Plant Community: Dune

All You Need to Know About the Dune Communities

By Ethan Freid, PhD
Botanist, Leon Levy Native Plant Preserve
efreid@bnt.bs

Herb/vine dominated

Shrub dominated

Invasive dominated

Dune systems occur along shorelines primarily on Atlantic-facing shores. The system as a limestone sand substrate is produced inorganically (oolites) and organically from coralline algae, broken shells, and corals.  The sand is deposited on the shore and is moved inland from wave action and wind.

The dune consists of a foredune, a top dune, and a back dune.  The foredune is typically steep, with the leading edge having species that can withstand consistent wave action at high tide and often have stolons or rhizomes that spread out across the open sand.  The top and back dune is usually a gradual slope away from the shoreline and dominated by herbs and shrubs, often with Uniola paniculata (Sea Oats) dominating.  In many areas of the central and southern Bahamas, different endemic species of Agave may be common in top and back dunes.

Over time the plants in the fore and top dune will trap sand and build the dune higher and further outward. In many areas of the central Bahamas, as dunes accrete sand, a series of ridges and valleys form depending on the rate of sand production over time.  In other areas of The Bahamas, as the dune builds outward, the back edge of the dune changes to a shrubland.  These areas can be dominated by species such as Chrysobalanus icaco (Cocoplum), Coccoloba uvifera (Sea Grape), Coccothrinax argentata (Silver Top), Genipa clusiifolia (Seven Year Apple), and/or Croton linearis (Granny Bush).  These areas have ceased being dunes and are classified here under DBEF-Shrublands.

Wetlands may form in low-lying areas behind the back dune when the water level is low enough to intersect the lens. These are usually slightly saline to brackish and can change in size and salinity depending on rainfall.

Dune systems in the northern and central Bahamas have been heavily invaded by Casuarina equisetifolia (Australian Pine) and Scaevola taccada (Sea Lettuce).  Both species have devastated dunes, reducing their biodiversity (including birds and insects) and causing erosion. The level of invasion can vary, and dunes may still be partially physically functional, even if not biologically so, even after heavy invasion.  Over a relatively long time, dunes with invasive species, in particular Casuarina (Australian Pine), lose their sand and height and will eventually have little to no sand.

Additionally, in many areas inhabited by humans, the dunes have been razed and built upon, and non-native species have been introduced.

Common species found in Dunes:

Dry Broadleaf Evergreen Formations
Forest/Woodlands/Shrublands/Dwarf Shrublands

Dry Needle Leaf Evergreen Formation
Pine Woodland

Dune

Freshwater Wetland

Human Altered

Rocky Shore

See References

Areces- Mallea. A. E., A. S. Weakley, X. Li, R. G. Sayre, J. D. Parish, C. V. Tipton and T. Boucher. 1999. A guide to Caribbean vegetation types: a preliminary classification system and descriptions. The Nature Conservancy. 156 pp.

Britton, N. L. and C. F. Millspaugh. 1920. The Bahama Flora. New York, N. Y. 695 pp.

Byrne, A. R. 1972. Man, and the variable vulnerability of island life: a study of recent vegetation change in the Bahamas. Ph. D. Dissertation. University of Wisconsin, Madison, Wisconsin. 311 pp.

Catesby, M. 1730 – 47. The Natural History of Florida, Carolina, and the Bahama islands. London. Vols I and II. 220 plates.

Coker, W. S. 1905. Vegetation of the Bahama Islands. In: Shattuck, George B. The Bahama Islands. Geographical Society of Baltimore. John Hopkins Press. 185-270 pp. + pl. xxxiii-xlvii.

Correll, D. S. and H. B. Correll. 1982. Flora of the Bahama Archipelago. A. R. G. Ganter Verlag K.-G., FL-9490. Vaduz. 1692 pp.

Currie, D., J. M. Wunderle, E. H. Freid, D. N. Ewert, and D. J. Lodge. 2019. The Natural History of the Bahamas – A field guide. Cornell University Press. 464 pp.

Daniels, M. L. 2016. A floristic study of a former land bridge in the Bahama Archipelago. Master Thesis – Miami University. Oxford, Ohio. 65 pp.

Franklin, J., J. Ripplinger, E. H. Freid, H. Marcano-Vega, and D. W. Steadman. 2015. Regional variation in Caribbean Dry Forest tree species composition. Plant Ecology 216 : 872-886.

Freid E. H. and M. A. Kerwin. 1998. Flora and vegetation of Bell Island (Exuma Chain), Bahamas. In: Wilson T. K. (ed) Seventh Symposium on the Natural History of the Bahamas. Bahamian Field Station Ltd, San Salvador, 41–52 pp.

Henry, P. W. T. 1974. Land Resource Study, No. 16: The Pine Forest of the Bahamas. Land Resource Division, Tolworth Tower, Surbiton, Surrey, England KT6 7DY. 178 pp.

Howard, R. A. 1950. Vegetation of the Bimini Island group, Bahamas. B. W. I. Ecol. Monog. 20 : 317-349.

Little, B. G., D. K. Buckley, R. Cant, P. W. T. Henry, A. Jefferies, J. D. Mather, J. Stark, R. N. Young. 1971-76. Land Resource of the Commonwealth of the Bahamas: Volume 1, Abaco. Volume 2, Eleuthera. Volume 3, Cat Island. Volume 4, Andros Island. Volume 5, Grand Bahama. Volume 6, Great Exuma, Little Exuma and Long Island. Volume 7, Crooked Island and Acklins. Volume 8, Mayaguana and Inagua. Land Resource Division, Tolworth Tower, Surbiton, Surrey, England KT6 7DY.

Little, B. G., D. K. Buckley, R. Cant, P. W. T. Henry, A. Jefferies, J. D. Mather, J. Stark, R. N. Young, and W. T. Gillis. 1977. Land Resource Study, No. 27: Land Resources of the Bahamas: A Summary. Land Resource Division, Tolworth Tower, Surbiton, Surrey, England KT6 7DY. 133 pp.

Nickrent, D. L., W. H. Eshbaugh and T. K. Wilson. 1983. Vascular Flora of Andros Island. Kendall/Hunt Pub. Co. Dubuque, IA. 156 pp.

Northrop, A. 1902. Flora of New Providence and Andros (Bahama islands). Mem. Torrey Bot. Club 12 : 1-98 + 49 pl. (Reprinted in Northrop, J. I. 1910. A naturalist in the Bahamas. Memorial volume. Columbia University Press. New York. 119-211 pp.

Proctor, G. R. 1954-55. Notes on the vegetation of the Turks and Caicos Islands. Nat. Hist. Soc. Jamaica 6 :149-152; 170-174, 199-203.

Smith I. K. and Vankat, J. L. 1992. Dry Evergreen Forest (coppice) Communities of North Andros Island, Bahamas. Bull Torrey Bot Club. 119 : 181–191.

Smith, R. R. 1993. Field guide to the vegetation of San Salvador Island, The Bahamas. Hartwick College, Oneonta, New York. 120 pp.

See Glossary

A physiognomically uniform group of Associations sharing one or more diagnostic (dominant, differential, indicator, or character) species which, as a rule, are found in the uppermost stratum of the vegetation. It is within a Formation.

The finest level of the classification standard. The Association is a physiognomically uniform group of vegetation stands that share one or more diagnostic (dominant, differential, indicator, or character) overstory and understory species. These elements occur as repeatable patterns of assemblages across the landscape and are generally found under similar habitat conditions. The Association refers to existing vegetation, not a potential vegetation type.

Diameter at Breast Height. Typically measured at 130 or 135 cm above ground.

An organism, group of organisms, or taxon that by its size, abundance, or coverage exerts considerable influence upon an association’s biotic (such as structure and function) and abiotic (such as shade and relative humidity) conditions.

A class of vegetation dominated by a life form of shrubs and/or trees under 0.5 m tall.  These types generally have greater than 25% cover of dwarf shrubs and less than 25% cover of trees and shrubs. Herbs and non-vascular plants may be present at any cover value. In rare cases (e.g., alpine and polar regions), dwarf shrub cover may exceed the cover of trees, shrubs, herbs, and non-vascular plants and be less than 25% of the total cover.

Multi-stemmed woody plants with a life form at a height of less than 0.5 m due either to genetic or environmental constraints.

Vascular plant that grows by germinating and rooting on other plants or other perched structures; sometimes called “air plants.”

A level in the classification based on ecological groupings of vegetation units with broadly defined environmental and additional physiognomic factors in common. This level is subject to revision as the vegetation Alliances and Associations are organized under the upper levels of the hierarchy. Different variables are applied to this hierarchical level in the sparsely vegetated class.

Overall structure or physical appearance – what the community and its dominant species look like, their height and spacing (height and canopy cover), and shape. It is descriptive of the life forms of the dominant species; for example, their size, leaf traits, and phenology (deciduous, evergreen).

In the broad sense

A class of vegetation defined by areas dominated by shrubs generally greater than 0.5 m tall with individuals or clumps not touching to interlocking.  Shrub canopy cover is generally greater than 25% while tree cover is generally less than 25%.  In rare cases, shrub cover exceeds the tree, dwarf shrub, herb, and non-vascular plant cover and is less than 25% cover.

Woody plants greater than 0.5 m in height that generally exhibit several erect, spreading, or prostrate stems; and have a bushy appearance. In instances where life form cannot be determined, woody plants greater than 0.5 m in height but less than 5 m in height will be considered shrubs.

Pertains to areas within tropical regions with variable (seasonal) temperature and moisture regimes; climatically, it has seasonal variation marked by dry/wet seasons rather than cold/hot seasons. Parts of this region are subject to sub-0º C (32º F) temperatures but rarely have freezing periods of 24 hours or longer; in the United States this term includes southern Florida and the southern tip of Texas.

Woody plants equal to or greater than 5 m in height and at least one main stem that is 2.5 cm in diameter at breast height (DBH) are considered trees. Trees in the Bahamas may have more than one main stem/trunk.

A class of vegetation defined by areas dominated by emergent trees generally greater than 5.0 m tall without a closed canopy cover with tree cover generally less than 70 %.  There is a shrub layer with various dominant species.

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