Trees of the Lower Suwannee Region: A Natural History

Part II. Bald-Cypress - A Flood Specialist

Florida’s lower Suwannee River and Cedar Keys region, including two outstanding National Wildlife Refuges, boasts more species of trees—as many as 130—than all but a few places in North America. Some of our trees are widely distributed in eastern North America, some are restricted to the southeastern coastal plain, and others reach their greatest prominence locally. A few years ago, our Friends of the Lower Suwannee and Cedar Keys National Wildlife Refuges organization designed a tee-shirt featuring six iconic species of trees occurring on the refuges. Our series of blog posts will begin by considering each of these six species. This, the second installment, focuses on bald-cypress.

Bald-cypress (Taxodium distichum) is emblematic of southern swamps and one of the most important trees on the Lower Suwannee National Wildlife Refuge, especially along the banks of the Suwannee River. Large and long-lived, cypresses are much treasured for their majestic appearance and the commercial value of their wood. Impressive as they are, today’s trees are scarcely more than a century old and likely pale in comparison to those harvested earlier, which may have lived upward of 1,000 years.

 

Distribution of Bald-cypress. Ranging throughout Florida and the southeastern coastal plain, the species is also widespread in the Mississippi River valley as far north as the Ohio River and into eastern and south-central Texas. In the east it extends northward to the Delmarva peninsula.

Bald-cypresses occur in floodplains and seepage swamps and even manmade ditches throughout their southeastern range. Although pegged here as “a flood specialist,” a less memorable but more apt descriptor might be “a saturated soil specialist.” Best known for tolerance of flooding, bald-cypresses are intolerant of shade and prolonged drought. Usually draped in wispy Spanish moss (Tillansia usneoides) these trees are emblematic of southern wetlands. Where one finds bald-cypress also likely nearby are tupelo trees (Nyssa species), American alligators (Alligator mississipiensis), cottonmouth moccasins (Agkistrodon pisicvorus), several kinds of turtles, formerly Ivory-billed woodpeckers (Campephilus principalis), and other plants and animals of the warm, moist lands of the American south. Bald-cypresses are usually a dominant, either forming dense uniform stands or standing above broad-leaved species of trees that share its habitats. 

Cypresses on the Suwannee. The cypress trees in this scene from the Suwannee River are taller than the broad-leaved trees with which they share the floodplain and those growing near the river channel are effectively protected from being shaded out by their neighbors.

Widely recognized features of bald-cypresses include the buttressed bases of their trunks The idea that the buttresses serve as props that help to keep the tall, top-heavy trees from falling over is obviously false—the expanded bases of these huge trees would be clearly insufficient to keep them balanced upright. However, the buttresses are above-ground extensions of long lateral roots that anchor the trunks and keep trees from falling over even in hurricane force winds. They also may protect the trees from becoming girdled. Their shape could protect the bark and cambium from being completely stripped by beavers. Absent abundant beavers, as in much of Florida, buttresses could perform a similar function in protecting the cambium of trees from abrasion by flotsam carried by floodwaters. 

Basin Swamp. This image along the River Trail on the Lower Suwannee refuge shows a basin swamp—one not inundated by the river and its twice daily tides. Note the presence of cypress knees and the fact that the cypresses, distinguished by their buttressed bases and straight smoothed-barked trunks are generally larger and straighter than the other trees occurring with them.

The function of cypress knees has occasioned much speculation. The knees arise from roots and may provide the roots with oxygen, which is scarce in the saturated soils of swamps. However, in studies removal knees had no discernible effects of tree growth or survival. Knees do produce their own networks of roots and may serve to add stability to the root system. Or they may function much as proposed for buttresses by intercepting debris carried by floods and keeping it from abrading the bark of the main trunk. The height of cypress knees appears to correlate closely with the average height of floodwaters where they are located, and this could support either the oxygen protection of bark ideas.

Germination of seeds and establishment of seedlings does not occur in standing water, and young trees cannot survive prolonged immersion. Therefore, successful reproduction may not occur every year. Given the longevity of adult trees, however, frequent production of young trees is usually unnecessary. 

Lightning Struck Cypress. This cypress on bank of the Suwannee River near Vista was long ago damaged by a lightning strike. Larger than its neighbors, it was likely passed over by loggers early in the twentieth century because its wood had little value. This image was made in early November when the cypress leaves had turned brown and were beginning to be shed.

Bald-cypress trees can become dominant even though intolerant of shade and prolonged drought. Tolerance of flooding seems to be of critical importance. Some trees that occur with them are likewise tolerant of flooding and also tolerant of shade. Bald-cypresses employ several strategies to overcome their intolerance of shade. They grow faster than potential competitors, become taller and rely upon their superior stature to avoid shading by other trees. They often grow in places where they are unlikely to be shaded out, as on the edges of river channels. They are long lived and do not rely on lavish reproduction for persistence—successful reproduction may await the development of openings in the forest. Bald-cypresses typically grow to a height of more than 100 feet and may live for many centuries. And saplings may grow slowly in the shade of other trees and wait for openings in the forest canopy upon which they grow rapidly to fill the openings.

Although needle-leafed conifers, unlike many of their relatives our cypresses are not evergreen. Kinds of trees that lose all their leaves annually are able to avoid loss of water during times when photosynthesis is negligible. And leaf loss makes trees less vulnerable to toppling in heavy winds.

The large size of bald-cypresses and their tall, straight trunks make them valuable sources of lumber. Light and easily worked, cypress wood is impregnated with resins and resistant to rot. These resins likely ward off insect pests and fungi in the xylem of living trees. Most marketable bald-cypress trees on what is now the Lower Suwannee refuge were logged by the early twentieth century. 

Old Cypress Stump. Owing to its impregnation with resins, cypress wood is slow to decompose, and this stump seen along the refuge’s River Trail is probably more than 100 years old. Elsewhere on the refuge stumps of cypress trees that were uprooted by road construction persist after many decades.

Resistant to decomposition, stumps from these long-dead trees are still in evidence, such as from the refuge’s Suwannee River Trail. Also, a smattering of older trees on what is now the refuge were never cut because they were unmarketable. The trunk of one such deformed tree can be seen from a boardwalk on the River Trail in the winter when most trees have lost their leaves. Another large tree, which was clearly damaged by a lightning strike is visible along the south shore of the river just downstream from Vista. 

Wetland in Flatwoods. This small wetland next to the Lower Suwannee refuge’s Tram Ridge Trail is part of a network of patchy depressions in pine flatwoods. dominated by small pond-cypresses and few other trees.

A close relative of bald-cypress is pond-cypress (Taxodium ascendens). Generally smaller than bald-cypress, pond-cypresses occur in standing water, unlike bald-cypresses, which are more often found in places with flowing water. Some botanists consider both trees to be varieties of a single species. Following the lead of the Atlas of Florida Vascular Plants, the two are here considered as separate species. They differ in several respects beyond size, the most notable being the leaves which in T. distichum are spread laterally whereas in T. ascendens they form erect bunches. Cypress trees on the Lower Suwannee refuge that occur in shallow depressions and roadside ditches throughout the pine dominated upland flatwoods are mostly pond-cypress. 

Comparison of Bald-cypress and Pond-cypress Foliage. Bald-cypress foliage is shown in the upper image, which also shows a maturing cone. The lower image made on the Dixie County side of the Lower Suwannee refuge, shows pond-cypress foliage.