Long-term development of tidal mitigation wetlands in Florida

Published source details Shafer D.J. & Roberts T.H. (2008) Long-term development of tidal mitigation wetlands in Florida. Wetlands Ecology and Management, 16, 23-31.
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This study is summarised as evidence for the following.

	Action	Category
	Reprofile/relandscape: brackish/saline swamps Action Link
	Introduce tree/shrub seeds or propagules: brackish/saline wetlands Action Link
	Directly plant trees/shrubs: brackish/saline wetlands Action Link

Reprofile/relandscape: brackish/saline swamps

A replicated, site comparison study in 2005 in Florida, USA (Shafer & Roberts 2008) reported that 12 of 17 mangrove creation/restoration sites (all reprofiled, along with other interventions) contained mangrove forests after 17–30 years – but that these differed from mature natural forests in overall complexity, tree density and canopy height. Statistical significance was not assessed. After 17–30 years, mangrove forests had developed in 12 of the 17 sites. Mangrove forests had not persisted in four sites and been deliberately removed from one. Nine of the sites that developed forests were surveyed in detail. The created/restored forests had a different overall structure to natural forests (data reported as a complexity index and graphical analysis). Created/restored forests contained 16,370 trees/ha on average (vs natural: only 6,594 trees/ha) and had a canopy height of only 3.7 m (vs natural: 6.4 m). Both created/restored and natural forests had a similar average basal area (28–31 m²/ha, and contained 1–3 tree species. Methods: In 2005, vegetation was surveyed in 17 sites (three 2 x 2 m plots/site). Between 1975 and 1987, all of these sites had been reprofiled to appropriate elevations for mangroves. All but one had also been planted with red mangrove Rhizophora mangle seedlings or propagules, and some (precise number not reported) had been planted with smooth cordgrass Spartina alterniflora. The study does not distinguish between the effects, on unplanted trees, of reprofiling, planting mangroves and planting cordgrass. Comparisons were made with previously published data from seven nearby natural forests.

(Summarised by: Nigel Taylor)
Introduce tree/shrub seeds or propagules: brackish/saline wetlands

A replicated, site comparison study in 2005 in Florida, USA (Shafer & Roberts 2008) reported that 12 of 17 sites planted with mangroves (along with other interventions) contained mangrove forests after 17–30 years – but that these differed from mature natural forests in overall complexity, tree density and canopy height. Statistical significance was not assessed. After 17–30 years, mangrove forests had developed in 12 of the 17 sites. Mangrove forests had not persisted in four sites and been deliberately removed from one. Nine of the sites that developed forests were surveyed in detail. The created/restored forests had a different overall structure to natural forests (data reported as a complexity index and graphical analysis). Created/restored forests contained 16,925 trees/ha (vs natural: only 6,594 trees/ha) and had a canopy height of only 4.0 m (vs natural: 6.4 m). Both created/restored and natural forests had an average basal area of 31 m²/ha, and contained 1–3 tree species. Methods: In 2005, vegetation was surveyed in 17 sites (three 2 x 2 m plots/site). All of these sites had been planted with red mangrove Rhizophora mangle between 1975 and 1987 (either propagules or seedlings; precise numbers not reported). Some sites had also been planted with smooth cordgrass Spartina alterniflora. All but one site was planted after levelling upland areas. The study does not distinguish between the effects, on unplanted trees, of planting mangroves, planting cordgrass and reprofiling. Comparisons were made with previously published data from seven nearby natural forests. This study included the sites in (7) and (10).

(Summarised by: Nigel Taylor)
Directly plant trees/shrubs: brackish/saline wetlands

A replicated, site comparison study in 2005 in Florida, USA (Shafer & Roberts 2008) reported that 12 of 17 sites planted with mangroves (along with other interventions) contained mangrove forests after 17–30 years – but that these differed from mature natural forests in overall complexity, tree density and canopy height. Statistical significance was not assessed. After 17–30 years, mangrove forests had developed in 12 of the 17 sites. Mangrove forests had not persisted in four sites and been deliberately removed from one. Nine of the sites that developed forests were surveyed in detail. The created/restored forests had a different overall structure to natural forests (data reported as a complexity index and graphical analysis). Created/restored forests contained 16,925 trees/ha (vs natural: only 6,594 trees/ha) and had a canopy height of only 4.0 m (vs natural: 6.4 m). Both created/restored and natural forests had an average basal area of 31 m²/ha, and contained 1–3 tree species. Methods: In 2005, vegetation was surveyed in 17 sites (three 2 x 2 m plots/site). All of these sites had been planted with red mangrove Rhizophora mangle between 1975 and 1987 (either seedlings or propagules; precise numbers not reported). Some sites had also been planted with smooth cordgrass Spartina alterniflora. All but one site was planted after levelling upland areas. The study does not distinguish between the effects, on unplanted trees, of planting mangroves, planting cordgrass and reprofiling. Comparisons were made with previously published data from seven nearby natural forests.

(Summarised by: Nigel Taylor)