Characteristics of mangrove swamps managed for mosquito control in eastern Florida, USA

Abstract

Manipulations of the vegetation and hydrology of wetlands for mosquito control are common worldwide, but these modifications may affect vital ecosystem processes. To control mosquitoes in mangrove swamps in eastern Florida, managers have used rotational impoundment management (RIM) as an alternative to the worldwide practice of mosquito ditching. Levees surround RIM swamps, and water is pumped into the impoundment during the summer, a season when natural swamps have low water levels. In the New World, these mosquito-managed swamps resemble the mixed basin type of mangrove swamp (based on PCA analysis). An assessment was made of RIM, natural (control), and breached-RIM (restored) swamps in eastern Florida to compare their structural complexities, soil development, and resistance to invasion. Regarding structural complexity, dominant species composition differed between these swamps; the red mangrove Rhizophora mangle occurred at a higher relative density in RIM and breached-RIM swamps, and the black mangrove Avicennia germinans had a higher relative density in natural swamps. Tree density and canopy cover were higher and tree height lower in RIM swamps than in natural and breached-RIM swamps. Soil organic matter in RIM swamps was twice that in natural or breached-RIM swamps. RIM swamps had a lower resistance to invasion by the Brazilian pepper tree Schinus terebinthifolius, which is likely attributable to the lower porewater salinity in RIM swamps. These characteristics may reflect differences in important ecosystem processes (primary production, trophic structure, nutrient cycling, decomposition). Comparative assessments of managed wetlands are vital for land managers, so that they can make informed decisions compatible with conservation objectives.

Perspectives on mosquito impoundments in eastern Florida, USA: Reply to Rey et al. (2009)

“…Consequently, differences between 2 sites, for example, which may be due to unknown factors other than impoundment type, can be confounded. Rey & Kain 1990) was misidentified as a breached-RIM site in Middleton et al (2008); however, reanalysis shows that the comparisons remain the same as originally reported, with the exception that tree height was lower, and canopy openness was higher in breached-RIM than in control and RIM swamps. Image source: US Geological Survey Middleton et al (2008) avoided pseudoreplication by identifying multiple sites within each of 3 categories: 10 RIM, 3 breached-RIM and 7 'control' sites, which were all spatially distinct and spread across >100 km of coastline in the IRL (see Fig.…”

“…The sampling design used by Middleton et al (2008) involved streamlined sampling of replicate sites in RIM, breached-RIM, and control categories (total of 20 sites), but with limited sub-sampling within sites. Rey et al (2009) criticize this approach and suggest more intensive sampling at fewer sites.…”

“…At some mosquito impoundments, permanent breaks in perimeter dikes (breached-RIM) allowed for more frequent water exchange with the adjacent lagoon. Middleton et al (2008) conducted a landscape-level comparison of these 2 management types (RIM and breached-RIM) with nondiked ('natural') areas dominated by mangroves.…”

“…Rey et al (2009, this volume) point out some of the complexities that challenged the study by Middleton et al (2008). Choices made during ecological studies are partly a reflection of the difficulties inherent in sampling at various landscape scales in complex systems.…”

“…Choices made during ecological studies are partly a reflection of the difficulties inherent in sampling at various landscape scales in complex systems. Rey et al (2009) list 'errors of fact' and 'methodological problems', which are minor or unfounded, and which do not invalidate the findings of Middleton et al (2008). Most issues raised by Rey et al (2009) were in fact carefully considered during study design.…”