Trees of the Lower Suwannee Region: A Natural History

Part III. Southern Live Oak – A Competitor

Florida’s lower Suwannee River and Cedar Keys region, including extensive conservation lands and 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 third installment, focuses on southern live oak. Some of the information in this post may repeat or overlap with last November’s post about the 17 species of oaks occurring in our neighborhood. That post can be found here.

Southern Live Oak (Quercus virginiana) is best known to people as the huge spreading trees often seen widely spaced in open fields throughout the southeast. Also memorable are the often-gigantic specimens seen along streets in the historic districts of southern cities and towns. This indeed is its common habit when grown in full sun, but southern live oak also occurs as a true forest species. When it occurs in forested surroundings it is often more erect, still branching, but reaching toward the forest canopy. Sometimes these trees might not be seen at all if it were not for the huge branches arching upward. So, even though the iconic image of the spreading, moss-draped oak that appears on our tee shirts represents a southern live oak, the image shown is unlikely to be often mirrored in the natural habitats of the refuges.

 

Live Oak Geography. Occurring throughout Florida and the lower southeastern coastal plain, southern life oaks also are widely distributed in south-central Texas, with outlier distributions in Oklahoma, northern Mexico, and western Cuba. They are absent from the extensive marshlands of southern Louisiana and much of the lower Mississippi Valley.

Southern live oak is moderately shade tolerant, and it shares dominance in certain climax communities with southern magnolia (Magnolia grandiflora); more about magnolia later and what it means to be a climax forest in this part of Florida. Southern live oak is long-lived, persistent in forest canopies, and slow to reproduce. These qualities relate in part to its shade tolerance, but other adaptations are at work.

Epiphytes on a Live Oak Branch. Like most live oaks this tree near the Dennis Creek trailhead on the Lower Suwannee National Wildlife Refuge's Shell Mound unit harbors epiphytes on its often horizontal branches. Epiphytes in this image are resurrection fern (Pleopeltis polypodioides) and Spanish moss (Tillandsia usneoides). Southern live oaks are almost always festooned with Spanish moss and it is difficult to envision one lacking heavy loads of moss. Unlike parasites, epiphytes do not take nutrition from trees, and their presence is almost negligible to their host trees.

Many species of oaks are adapted to withstand fire and have developed extraordinarily thick bark, the ability to sprout readily after a top kill and, like southern live oak's relative dwarf live oak (Q. minima), the strategy of keeping much of their living biomass beneath the ground surface. Q. virginiana is not particularly invested in any of these strategies but nevertheless is relatively resistant to fire. The trees normally occur in areas with ample soil moisture that are not particularly prone to wildfires. Also, their wide spreading habit and thick leaf cover cast shade that inhibits undergrowth that might carry fire. Its leaves, including shed leaves, are not highly combustible. And while moderate fires might reach low-hanging branches, they would be less likely to reach and damage the trunk, with its critical connection to the roots.

Owing to its extraordinary strength the wood of live oaks was much valued in the construction of wooden ships. Live oak planking became legendary during the Revolutionary War when “Old Ironsides”—the USS Constitution—was reported to repel British cannonballs. Another use of live oak in ship building involved employing bent limbs as pre-formed internal braces after these extra strong pieces were milled down to fit. In the age of wooden warships live oak trees were considered strategic materials and were provided with governmental protection.

 

Live oak along the Lower Suwannee refuge's Nature Drive. Along portions of the southern half of the Nature Drive old live oak trees arch over the roadway.

One place on the Lower Suwannee refuge to see some impressive specimens of southern life oak is on the southern half of the Nature Drive, beginning at the junction of the drive with Cabin Road and continuing to the Barnett Creek Road. Massive old live oaks in some places arch completely over the road. This part of the road traverses mesic (wet) areas and in some places comes quite close to tidewater. Along some of this stretch occasional damage from storm surges accompanying hurricanes is likely. Construction of the road, probably in the early twentieth century, disrupted the normal hydrology, resulting in roadside ditches and possible drying of nearby areas. Other kinds of disturbance may have occurred, but the oaks have persisted. They appear not to have been heavily logged, and most commercial logging done locally focused on pines in the uplands and cypresses in the river bottoms.

Another species of oak in our area is the closely related sand live oak (Q. geminata). Even more restricted to the southeastern coastal plain, this species is generally smaller and more adapted to drought. Some authorities, including the U.S. Forest Service consider Q. geminata to be a subspecies of Q. virginiana, but this seems doubtful as the two often occur side by side throughout our area. Conceivably the two species might hybridize, but they rarely do so because southern live oak flowers earlier than sand live oak. Sand live oaks can become quite large in favorable conditions, and those in the wetter Gainesville area vie with southern live oaks in size.

 

Sand Live Oaks on the Tram Ridge Trail. These trees, near the northeastern end of the namesake tram ridge are sand live oaks. Their presence here is due to the dry, sandy nature of the soil. Although most often occurring as “scrub oaks,” in suitable conditions individual sand live oaks can attain large size. Although relatively small, those in this image have assumed a growth habit similar to southern live oaks grown in the open.

Comparison of the Leaves of Southern Live Oak and Sand Live Oak. The cluster of leaves at the left of the image is from southern live oak and that on the right is from sand live oak. Southern live oak leaves are relatively flat and wide, as opposed to the narrower, recurved (curled downward on the long axis and curled under on the short axis) leaves of sand live oak. The dual curvatures create a cup-like hollow on the undersides of leaves, creating a dead air space that traps humidity and helps to prevent water loss. The undersides of leaves of both species, seen in the turned over leaves nearest the three o’clock position in each cluster, differ in that southern live oak leaves are pale green, not too much different from the upper leaf surfaces. The undersides of sand live oak leaves are whitish, due to the presence of tiny hair-like projections that also retard moisture loss due to evaporation. The sand live oak leaves shown are from the Gainesville area; leaves of trees on sand ridges in coastal regions are often much narrower.

A third species of live oak, the already mentioned dwarf live oak (Q. minima) also occurs locally but is far different in its appearance and ecology from the other two. Not a tree in the normal sense, Q. minima has tiny above ground parts, usually less than a foot tall, and it occurs as a ground cover in fire-maintained flatwoods habitats.

Sand ridges throughout the Lower Suwannee refuge and coastal islands support scrubby oaks, many of which are sand live oak. They are often joined by myrtle oak (Q. myrifolia), also a small to medium size tree. Where fires are frequent, both may occur as shrubby thickets, in extreme instances producing so-called clone domes. A third oak, Chapman’s oak (Q. chapmani) is frequently present also. Although often a small tree, Chapman’s oak is more often shrub like. These three oaks are adapted to dry conditions and on the refuge may seen along State Road 247 in high spots where the road undulates over a series of old sand dune. Others are visible along the headquarters entrance road just beyond the bat house.

 

Southern live oaks, sand live oaks, and dwarf live oaks may occur in relatively close proximity, occupying often nearby sites that differ in available moisture and frequency and intensity of fires. Southern live oak requires relatively mesic conditions that are not subject to frequent, hot fires. Sand live oaks are most common in drier sites with occasional hot fires that may damage or destroy all above-ground parts. Dwarf live oak commonly occurs in flatwoods sites that are subject to frequent low-intensity fires.