by George Gann

While the preservation and restoration of remnant hammocks in Dade County must be a top conservation priority, the restoration ("creation") of new hammocks in highly disturbed areas can also contribute greatly to the achievement of regional biodiversity conservation goals. In addition, hammocks are aesthetically pleasing, contribute to the conservation of energy resources, and reduce long-term maintenance costs in urban and suburban landscapes. They also provide wonderful habitats for native wildlife.

There are at least three different hammock types in Dade County: rockland hammock, prairie hammock, and maritime hammock (see Guide to The Natural Communities of Florida, FNAI and DNR, 1990). Rockland hammock is the most familiar type, and was historically found in scattered locations on the Miami Rock Ridge - the elevated area of oolitic limestone stretching from Long Pine Key in Everglades National Park to near the present location of Ft. Lauderdale - as well as in the Florida Keys and Big Cypress. Prairie hammock, on the other hand, was historically found on elevated areas in marl prairie or marsh communities, while maritime hammock was found on stabilized dune systems on barrier islands such as Miami Beach. The maritime hammock community has been all but obliterated by development in Dade County, while prairie hammock has received substantial protection within Everglades National Park. Rockland Hammock has received significant protection in Everglades National Park and in Big Cypress National Preserve, but has been severely impacted by development throughout most of the Miami Rock Ridge and in the Florida Keys.

From a structural standpoint, these three hammock types are very similar. All are broad-leaved, mostly evergreen, closed forests typically dominated by trees and shrubs of West Indian origin. In some cases, temperate species are dominant, and many authors distinguish between tropical hammocks dominated by West Indian species and temperate hammocks which, in Dade County, are dominated principally by live oak (see Appendix 3 in FNAI and DNR 1990). These guidelines refer to the creation of rockland hammocks which are dominated by tropical species.

Unlike other indigenous natural communities, rockland hammocks can be created almost anywhere within the urban and suburban environment. Even the smallest spaces between buildings can house "micro-hammocks" of small trees and shrubs. Rockland hammocks are well suited to residential yards, as well as to forest islands within commercial and institutional developments (such as schools), and even within median strips and swales along highways. The main area where rockland hammocks are not well suited is on barrier islands from Key Biscayne northward, where maritime hammocks and other coastal communities should be restored.

The first step to rockland hammock creation is site preparation. All lawn grass should be killed, and other invasive exotics removed from the hammock creation site. Certain exotic trees may sometimes be left as nurse crops to provide temporary canopy, and may be later removed.

In terms of plant selection, remember that hammocks are diverse communities, and for best results, this diversity should be mimicked. In general, at least ten species of trees and shrubs should be used within a hammock creation project. A higher diversity is recommended. Trees and shrubs should be planted at densities no lower than one plant per 50 square feet of planting area, and no higher than one plant per 25 square feet of planting area. Canopy and subcanopy trees should compose no less than 50 percent of the installed plants. Attached is a list of species recommended for hammock creation which includes those species with relatively wide ranges and broad ecological tolerances. Many native species, however, are confined to rather limited ranges (such as Gulf Licaria which is known only from Brickell Hammock), and for a variety of conservation reasons should not be planted outside of their historic ranges. The use of species with more narrow ranges is recommended within appropriate locations, but this requires in-depth study to make sure that the species in question are really native to the vicinity of the project site.

Two to three gallon containers (plants 2-4 feet in height) and seven to ten gallon containers (plants 4-8 feet in height) are the container sizes recommended for hammock creation. In general, no more than fifty percent of the plants installed should be in seven to ten gallon containers. Balled and burlapped (field grown) material can also be used if larger specimens are desired. It should be noted, however, that field grown trees and shrubs are much more expensive and take longer to establish than containergrown materials.

The planting hole should be dug so that the plant is level with the surrounding ground surface, and will comfortably fit within the planting hole. The planting hole should not be significantly larger than the root ball of the plant to be installed. The material excavated from the hole should be used as back fill; no soil amendments or fertilizer should be placed in or around the planting hole. Once the plant is placed in the planting hole, place half of the back fill in the hole and use a garden hose to water in the back fill, thus eliminating air pockets under and around the plant. Once this water has drained away, place the remaining back fill in the hole and again use a garden hose to flush out any remaining air pockets. During this process, use a shovel to lightly (not firmly) pack in the back fill around the plant. Finally, level out the planting surface so that it grades smoothly into the surrounding terrain.

After all plants are installed, a 4-6 inch top dressing of mulch or wood chips should be applied to the planting area. Wood chips obtained from a local tree-trimming company is recommended over commercially-produced mulch. Under no circumstances should cypress mulch or pine chips be used. If commercially-produced mulch is used, then melaleuca or eucalyptus mulch is preferred. When applying mulch, make sure not to cover the trunks of the installed plants.

Careful watering is essential to successful hammock establishment. In general, each watering should be equivalent to one inch of rainfall. During the first two weeks after installation water once per day, during the next two weeks water every other day, during the next four weeks water twice per week, and during the next four weeks water once per week. If field grown materials are installed, water them at least once per month for the following year. Additional watering may be necessary during hot, dry periods during the spring and summer. Of the various types of watering systems which are available, soaker hoses are the most highly recommended. Soaker hoses should be laid down before the mulch top dressing is applied, and should be placed within 2-4 inches of each installed plant.

Long-term maintenance of created hammocks basically involves weeding, trimming, and sometimes re-mulching. If the site has been properly prepared and mulch has been applied, then few weeds should invade the planting area. In general, plan on doing a light weeding every two to three months. Once the canopy has formed, weeding will be necessary every six months or so. The only area which should require more frequent weeding is where the planting area interfaces with any remaining lawn areas, as lawn grasses and weeds will continuously invade the edges of the hammock. To combat this problem, some people install wood, rock, or plastic borders between the lawn area and the hammock to prevent the lawn from spreading into the hammock. Whenever weeding, make sure to not pull up seedlings of native trees and shrubs!

Within a year of installation, the trees and shrubs will show significant growth. Select trimming is recommended every six months or so to keep the understory relatively open, and to promote canopy development. In general, the lateral branches of trees and large shrubs should be removed a few at a time, making sure that no more than one third of the total leaf area is removed in any one trimming. Some medium shrubs (especially shiny-leaved wild coffee) may also be trimmed in this manner. These treatments should be continued until the lower branches of trees and large shrubs are above head height. Medium and small shrubs should be trimmed downward if they become too overgrown.

In general, a second mulching will not be required. However, in some cases, the mulch may be too thin or may oxidize (decompose) relatively quickly and a complete or partial re-mulching may be required. In general, you can tell if the mulch is too thin if an abundance of weeds begins to appear within the planting area.

These guidelines provide the basics of rockland hammock creation. Once begun, however, the restoration of hammocks can turn into a life-long experience which is both educational and rewarding. Once the basics are mastered, then other elements of hammock restoration, such as the introduction of rare plants as well as plants that provide food for specialized wildlife species, can be implemented.

Reprinted from the June, 1995, Tillandsia, the Newsletter of the Dade Chapter Florida Native Plant Society.

5/20/01
RECOMMENDED SPECIES FOR ROCKLAND HAMMOCK CREATION IN DADE COUNTY:

Large Trees
Scientific Name	Common Name
Bursera simaruba	Gumbo-limbo
Ficus aurea	Strangler Fig
Ficus citrifolia	Short-leaf Fig
Mastichodendron foetidissimum	Wild Mastic
Quercus virginiana var. virginiana	Live Oak

Medium Trees
Celtis laevigata	Hackberry
Citharexylum fruticosum
Fiddlewood
Coccoloba diversifolia	Pigeon-plum
Chrysophyllum oliviforme	Satinleaf
Dipholis salicifolia	Willow-bustic
Diospyros virginiana	Persimmon
Drypetes lateriflora	Guiana-plum
Exothea paniculata	Inkwood
Krugiodendron ferreum	Black Ironwood
Morus rubra	Red Mulberry
Nectandra coriacea	Lancewood
Sapindus saponaria	Soapberry
Simarouba glauca	Paradise Tree

Small Trees
Ardisia escallonioides	Marlberry
Eugenia axillaris	White Stopper
Myrsine floridana	Myrsine
Trema micrantha	Florida Trema

Large Shrubs
Hamelia patens *	Firebush
Myrica cerifera var. cerifera *	Wax-myrtle
Zanthoxylum fagara	Wild-lime[Spiny]

Medium and Small Shrubs
Callicarpa americana *	American Beautyberry
Cassia ligustrina *	Privet Cassia
Psychotria nervosa	Shiny-leaved Wild-coffee
Psychotria sulzneri	Soft-leaved Wild-Coffee
Randia aculeata	White Indigoberry

* These species are more typically found on the edges of hammocks. They may be used to facilitate hammock development, to add color, and to attract wildlife. In the long run, they will be shaded out in the hammock interior.

George Gann, Director
The Institute for Regional Conservation
22601 S.W. 152 Avenue, Goulds, Florida 33170
http://www.regionalconservation.org
phone 305-247-6547

Dade Chapter of the Florida Native Plant Society
PO Box 570598
Miami, FL 33257-0598
phone 305-255-6404