Carbon dioxide balance of a tropical peat swamp forest in Kalimantan, Indonesia

Tropical peatlands, which coexist with swamp forests, have accumulated vast amounts of carbon as soil organic matter. Since the 1970s, however, deforestation and drainage have progressed on an enormous scale. In addition, El Niño and Southern Oscillation (ENSO) drought and large‐scale fires, which grow larger under the drought condition, are accelerating peatland devastation. That devastation enhances decomposition of soil organic matter and increases the carbon release to the atmosphere as CO₂. This phenomenon suggests that tropical peatlands have already become a large CO₂ source, but related quantitative information is limited. Therefore, we evaluated the CO₂ balance of a tropical peat swamp forest in Central Kalimantan, Indonesia, using 3 years of CO₂ fluxes measured using the eddy covariance technique from 2002 through 2004. The forest was disturbed by drainage; consequently, groundwater level (GL) was reduced. The net ecosystem CO₂ production (NEP) measurements showed seasonal variation, which was slightly positive or almost zero in the early dry season, and most‐negative late in the dry season or early the rainy season. This seasonality is attributable to the seasonal pattern of climate, tree phenology and fires. Slightly positive NEP resulted from smaller ecosystem respiration (RE) and larger gross primary production (GPP) under conditions of high photosynthetic photon flux density (PPFD) and large leaf area index (LAI). The most‐negative NEP resulted from smaller GPP and larger RE. The smaller GPP was related to high vapor pressure deficit (VPD), small LAI and low PPFD because of smoke from fires. The larger RE was related to low GL. Annual NEP values were estimated respectively as −602, −382 and −313 g C m⁻² yr⁻¹ for 2002, 2003 and 2004. These negative NEP values show that the tropical peat swamp forest, disturbed by drainage, functioned as a CO₂ source. That source intensity was highest in 2002, an ENSO year, mainly because of low PPFD caused by dense smoke emitted from large fires.     

A comparison of sites suitable for the seedling establishment of two co-occurring species, Swintonia glauca and Stemonurus scorpioides, in a tropical peat swamp forest

Spatial and temporal ground-surface dynamics are major factors that affect regeneration and species coexistence in tropical peat swamp forests. We studied the seedling survivorship and morphological features of two tree species that play important roles in maintaining the ground-surface dynamics of a peat swamp forest in Sumatra. Large Swintonia glauca trees form mounds, whereas large Stemonurus scorpioides trees occupy non-mounds. We monitored the demography of naturally dispersed Swintonia and Stemonurus seedlings that germinated in 2000. Survivorship of Swintonia seedlings was high under conditions of late germination, high-light environment, and elevated ground surface, and was negatively affected by distance to the nearest conspecific adult. Survivorship of Stemonurus was high under conditions of early germination and high conspecific seedling density, and was also negatively affected by distance to the nearest conspecific adult. The allometric features of Stemonurus seedlings indicated characteristics of stress tolerance, that is, low growth rate and thick, porous roots. Stemonurus, which has large wingless seeds, regenerated in non-mounds around the parental trees, while winged Swintonia seeds dispersed farther from the parent and established in patchily distributed gaps and mounds. Thus, Swintonia seedlings can survive on non-mound sites within gaps and possibly create mounds, while Stemonurus seedlings tend to maintain non-mounds around the parental trees.     

Release of inorganic N,P and K in peat soils; effect of temperature,water chemistry and water level

In the Netherlands, fens that are fed by polluted river water are often eutrophic, whereas fens fed by calcium-rich groundwater often are mesotrophic. Differences in trophic status can not always be attributed to differences in the nutrient load of the water. In this paper we try to determine if the inflow of river water in fens, in fact, accelerates the soil nutrient release, thereby creating more eutrophic conditions (‘internal eutrophication’). For this purpose, we compared nutrient release rates (N, P and K) in soil cores fromSphagnum peat andCarex peat saturated with different media, that were artificially created to mimic the three basic water sources: polluted river water, unpolluted calcium-rich groundwater and rainwater. In addition, we studied the effect of temperature and water level on nutrient release rates. The experiments proved thatSphagnum peat released much more P and ammonium thanCarex peat. The strong site effect proved consistent throughout the water chemistry treatments, which indicates that soil quality may be the most important agent determining nutrient release rates. Nevertheless, it was established that water chemistry and water level are of significant influence on nutrient release rates in peat soils. In particular, river water stimulated P release by the peat, most notably in theSphagnum peat. P-release in both soils was only minor when the soils were incubated in clean Ca-rich groundwater. It is suggested that P release is strongly associated with soil chemical processes, and that high P release rates after incubation in river water are due to the high sulphate content of the water. The net release from the soil of ammonium, potassium and phosphate increased with increasing temperature. A freezing treatment significantly increased nutrient availability. The results of the experiments are examined in the context of hydrologic management strategies for the conservation of fens in agricultural landscapes.     

Engineered water level management facilitates recruitment of non-native common carp, Cyprinus carpio, in a regulated lowland river

River regulation can advantage non-native aquatic biota at the expense of native species. Nevertheless, flow regulating structures are sometimes used with the aim of achieving positive environmental outcomes in aquatic ecosystems. In the lower River Murray, Australia, drought-induced water level recession and acid sulfate soil exposure prompted the construction of an earthen levee, isolating a section of river channel (the Goolwa weir pool (GWP)) within which water levels were managed to mitigate a risk of water body acidification. The present study aimed to determine the impact of water level management on the fish community by investigating variation in species abundance and recruitment between sites subject to water level management in the GWP and unmanaged sites in Lake Alexandrina. Prior to levee construction, in August 2009, the abundance of the non-native common carp was similar in the GWP and Lake Alexandrina. Following water level management, in December 2009 and April 2010, the abundance of common carp in the GWP was approximately 1000 and 250 times greater than abundance in Lake Alexandrina, as a result of recruitment of young-of-year fish. No native freshwater species were significantly more abundant in the GWP in August 2009, December 2009 or April 2010. The results of this study suggest that the isolation of a river reach and a managed rise in water level facilitated spawning and recruitment of a non-native fish species. As such, the ecological benefits and risks of restoration and mitigation projects that involve the construction of flow regulating structures and water level management should be carefully considered.     

Influences of edaphic factors on the distribution and abundance of a rare palm (Cyrtostachys renda) in a peat swamp forest in eastern Sumatra,Indonesia

Tropical plant community ecology is often assumed to be driven largely by stochastic disturbance, replacement and demographic processes despite a general lack of information about the physical environment. Tropical soils are more diverse, at regional, intermediate and local scales than usually is recognized. This study was conducted to test hypotheses about the importance of edaphic parameters in determining the abundance and distribution of the rare lipstick palm Cyrtostachys renda Blume and its co‐occurrence with other plants. Eight of 11 tropical tree species were positively associated with C. renda. For Gluta renghas, Shorea parvifolia, Eleiodoxa conferta, Pandanus terrestris and Korthalsia flagellaris, the association with the palm was strong. The palms E. conferta and K. flagellaris appeared to have similar ecological and habitat requirements. The lipstick palm is adapted to specific edaphic conditions related to soil quality and drainage. It prefers fine sand, well‐drained soil and low mineral content, reflected in associations between these variables and stem density, clump density, clump size, frequency, basal area and canopy circle area. High levels of soil Ca^{+ +}, Mg^{+ +} and K⁺ are associated with sites where the palm is absent. The C/N ratio of soils appears to influence palm densities and sizes. All known populations occur in habitats with C/N‐values less than 19, with the largest populations in areas with C/N‐values of 13. Our findings suggest that edaphic variables are important determinants of the abundance and distribution of this tropical peat swamp forest species.     

Requirement for particular seed-borne fungi for seed germination and seedling growth of <Emphasis Type="Italic">Xyris complanata</Emphasis>, a pioneer monocot in topsoil-lost tropical peatland in Central Kalimantan,Indonesia

Hawaii yellow-eyed grass (Xyris complanata: Xyridaceae) inhabits infertile, acidic peat soil in the rainy tropical zone in Southeast Asia. This monocot plant produces a large number of dormant seeds in order to make a large deposit to seed bank in the soil. Under laboratory conditions, surface-sterilized X. complanata seeds are rarely able to germinate on sterilized peat moss bed; they require inoculation with either seed epiphytic or soil fungi to facilitate active seed germination. In the present study, three different genera of seed epiphytic fungi were isolated, and two common fungal genera, Fusarium sp. (strain R-1) and Penicillium sp. (strain Y-1), were found to promote seed germination of X. complanata. In sterile peat moss beds, the germination-stimulating fungi also showed growth-promoting effects on X. complanata seedlings. These results suggest that the seed germination-promoting fungi likely function as genuine partners for X. complanata in tropical open peat lands.