"Outside of areas that are planted with a species like loblolly or long leaf pine, what changes have been occurring to the vegetation as a result of anthropomorphic activities in southern GA?"

 I don't know that I could answer that question as full as some of the academics/researchers such as Bruce Allen up at the SRS (affectionately known as the "bomb plant" around here)

It is probably the same old song as in the rest of the country with perhaps a different refrain...Fire or lack thereof.

While Georgia is a metes & bounds state, it's land distribution mimics the US on a smaller scale. At the time it became a state, Georgia was only settled along the immediate coast and up a narrow strip along the Savannah River opposite South Carolina. These original eight parishes later known as counties along with the first two Indian cessions in the late 18th century have evolved into what are known as the "headright counties" and many of the boundaries are as Lee or Charlie have previously stated; "the run of the branch", "the high water mark of the swamp'' or even the more ambiguous "edge of the swamp" or "running along the lands of xxxx xxxx" with no further cadastral description.

About 25 years ago I was working on an elderly lady's land that had been in her family forever. Upon inquiring about a plat, she produced a copy of a headright grant for 210 acres of "vacant pine lands" from the state of Georgia to one of her forebears dated in 1810. The legal description was basically; bounded on the west by the "run of Big Branch", bounded on the south by "lands of xxxx xxxx" and bounded on the east and north by "vacant pine lands", not much else in the way of cadastral detail and accompanied by a roughly hand drawn rectangle on the edge of the paper. The parcel itself has never been surveyed according to the landowner and courthouse records. Neighboring parcels had been surveyed and the resulting land while close to the original description in acreage, was four sided but more in the shape of an elongated irregular triangle than the hand drawn almost square rectangle on the original grant. I made a photocopy of it to keep, now if I can just find where I filed it ;-)

The remainder of the state was still Indian territory and was ceded over a period of time from about 1810 to just prior to the war between the states by treaty or sale in about almost a dozen transactions. Remember the Yazoo Land Fraud from history class? Each of these treaty lands where surveyed into regular divisions of land districts and subdivided into land lots similar to US townships and sections. Problem was, there were no common meridians and base lines between treaty cessions and while most districts and lots were similar with lots around 480 acres, a few were surveyed with much smaller lots and one was even surveyed off of a diagonal base line resulting in districts and lots skewed 45 degrees. These areas are now known as "lottery counties" and district and lot numbers are part of the legal description. As far as I know there have been no research into archives of surveys for witness tree research such as Charlie did for the NE.

I have looked at numerous plats surveyed in the early 20th century that while definitely not in the times of first settlement of the area, they do predate the pine plantations of industrial lands after the second world war and the agricultural boom of the seventies. From what I recall, most corner markers down here were either lightered stumps on upland corners and cypresses in bottomland corners. Naturally with the preponderance of natural boundaries on the larger landholdings of that period, it would make sense that most parcels would corner in the branches with cypress as witness trees. Of course lightered stumps, lasting virtually forever (until the appearance of Hercules Chemical on the scene ;-), would be favored also.

Probably the best account that I am aware of is that of the Bartrams, father and son, of Philadelphia who traveled extensively through the southeast in the late 18th century and kept diaries of their observations which make for fascinating reading. Reprints are still available mail-order from Dover Press in NYC. One at least being a botanist makes notes of the plants and trees. This area was described as a vast plain of pines, broken by impenetrable bays. Their descriptions of the inhabitants, both the Indians and white settlers, their modes of travel, the weather and more make for good rainy day reading.

Back to my comment about fire, referencing the Bartrams description and others since, was evidently a relatively open longleaf savannah frequently burned. The slash pine was relegated to the wetlands were fire was a little more infrequent. The area was extensively logged by water originally and later in the later half of the 18th century by the appearance of railroads. The soil being very sandy and poor, there were no plantations as in other parts of the south. There were plantations along the tidal reaches of the coast for rice, long staple cotton and indigo. These were largely eliminated and broken up during the War of Northern Aggression. The interiors where largely referred to as the "pine barrens". Later the lands where utilized as the turpentine industry headed south out of the Carolinas. The RR logging would come in waves. The large companies such as the Dodge Lumber Company out of NY or Philadelphia would move in, cut out all the LL, pull up their rails and move elsewhere. Usually these large parcels which were obtained often with an element of fraud were then sold off to large cattle operations, also generally out of the NE. Certain areas are still referred to as Thompson's Pasture or Adamson's pasture or the like. 

These companies continued to burn the woods (or what was left of them) regularly to improve browse. Union Bag was the first large paper company to move in the area in the mid 30's and constructed a mill in Savannah. They bought out many of these large cattle company holdings such as the Sapelo Cattle Company and converting the rangeland to planted slash pine. Others soon followed the lure of cheap land, labor and abundant water till they controlled a majority of the land in certain areas. Cattle still remained a important factor for a while after the war as Georgia remained an open range state until the mid fifties when the fence law was enacted largely by the perseverance of the paper companies. While the state had an office of the State Forester since the early 20th century, fire protection was minimal until the development of the TPO's after the second world war. 

These TPO's established fire towers and strung the first telephone lines in the interior to report fires. Largely during the 50's the TPO's were converted or ceded to the new Georgia Forestry Commission and by about 1970 state fire protection was universal. With the demise of open range and the appearance of "valuable timber" just about all wildfire was suppressed allowing the harvested LL pine to be replaced by the much more opportunistic Slash pine and on certain sites hardwood ingrowth. Up until the 80's, industry continued to burn it's lands on a regular rotation until the appearance of I-95 and other highways, snowbirds, aggressive personal injury lawyers and a few big lawsuits put an end to it. Since the big fires of the mid 90's, Florida and Georgia have written some prescribed fire laws offering a modicum of protection and we are seeing a little resumption of burning on both industry and private lands.

So you have industry lands, largely third and fourth generation plantations, following cattle and RR logging. And NIPFL (Non industrial private forest landowners) who have lands largely populated by Slash Pine which was high graded (by size and vigor, not species) by years of turpentining. Usual practice was to work all the faces over 12 in DBH for 10 years or so and then cut. Also with the advent of cheap chemical fertilizers, mechanized equipment and irrigation, the upland sites of the lower coastal plain began to be converted to agricultural use. This increase of land clearing continued with a big bump in the 70's with record grain prices and then collapsed in the early 80's. This about the same time as the demise of the turpentine industry led to massive liquidations of timber to save the farms from foreclosure. Naturally the harvest consisted of all merchantable timber, in effect a diameter limit cut of about six inches, and no money for any remediation. Along comes CRP in 1985 and tremendous areas of farmed fields go into planted loblolly and slash pine stands drastically changing the landscape in many areas. Actually there was a previous program in the 50's and 60's, the soil bank program, that had the same effect, but much of this land was recleared for the grain boom of the late 70's. 

The elimination of the boll weevil and a bump in cotton prices for a few years in the 90's resulted in some clearing, but the world cotton prices dropped before much could happen and then CRP reappeared on the scene in 95. This time however the NIPFL had to plant longleaf to reenter the program. We have had several thousand acres put back in LL thanks to this. The majority of our timber harvests now are either thinning of plantation pines or clear cutting of degraded natural stands. Diameter limit or high grading in pine is about extinct do to lack of "victims"

Our land is cut through with several rivers with wide bottoms. Most are blackwater rivers and relatively poor hardwood sites. A few such as the Altamaha and Savannah in Georgia are red water originating in the piedmont and mountains with fertile hardwood sites. The piedmont was the site of plantation agriculture and this continued with very damaging cotton farming practices until the arrival of the boll weevil in the 20's and the depression of the 30's. Most all the topsoil was washed into these rivers and the red color and rich bottoms are a "legacy" of this period continuing until today. This land in the piedmont has since reverted back to pine forests and some of those areas absorbed into Atlanta suburbia. In the meantime the hardwoods in the river bottoms have been high graded over the years. Cypress and Tupelo by grade and the better drained bottoms by species. The result, poor quality second growth cypress and tupelo where nothing else will grow and bottoms dominated by water/laurel oak, red maple and other tolerant species. 

Surprisingly the best remnant hardwood compositions remain where some of the last RR logging (it persisted until about 1960 in the river swamps) utilized complete clearcuts or at least destroyed everything allowing a decent mix of intolerant oaks and ash to regenerate. These largely ignored and degraded river bottoms became the focus again the past few years as the paper mills (and market conditions) have changed their focus from brown and bleached craft products to unbleached hardwood pulp. The industry has largely stripped their hardwood holdings during four years of record drought prior to signing on with all these third party forest certification programs. The result a mixed bag perhaps, I think they where duplicitous in their activities, but perhaps the silver lining is that some day way down the road, these bottom land hardwoods will come back better thanks to the complete clearcut. But back to your question of their original pre European Composition. Bartram writes of the Altamaha and Oconee flowing clear. Could be man's legacy of poor agriculture resulted in the fertility of these sites today. Perhaps they were originally not much different than the sandy acidic bottoms of our smaller blackwater rivers.

Enough...