need more open ground for foraging on insects, berries, and succulent plants.  Modern day livestock play the beneficial ecological role that extinct or extirpated megafauna–mastodons, bison, horses, etc.–used to provide for the turtles.  The turtles need large ungulates to keep excess plant growth in check.

Wood Turtles

The wood turtle (Clemmys insculpta) is a closely related but larger species that also used to range farther south during the Ice Age.

Range map of the wood turtle.  Fossils of wood turtles, a species that prefers cooler climate, have been recovered from Ladds Mountain, in Georgia.

Paradoxically, fossils of the red-bellied turtle, a species that today is limited to Florida, have also been found at Ladds.  Based on carbon dates, at least one scientist believes they occupied the same range during the same period of time, suggesting a more moderate phase of climate occurred during one particular point of time compared with today.  During this climate phase summer must have been cooler but winters must have been warmer.

Source:

Kingsbury, Paul

“Turtle Power: A rare reptile helps restore a Tennessee wetland”

Nature Conservancy  Autumn 2010