Posts Tagged ‘sand laurel oak’

Squirrels and Blue Jays vs Acorn Tannins

December 12, 2020

For over 10,000 years acorns were the most important source of food for Native Americans wherever oak trees were common.  Acorns are an important source of food for animals too for everything from mice to bison.  However, acorns contain tannins, a substance difficult to digest and even toxic for some animals.  For example horses that eat too many acorns may die. Oak trees rely on animals to spread their seed, but if too much of their seed is consumed, their populations will decline.  The nutritional value in acorns attracts hungry animals, but the tannins act as a semi-deterrent.  Acorns from species in the white oak family evolved a different strategy for coping with acorn predation than species in the red oak family.  White oak acorns contain less tannins and are more palatable, so squirrels and jays prefer these and spread them throughout the landscape, but they germinate as soon as they are buried in the fall.  When a squirrel or jay tries to retrieve them later, it is too late.  White oaks only lose acorns that are consumed immediately.  Acorns from oaks in the red oak family are high in tannins, but the tannins are concentrated in the bottom half of the acorn.  Squirrels gnaw on the top half and abandon the bottom half.  If enough of the bottom half is left, the acorn can still germinate, though red oak acorns don’t need to germinate until spring because squirrels and other animals don’t want to eat the part of the acorn with such an high concentration of tannins. This year the sand laurel oaks (Quercus hemispherica), the most common oak species in my neighborhood, are producing a bumper crop of acorns, and the squirrels are gnawing the tops of them but leaving the bottoms.

Squirrels eat the tops of acorns from oak trees in the red oak family.  These acorns, found in my backyard, are from a sand laurel oak. also known as Darlington oak.  The top part of acorns have less tannins which are hard for most animals to digest.  Nevertheless, squirrels risk death from the 8 cats that live in my backyard to exploit this food source.  Oaks can germinate from acorns with the tops gnawed off.

Squirrels fed a diet of just red oak acorns in an experiment ate less.  Blue jays fed a diet of red oak acorns in an experiment actually lost weight.  Squirrels living in a location with mostly red oaks must vary their diet with other foods such as white oak acorns, nuts, fungi, berries, and insects.  Blue jays fed a diet of red oak acorns and acorn weevil larva maintained their weight, showing how blue jays can survive in the wild on a diet of mostly red oak acorns because the infestation rates of acorns by weevil larva are high.  Incidentally, oak trees were able to quickly colonize New England and southern Canada following deglaciation at the end of the Ice Age because of the acorns that were spread by blue jays.

Tannins posed an obstacle for hungry Native Americans as well.  According to Euell Gibbons, Native Americans processed the acorns by boiling them in water to leech out the tannins.  It’s necessary to periodically change the water–a tedious process.  I tried this years ago with the sand laurel oak acorns in my yard.  After dumping the water out and replacing it 8 times, I got tired of the process and gave up.  The acorns were becoming less bitter, but still not palatable enough to eat in a satisfying quantity.  Native Americans with no modern day supermarkets were most persistent from necessity.

References:

Chang-Macoubrey, A;  A.E. Hagerman, and R. L. Kirkpatrick

“Effects of Tannins on Digestion and Detoxification Activity in Gray Squirrel (Sciurus carolinensis)”

Physiological Zoology 20 (3) 1997

Johnson, W., Libby Thomas, and Curtis Adkinson

“Dietary Circumvention of Acorn Tannins by Blue Jays: Implications for Oak Demography”

Oecologia 99 (2) 1993

 

 

The Woods of Home

May 30, 2012

My home is located on the top of a fall line hill in south Richmond County.  The top of the hill resembles a plateau that stretches flat for several square miles, and it is bisected by Piney Grove Road and Hephzibah-Mcbean Road.  An ephemeral creek bounds the north end of the pleateau before the topography rises.  Mcbean Creek, a more substantial tributary of the Savannah River, borders the south end of the plateau where the elevation falls.  I hypothesize Mcbean Creek is at least 7,000 years old, originating when water tables across the south rose following the dissolution of glacial Lake Agassiz in Canada (https://markgelbart.wordpress.com/2011/01/06/temporal-correlations-between-lake-agassiz-the-okefenokee-swamp-and-ancient-flood-myths/).  Mcbean Creek may have sporadically dried up and reappeared in correlation with glacial-interglacial cycles over millions of years because this is a low lying area closer to the water table than a hill and would be likely to host a stream during wet climate phases.

This tree has the thickest trunk of any in my neighborhood.  It is a sand laurel oak (Quercus hemisphaerica) aka Darlington oak with a 4.9 foot diameter.  It’s only about 50 feet tall.  Very few trees in my neighborhood get taller than 60 feet.  The soil is poor.  Sand laurel oak  is the co-dominant tree in this part of Richmond County along with loblolly pine.  It looks almost exactly the same as laurel oak (Quercus laurifolia).  The latter has small hairs growing on the underside of the leaves.  Other than that, the only difference is habitat requirements.  Sand laurel oak requires dry sandy soils and will not grow at all in moist conditions.  Laurel oak only grows in moist soils and will not grow at all in dry sandy soils.  Fossil mastodon dung from the Aucilla River contained laurel oak twigs and acorns.

Another nice specimen of sand laurel oak almost as thick as the one in the above photo.  It is an evergreen species like the more well known live oak.

The soil in this immediate region is of poor quality and sandy.  Over 30 million years ago, south Richmond County was a sea shore, explaining the origin of all this sand.  During later dry climatic phases when streams and rivers dried up and vegetation cover was reduced, even more sand was exposed and the wind blew additional layers on top of what was already here.  Eocene age sea shells were found on the Burke County side of Mcbean Creek circa 1900, but I think that fossil locality has been obliterated by a sand mine.

The sandy soil supports nice stands of second growth forest dominated by sand laurel oak and loblolly pine.  Other common trees include southern red oak, slash pine, shortleaf pine, black cherry, sweetgum, magnolia, hickory, sassafras, American holly, and persimmon.  The undergrowth consists of Virginia creeper, greenbriar, muscadine grape,  haw, and beautyberry.  In recently cleared areas pokeweed, dog fennel, sassafras, sumac, blackberry, low bush blueberry, prickly pear cactus, and bahia grass sprout rapidly.  Several areas nearby support acres of a small blackberry of mediocre quality.  Few of the trees appear to be older than 60 years, evidence that by early in the 20th century this entire region had been completely clear cut.  The soil seems too poor to have ever been productive cropland, so I assume the land was mostly used as horse pasturage in the days when the main mode of transportation was horse and buggy.  100 years ago, the population of horses in America was much higher than it is today.

The woods behind my house.  None of the trees in this forest appear to be much more than 60 years old.  I found the trace of an old wagon road back here.  It was probably a dirt road that went through a field or horse pasture. 

I’ve often contemplated the forest compostion of my neighborhood before European colonization.  William Bartram traveled along the Savannah River when he journeyed through south Richmond County and he missed my neighborhood by at least 5 miles.  Nevertheless, I base my speculation on his descriptions of similar latitudes in Georgia.  I’ve seen no evidence that Indians ever settled directly on this plateau, but their annual fires probably spread here, and I’m sure it was part of their hunting territory. (One of the oldest pine trees on my property has burn marks on the trunk.  My house was built in 1983.  The tree is ~60-70 years old.  This suggests a fire between 30-70 years ago.) I hypothesize the 18th century forest here was an open woodland with a greater diversity of plants than is hosted here today.  South Richmond County is on the border of 2 ecotypes: oak-hickory-pine of the piedmont and longleaf pine savannah of the coastal plain.  During colonial times the plateau (a dry ridge) was likely open woods consisting of sand laurel oak, post oak, blackjack oak, and longleaf pine with lots of grass and wildflowers growing between the widely spaced trees.  Many of the trees were hundreds of years old and had large diameters.  Bamboo cane probably grew in thick impenetrable stands along the creeks that border this flat-topped hill.  While driving along Hephzibah-Mcbean Road, I’ve noticed 2 trees that may be longleaf pine, but I haven’t had a chance to measure the needles in order to make an accurate identification.  This slow growing species has been completely replaced in Richmond County by faster growing loblolly and slash pines.

Determining what the landscape looked like before the Indians settled the region is a bit more complicated.  Climate fluctuated rapidly during the Pleistocene, leading to many compositional changes.  Though sand laurel oak dominates this region now, it is near the northern periphery of its range.  During cold stadials it may have been completely absent and probably didn’t colonize the area until the Boling-Alerod interstadial, a warm spell that began 15,000 years BP.  The Last Glacial Maximum (~28,000 BP-~15,000 BP) likely saw a desertlike landscape in this area with wide open spaces consisting of clumps of grass, bare soil, scrub oak thickets, and scattered pine forests.  The abundant prickly pear still present here may be a relic from this climatic phase.  Warmer and wetter interstadials probably saw a greater influx of oaks and hickories and a temporary return to forested conditions.

I often wonder what was the exact final date that a species of extinct megafauna last crossed withing a square mile of where my home now stands.  Two studies have concluded that megafauna populations began to decline as early as ~15,000 BP (https://markgelbart.wordpress.com/2010/05/13/2-concentration-of-dung-fungus-sporessignificant-megafauna-populations/).  All terminal dates on megafauna fossils fall between ~13,500 BP-~12,000 BP in calender years.  I’m convinced some species lasted somewhat longer than this, but the overall populations were reduced enough so that the final remnant populations don’t show up in the fossil record.  Occasionally, carbon dates of megafauna come back reading younger than these widely accepted terminal dates, but these are always dismissed as being contaminated samples.  That may be the case for some of them, but I wouldn’t be surprised if megafauna populations did linger in scattered locations long past the accepted terminal dates of extinction.  In any case my curiosity burns over when the last time a mammoth or a saber-tooth or a long-nosed peccary crossed what is now my neighborhood.  Was it 15,000 years ago? 12,000 years ago?  9,387 years ago?

Today, the only wild native megafauna to inhabit my neighborhood is the white tail deer which I frequently see directly or indirectly (tracks).  I’ve seen coyotes, a bobcat, gray foxes, opposums, raccoons, armadilloes (only as road kill), cottontail rabbits, and lots and lots of gray squirrels.  The avifauna nesting on my property includes chimney swifts, mockingbirds, cardinals, eastern kingbirds, and tufted titmice.  Mourning doves, crows, blue jays, brown thrashers, bluebirds, chipping sparrows, robins, pileated woodpeckers, flickers, red-headed woodpeckers, downy woodpeckers, and quail are all either common residents or occasionals.  Turkey vultures, black vultures, red-shouldered hawks, marsh hawks, Mississippi kites, barrred owls, and screech owls are the meat-eating birds that have inhabited my neighborhood recently.  A wood stork passing through is the only rare bird I’ve ever seen here.  Cattle egrets are the most recent edition to my neighborhood bird checklist.  Two weeks ago, I saw them foraging in a field around the corner from my house.

Of snakes I’ve seen timber rattlers, corn, gray rat, eastern king, black racers, and hog-nosed.  Anole lizards, thirteen-lined skinks, and little sand skinks make up the lizard population.  Box turtles occasionally march by, and I’ve even seen quite large chicken cooters and snapping turtles far from water.  Toads, bullfrogs (found in our septic tank and toilets), and green tree frogs represent the amphibians.

Look What the Cat Dragged In

A former boss once used that expression when I showed up for work one day.  What a jerk.  He was a dumb jock redneck with a reputation for cheating on his wife.  I think I’m a more substantial man than any of the following creatures my cats have murdered.  The victims of house cat predation represent a good account of the small animals that live in my yard.

A baby possum.  The cat broke its neck but didn’t eat it.  Lucky thing…possums carry trichinosis.

Eastern mole.  A common victim of the murderous cats.

Short-tailed shrew.  The most common small animal killed by the local cats.

Remember a month or two ago when I wrote a blog entry about the cedar waxwings flocking to my yard.  One of the poor birds went after some low-hanging holly berries.  The berries just happened to be growing in a spot where the cat rested and napped.  The bird must have flown right into the cat’s paws.  Cardinals and brown thrashers also frequently fall victim to the cats.

Other victims of my cats that I haven’t been able to take a photo of include a star-nosed mole, 2 house mice, baby rabbits, baby rat snakes, anole lizards, skinks, green tree frogs, and large insects.  A semi-feral cat that formerly inhabited the woods behind my house was able to kill full grown squirrels.  Noticeably absent are native field mice (Peromyscus sp.).  I haven’t ever seen a single one nor any signs of any in my yard.  Hmm?  Augusta, Georgia is not officially within the range of the star-nosed mole, but my cats prove the range map is wrong.

Supposed range of the star-nosed mole.  Scientists need to expand it to include south Richmond County.  My cats killed 1  a few years back.  However, for that 1 star-nosed mole, they’ve killed at least 10 eastern moles which must be far more common.

Lone Ranger and Hissy Fit.  They kill a lot of small creatures.  Lone Ranger got so sick last week, I was sure she was going to die, but she’s better now. She’s a slutty runt.  She mated with her own brother.