-1 A tropical freshwater wetland: II. Production, decomposition, and peat formation Rodney A. Chimner 1,2, * and Katherine C. Ewel 1 1 USDA Forest Service, Pacific Southwest Research Station, Institute of Pacific Islands Forestry, 1151 Punchbowl Street, Ste. 323, Honolulu, HI 96813, USA; 2 Current address: Natural Resource Ecology Laboratory, Colorado State University, 200 W. Lake Street, Ft. Collins, CO 80523-1499, USA; *Author for correspondence (e-mail: rchimner@nrel.colostate.edu; phone: +1-970-491-2162; fax: +1-970-491-1965) Received 23 December 2004; accepted in revised form 19 January 2005 Key words: Carbon cycling, Decomposition, Kosrae, Micronesia, Peatlands, Plant production Abstract As much as 10% of the total carbon stored in peatlands occurs in the tropics. Although tropical peatlands are poorly understood scientifically, they are increasingly exploited for a variety of human uses. Our objective was to measure baseline carbon cycling data in one type of tropical peatland in order to understand better how peat accumulates in these ecosystems. Average plant production for two study sites on the island of Kosrae in the Federated States of Micronesia over 2 year was 1122 g C m 2 year 1 , of which 1058 g C m 2 year 1 was aboveground plant production (bole, buttress and litterfall). Although leaves contributed a high proportion of total plant productivity, their rapid decomposition left little carbon for peat accumulation. In contrast, fine roots only contributed 10% to plant productivity, but their slow decomposition allowed them to accumulate as peat. Wood (branches and stems) probably contributed the most carbon to the formation of peat. Despite being on the soil surface, small branches decomposed more slowly than leaves because of their high C:N and lignin:N ratios. In summary, we suggest that tropical peatlands in Micronesia accumulate peat not because of high plant production but rather because of slow decomposition of roots and wood under anaerobic conditions that result from nearly constant high water levels. Introduction Tropical peatlands represent as much as 10% of the total carbon stored in peatlands (Immirzi et al. 1992), which cover roughly 4 million km 2 or 3% of the Earth’s land surface (Maltby and Proctor 1996). They can be up to 10 m deep, and accu- mulation rates can be rapid, averaging 4–5 mm/ year, with some sites as fast as 5–10 mm/year (Maas 1996). These rates are significantly faster than in most temperate and boreal peatlands, which accumulate less than 1 mm/year, often slower than 0.5 mm/year (Gorham 1991; Gorham et al. 2003). Although tropical peatlands are poorly understood scientifically, they are increas- ingly exploited for peat extraction, fisheries, fossil fuels, minerals, forestry, and agriculture (De la Cruz 1986; Rieley et al. 1996; Junk 2002). Tropical peat- lands are at greater risk than remote temperate and boreal peatlands (such as in Canada and Russia), because they are often situated in densely populated low-lying coastal areas (Rieley et al. 1996). With Wetlands Ecology and Management (2005) 13:671–684 Ó Springer 2005 DOI 10.1007/s11273-005-0965-9