Changing Forest Composition in Northwest Florida over the Past 40,000 Years

Camel Lake is an ancient body of water located 30 miles west of Tallahassee, Florida in Liberty County.  Geologists haven’t been able to determine if it’s a limestone sink lake or an aquifer positioned near the surface of the land.  It’s not a large lake being 500 yards in diameter, and it is sometimes referred to as a pond.  Today, open pine savannah consisting of longleaf pine, turkey oak, and wiregrass surround the lake.  Cypress trees, Spanish moss-covered live and laurel oaks, myrtle, and titi grow adjacent to the water.  In 1986 three scientists took a core of the lake bottom.  They counted pollen grains, catalogued plant macrofossils, and carbon dated differing levels of the core.  The information they gathered provides a diary of changes in plant composition in the vicinity of Camel Lake over the past 40,000 years.

Shoreline at Camel Lake, Florida.  A core of sediment taken at this lake found Pleistocene -aged pollen dating to as old as 40,000 years BP.  They found plant macrofossils in abundance as well including needles resembling those from longleaf pine, leaves similar to those of live oak, a species of quillwort no longer found south of North Carolina, and many other species.

The period of time from ~40,000-~31,000 BP is known as the Mid-Wisconsinian Interstadial.  The climate during this era was at least as wet as today, and maybe more so, because the glacial ice covering much of Canada was in a meltwater phase, and more moisture flowed into the atmosphere.  But it was still the Ice Age and temperatures were slightly cooler than those of today, reducing evaporation rates.  The cooler temperatures and increased precipitation fostered a mesic forest in northwest Florida dominated by high numbers of oak (comprising 40% of pollen totals), hickory, elm, ash, and hornbeam.  Cypress, sweetgum, sycamore, and myrtle were also common.  Chestnut didn’t range this far south in this part of Florida during Colonial times, but during the Mid-Wisconsinian Interstadial, chestnut pollen was abundant in the air.  The authors of the below referenced paper believe the pollen was from the American chestnut, rather than chinkapin which is a small bush.  The pollen from these 2 related species can’t be distinguished, but the amount suggests it originated from great forests of chestnut, not small understory bushes.  At the beginning of the mid-Wisconsinian Interstadial pine was still common, but pine pollen dropped to less than 20% as the climate warmed.

Pollen graph from the below referenced paper.  Shows the pollen levels from the last 40,000 years.  Click to enlarge.

Between ~31,000-~29,000 a transitional phase occurred.  The climate rapidly began to become colder and drier as the Laurentide Glacier over Canada resumed expansion.  Pine increased in abundance and oak remained common but chestnut, beech, and hornbeam disappeared.  Marsh elder, a plant that thrives in fluctuating water conditions, was common, indicating dramatic dry/wet seasons.

The Last Glacial Maximum, the coldest stage of the most recent Ice Age lasted from ~29,000 BP-~14,000 BP.  Pine pollen increased to over 80%.  Oak, hickory, and cypress were still present but at low levels.  A low diversity and density of plants covered the landscape.  Shallow water plant species macrofossils, such as quillworts and small pondweed, dominate this level of the core, showing lower water levels within Camel Lake.

A sudden change in climate is evident in the part of the core dating to between ~14,000 BP-~12,000 BP.  Pine pollen immediately drops from over 80% to less than 20%.  Hickory increased to an astonishing 25%.  A forest represented by this much hickory has no modern analogue.  Spruce represented 8% of the pollen and was soon joined by beech also representing 8%.  A hickory-spruce-beech forest interspersed by small prairies where grass, ragweed, wormwood, composites, and marsh elder grew composed the landscape.  Scientists initially misinterpeted the results of their study from this time period and proposed that this phase was the coldest of the Ice Age in Florida, colder even than the LGM.  However, this was before the discovery of Critchfield’s spruce, an extinct species of spruce thought to have grown in temperate climates.  Though Camel Lake produced no macrofossils of Critchfield’s spruce, it was probably the species exuding the pollen discovered in the core.  Critchfield’s spruce macrofossils have been found in Louisiana and southwest Georgia (https://markgelbart.wordpress.com/2011/09/03/the-extinction-of-critchfields-spruce-picea-critchfieldii/) .  With this in mind a better interpetation of the data indicates temperatures only slightly cooler than those of today and with increasing atmospheric moisture during this time period.

How did a forest of hickory, beech, and an extinct species of spruce frequented with prairie openings become the dominant type of flora for 2,000 years here?  I propose that megafauna and passenger pigeon foraging suppressed the spread of oaks which normally dominate in this type of climate.  Llamas, deer, peccaries, bison, bears, and passenger pigeons gobbled up the acorns.  But hickory nuts have hard shells, beech can grow from sucker roots, and spruce cones were not as palatable.  These defense mechanisms gave them an advantage over oaks. Increased frequency of thunderstorms spawned lightning-induced wild fires that created the prairie openings.  I regard this time period as harboring a particularly interesting environment in northwest Florida, the likes of which may never be seen again.

From ~12,000 BP-at least ~10,000 BP an increase in oak, sedge, and grass suggests a drier warmer climate.  The climate became so dry between 10,000 BP-7760 BP that no sediment was deposited and there is no pollen record for that time period here.  Since ~7760 BP the modern composition of plants as discussed in the first paragraph of this essay has predominated.  Climate has changed little over the past 7700 years following the final dissolution of the massive glacial Lake Agassiz in Canada…at least in comparison with Ice Age climate fluctuations. (See also https://markgelbart.wordpress.com/2011/01/06/temporal-correlations-between-lake-agassiz-the-okefenokee-swamp-and-ancient-flood-myths/)

Reference:

Watts, W.A.; et. al

“Camel Lake: A 40,000 Year Record of Vegetational and Forest History from Northwest Florida”

Ecology 73 (3) pp. 1056-1066 June 1992

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The Vanishing Chinkapin (Castania pumila)

Photo from google images of chinkapin nuts in a burr.

The chinkapin, a shrubby relative of the American chestnut and not to be confused with the similarly named chinkapin oak (Quercus muhlenberger), used to be locally common, growing on the tops of rocky hills in the piedmont region of the southeast and in the undergrowth of open pine savannahs on the coastal plain.  The early explorer, John Lawson, reported the trees as so common that hogs fattened on the nuts.  He described the nuts as smaller, rounder, and sweeter than those of its relative, the chestnut.  Most sources state that it was the better tasting of the two.  William Bartram found chinkapin growing in association with chestnuts and chestnut oaks (Quercus prinus) on the tops of rocky piedmont hills, a forest type that contrasted with that of the surrounding area which was mostly an oak forest but in the valleys between the rocky hills a much richer forest of black walnut, beech, hackberry, tulip, and sycamore grew.  Moist creek bottoms and richer soils kept the latter area from burning, but the thin dry soils at the tops of rocky hills endured frequent fires.  Oak and chinkapin thrive in fire prone sites because they’re shade intolerant and need open areas to grow.

Most of the jobs I’ve had in the Augusta, Georgia area have taken me to just about every neighborhood in Richmond and Columbia Counties.  I used to survey lawns for Orkin Lawn Care, and I worked for many years as a route manager for the Augusta Chronicle. While working I, of course, took note of the vegetation (ecology has always held a great interest for me), and I’ve never seen a chinkapin.  Botanists warn the chinkapin is in decline for a number of reasons: fire suppression, chestnut blight, and suburban development.  Without fire, shade tolerant trees begin to dominate, and chinkapin can’t grow in the shade.  The chestnut blight completely destroyed the once common chestnut forests.  The chinkapin is also susceptible but is better able to survive because it is a shrub that resprouts and can produce a crop of nuts before it dies back again from the disease.  Still, the blight reduces overall nut production.

The chestnut blight was a disaster for the ecosystem.  Chestnuts and chinkapins were important sources of food for wildlife.  Now, trees such as tulip, which produce no mast, have replaced chestnuts.  They may be beautiful trees but animals can’t eat beauty.  I think the lack of chestnuts explains why I saw almost no wildlife on my trip to the Smoky Mountains National Park last summer (see my blog entry “Gatlinburg, Tennessee: Tale of a Tourist Trap Nightmare” which is I believe in the June 2010 archives).

The chinkapin has two interesting adaptations that help it survive as a species.  It germinates quickly in the fall.  The nut ripens from September to November, and they produce heavily–up to 1500 nuts per bush, beginning when they’re just six years old.  Squirrels disperse the species by burying the highly valued food, but the chinkapins foil the squirrels when they germinate immediately.  After they’ve become a seedling, the squirrel can’t utilize them.  Fall germination prevents animals from destroying the entire progeny, but by producing a nut with high food value, they motivate the squirrels to disperse them.  The other adaptive characteristic is its ability to resprout vigorously.  Fire may kill the main trunk, but chinkapin will resprout and form thickets.  Deer also find chinkapin a favored food and will browse down the main trunk, causing the shrub to resprout and create thickets.  Their thickets provide great cover and food for turkey and grouse.

Fossil evidence shows that turkey and grouse were quite common in upland Georgia during the Pleistocene–both left abundant specimens at Ladds and Kingston Saltpeter Cave in Bartow County.  Two studies of sediment cores in Georgia found that chestnut/chinkapin made up about 2%  of the pollen spectrum during the Pleistocene.  Both sites (Nodoroc and Grays Reef) date to about 30,000 BP.  Chinkapin surely was a common component of the open oak and pine savannahs so prevalent then.  Its ability to resprout and fall germinate is an ancient adaptation to survive fire and megafauna foraging.  The more such animals as mastodon, horse, llama, and deer browsed, the more this shrub would bounce back and form thickets ideal for bird life.

The Indians used to cook chinkapin and hickory nuts with their venison in well-rounded stews.  Chinkapins are a nice starchy substitute for bread or potatoes; hickory nuts provided a nice oily substitute for butter.  Chestnuts, unlike most other nuts, are primarily a carbohydrate based food, rather than a fatty form of sustenance.  They’re sweet and bready and act as a laxative.  I hate to buy expensive imported European chestnuts when I think how abundant and cheap American chestnuts and chinkapins used to be.