The Southern Florida Coastal Plain ecoregion covers an area of approximately 22,407 km² (8,651 mi²) across the lower portion of the Florida peninsula, from Lake Okeechobee southward through the Florida Keys (fig. 1). It is comprised of “flat plains with wet soils, marshland and swamp land cover with everglades and palmetto prairie vegetation types” (U.S. Environmental Protection Agency, 2002). The nutrient-poor environment of the ecoregion, particularly that of the Everglades, has been subject to run-off from urban and agricultural sources, which has led to changes in habitat health and diversity. Moreover, surface water levels and sheet flow in the Everglades are very sensitive to any differences in topography due to the ecoregion’s exceedingly expansive and flat terrain. As a result, changes of only a few centimeters in elevation may have significant impact on plant and animal communities.

The climate is generally frost-free and subtropical, consisting of a dry and a wet season. About 1,400 mm (55 in) of rain fall annually in the ecoregion, with approximately 1,060 mm (42 in) of rainfall occurring in the wet season between June and September. The warm dry season, from October to May, allows for year-round crop production and has been instrumental in the cultivation of winter vegetables. Sugarcane is also widely grown and has formed the basis of the domestic sugar industry since the early 1960s. The ecoregion underwent extensive land cover change between 1950 and 1970 due in large part to the implementation of water control measures, widespread use of air conditioning, mosquito control measures, improvements in transportation infrastructure, and efforts on the part of developers and government officials to promote Florida’s growth potential (Solecki, 2001).

Figure 1. The Southern Florida Coastal Plain. The randomly selected sample blocks are shown along with land use/land cover data from the 1992 National Land Cover Dataset. Click on image to enlarge

This ecoregion experienced 5.8 percent change during the study period, a moderate amount of land cover change in comparison to other ecoregions and, in particular, its neighbor, the Southern Coastal Plain, which had 24.9 percent change (fig. 2). An estimated 4.4 percent of the area (986 km²) (381 mi²) converted to other land covers just once, and 1.4 percent of the ecoregion (314 km²) (121 mi²) converted more than once (table 1). Approximately 94.2 percent of the ecoregion’s land cover remained unchanged. The spatial distribution of change was very uneven, with high amounts occurring in urbanizing coastal areas and relatively little change inland, where the presence of reserved lands inhibited change.

Estimated change per interval varied from a high of 2.5 percent between 1973 and 1980 to a low of 1.4 percent between 1992 and 2000 (table 2). The two intervening intervals—1980 to 1986 and 1986 to 1992—had 1.7 and 1.9 percent change, respectively.

The estimated average annual rate of change was 0.3 percent. The 1973 to 1980 interval showed the highest rate of change at 0.4 percent (table 2). During this interval, the leading conversions were from wetland to agricultural land and a fire-related transfer from non-mechanically disturbed land to wetland. The interval with the least change, 0.2 percent, was the 1992 to 2000 interval. The leading conversions during this interval were from agricultural land to developed land and from wetland to non-mechanically disturbed land, again due to fire.

Percent change of area by land cover type indicates which land covers changed significantly between intervals and which were relatively stable (table 3 and fig. 4). Developed lands increased in each interval, from 2.3 percent of the ecoregion in 1973 to 4.1 percent in 2000. Agricultural land increased as well, from 17.2 percent in 1973 to 18.4 percent in 1980, but then declined in each subsequent interval, back to 17.3 percent of the ecoregion in 2000. Non-mechanically disturbed land fluctuated between zero percent and 0.6 percent during the intervals between 1973 and 1992, reflecting the natural cycle of fire and regrowth in the Everglades. In 2000, non-mechanically disturbed land represented an estimated 0.3 percent of the ecoregion. Wetlands declined in each interval, except the third interval, and overall from 73.7 percent in 1973 to 72.2 percent in 2000, primarily as a result of expanding agricultural land and developed land covers.

Table 3: Estimated ecoregion land cover classes by percent and area (km²)

Wetland to agricultural land was the most common conversion, with an estimated 348 km² (134 mi²) converted between 1973 and 2000 (table 4). Indeed, the highest rate of change occurred in the first interval (1973 to 1980), as 284 km² (110 mi²) of wetland covers converted to farmland. Conversions of non-mechanically disturbed land to wetland, and wetland back to non-mechanically disturbed land were the second and fourth most common conversions, respectively. These transitions reflect the natural role of fire and habitat renewal in wetland areas. Agricultural land to developed land was the third most common conversion. However, when conversions to developed land from agricultural land, forest, mechanically disturbed land, wetland, and grassland/shrubland are combined, more land—an estimated 413 km² (159 mi²)— is converted to developed land than any other cover type during the study period. Conversions to developed land increased after 1980, as a significant amount of agricultural land that had been converted earlier from wetland became urbanized. Wetland, despite a continual decrease between 1973 and 2000, remained the dominant land cover.

Figure 3. Average annual rates of change for each ecoregion in the Eastern region. Click on image to enlarge

Table 1: Amount of overall spatial change detected in ecoregion and proportion of ecoregion that experienced change during one or multiple time periods

Table 2: Estimated amount of change by time interval, 85-percent confidence interval, and normalized annual rates of change.

Figure 2. 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. Click on image to enlarge

Figure 4. Net change by land cover class for each interval. Click on image to enlarge