Today John and I haunted Jonathan Dickinson State Park, near Hobe Sound Florida, finding the flora abloom, at least in marshy meadows, nature’s garden complete with blooming butterworts, orchids, meadowbeauties, milkworts, sundews, tillandsias, and too much splendor to portray with a list.
The practical mission is John’s serial long-term photo record of “what happens after a burn.”
The blaze was about a year ago, and by now the scorched earth lies under fresh green oak boughs. Oaks resprouted “from scratch” in a year? Well yes, about a foot tall with no ambition to rise higher. These are dwarf live oak, Quercus minima, resurrecting to new life from fireproof subterranean rhizomes.
Are dwarf live oaks tiny representatives of the big live oaks (Q. virginiana) shade trees festooned with Spanish moss across the South? Almost. Harvard University botany demigod Charles Sprague Sargent long ago perceptively classified both as extremes of a single species.
The same question extends to a second locally abundant small oak plausibly interpretable as a variant of big Quercus virginiana. This is sand live oak, Quercus geminata. With variation, it is most often a shrub or smalli tree intermediate in size between big virginiana and little minima.
What is the relationship among the three? Molecular data can settle kinship, whether for Maury Povich or for curious botanists. A useful DNA-centered study for today’s tree trio shows live oak, sand live oak, and dwarf live oak together to comprise one exclusive branch on the oak evolutionary tree. The three are most closely related to each other than any is to any other oak. In short, it would be “legit” to see three varieties of one variable species, or alternatively as three sister species, the latter interpretation prevailing nowadays.
There is a compelling case for giving each its own species designation. Chevrolet and Buick are varieties of GM yet have their own “species” identities. Our three live oaks have diverged from a common origin over time into fairly distinct identities. Oaks are famous for hybridizing, yet live oak, sand live oak, and dwarf live oak, all living intermixed, seem to have evolved barriers to criss-crossing, although Q. geminata and Q. minima can form a rare hybrid called Q. succulenta. More prevalent is hybridization by each with distant cousins outside the trio.
The DNA study mentioned above is the 2015 work of botanist Jeannine Cavender-Bares and collaborators. They noted how our three live oaks diverge most saliently along lines of response to fire: Q. virginiana massive, long-lived, sturdy, and intolerant of fire; sand live oak mid-sized with grudging ability to regrow after fire; and dwarf live oak dependent on fire. Maybe it is all about diversification into habitats with different fire patterns.
All that said, there is an asterisk. Quercus virginiana seedlings make a thick underground tuber before the tree grows into a mighty oak for 500 years. Should the baby seedling be grazed, burned, or flooded it can resprout from its tuber for a second chance. Could Quercus minima be sort of an “infantilized” live oak that remains small and took that original fireproof temporary “tuber” from its ancestor and expanded upon it?
Dwarf live oak has an odd foliar feature. The earliest leaves on a branch have lobed toothy margins. As the branch elongates, however, the younger leaves develop toothless.
Why make a transition like that? Here is a speculation. I think teeth and lobes on leaf margins help dissipate heat. Maybe when the twigs are young and close to the sun-baked Florida sand below the cooling wind, where fire burned away all shade, perhaps the leaves need to shed heat. Later, as the branches rise into the breeze, and as overhead shade increases during fire recovery, the overheating problem diminishes, making the lobed heat-shedding leaves obsolete. Only a guess.