Preservation of Species: an Alternative Method

Anne S. Bradburn

The Crosby Arboretum
1986 Ridge Road, Picayune, Mississippi, U.S.A.


With its system of seven natural areas in the Pearl River drainage basin, Mississippi, United States of America, the Crosby Arboretum preserves not only individual species but entire plant communities. The program and management methods are described.


For this group, it is certainly not necessary to review the history of botanic gardens and arboreta. Suffice it to say that from the very first botanic garden, be it Padua or Pisa, botanic gardens and arboreta have served as collections of exotic plants; first assembled for their medicinal values, and since the great age of exploration in the 19th century, as collections displaying unusual and exotic specimens, the more unusual the better.

Creating a garden using only native plants would have been thought absurd.

Indeed, when the Crosby Arboretum was conceived a brief 12 years ago, the notion of using only native plants was still thought by many to be absurd. But that is what we have done....create an arboretum using only native plants in natural settings. This is a particularly challenging task in the Piney Woods of south Mississippi where the flora lacks spectacular beauty such as is found, for instance, in the rain forests here in Brazil.

The Crosby Arboretum was and is dedicated to the preservation, and display of the flora of the Pearl River drainage basin. In so doing, we preserve and protect NOT individual species but groups of species, entire plant communities which also, and not incidentally, maintains the dependent animal populations.

It quickly became apparent that on the original 64 acre Arboretum site, it would be impossible to display the wide range of habitats necessary to achieve our goals. So with the help of Dr. Sidney McDaniel, botanist of Mississippi State University, an initial series of natural areas was chosen, each representing a floristically different ecosystem found in the Pearl River drainage basin. It is this system of natural areas which makes us unique. For although there are an increasing number of botanic gardens and arboreta who now display native plants, and some are reconstructing natural vegetation types, none have had these combined as their sole mission. We were indeed glad to find one session of this Congress devoted to preservation in situ.

The geographical extent of the Arboretum

The Crosby Arboretum currently manages eight discontiguous areas in the lower Pearl River Basin. With time, additional sites will be added.

Because what we do is so dependent on where we are, a bit of geography is perhaps in order. The Pearl River runs roughly parallel to the Mississippi River and drains an area of approximately 16 000 square miles, or an area larger than Belgium or the Netherlands, slightly smaller than Costa Rica, and almost the same size as the Brazilian state of Rio de Janeiro. The climate is generally uniform and can be called temperate to sub-tropical. Annual rainfall averages 60 inches, with heaviest rains in the late spring to summer months. Torrential rains and strong winds, often with drastic effects upon vegetation, accompany the occasional hurricane which comes on shore. Frosts may occur from November until late March, but winters are generally quite mild with only rare snow falls.

The major natural plant communities of the Pearl River Basin in Mississippi and Louisiana are quite varied and have developed primarily as the result of distinct fire and moisture regimes.

The Gulf Coast Plain of the United States is best known as "the Piney Woods", but Beech-Magnolia, Cypress-Tupelo Swamp, Bottomland Hardwood, Titi Forest, Seepage Bogs, as well as Pine Savannas are vegetation types found within the region, and thus also are represented in Crosby Arboretum Natural Areas. Each of these ecosystems requires its own maintenance program. In today's world with its increasing pressures from population and consequent development, natural areas are NOT maintained by simply doing nothing!

Management policy

Today, I would like to briefly outline the management policies for four of the Arboretum properties: Talowah, Steep Hollow, and Hillside Bog Natural Areas, and then discuss restorations underway at Pinecote, our interpretative center.

First each area was mapped. Ground-level brass markers were used to define boundaries. Second, a complete plant inventory was made for each area. Later a permanent plot, 100 x 100 feet, was laid out on each Natural Area. The plot position was selected as best representing the natural vegetation of the Area. These plots were also delineated by brass ground-level corner markers. Plants within each permanent plot were identified and mapped in 10 foot linear sections. These spacial relationships have been replicated in the development of our interpretive center at Pinecote. I should perhaps say here that visitation to all natural areas is strictly regulated.

Fire management

First and foremost the Piney Woods result from fire. Historically, and pre-historically, pine forests of the southeastern United States were subjected to lightning-instigated fires. These naturally occurring fires came at irregular intervals, estimated as often as five out of every ten years. Unobstructed by contemporary roads or other man-made barriers, fires swept across thousands of acres of the Coastal Plain. Fire is therefore our most important management tool.

At Talowah, we maintain 200 acres of long-leaf pine forest. The species, the majestic Pinus palustris Miller, actually requires fire. Called appropriately the grass stage, these trees remain as small seedlings, while developing exceptionally strong root systems. Once touched by fire, individuals grow rapidly producing the long-lived tree which once covered much of the northern shores of the Gulf of Mexico.

South Mississippi was deforested in the first three decades of the twentieth century, and has now become alternately either a monoculture of slash pine or of loblolly pine. These species of trees do not require fire and rapidly reach sizes suitable for the pulp industry. Talowah represents the oldest standing long-leaf pine forest in Mississippi, and with our management program we hope to demonstrate to local foresters that it is possible to maintain a natural long-leaf forest and make some profit on the timber. To do this, we have initiated a policy of growing-season burning along with selective harvesting. Usual forestry practice calls for burning in the winter, thus selecting for pine, the money crop. Periodic growing-season burns create this open park-like appearance, releases the accompanying and also fire-dependent rich herbaceous flora, and suppresses the development of woody shrubby vegetation, thus maintaining the natural long-leaf ecosystem.


The stability of the Talowah long-leaf forest is directly related to what happens to the surrounding lands. So education is an important part of our maintenance programs. We have been able to convince the owners of about 3000 thousand acres of land abutting Talowah to replant their acreages in long-leaf pine.

Controlled access

Another major problem in maintaining natural areas, at least in the southern United States, is trash and garbage dumping. At Talowah, we have installed large gates across all entry points which correspond with fire breaks and have allowed unrestricted vehicular access. These physical barriers, along with continuing educational programs, have at least for now stopped the dumping.

Rare species diversity

We have identified 194 species at Talowah, including a rare grass, Sorghastrum apalachicolensis Hall, known only from the state of Florida where it was first described, Talowah, and another of our natural areas, Steep Hollow.

Steep Hollow is the newest member of the Crosby Arboretum Natural Area System, and one of the more interesting. It was established to protect the rare bog spicebush Lindera subcoriacea Wofford. Both male and female individuals are present here, and abundant fruit has been produced. Steep Hollow also contains bog flax, Linum macrocarpum C.M. Rogers, previously thought to be extinct. This species is only known from this site in Mississippi and two locations in the state of Alabama. Steep Hollow is quite diverse and includes 'quaking' bogs, long-leaf pine slopes and areas of sweetbay and tupelo gum swamps. The plant inventory is not yet complete, but the total number of species at Steep Hollow is proving to be the highest found among our current natural areas.

While other gardens have recently developed methods for propagating native North American pitcher plants (Sarracenia spp.), The Crosby Arboretum maintains and preserves pitcher plants at three separate locations. This site, Hillside Bog, contains 20 acres of Sarracenia alata (Wood) Wood, the yellow pitcher plant, along with at least five species of native orchids: Calopogon pallidus Chapman, Calopogon tuberosus (L.) BSP, Cleistes divaricata (L.) Ames, Spiranthes praecox (Walt.) Wats., and Habenaria ciliaris (L.) R.Br.

Long-term research on this site by Dr. Robert Peet of the University of North Carolina has shown that this area has the highest species diversity per square metre yet found in North America.

Increasing species diversity by fire and controlled access.

Again, the management program for Hillside Bog is centered around fire. We have scheduled growing-season burns for three out of five years. This has released an entirely new spectrum of grasses and other herbaceous plants. Four years after Dr. Peet completed his study, it is still possible to see not only the outlines of his plots, but the paths he and his workers took to reach these working sites. Visitation to this Natural Area is limited to groups of not more than 10 persons, and not more than one group in a month. Even this amount of usage will probably require the installation of wooden board-walks to preserve this very fragile habitat. Hillside Bog is the only Crosby Natural Areas to have been fenced. Neighboring residents have become most helpful in minimizing unwanted intruders. All-terrain vehicles driven by area hunters had been a real problem.

Diversity through succession

We have another pitcher plant bog which we have not and do not plan to burn. At Crane Pond Bog we present an excellent example of the succession toward hardwood vegetation which occurs in the absence of fire in the Piney Woods. We are monitoring this succession through the permanent plots.

The Pinecote Interpretive Center

Information gleaned from all the natural areas has been used at our interpretative center, Pinecote. We began with a secondary pine savannah which had arisen after the property had been terraced and used in the 1930s for strawberry cultivation. First we laid out a 100 foot square grid over the entire 64 acres. Plants were identified to species for each square. The plant inventory is to be repeated at five-year intervals which will allow us to monitor changes in vegetation through time. Next, we installed a 2.5 acre pond modelled after local and naturally occurring beaver ponds, with winding shorelines bordering waters of differing depths. This has allowed us to develop aquatic exhibits, featuring several types of ecosystems,.....again using only plants native to the Pearl River drainage basin. In the water itself, we have started a bald cypress grove planted around bald cypress trees already present, lily ponds, striking rush displays, Iris colonies, and fields of Orontium aquaticum L.

At the southern end of Pinecote, we are re-creating a bog, re- establishing the vegetation which actually should have been present before the area was terraced and drained for the strawberries. Pinecote is a very wet place. A few inches in elevation can make a great difference in moisture content and the resulting plant life. Plants introduced into the Pinecote Bog have come from sod plugs taken ahead of the bulldozers in several new nearby subdivisions. We now have not only re-established pitcher plants, but also the four species of the orchids Rhexia, Eryngium, Sabatia, Eriogonum, Liatris, the list goes on and on, to reproduce the whole range of natural seepage bog vegetation.

Almost everything at Pinecote has more than one use. The paths, often developed along old strawberry terraces, act as fire breaks. In the reconstructed bog area and in the accompanying pine savannah, these paths/fire breaks delineate five sections. Here we maintain a series of programed burns which enhance the bog vegetation, and provide a wonderfully vivid educational tool by making it possible to show at any one time, different stages of burn-rejuvenated vegetation.

Our director, Edward L. Blake, a fine landscape architect, has crafted this lovely Arboretum. Designing with nature, and with great delicacy, his creations appear spontaneous. We use Pinecote as a magnet to direct our public to look at what is their natural world in a new way, and to convince our public that what is in their own back yards can be beautiful.

Organic management methods

The Crosby Arboretum is also setting an example by using no fertilizers, no pesticides, in fact, absolutely the minimum of chemicals of any kind. This is an important lesson as humankind makes what must be a global effort to clean up both the air we breathe and the earth's decreasing water resources.

The Mission

Botanic gardens and arboreta have a special role in the preservation of biological diversity. We have begun to preserve "endangered species" in pots. We are correctly concerned about preserving germplasm. But is this enough?

Surely saving plant communities, in situ preservation, must become a larger part of all gardens' programs. How else will the world take us seriously when we ask others to preserve their forests?

We urge you to join with us from the Crosby Arboretum, at Picayune, in the small state of Mississippi and become a garden where Nature Teaches.

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