A Tale of Two Oaks

Trees are an integral part of our water cycle. Their roots draw down rain to replenish our aquifer and prevent soils from eroding. Their shade create cooling islands. Fall and winter are ideal times to plant trees. Our Santa Fe River, along with our member sponsors, are offering free trees through our program called Shades of Green.

If you have ever wondered about the tannic affects trees have on the river, please read on. This paper is published with the permission of the author, Ken Sulak. References to Goners and Goner-Grams are of the author’s musings to a group of fellow naturalists.

OSFR President Joanne Tremblay
joanne.tremblay@oursantaferiver.org
“Giving Our River A Voice”

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Bitter and The Sweet – The Red and The White – A Tale of Two Oaks 

Ken Sulak 

5 December 2024 – Science for the Layman 

With over 500 species, oaks represent one of the most dominant and most familiar taxons of trees in the  Northern Hemisphere. These members of the Beech family, Fagaceae, all in the genus Quercus in North  America, include 90 species. Oaks (the name from the Proto-German word ‘aiks’) range from rapid growing, rather short, and short-lived shrubs like Chapman Oak (Quercus chapmanii) to slow-growing,  majestic giants that can live hundreds of years, like the 10-ft diameter Cellon Oak, a champion Southern Live Oak (Quercus virginiana) located north of Hague in Alachua County, Florida (named in honor of noted and accomplished South Florida horticulturalist George Beauregard Cellon, 1862-1945, born in Hague). 

One California Live Oak (Quercus agrifolia), the oldest oak tree in North America, is estimated to be 1000- 2000 yrs old. Most oaks are prolific in the production of acorns, tens of thousands in a single year’s ‘mast’  of an individual Laurel Oak (Quercus laurifolia), for example. But not all oaks attain great age, and not all  are that so prolific. Oak species do not all follow similar life trajectories. 

Evolving in the middle Eocene Epoch (~50 million years ago), oaks display a range of adaptive life history  strategies. Leaving aside the aggressive shrubby oaks that rapidly colonize and monopolize dry, sandy,  abandoned pastures, two very different strategies predominate among familiar North Florida Oaks of large  stature. This GONERS-Gram is an evolutionary Tale of Two Oaks, two species with rather different life  history trajectories. To a certain degree, they exemplify two distinct species groups (what botanists call ‘Sections’ the Red Oaks (Section Verentes) with pointed leaf tips and the White Oaks (Section Lobatae) with rounded leaf lobes. This Tale is about two prominent oak species in the Southeast, the Southern Red  Oak (Quercus falcata) and the Southern Live Oak. All oaks, indeed all tree species, share one overarching  goal that has shaped their life histories – to gather as much life-giving sunlight as possible to power  photosynthesis and growth, out-competing all other neighboring trees in that regard. But just how oaks  get that accomplished varies dramatically in terms of evolutionary adaptation in the Southern Red Oak (member of the Red Oak clan) versus the Southern Live Oak (member of the White Oak clan).

The Southern Red Oak prefers high, generally dry, sandy soil, originally occurring (prior to inroads of 19^th Century European-American settlers and loggers) mainly in mixed hardwood hammocks, islands within  the vast primordial post-glacial Longleaf Pine (Pinus palustris) monoculture, a conifer wildernessstretching  from Virginia to Texas. Crowded by competing hardwoods in those hammocks and in present-day second growth forests, Red Oak seeks to claim a part of the forest canopy by growing very fast, very straight, and  tall (about 80 ft in a mature tree). Typically, only minor branching occurs for the first 30-60 ft of tree trunk, energy investment going instead to the upward quest, seeking the sun. This same strategy is employed  by Bald Cypress and Slash Pine. In this forest setting Red Oak spreads a modest crown at a height equal  to or taller than competing trees, like Southern Magnolia (Magnolia grandiflora), Sweetgum (Liquidamber  styraciflua), Pignut Hickory (Carya glabra), and Swamp Chestnut Oak (Quercus michauxii). In striking  contrast, Southern Live Oak, also with an affinity for dry, sandy soil, pursues a different strategy. It mainly  occupies areas with more open exposure to the sun, such as high river banks, the fringes of springs, and  hardwood hammock edges. If it does sprout within a woodland hammock, in close company with other  hardwoods, Live Oak can grow fairly straight and tall without branching for the first 20-30 ft. That such  tall, straight Live Oaks do exist is attested to by the thirty 40-ft long, 12×12 inch square-stock foundation  beams of the 1852 Allen Mill on the Suwannee River – each of handhewn Live Oak. More typically, Live  Oak grows in open situations, and in gnarly fashion, branches snaking out horizontally in all directions starting only 6-10 ft up from the ground, and continuing to proliferate upper branches that twist and turn,  seeking the sun, forming a low, spreading crown. This is the archetypical and picturesque Live Oak of  southern pastures, rarely exceeding half the height of a Southern Red Oak. Conversely, when a Red Oak  is out of its element, when it sprouts or is planted in an open field, it mimics somewhat the modest stature  and bushy, spreading form (but not the serpentine limbs) of a Live Oak. No need to shoot straight up tall  in the absence of competitors. 

Once a Southern Live Oak stakes out its land claim, it tolerates few interlopers on that turf. Its roots and  decaying leaves exude allelopathic phytochemicals, killing or suppressing the sprouting seeds and  seedlings of other trees. Its heavily leafed crown also shades out the seedlings of most other trees. Few  competitors can get a foothold beneath a mature live oak. While also somewhat allelopathic, Southern  Red Oak is more forgiving, with other tree species often growing in close proximity. The bark and leaves  of all oaks contain tannins, bitter, phenolic substances that latch onto amino acids and proteins – making  life difficult for insects that are intent on munching oak leaves. The brown spherical acorns of Southern  Red Oak acorns contain lots of tannin, and taste bitter and astringent. As in all red oak species, they take  two years to ripen. In contrast, the elongate chocolate-brown to black acorns of Southern Live Oak contain  much less tannin. Typical of all white oak species, they mature in one year. And, they are edible. I find  them generally bland or slightly sweet, slightly astringent when raw – better roasted – reminiscent of roasted chestnuts. Some folks prepare the acorns first in boiling water to extract the tannins. 

In addition to differing in fundamental growth form, Red Oak and White Oak leaves also differ substantially.  Like all red oaks, the Southern Red Oak has thin leaves with pointy-tipped lobes. The dull leaves vary in  size, but most are large, up to 8-9 long. Broad and deeply-divided, with either 3 or 5 primary lobes, they  also vary considerably in shape, each rather delicately sculpted. Like individual humans, individual leaves  may be very slender in the waist or rather robust.  

Extremes of variable shape in pointy, leggy Southern Red Oak leaves,  

newly fallen to the forest floor in Autumn. Shown here top side up.

What’s the point of being thin-skinned, deeply-divided, and pointy? It has to do with the deciduous habit,  a form of plant hibernation, originally an evolutionary adaptation to cold climates with short growing  seasons. Emerging from winter dormancy, the newly emergent leaves of Southern Red Oak need to swing  into action fast to crank up photosynthesis. Thin, divided leaves with lots of leaf edge offer what is termed  a high surface to volume ratio, facilitating ‘hydraulic connectivity’. Scientists like such big words. That  simply means they are more efficient at moving and losing water via transpiration, evaporation through  tiny leaf pores called stomata, prompting sap flow and nutrient delivery up the trunk and out the branches.  The slender pointed tips also provide drip-edge, good at shedding moisture, a useful capability during a  Florida summer thunder-buster. This is facilitated by the thin, flexible basal leaf stem, or petiole, allowing  the leaf to bend downward to droop and dri; when laden with rain water. 

Southern Live Oak exhibits the evolutionary counterpoint, thick-skinned, stiff, undivided, elliptical leaves  with smooth, generally untoothed edges, with a subdued, bluntish tip and a short, stiff petiole. However,  newly emergent leaves sometimes have low, wavy teeth. Leaves like those of Live Oak have a lower surface  to volume ratio as is typical of trees with evergreen foliage in North Florida. These include Southern  Magnolia, Yaupon (Ilex vomitoria), American Holly (Ilex opaca), and Carolina Laurelcherry (Prunus  caroliniana). Hardwood evergreen leaves sport a waxy, glossy cuticle, adapted to resist freezing, retard  transpiration, and retain water during dry periods. These thick tough evergreen leaves are generally dark  green, packed with green chloroplasts, engineered to enable photosynthesis to continue year-round.  Tough customers: drought – no problem; low light – no problem; occasional freeze – no problem,  withstanding storm rain – no problem either. They stand proud, no drooping – presenting as much surface  area as possible during the short days and low sun angle of winter, when sunlight is a precious commodity.  It helps that all their deciduous neighbors have kindly dropped their sun-blocking leaves. Nature is a  complex and elegant dance in time and space. 

Not much variability among the smooth-edged, stiff-rimmed, boat 

shaped, newly-fallen leaves of the Southern Live Oak. A newly emergent  

toothy leaf at top, next to a leaf of the more prevalent toothless shape  

below. Shown here bottom side up. 

Back to Southern Red Oak. Either slim and trim or plus-sized, all of its dead leaves are thin and brittle,  easily broken when the reddish-brown autumn leaves grudgingly fall to the ground, many clinging to the  branches all winter – although this deciduous tree goes fully dormant in the winter. Reluctant to admit  defeat, those worn-out leaves remind me of the valiant ‘Black Knight’, keeper of the ‘Bridge of Death‘ in  Monty Python’s ‘Holy Grail’- declaring ‘Tis but a flesh wound’ when all his arms and legs have been  chopped off by King Arthur. When they ultimately do concede defeat, those fragile Red Oak leaves  fragment and decay rapidly on the forest floor, readily releasing their great load of stream-darkening  tannins. In my months-long controlled leaf tannin leaching experiments, I found that Southern Red Oak is among the true champions of tannin production, turning transparent Floridan Aquifer spring water or  pure rainwater brown-black and opaque in just a few weeks. No wonder its acorns are seriously bitter.  Makes me wonder about the palate of acorn-loving squirrels.  

Alternatively, when it comes to it rather distinctive foliage, the Southern Live Oak is a different beast  altogether. The glossy elliptical leaves are small, 2-5 inches long, and smooth edged – unsculptured, no  lobes or divisions, and no pointy bristles. Live Oak is evergreen, does not surrender its thick, dark green  boat-shaped leaves at one fell swoop in autumn, nor does it take a multi-month hiatus from the job of  gathering solar photons to convert water, nitrogen, and oxygen into cellulose and lignin. Old leaves are  shed piecemeal throughout the year, although in North Florida there is that one week of massive shedding  in January or later, simultaneously accompanied by the flush of new leaves. You could call Live Oak semi evergreen. Regardless, fallen leaves – resistant to insect attack in life, remain tough and resilient in death,  resistant to fragmentation after many months on the ground, and reluctant to release contained tannins.  Accordingly, although large Live Oaks are the riparian guardians atop riverbanks and around springs,  dropping millions of leaves annually, they are a minor factor in the darkening of the waters.

Back to my tannin leaching experiments, it took Live Oak leachate solution a month to become tinged light yellow orange, and a full four months to become a semi-opaque reddish. This ‘Tale of Two Oaks’ would make a  better story if all species of Red Oaks where tannin leaching champions, while all species of White Oaks were tannin weaklings, The Red and The White in counter-position. Alas, evolutionary adaptation is  neither so simplistic nor so symmetrical. Turns out from my tannin leaching trials that while yet another  of the Red Oak clan species, the Water Oak (Quercus nigra) indeed nearly equals its Southern Red Oak  fellow as a tannin champ, the overall grand champion among riparian hardwoods turns out to be a White  Oak clan species, the Swamp Chestnut Oak. 

Comparative tannin-induced color and optical density of leaf leachates of eleven riparian  tree species after my four-month leaching trials in Floridan Aquifer groundwater. Optical  transparency (the inverse of optical density) is given in Lux values. The lower the Lux, the  more opaque the leachate, relative to the Lux value measured for the crystal-clear  groundwater control. Leachates with Lux values of 1-4 are intensely black.

How Southern Red Oak got so-dubbed is a matter of controversy. Some folks attribute the name to the  dull reddish-brown color of the clingy fall foliage. Others say it comes from the color of the bark, but that  does not look red to me. And still others attribute the name to the pinkish-reddish color of the sawn  lumber. That last descriptor seems like a winner since the lumber of White Oak species is whitish by  contrast, and both have been marketed by color – just like the utilitarian commercial dubbing of white  pine versus yellow pine lumber. Regardless, the difference in wood color reflects a deeper evolutionary  and structural dichotomy between the wood of Southern Red Oak versus that of Southern Live Oak, and  of Red versus White oaks in general. Linear fluid transport channels in tree trunks transport water plus  minerals up (xylem), and water plus sugars up and down (phloem). Those channels, which give wood its  grain, remain open in the trunk of Southern Red Oak, resulting in a porous grain in sawn lumber. The wood  is easy to work, with an attractive grain, and widely used to make furniture. But it is also susceptible to  decay, and does not take paint well, rendering Southern Red Oak unsuitable for outdoor uses. In contrast,  those channels become solidly filled in the tight-grained White Oaks, making the wood denser, harder,  stronger, more weather tolerant, and paint-friendly. Nonetheless, the bends and twists of Southern Live  Oak render it generally unsuitable for timber framing and siding – compared to its tall, straight northern  relative, the White Oak (Quercus alba). However, for centuries, until the advent of steel-hulled ships  during the Civil War, it was extensively employed in wooden ship construction. 

 This Tale of Two Oaks concords fairly well with overall differentiation of Red Oak Section species versus White Oak Section species in terms of life trajectories and concordant attributes. However, all oaks in  general present something of an ecological enigma, not fitting neatly into classical ecological paradigms.  For example, many plant and animal species are rather nicely accommodated by MacArthur and Wilson’s  classic 1967 paradigm, ‘r’ and ‘K’ theory. Simply stated, this theory advances two predominant alternative life strategies in nature. Thus, ‘r’ species emphasize reproduction, producing large numbers of progeny that grow fast, populate rapidly, but die young. For such prolific species, juvenile mortality of 99% is both  typical and acceptable. The few survivors grow rapidly to adulthood, usually living only long enough to  reproduce once. But they produce copious offspring. A Bull Thistle (Cirsium vulgare) is a good ‘r’-strategy  example, shooting up rapidly, living just long enough to sport a cluster of purple flower heads, each  releasing thousands of aerial parachute seeds willy-nilly to the wind, then withering soon thereafter. A  metaphor for human life as well – long in terms of Bull Thistle years, but too short upon reflection in an  old guy like me. Prompts me to insert a poem I penned a few years ago in a brief GONERS-Gram, upon  turning 76.

What Happened? – Ken Sulak 

What Happened? 

Yesterday, I was tall, straight, and strong – 

All pink-purple and green – 

And a prickly fellow at that – 

Not one to be trod upon – 

Nor bent over by the wind – 

I felt I could live forever. 

What Happened? 

Today, I am leaning sideways – 

My once-coiffed crown is all disheveled –

All my proud colors turned now to brown and white – 

Buffeted and torn apart by the slightest breeze – 

Forever did not last very long. 

What Happened? 

Seems like it only yesterday I was thirty-five – 

Looking ahead, full of bravado, devoid of care – 

Today now suddenly more than twice as old – 

Considering how little I have done – 

Buffeted and torn apart by the slightest breeze – 

Looking back more often than ahead. 

Back to the Tale as hand. ‘K’ species on the other hand emphasize growth and longevity – investing much  more in the individual, producing rather few offspring that grow slowly, mature late, and live long. We  humans are a good example of a ‘K’ selected species, predictably living to 75 years of more, some to a  century – becoming reproductive only after about 15 years, each female producing rather few offspring.  But oaks represent a paradox. Like typical ‘r’ species, oaks do indeed produce many thousands of acorns  at a time, of which few will sprout, and even fewer survive of the hundreds of thousands shed in a lifetime.  However, like a typical ‘K’ species, the individual is emphasized, sprouting up quickly, but growing slowly thereafter, maturing only after several decades. No wonder oaks have been so successful as dominant  North American trees. They have it both ways. Indeed, while oak flowers are produced in separate male  or female versions, the flowers of both sexes co-occur on the same tree. The long, stringy, trailing male  catkins are what lie thick on the forest floor in spring. Their copious pollen, together with pine pollen, is  the yellow dust coating your car. Acorns arise from the adherent and inconspicuous female flowers. 

There is one final chapter in this Tale for GONERS, the exploitation of both Red and White Oaks as hosts to gall-inducing microwasps. You may not be aware of the existence of these tiny Hymenoptera (membrane-winged insects including bees, wasps, hornets, and sawflies), the size of smallish ants. These  pudgy non-stinging gall wasps, family Cynipidae are the Lilliputians of the wasp world. There are over  1000 species of these diminutive insects which spend most of their short lives as larvae, grubs with  munching away for months or years with small galls on the thin outer branches and leaves of hundreds of  oak species. The adults generally live only a few days, just long enough to deposit eggs. Their life cycles  are very complex, involving alternating sexual and asexual generations, each using a different type of gall.  The most basic galls, like the potato gall or the gouty gall, take the form of woody swelling on thin branches.  The gall may form simply as the protective response of the oak to the female wasp using her sharp  ovipositor to insert an egg into a thin, young branch – like human skin forming a thick pad to sequester a  splinter. Other galls take the form of elaborate, specifically sized and shaped galls, often very different  from anything the oak would normally produce. My guess is that the gall wasp has somehow (viral  transfer?) stolen segments of RNA from host tree, re-inserted with the wasp egg, to fool the oak into  producing a nifty new structure to house its unwanted guest. But all of that is another story. The point  here is that Southern Live Oak is host to at least six different microwasp species, each with its own  distinctive gall type – a few are shown below. However, Southern Red Oak seems unfriendly to  microwasps, maybe due to is heavy load of bitter astringent tannin, a natural deterrent to many would-be  leaf munchers. So far, I have discovered only one type of gall on its leaves, and then only once in about  ten years of exploring thousands of fallen leaves and low branches.

A few Live Oak microwasp galls, their guest Cynipid wasps, and a microwasp grub munching away on the  pulp provided by its gall-forming host tree. Top, left to right: Live Oak pea galls ~5 mm diameter; the Live  Oak Pea Galler wasp, Belonocnema treatae, a bit bigger than a Fire Ant; unknown microwasp grub.  Bottom, left to right: Live Oak bullet galls on small branch; the Live Oak Bullet Gall microwasp, Disholcapsis quercusvirens ~4mm long. Live Oak Rosette Gall of unknown microwasp. 

What I am calling a Woodrose Gall of an unknown microwasp, firmly  

seated upon a fallen leaf of Southern Red Oak. The only microwasp gall I  

have yet discovered using this Red Oak species as its host. 

Ah, there you have it – the Tale of Two Oaks: The Bitter and The Sweet – The Red and The White – The  Reluctant Host and The Welcoming One. The tall and stately Southern Red Oak, shunned by microwasps,  versus the magnificent sprawling Southern Live Oak, a microwasp favorite. This is a tale undoubtedly  flawed and woefully incomplete, like all human enterprise. Keep in mind is my non-botanist interpretation  from field and microscope explorations, replete with my own speculations and mistakes. Apologies for a  tale more lengthy than the normal GONERS-Gram, but compensating somewhat for being rather silent for  a long spell. Writing for me is as much a learning experience, every time – as it is a sharing experience. 

Humbling as well – when you try to write, to bring what you know together, realizing then how little you  actually do know, and how much in Nature remains to be explored and understood – or perhaps left to  remain a mystery. Mystery and wonder are good things for the soul. Good sometimesjust to just immerse  in the awe of it all, and contemplate the many deep inscrutable mysteries, the unfathomable intricacy, and  the pervasive beauty of the Universe, often writ small here on our Planet Earth. 

POSTSCRIPT 

‘Natura nusquam magis quam in minimis tota sit’ ‘Nature is nowhere to be seen in greater perfection  than in the very smallest of her creations’ – Pliney the Elder: Historia Naturalis Book XI Insecta ~AD 77