Litterfall dynamics in carbonate and deltaic mangrove ecosystems in the Gulf of Mexico

From 1996 to 2002, we measured litterfall, standing litter crop, and litter turnover rates in scrub, basin, fringe and riverine forests in two contrasting mangrove ecosystems: a carbonate-dominated system in the Southeastern Everglades and a terrigenous-dominated system in Laguna de Terminos (LT), Mexico. We hypothesized that litter dynamics is driven by latitude, geomorphology, hydrology, soil fertility and soil salinity stress. There were significant temporal patterns in LT with litterfall rates higher during the rainy season (2.4 g m(-2) day(-1)) than during the dry season (1.8 g m(-2) day(-1)). Total annual litterfall was significantly higher in the riverine forest (12.8 Mg ha(-2) year(-1)) than in the fringe and basin forests (9.7 and 5.2 Mg ha(-2) year(-1), respectively). In Southeastern Everglades, total annual litterfall was also significantly higher during the rainy season than during the dry season. Spatially, the scrub forest had the lowest annual litterfall (2.5 Mg ha(-2) year(-1)), while the fringe and basin had the highest (9.1 and 6.5 Mg ha(-2) year(-1), respectively). In LT, annual standing litter crop was 3.3 Mg ha(-1) in the fringe and 2.2 Mg ha(-1) in the basin. Litter turnover rates were significantly higher in the fringe mangrove forest (4.1 year(-1)) relative to the basin forests (2.2 year(-1)). At Southeastern Everglades there were significant differences in annual standing litter crop: 1.9, 3.3 and 4.5 Mg ha(-1) at scrub, basin and fringe mangrove sites, respectively. Furthermore, turnover rates were similar at both basin and fringe mangrove types (2.1 and 2.0 year(-1), respectively) but significantly higher than scrub mangrove forest (1.3 year(-1)). These findings suggest that litter export is important in regulating litter turnover rates in frequently flooded riverine and fringe forests, while in infrequently flooded basin forests, in situ litter decomposition controls litter turnover rates.