Webb, Frederick J., Jr. (ed.) / Proceedings of the 17th Annual Conference on Wetlands Restoration and Creation : May 10-11, 1990
Morrison, Douglas, et al.
Effects of freshwater discharge from finger canals on estuarine seagrass and mangrove ecosystems in southwest Florida, pp. 115-126 PDF (4.2 MB)
Typha Invasion of Mangrove Ecosystem Typha has invaded MPAP saline wetlands through Spreader breaks and along the resultant channelized flow paths. Using Lee County Government aerial photographs, we estimate that Typha began invading the MPAP wetlands in 1983-84. Typha occurs as far as 2 km into the wetlands, nearly to Matlacha Pass (as of March 1990). Currently, the invasion is mainly restricted to the imnediate vicinity of the banks of the flow paths--tidal creeks. Typha is also invading areas of mangrove seedlings and juveniles (<1 m shoot height) near the flow paths. The invading Typha occurs in patches or stands which range in size from 5 m2 to about 1000 M2. Typha distribution was correlated with sediment and surface water salinities (Morrison et al., 1989). Typha abundance varied seasonally (P<0.05) in the Typha dominated stands at the mangrove-cattail monitoring sites (Table 4). Abundance increased during the wet season and peaked in November. Typha then declined throughout the dry season. Typha seasonality was most closely correlated with sediment salinity, and secondarily with surface water salinity (Morrison et al., 1989). Table 4. Typha shoot and leaf densities (No./m2) in the Typha dominated stand at Mangrove-Typha monitoring site B. Values are means ±SE N=10). Feb. 1989 May 1989 Aug. 1989 Nov. 1989 Feb. 1990 Shoot Density 28.4±3.7 7.0±1.0 18.7±3.7 31.0±5.4 9.0±1.1 Leaf Density 103±17 15±2 140±31 208±40 53±34 Typha in the mangrove-cattail transition zone exhibited the same seasonal pattern as in the Typha dominated stands (Table 5). The seasonal die-back during the dry season likely reduced the rate of Typha invasion into the mangroves. Nevertheless, Typha extended its range at both study sites. From August to November 1989 at Site A, the Typha stand expanded 3-4 m along the creek bank into an area occupied previously only by mangroves. This invasion continued during the dry season, with a one meter expansion from November 1989 to February 1990, even though the main stand was undergoing die-back. Rhizophora abundance in the Site A transition zone declined significantly (P<0.05) during the study (Table 6), while Typha was expanding its range. Rhizophora shoot density in February 1990 was one- third that in February 1989. 122
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