Posts Tagged ‘Charles Wharton’

The Torreya (Torreya taxifolia) is Missing its Megafaunal Disperser

September 5, 2014

The torreya (Torreya taxifolia), also known as the stinking cedar because its crushed needles give off a strong resin odor, is a relic species thought to have been more widespread during warm climatic phases of the Pleistocene.  It likely diverged from an ancestor that was even more widespread during the Miocene when warm moist forests occurred all across North America and Asia.  T. taxifolia  is an extremely rare species confined to just the east side of the Apalachicola and Flint Rivers, while a closely related sister species (T. californica) is native to California where it is found in several disjunct populations. 

Pleistocene Ice Ages fostered the spread of arid grassland environments that were unsuitable for torreyas.  Under these conditions the torreya retreated to moist refugia on steep ravines of the Apalachicola and Flint Rivers. Connie Barlow, author of the below referenced book, thinks the torreya  formerly expanded its range as far north as the southern Appalachians, following the end of Ice Ages.  They are better adapted to live in an Appalachian cove forest rather than the environments surrounding their current range.  She hypothesizes the torreya’s current rarity is the result of its disperser’s extinction.  She suspects the giant tortoises (Hesperotestudo crassicutata and H. incisa) ate the torreya cones and defecated the seeds intact.  As the climate warmed following the end of Ice Ages, the tortoise’s range expanded and torreya trees spread in correspondence with this range expansion.  She believes the tortoises were the torreya’s main disperser. Squirrels can disperse the seeds but they are more likely to eat and destroy them, and other mammals are all potentially more likely to destroy the seeds with their teeth when they consume the cones. Tortoises don’t have teeth.  Furthermore, torreya cones contain turpene which is toxic to mammals but not to reptiles.  Now that tortoises are extinct, the torreya is stuck within a tiny range where it is probably going to succomb to fungal diseases. 

Barlow’s hypothesis will be difficult to support with concrete evidence–plant macrofossil remains from warm climatic phases of the Pleistocene are rare in this region.

Connie Barlow and her husband with a very rare Torreya tree.  She hypothesizes that its rarity today is due to the extinction of its most probable disperser–the giant tortoise.

Torreya taxifolia range map.png

Torreya taxifolia range map.

Torreya trees grow in natural communities the late naturalist, Charles Wharton, referred to as “torreya ravines.”  These are cool moist micro-environments also known as steepheads, and they only occur on the east side of the rivers.  The dominant trees in a torreya ravine are red maple, southern sugar maple, beech, magnolia, basswood, elm, torreya, and sabal palm.  Most of these species have northern affinities and are more commonly found in Appalachian cove forests.  Other plants found in torreya ravines also represent species of northern affinities such as strawberry bush, hydrangea, and redbud.  Wharton found torreya growing with beech, sourwood, and plum in the Faceville Ravine on the Flint River.

Wharton catalogued Torreya Ravines in his book The Natural Environments of Georgia written in 1978.  A more recent updated version of that book (The Natural Communities of Georgia) written by several authors and published last year does not mention torreya ravines.  I fear this means torreya trees may already be extinct in Georgia.  Wild torreya trees can still be found in Torreya State Park in Florida.

Mature torreya trees grow to 60 feet tall, but today few wild torreyas exceed 6 feet before dying back due to fungal disease.  Torreya trees have been transplanted to the Biltmore Estate in Asheville, North Carolina where they are doing much better than the wild trees.  Torreya trees growing on the Biltmore Estate survived a freeze of -30 F.  This shows they are capable of surviving in more northerly latitudes, and this supports Barlow’s hypothesis.

References:

Barlow, Connie

The Ghosts of Evolution

Basic Books 2000

Wharton, Charles

The Natural Environments of Georgia

Georgia Department of Natural Resources 1978

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The Natural Communities of Georgia by Leslie Edwards, Jonathan Ambrose, and L. Katherine Kirkman

May 6, 2013

The Natural Communities of Georgia is a beautiful and exhaustive encyclopedia of all the natural environments that exist within the state boundaries.  It’s an updated version of the late Charles Wharton’s 1978 book–The Natural Environments of Georgia.  This book is dedicated to him.

The Natural Communities of Georgia was published by the University of Georgia Press in February 2013 after almost a year’s delay.  It’s reasonably priced by Amazon at $46, considering it is a hardback with 674 pages, hundreds of color photographs, and dozens of illustrations and maps.  Color photographs can make a book prohibitively expensive to produce.  I eagerly purchased a copy of this book as a birthday present to myself.

Although 3 co-authors are given credit for writing this book, there are an additional 12 contributing authors listed inside, making this book quite a collaborative effort.  They could have used me as a contributing writer for the section about the Pleistocene.  They covered the Pleistocene in 2 or 3 paragraphs, and because it was the end of the chapter, most of the rest of the last page was blank.  People who regularly follow my blog know I could have easily filled that big blank page with interesting information about Pleistocene Georgia.  Whoever wrote their brief section about Pleistocene Georgia slightly missed the mark about 1 tidbit of trivia.  The author listed some of the mammal species found in Georgia during the Pleistocene and included the ocelot followed by the word, possibly, in parenthesis.  This isn’t entirely incorrect.  An individual fossil of an ocelot was found in Florida, so ocelots may have roamed Georgia then.  But I’m sure the author was referring to specimens found in 2 fossil sites in Georgia that represent a species from the Leopardus genus which includes the margay and the jaguarundi, not the ocelot.  I’ll write about these finds in my next blog entry and clear up that author’s confusion.

The format of The Natural Communities of Georgia is convenient for the reader.  The book is organized into 5 parts corresponding to the 5 ecoregions of Georgia.  The authors give an overview of each ecoregion, then discuss each type of environment found within the ecoregion.  Sidebars featuring an animal or plant commonly found in each environment are included.  Sidebars showing featured places where an example of each environment can be found conclude each section.  Detailed directions are given, so the reader can use the book as a guide to seek out each type of environment.  The following is a list of all the natural environments discussed in the book along with an example featured place.  I’ve already discussed and/or visited some of these sites.  A * denotes the ones I’ve either already blogged about or have visited.

BLUE RIDGE ECOREGION

*Northern Hardwood and Boulder Forest–The Summit of Brasstown Bald

Montane oak forest–Whitney Gap Trail on Wildcat Mountain

Cove Forest–Sosebee Cove Trail

Low to Mid elevation oak forest–Bear Hair Gap Trail

*Pine-Oak woodlands–Tallulah Gorge State Park

Ultramafic Barrens and Woodlands–Davidson Creek Botanical Area

High Elevation Rock Outcrops–Blood Mountain

Low to Mid elevation Domes, Glades, and barrens–Bog Cedar Mountain

*Low to mid elevation acidic cliffs and outcrops–Tallulah Gorge State Park

Mountain bogs–Songbird Trail at Lake Conasauga

Seepage Wetlands–Track Rock Gap Archaeological Area

Spray Cliffs–Helton Creek Falls

Flood Plains, bottomlands–Jacks River Trail

CUMBERLAND RIDGE AND VALLEY ECOREGION

Mesic Forest–Shirley Miller Wildflower Trail

*Dry Calcareous Forest–Chickamauga Battlefield Park

Acidic Oak-Pine-Hickory–Cloudland Canyon State Park

*Pine Oak woodland–Zahnd Natural Area Lookout Mountain

*Montane longleaf Woodland–Berry College

*Calcareous Cedar Glades–Chickamauga Battlefield Park

*Calcareous Prairie–Berry College

Acidic Glades–Rocktown

Calcareous Cliffs–Pigeon Mountain Wildlife Management Area

Acidic Cliffs–Cloudland Canyon State Park

*Flatwoods–Berry College

Calcareous Seepage Fens–Mosteller Springs

Acidic Seepage Wetlands–Keown Falls Tract

*Sagponds–Zahnd Natural Area

Floodplains, bottomlands–Coosa River Lock and Dam Park

PIEDMONT ECOREGION

Mesic Forest–Chicopee Woods

Oak-Pine-Hickory–Chicopee Woods

Pine-Oak Woodlands–Red Cockaded Woodpecker Trail

Prairies–Pickett’s Mill Battlefield Park

Granite Outcrops–Davidson-Arabian Mountain

Glades, Barrens–Kennesaw Mountain

*Ultramafic Barrens–Burke’s Mountain

Flatwoods–Monticello Glades in the Oconee National Forest

Seepage Wetlands–Dawson Forest Wildlife Management Area

Floodplains, Bottomlands–Alcovy Conservation Center

COASTAL PLAINS ECOREGION

*Sand Dunes–Ohoopee Dunes Natural Area

Dry Upland Longleaf Pine Woodland–Reed Bingham State Park

Mesic Longleaf Pine Woodland–Silver Lake Wildlife Management Area

Dry Evergreen Oak Woodland–Big Hammock Natural Area

Dry Deciduous Hardwood Forest–Providence Canyon Recreation Area

Mesic Slope Forest–Montezuma Bluffs Natural Area

Granite Outcrops–Broxton Rocks

*Eocene Chalk Prairie–Oaky Woods

Pitcher Plant bogs–Doe run pitcher plant bog

Shrub bog–Townsend Wildlife Management Area

Cypress-Gum Pond–Big Dukes Pond Natural Area

Depression Oak Forest–No publicly available area

Riverine floodplains, bottomlands–Ebenezer Creek Boat Ramp

*Bottomland Hardwood–Moody Forest

River Banks Levees–Altamaha Park

Small Stream Floodplain Forest–Little Ocmulgee State Park

Okefenokee Swamp–Okefenokee Swamp National Refuge

MARITIME ECOREGION

Intertidal Beaches–Jekyll Island

Maritime Dunes–Jekyll Island

Maritime Forest–Crooked River State Park

Interdunal Wetlands–Jekyll Island

Salt Marsh–Earth Day Nature Trail

Freshwater and Oligohaline Tidal Marsh–Butler Island Altamaha Wildlife Management Area

Tidal Swamp–Lewis Island Wildlife Management Area

I’m going to use The Natural Communities of Georgia as a reference in future blog entries, focusing on their paleo-origins.  Much of my rumination will be speculation.  Some of these environments, such as open pine savannahs. are ancient and may have originated as early as the Cretaceous, though with significant floral and faunal turnover.

Oh, and I’m making a note to self here to buy The Road Side Geology of Georgia when that book is published.

Sagponds Contain a Partial Pollen Record of Ice Age Vegetation in Northwest Georgia

February 2, 2012

In the southern Appalachian mountains when groundwater dissolves underlying limestone the ground slumps to a granite bottom, creating an interesting environment known as a sagpond.  These differ from sagponds located in California which are formed from strike-slip faults.  Georgia sagponds form from the same geological principle that creates limesink lakes in Florida.  Dr. Charles Wharton counted as many as 96 sagponds per square mile in Bartow County.  They range in size from a few feet across to several acres.  Some go seasonally dry; others retain water year round.  Scientists recognize 4 types of sagponds.  Dry sagponds drain within an hour after rain stops.  Young sagponds, where the ground hasn’t finished slumping, hold water during winter and spring.  Mature sagponds are partially filled with colluvial silt and retain water year round.  Extinct sagponds have been completely filled with silt but still might be moist enough to support a marsh.

Topographical map of Green Pond.  Sagponds often form on mountains and provide wetland habitats in otherwise dry upland environments.

These low wet areas dotting the otherwise dry upland ridge and valley region host disjunct populations of at least 49 species of plants that are normally found on the coastal plain, including the evergreen laurel oak, gallberry (a type of holly), fetterbush, rock rose,  joint grass, panic grass, beaked rush, and many others.  Common aquatic plants found in sagponds are tupelo, buttonbush, red maple, and sedges.  Buttonbush and tupelo tend to grow in the middle of a sagpond; grass and sedge grow on the edges; than there is a heath zone ringed by a lowland woods consisting of loblolly pine, laurel oak, and red maple.

Page from the book Natural Environments of Georgia with a photo of a dry sagpond in Bartow County.

Photo by Alan Cressler of a sagpond on Keel Mountain in Madison County, Alabama.  I couldn’t find any photos on the web of sagponds in Georgia, though there are supposed to be a lot of them.

Dr. Wharton reports that Bloody Pond in Chickamauga Battlefield Park has a large stand of willow oaks.  (While researching this topic, I discovered that there are at least 2 other Civil War era battlefields with areas known as “Bloody Pond.”)

Scientists looking for ancient pollen and Pleistocene-aged plant macrofossils have excavated and cored several sagponds–Bob Black Pond, Quicksand Pond, Green Pond, Pigeon Mountain Marsh, and Lookout Mountain Marsh.  The pollen record from all these sites combined cover a timespan of between ~34,000 Bp-~10,000 BP in calender years.  Some of the studies date to before scientists realized carbon-dating gave dates too young when compared to tree rings.  The data I give in this discussion mention dates I’ve adjusted.  They’re just rough estimates based on the inaccurate dates from the early studies.

Pollen from Green Pond, believed to date to the Farmdalian Interstadial, suggests an environment in northwest Georgia consisting of dry oak and hickory woodlands with prairie openings.  Dr. W. A. Watts (of Penn State but now retired) conducted this study in 1973 and gave carbon dates of 29,630 BP- 25,000 BP which should be adjusted to about 34 ka BP-30 ka BP.  Pine pollen was scarce.  ~28,000 years ago pine and spruce pollen began to increase, indicating an abrupt change to a cooler drier climate.  Surprisingly, pond cypress was locally present.  This shows that individual plant species ranges didn’t always change in predictable patterns.  Pond cypress is absent in this region today, despite a warmer climate.  Shortly after this date, the pond filled with sediment and the pollen record ends for this site.  Conveniently, this is when the pollen record from sediment cored from Bob Black Pond, which Dr. Watts also studied in the early 1970’s, begins. 

Dr. Stephen Jackson of Wyoming University also studied Bob Black Pond over 20 years later.  He found boreal forest species dating to about 22,000 BP.  In addition to pollen he found plant macrofossils of white pine, red pine, jack pine, white spruce, Critchfield’s spruce, and paper birch.  Critchfield’s spruce is an extinct species thought to be adapted to temperate climates, and white pine still grows on the mountains of north Georgia, but the other 4 species no longer range much further south than Canada.

Jack pine present day range map.  This species lived as far south as northwest Georgia during the LGM.  Today, it lives no further south than northern Michigan.  Red pine is restricted to New England.  White spruce lives across Canada as does paper birch.

There’s no doubt the climate in north Georgia during the Last Glacial Maximum was cooler than that of today, but it wasn’t necessarily as cool as present day southern Canada, despite the presence of Canadian species of trees.  Scientists may have originally misinterpeted this data when they assumed the climate here was comparable to today’s southern Canada.  Pine and grass grow better in atmospheres with lower CO2 than broad-leafed trees.  So moderately lower temperatures combined with lower CO2 levels allowed northern species of conifers to compete better with oaks, maples, and other broad-leafed trees for space in the southern Appalachians.  It’s a good thing for the boreal species too because their present day range was completely under miles of ice then.

Fossil pollen from Pigeon Marsh in Walker County dates to approximately the LGM.  Jack and red pine pollen ranges from 25%-45%, oak pollen ranges from 30%-40%, and spruce pollen ranges from 1%-2%.  Hickory and chestnut were present but not abundant.   After the LGM, as the climate remained cool but became more moist, beech became the dominant tree here until the modern floral composition took over.

During the Pleistocene sagponds would’ve been prime foraging grounds for herds of hungry mastodons.  Sagponds supported the kinds of aquatic plants (especially buttonbush and pond cypress) that we know mastodons ate from analysis of their coprolites.  And indeed, fossil evidence of mastodons has been found in the ridge and valley region of Georgia and Tennessee.

References:

Watts, W. A.

“The Vegetation Record of a Mid-Wisconsinian Interstadial in Northwest Georgia”

Quaternary Research 3 (2) 1973

Wharton, Charles

The Natural Environments of Georgia

Georgia Department of Natural Resources 1980

The Natural Environments of Georgia by Charles Wharton

March 23, 2011

The Natural Environments of Georgia by the late Charles Wharton is a book I remember reading between classes in the Augusta College library in 1986.  Then as now,  local ecology and natural history fascinated me.  For my recent 3 part blog series about the Okefenokee Swamp, I read a research paper that referenced this book and reminded me about it.   I knew this source would provide a great deal of fodder for my blog, so I began to search for it.  It’s out of print, and the only copy on sale at amazon.com is a used one for $186 which is about 10 times what I’m willing to pay for it.  The east central Georgia library has 62 copies of the book, so I asked for an interlibrary loan.  Again no dice–it’s considered a reference book, and they don’t loan it out.  Finally, I went out of my way to the downtown library to look at it, but I only had an hour.  I had to cram the 200 page book into my brain instead of being able to digest the interesting details at my leisure.  Research shouldn’t be this hard.

Dr. Wharton lists 100 different types of natural environments in Georgia, but this is an arbitrary and somewhat redundant list.  A new version of this book (which was originally written in 1979) is due from the University of Georgia Press within the next 2 years, and they list 72 types.  The new version will be entitled A Guide to the Natural Environments of Georgia, and I expect it to be an expensive volume.

Many of the plant associations found in these myriads of environment types probably date back well into the Pleistocene and perhaps earlier.  Certainly, some Pleistocene plant associations no longer exist.  Part of north Florida once consisted of a forest of spruce, beech, and hickory, a combination of trees now found nowhere in the south, at least naturally.  A plant fossil site near Winder, Georgia known as Nodoroc suggests a forest of northern pines (red and white), southern pines (shortleaf), and oak along with hickory, chestnut, and fir, and interspersed with many grassy meadows–another environment not found today.  All forest types including the extinct Critchfield’s spruce as a component, of course, no longer exist.  Critchfield’s spruce was a temperate species once widespread in the southeast.

The composition of plants within an environment depends on many factors, chief among them is chance.  Many plant species have a wide tolerance for different climates and soil conditions.  Some compete better than others according to environmental conditions, but still dumb luck plays a big role in the distribution of different kinds of plants.  For example wind blows seeds of one plant in one direction creating a pure stand here, but it didn’t blow in the opposite direction making that plant absent there.  A series of annual freezes destroys the fruits of a tree, wiping out that species here, but not there on a sunny southern facing slope.  Fire burns up a forest transforming it into a meadow here, but leaves a stretch of wood there on the other side of a stream.  Animals consume all the acorns here allowing beech which can reproduce from sprouts to dominate, but over there a score of acorns go uneaten and a lot of oaks still grows.

I’ve already discussed open pine savannahs and cypress swamps in previous blog entries.  Here are a few other types of environments Charles Wharton catalogued in his book.  I’ve focused on common environments of central Georgia.

Alluvial River and Swamp Systems: Piedmont Region

Dr. Wharton states this type of environment made up about 9% of Georgia’s landmass.  Common trees included river birch, sycamore, sugarberry, green ash, red maple, box elder, water hickory, and oak.  Stands of water, cherrybark, overcup, and swamp chestnut oaks outnumbered stands of just water and willow oak.  Thick stands of giant river cane or bamboo forming impenetrable thickets occurred at the heads of creeks.  These were rich environments providing lots of forest mast and bamboo forage for the megafauna to eat.  Bison and mammoths could graze year round upon the cane which is a giant grass, and munch down on acorns in the fall and winter as well.  Early naturalist explorers such as William Bartram and John Lawson found canebrakes that stretched for miles.  The Indians maintained them with fire.  Now, canebrakes exist as small patches vanishing in the face of development and fire suppression.

Bluff and Ravine Forests with Northern Affinities

Disjunct populations of plant species that normally range in the north exist along the Mississippi River in southern Louisiana.  Ecologists theorize that during the last Ice Age cold meltwater from midwestern glaciers rushed down the mighty Mississippi and hit warm southerly fronts creating foggy moisture which got trapped in river valleys with steep bluffs.  These blufflands host beech, shumard, white, and chinkapin oaks, tulip, magnolia, elm, basswood, mulberry, Florida sugar maple, pignut and bitternut hickory, white ash, hackberry, sycamore, holly, spice bush, paw paw, hydrangea, silver bell, red bud, hop hornbeam, elderberry, giant bamboo cane, 11 species of fern, nettles, ginseng, and many other plants that prefer cool moist conditions.  Such bluff forests are also found on the Atlantic coastal plain as far south as north Florida suggesting a similar climatic explanation here as well, though no rivers in what is now Georgia drained directly from glacial meltwaters.

Oak-Hickory-Pine Climax Forests

Soapstone outcropping in suburban Atlanta.  This land was never farmed because it was too rocky, and a good example of oak-hickory-pine climax forest grew here.  The Woodland Indian culture carved bowls into the stone before the development of ceramic pottery.  Picture from google images.

This type made up 50-75% of the Georgia piedmont before European settlement.  Dr. Wharton gave 2 examples: one in Elbert County and the other in Dekalb County.  The latter is known as Soapstone Ridge.  People from the Woodland Indian culture (3000-1500 BC) chipped bowls in the abundant soapstone located in this region which is right off the Atlanta bypass.  They heated stews by dropping hot rocks in the bowls.  The development of ceramic pottery put an end to this practice.  The chipped bowls are still visible in many rocks.  The rocky soils prevented the development of agriculture, but now a subdivision known as Soapstone Ridge (what else?) has fragmented the forest.  These forests hosted red, white, and black oaks, pignut, shagbark, and mockernut hickories,  shortleaf and loblolly pines, and red maples.  Formerly, before the blight decimated the species 100 years ago, chestnut was a common component.  Soils within this region containing high levels of iron and magnesium also host Oglethorpe oak, mulberry, basswood, and redbud.

Shortleaf-Loblolly Pine Climax Forest

Regions within the oak-pine-hickory climax type that are continuously burned become dominated by fire resistant pines.

Oak Savannahs and Woodlands

This is an extremely rare type within the oak-hickory-pine climax type that was probably more common during the Pleistocene when dry cycles of climate  created a landscape of widely spaced shortleaf pine, red, scarlet, post, and blackjack oaks, blueberry and haw bushes, and grass.  Today, this type of environment only occurs on thin soils.

Beaver Ponds

Photo by Karan Rawlins from google images.  This is a beaver pond somewhere in Georgia.

Without humans limiting their numbers, beavers dammed most of the abundant creeks in what is now central Georgia creating long chains of beaver ponds.  If beavers completely chewed down all the trees in a vicinity, they abandoned the area and sediment filled the ponds until the ponds transformed into a marsh.  After enough willow trees resprouted the beavers would return.  Treeless marshes were the preferred habitat of the extinct giant beaver.  Therefore, it’s reasonable to suppose that the present day beaver (Castor canadensis) created habitat favorable for the extinct giant beaver (Castor ohioensis).  Beavers don’t build dams on large rivers but instead live in riverside tunnels.  When trees grow scarce, they will dig canals connecting their home pond with distant woodlots.

Dr. Wharton’s book has a neat aerial photograph of a chain of beaver ponds along a tributary of the Flint River.  A hunter told him that one of these ponds alone held 1000 ducks.  King rails and Virginia rails, both of c0nservation concern in the state, live here.  Pickerel, buffalo fish, bowfin, and many other fish species swim in this pond–if it still exists.  Remember, the book is 30 years old.

Successional Forest Stages

An area in the piedmont stripped of its trees will soon become a grassy field with annual flowers.  If stripped of soil too, a stage where moss grows and soil builds will occur.  During the Pleistocene, megafauna foraging and fires probably prolonged the grassy meadow stage.  Next, perennials and pine tree and sweetgum seedlings, their seeds windborne, begin to take hold.  Berry bushes too, their seeds carried in bird turds, form colonies. Pine trees grow quickest and dominate while oaks try to catch up.  Eventually, oaks and hickories shade out the pines and they dominate.  Shade tolerant trees such as maples are the final colonists.  A mature piedmont forest was something beautiful and awe-inspiring, according to William Bartram who saw much of Georgia before Europeans ruined it. 

Granite outcroppings

1902 map of granite outcroppings in central Georgia.

Some rare plants live in shallow solution pits in this type, but mostly they’re just bare rock.  Below is a link to a virtual tour of Heggies’s Rock in Columbia County, Georgia.  In my opinion the surrounding woods are much more beautiful than the naked granite.   There are sandstone outcroppings in the coastal plain.

 http://rtvpix.com/RE-9060-GDK4AO-01