Southern Coastal Plain

Click to see available downloads for this ecoregion

Ecoregion Description

The Southern Coastal Plain is a subtropical, low-elevation ecoregion situated between the Gulf of Mexico and the Atlantic Ocean (fig 1).  It covers approximately 143,843 km² (55,538 mi²), including the central and northern parts of Florida and southeastern Georgia.  The coasts of Mississippi and Alabama are included in the ecoregion, as well as a small part of Louisiana.  A series of discontinuous barrier islands, beaches, and sand dunes occur along the coast.  The interior of the ecoregion has many large lakes, karst springs, and sandy hills.  Swamps and marshlands occur across the ecoregion, from the large Okefenokee Swamp preserve in the north to the northern boundary of the Everglades, which lies in the adjacent Southern Florida Coastal Plain ecoregion to the south.  Large natural disturbances that impact the area relatively frequently include hurricanes and tropical storms, as well as wildland fires. 

The climate is warm and humid temperate, and the ecoregion receives abundant precipitation of between 1,000 and 1,500 mm (40 to 60 in) annually.  The combination of long frost-free periods of more than 240 days and plentiful water has historically enabled the production of specialized crops.  The citrus industry focused its intensive orange grove production on the southern interior and southeastern coast (fig 2), although there has been a recent migration to the south to avoid killing frosts exacerbated by wetland loss (Marshall and others, 2003).  Pastureland has also been an important agricultural resource.  Extensive pine plantations, employed for timber production, are a relatively common use of forests in the ecoregion (fig 3).  Approximately one-third of Florida’s forestland is comprised of commercial pine stands that are harvested and regenerated at a relatively fast pace, primarily in the northern part of the state (Carter and Jokela, 2002). 

Substantial population growth has occurred, causing an expansion of urban and developed land (fig 4).  Between 1970 and 2000, the population increased by more than 140 percent, from 4.2 million to 10.3 million people.  Large urban areas are prevalent on the Florida peninsula, including Orlando, St. Petersburg, Jacksonville, and Tampa.  Tampa Bay is also one of the ten largest ports in the United States.  Aside from agriculture and the extensive pine plantations, tourism and associated service industries are important economically.  Mining of rich phosphate reserves, used primarily in agricultural fertilizers, is also significant (fig 5).   

Originally, pine and mixed hardwood forests covered much of the ecoregion.  The native longleaf pine (Pinus palustris) was the dominant tree species; however, its current extent has been reduced by as much as 98 percent (Wear and Greis, 2002).  Forests have been cleared for lumber and converted to pine plantations that favor the faster growing slash (Pinu elliotii) and loblolly pine (Pinus taeda L.) species.  Longleaf pine and other forests have also been converted to cropland, pasture, mining, and urban uses. 

Contemporary Land Cover Change from 1973 to 2000

The Southern Coastal Plain had the highest amount of overall change of all Eastern U.S. ecoregions.  An estimated 24.9 percent of the ecoregion underwent one or more changes between 1973 and 2000 (table 1 and fig. 6).  An estimated 13.4 percent underwent just one change, and 11.5 percent underwent two or more changes.  Multiple changes are indicative of cycles of timber harvesting and reforestation that occur throughout the study period.

The highest rates of change occurred in the most recent two time intervals, when the average annual rate was 1.6 percent (table 2 and fig. 7).  The slowest rate of change occurred between 1973 and 1980, when the annual rate was 1.3 percent. 

The individual land cover statistics show that forest is the predominant cover, despite the decline from a high of 28.5 percent in 1973 to a low of 24.3 percent in 2000 (table 3).  Wetlands also declined, from 23.1 percent in 1973 to 20.7 percent in 2000.  Agriculture saw a similar decline from 10.8 percent to 8.0 percent during the study period.  The ecoregion estimates indicate a substantial amount of decrease in the total area of phosphate mines, which caused an overall mining decline from 2.0 percent to 0.8 percent. 

Developed land had a large overall gain during the study period, increasing from 14.8 percent to 21.0 percent, becoming the second most common land cover type by 2000.  Grassland and shrubland also increased, from 5.2 percent to 6.8 percent.  The disturbance categories (mechanically disturbed and non-mechanically disturbed) both had moderate increases.  Overall, the mechanically disturbed category increased from 2.3 percent to 3.8 percent.  Forest, agriculture, and developed land each covered more than 20 percent of the ecoregion in 2000, suggesting a highly variable pattern of land use and land cover.

Net change statistics show that developed land expanded by 6.2 percent between 1973 and 2000 (table 3).  Grassland and shrubland had the next highest gain at 1.6 percent.  Mechanically disturbed land increased by 1.5 percent, primarily due to the cutting of forestland. The largest net decline was a 4.2 percent loss of forest between 1973 and 2000.  Other net changes included declines in agriculture (–2.8 percent), wetland (–2.4 percent) and mining (–1.2 percent) (fig. 8).

The leading land cover change in all four time periods was the conversion from forest to mechanically disturbed land (table 4).  The reforestation of mechanically disturbed land was the second most common conversion.  These changes are typically cyclic due to forest harvesting and regrowth.

Net change statistics in the Southern Coastal Plain tend to mask much larger gross changes (i.e., overall losses and gains) that may have occurred in a cover type.  For example, the ecoregion experienced significant loss of forest due to mechanical disturbance, but it also experienced significant gains in forest cover due to reforestation.  Additional forest declines most likely occurred from the loss of forested wetlands.  Nearly 60 percent of the net decline of wetland cover was caused by conversion to developed land during the study period.

The 6.2 percent change in developed land was the highest net increase in all Eastern U.S. ecoregions.  Overall, development occurred primarily on agricultural land (2,707 km² or 1,045 mi²), as well as forests (2,637 km2 or 1,018 mi²) and wetlands (2,025 km² or 782 mi²).  Between 1973 and 1980, wetlands were the largest source of land converted to developed cover (937 km² or 362 mi²), although the extent of the conversions diminished by 2000.  Agriculture was the dominant source for developed land in the 1992 to 2000 interval, when an estimated 987 km² (381 mi²) were converted. 

References

Carter, D.R., and Jokela, E.J., 2002, Florida’s renewable forest resources, CIR1433: Gainesville: University of Florida, Institute of Food and Agricultural Sciences, Florida Cooperative Extension Service, 9 p.

Marshall, C.H., Pielke, R.A., Sr., and Steyaert, L.T., 2003, Crop freezes and land-use change in Florida: Nature, v. 426, p. 29–30.

Wear, D.N., and Greis, J.G., eds., 2002, Southern forest resource assessment, General Technical Report SRS-53: Asheville, N.C., U.S. Department of Agriculture, Forest Service, Southern Research Station, 635 p.

Table 1.  Estimated overall spatial land cover change between 1973 and 2000

Table 2.  Total and annual rates of land cover change for each time interval

Table 3.  Estimated land cover area for each land use and land cover class between 1973 and 2000 

Table 4.  Leading land cover conversions for the four time periods 

Figure 1.  Southern Coastal Plain and surrounding ecoregions. The 35 randomly selected 100-km² sample blocks are shown along with land-use/land-cover data from the 1992 National Land Cover Dataset.

Figure 6.  The overall spatial change in all Eastern U.S. ecoregions.  Each bar chart shows the proportion of the ecoregion that experienced change on 1, 2, 3, or 4 dates.

Figure 7.  Estimates of land cover change per time interval normalized to annual rates of change.

Figure 8.  Land cover changes are shown for the four time intervals of the study.