Well, what do you do when the house is as ready as possible and you’re sitting waiting for Matthew? Hunker in the bunker and write a blog. Putting up the hurricane shutters revealed a little native Florida, bringing forth lizards, a tree frog, a nervous zebra longwing, and a friendly wasp solo in its papery nest. Hope they all creep, buzz, and flutter to safety. Butterfly in a hurricane!? Sounds like my autobiography.
Standing tall in the face of the big blow are Bald Cypresses.
The relationship between Bald Cypress and Pond Cypress gets a word. Modern molecular studies show the two as so close genetically that most botanists treat them as varieties of the same species, as for example Flora North America.
Our blog has a pre-existing condition on the tree’s knees: CLICK FOR KNEES
Today’s question is, why is Bald Cypress deciduous? After all, we don’t have many fully leaf-dropping trees in South Florida. So why such a prominent exception?
Why do deciduous trees exist to begin with? In many warm climates having a dry season trees shed foliage when water is too limiting for photosynthetic efficiency. I used to work in Venezuela where people raking and burning leaves at the curb reminded me of October in Michigan. Where’s the cider?
Maybe the Florida dry season could have something to do with the baldness. But then again, these are trees of the wettest habitats, and only a few local trees shed in our not-that-dry winter/spring anyhow. So dodging the Florida dry season is not a gratifying explanation.
As with all evolutionary questions, it pays to look broadly in space and time. Bald Cypress once spread across much of cold North America, to be shoved into the Southeastern U.S. by glaciation. A northern origin helps explain deciduousness, given that most cold-climate trees dare to bare. Perhaps Bald Cypress brought the condition from cold beginnings as I brought my ice skates. Some of our other local deciduous trees, such as red maple and pop ash, are snowbirds as well, and interestingly swamp-dwellers likewise.
Yet writing off BC’s seasonal twig-shedding as northern baggage may not say it all. This is the alpha tree of our swamplands, and seasonal baldness seems to agree oddly with its Florida lifestyle no-matter the point of origin.
In the large world of conifers, deciduous species are unusual. They are Taxodium, its close relatives Metasequoia and Glyptostrobus (which also makes knees), and the more distantly related Larches, including Tamaracks. Maybe this leaf-droppy crew tends to have something in common to help explain such rare deciduousness in conifers which otherwise cling to their needles even in the far north. One thing the deciduous conifers have in common is prior life in ancient near-arctic wet forests.
The deciduous conifers all went through long formative periods where root function is especially challenged. And yes, I’m out on a thin speculative limb. Metasequoia is almost extinct so ignore it. The other deciduous conifers flourish far from the ancient arctic, yet all with proclivities for habitats with impaired root function. True of Bald Cypress? Absolutely: no matter how you interpret the knees, they probably have to do with horrid soils, which not only are oxygen-deprived under water but also probably not generous with nutrients, toxic, and not hospitable to symbiotic microbes.
Not documented so far as I know for Bald Cypresses, but research shows deciduous larches to have special adeptness at transforming sugars from the foliage to permanent stem wood before ditching their temporary cheap leaves.
If Taxodium arrived here from far north, has it adjusted visibly to the Southeast after arrival? Maybe that adjustment is the variety we call Pond Cypress. Pond Cypress seems to have leaves adapted especially to diminish the water loss root-challenged trees can’t afford…less flat, arranged all around the twig, and pressed more or less together around it.
So to sum up my daydream, maybe Bald Cypress came southward pre-armed to deal with root-nasty conditions, and then went a little farther by spawning even-more-self-protective Pond Cypress? Something to think about here in the cone of increasing certainty.