Vegetation component:

1) Mangrove forest ecosystems may not be able to survive the combination of large-scale disturbance and sea level rise. - This study shows that the combination of large-scale disturbance, such as that from hurricanes, and sea level rise can cause the conversion of mangroves to intertidal mudflat. Hurricane disturbance can cause wide spread tree mortality which in turn leads to a lowering of sediment surface elevation. With the wetland surface becoming lower the forest becomes much more susceptible to the influence of rising sea level (Fig. 1V).

Relevance to resource managers: Resource managers need to consider ways to re-forest mangrove areas following large scale disturbance.

This study supports the second bullet under "Milestones, Products, and Payoffs" of Question 8.2 of the "Strategic Plan for the Climate Change Science Program Final Report, July 2003". (See section starting with "Reports describing the potential consequences of global....")

Figure 1V. Mangrove forest and barren mud flat located in the Big Sable Creek region of Everglades National Park. Prior to the Great Labor Day Hurricane of 1935, the mud flat was in fact a mangrove forest. The forest failed to recover from the storm disturbance. Our sampling of Sediment Elevation Tables (SETs) in both habitats has shown that the mud flat is continuing to lose elevation, some 70 years after the storm. [larger image]

2) Dead wood is generated in large pulses by disturbance events such as hurricanes. The dead wood plays an important role in the cycling of carbon, nitrogen and phosphorus. - In the immediate aftermath of a large-scale disturbance, massive quantities of woody debris and leaves begin decomposition. This can lead to a pulse of nutrients being released. This is followed by a period during which the wood actually serves as a sink. Decaying wood remains in the ecosystem for a century or more.

Relevance to resource managers: In any mangrove clearing or trimming exercise, the wood should be left in place rather than placed in an aquatic environment.

This study supports the second bullet under "Milestones, Products, and Payoffs" of Question 8.2 of the "Strategic Plan for the Climate Change Science Program Final Report, July 2003". (See section starting with "Reports describing the potential consequences of global....")

3) Vegetation has been changing in the coastal Everglades prior to 1940, the year used as the "base condition" for the Comprehensive Everglades Restoration Plan. - This study demonstrates that vegetation change in the coastal Everglades was underway prior to the 1940 baseline assumed in the Comprehensive Everglades Restoration Plan. This is true in areas such as the C-111 basin, Cape Sable, and the southwest coastal areas of Everglades National Park.

Relevance to resource managers: Restoration goals or targets for some areas of the park need to be re-examined.

This study supports the second bullet under "Milestones, Products, and Payoffs" of Question 8.2 of the "Strategic Plan for the Climate Change Science Program Final Report, July 2003". (See section starting with "Reports describing the potential consequences of global....")

4) The phenomenon of "vegetation die off" observed in Florida Bay appears to be a long term, cyclical process, not related to freshwater runoff, but possibly to sea level variation. - Initially it was felt that the die-off of mangroves and herbaceous vegetation on the islands and northern coastline of Florida Bay was related to upstream water management and reduced inflows leading to hyper-salinity. Our study has shown that hyper-salinity on the islands occurs as a result of natural hydrological and biological processes and had been documented long before canals were dug in south Florida. Our current working hypothesis is that the cyclical nature of the die-off is related to the 19.6 year periodicity of perigean spring tides.

Figure 2V. Percent cover of herbaceous vegetation on North Dump Key, Florida Bay. The data represent the average ( ± 1 SD) of six 1 m2 quadrats. The period from 1995 to 2000 was marked by lower average sea level and higher than normal rainfall. This resulted in decreased soil salinities and increased herbaceous vegetation cover. [larger image]

Relevance to resource managers: This is a naturally occurring process that managers need to be aware of, but not necessarily concerned about. Monitoring needs to occur to make sure that human factors do not alter the natural pattern.

This study supports the second bullet under "Milestones, Products, and Payoffs" of Question 8.2 of the "Strategic Plan for the Climate Change Science Program Final Report, July 2003". (See section starting with "Reports describing the potential consequences of global....")

5) The three species of mangroves in Florida have well defined allometric relationships that can be used to predict biomass and productivity. - Our results have demonstrated that simple linear regression models can use tree diameter to accurately predict biomass and productivity in the mangrove forests of Everglades National Park.

Figure 3V. Log-log (base 10) relationship of total dry biomass as a function of diameter at breast height for three species of mangroves in Florida. [larger image]

Relevance to resource managers: Resource managers have a new tool for use in assessing restoration success.

This study supports the second bullet under "Milestones, Products, and Payoffs" of Question 8.2 of the "Strategic Plan for the Climate Change Science Program Final Report, July 2003". (See section starting with "Reports describing the potential consequences of global....")

5) Important elements for plant growth show marked gradients across the coastal zone. For example, ammonium, a form of nitrogen, is present in low concentrations in mangrove forests, but relatively high concentrations in adjacent sawgrass prairies. Reasons for these patterns are unknown at present but they might be a result of differences in hydrology and/or fire regime between communities.

Figure 4V. Concentrations of ammonium (mean ± 1 standard deviation) in the sediment along a transect from the edge of a coastal tidal river, into a sawgrass prairie. Data are shown for two depths in the sediment (30 and 60cm) and for two seasons (summer and winter). Station 1 = tall mangrove forest adjacent to the river, Stations 2 and three = shorter mangrove forest some 100m and 200m respectively, away from the river. Station 4 = mixed short mangrove forest with sawgrass, 270m from the river. Station 5 = sawgrass prairie some 350m from the river. [larger image]

Relevance to resource managers: The influence of hydrologic and fire regimes on nutrient dynamics is poorly understood. As CERP alters the hydrology of the Everglades, and also the fire regime, studies are needed on how this will influence plant available nutrients.

This study supports the second bullet under "Milestones, Products, and Payoffs" of Question 8.2 of the "Strategic Plan for the Climate Change Science Program Final Report, July 2003". (See section starting with "Reports describing the potential consequences of global....")

6) The concentration of iron (Fe) in sediment porewater appears to be related to density and distribution of the mangroves Avicennia germinans and Rhizophora mangle. - The relationship is a positive one for Rhizophora. As Fe increases in the sediment, stem density of Rhizophora increases. For Avicennia, the relationship is inverse, increasing iron concentrations result in decreasing stem density.

Figure 5V. Relationships between stem density and sediment porewater iron concentration for Avicennia and Rhizophora. [larger image]

Relevance to resource managers: The concentration of nutrients and other compounds in the sediments of mangroves and marshes is influenced by a number of factors, including hydrology and salinity. As CERP progresses, it will alter both the hydrology and salinity regimes of the coastal Everglades, and also the concentrations of nutrients and other elements. Studies are needed on how this will influence sediment porewater chemistry and plant community structure and composition.

This study supports the second bullet under "Milestones, Products, and Payoffs" of Question 8.2 of the "Strategic Plan for the Climate Change Science Program Final Report, July 2003". (See section starting with "Reports describing the potential consequences of global....")