JARS v38n2 - The Native Habitat of Chapman's Rhododendron

The Native Habitat of Chapman's Rhododendron
Robert W. Simons, Gainesville, FL
Reprinted from Indiana Chapter Newsletter

The early Spanish explorers described Florida as a land of flowers - hence the name. It was a dramatic land, with most of the uplands covered with a vast forest of longleaf pines, and the lowlands supporting either forests of huge bald-cypress trees mixed with hardwoods, or open marshes and grassy "prairies". The most obvious and spectacular force that shaped the ecology of both the long-leaf pine forests and the prairies was fire. Wildfires swept across large areas of the southeastern coastal plain of North America every year, burning any particular acre of longleaf pine forest on an average of probably about once every two years. These fires were frequent enough so that there was not enough fuel buildup to support really disastrous fires. Thus, the pines, with their insulating bark, survived. However, most other trees were eliminated, allowing sufficient sunlight and freedom from competition so that a great diversity and abundance of wild-flowers could grow.

Some species of shrubs are also adapted to these conditions, which have existed for at least several million years. With the exception of saw-palmetto, which loses only its leaves to the fires, all of these shrubs survive by sprouting back vigorously after being killed to the ground by each fire.

One of the least common of these vigorously sprouting shrubs is Chapman's rhododendron, Rhododendron chapmanii , a rare plant endemic to three small areas in North Florida. The main reason it is so rare is that it is very narrowly and inflexibly adapted to a very specific and uncommon habitat. Not only does it always grow beneath longleaf pine, Pinus palustris (or where longleaf pine used to grow), but it always grows adjacent to a bog dominated by Cliftonia monophylla (titi) on sands with abundant organic matter that are well drained at the surface, permanently saturated with soft, acid water just below the surface, and yet never subject to flooding.

Very few places have the extremely constant water table required by R. chapmanii , and most of those that do support dense stands of hardwood trees or large shrubs that would shade out the rhododendron. It currently grows on only about 400 acres of habitat. There is a small spot of less than one acre on the northern Florida peninsula at Camp Blanding. The rest is about evenly divided between two locations in the middle panhandle of Florida. The panhandle locations are not single, continuous populations, but, rather, are scattered populations at about 18 different sites.

The total population of Rhododendron chapmanii in the wild is about three thousand plants. One very favorable ten acre site contains about two thousand of these (very rough estimate). The remaining one thousand plants are scattered about in groups of 6 to 200 at the other 17 sites. There is a possibility that not all the sites have been found, but it is very doubtful that the wild population is more than double that reported.

Chapman's rhododendron grows in association with several other shrubs, none of which get much over head high at their largest. This is due, in some cases, to the combination of fire and the dwarfing effect of the nutrient poor soils. Examples of this are the small size of the Quercus geminata (sand live oak), Quercus myrtifolia (myrtle oak), Cyrilla racimiflora (white titi), Lyonia ferruginea (crooked-wood), and Myrica cerifera (wax myrtle). Others, including R. chapmanii , are normally less than six feet tall, such as Serenoa repens (saw palmetto), Quercus pumila (runner oak), Ilex glabra (gallberry), Lyonia lucida (fetterbush), and Leucothoe racimosa (stagger bush). The rest are very small shrubs that rarely get over one foot tall, such as Vaccinium myrsinites (dwarf blueberry), Gaylussacia dumosa (dwarf huckleberry), Kalmia hirsuta (dwarf laurel), Quercus minima (dwarf live oak), and Hypericum microsepala (a dwarf St. John's wort).

Plants that are always present and common to abundant in association with R. chapmanii are: Pinus palustris (historically), Serenoa repens , Ilex glabra , Quercus geminata , Lyonia ferruginea , Vaccinium myrsinites , Aristida stricta (wire grass), and Pteridium aquilinum (bracken fern). Three others always present, but uncommon, are Osmanthus americanus (wild olive), Quercus myrtifolia , and Ilex coriacea (big gallberry).

When in bloom for a two week period around April first, Chapman's rhododendron is by far the most strikingly beautiful shrub in this association. Its pale to bright pink flowers are produced in abundance every spring, and sometimes there is a second blooming of a few flowers in November. When not in bloom, R. chapmanii is quite inconspicuous. Its 1½ inch long, obovate, evergreen leaves and irregular shape composed of a few stiff, upright stems blends in well with the surrounding evergreen oaks and ericaceous shrubs.

Unfortunately, its pretty flowers have gotten it into some trouble in the past. Nurserymen and others have dug many plants from the wild, and, in some cases, such as at Camp Blanding, have severely reduced the wild population.

Of far greater impact, however, is the threat of habitat destruction. Most of the habitat and population at Camp Blanding was destroyed by engineering work during World War Two. At least two other sites of over 100 plants each have been totally destroyed in the panhandle - one by a landfill and the other by land clearing. Various other sites have been partially destroyed by a wide range of human endeavors. Hopefully, this sort of massive destruction is a thing of the past. With its status as a federally listed endangered species, R. chapmanii has gained a lot of recognition and support. The people who manage the lands where it grows are aware of its importance and are doing what they can to protect it.

The most serious remaining threat is probably the drainage of wetlands in the areas where it grows. Chapman's rhododendron is so narrowly adapted with respect to soil water conditions, that any change is likely to be detrimental. A second continuing threat is the likelihood that fire will not occur frequently enough to prevent some of the oaks and larger shrubs from shading out R. chapmanii . Although the ideal burning cycle would probably be every two to four years, the recommended schedule in the U.S. Fish and Wildlife Service Recovery Plan is every five years, and current practice is probably closer to every ten years or longer.

However, with all its problems, Chapman's rhododendron is not in immediate danger of extinction. It is currently being protected and managed well enough so that it can continue to exist in the wild far into the future, though perhaps in declining numbers. If the more important recommendations of the recently published Recovery Plan are implemented, it should do even better, perhaps even gradually increasing in numbers.

Finally, one of the encouraging qualities of R. chapmanii is its enormous reproductive potential. Although currently the species does not reproduce from seed in the wild very well, if at all, each wild plant growing in sufficient sunlight produces literally thousands of viable seed each year. With proper techniques (using ground sphagnum as a seed bed and growing the plants in well aerated and very well drained acid soil), it is possible to grow thousands of plants each year for either re-establishing wild populations or producing plants for commercial sale. The latter possibility has been going on for some time, and high quality seedlings are available for shipment from the following nurseries:

Salter Tree Farm, Madison, Fla. 32340

Steven Riefler, Chipley, Fla. 32428

Robert W. Simons, Gainesville, FL

Bibliography
Chapman, A.W. 1860. Flora of the Southern United States, Ivison, Pinney and Co., New York. 621 pp.

Duncan, W.H. and T.M. Pullen. 1962. Lepidote Rhododendrons of the Southeastern United States. Brittonia 14:290-298.

Folkerts, G.W. 1982. The Gulf Coast pitcher plant bogs. American Scientist. Vol. 70, No 3:260-267.

Godfrey, R.K. 1979. Chapman's Rhododendron, pp 57-58 in: D.B. Ward (ed.). Rare and Endangered Biota of Florida, Plants, Vol. 5. University of Florida Press, Gainesville.

Simons, R.W. 1983. Recovery Plan for Chapman's Rhododendron, Rhododendron chapmanii A. Gray. U.S. Fish and Wildlife Service, Atlanta, Ga. 41 pp.

Small, J.K. 1933. Manual of the Southeastern Flora. University of North Carolina Press, Chapel Hill. Reprint. 1554 pp.

Totten, H.R. 1944. A station for Rhododendron chapmanii in eastern Florida. Proc. Florida Acad. Sci., Vol. 7, Nos. 2-3.