Nee Soon Research Articles

Pycnarrhena(Menispermaceae), a new generic record for the native flora of Singapore

A collection made from Nee Soon Swamp Forest in 2005 is confirmed as a specimen of Pycnarrhena fasciculata (Miers) Diels (Menispermaceae). This represents the first record of the genus Pycnarrhena for the native flora of Singapore.

Flowpath influence on stream acid events in tropical urban streams in Singapore

AbstractWe investigated processes contributing to periodic acidification events in headwater streams of Nee Soon Forest Catchment (NSFC) in Singapore by monitoring hydrochemical changes in response to rainfall inputs. Stream chemistry response to most rainfall events was characterized by decreases in pH from means ranging from 5.1 to 5.3 to below 4.8–5.0 and corresponding increases in specific electrical conductivity from baseflow values of 15–30 to 50–80 μS cm−1, indicative of low‐total dissolved solids in stormflow. The decreases in pH in the streams, which are typically acidic year‐round, were related to occasional highly acidic rainfall inputs (pH ~4.05) and likely the flushing of organic acids into the stream by shallow subsurface flow interacting with surface litter and/or organic‐rich soil horizons. The interaction of rainwater runoff with organic matter in the soil matrix possibly alters the chemical composition of stormflow, influencing pH. Decomposition of instream organic matter also reduces stream water pH. Leaching experiments revealed that the overland flow passing through organic matter and A horizon material has the potential to lower stream water pH by approximately a half unit or more, in part, by flushing nitrates that were produced by microbial decomposition of organic matter and/or precipitated sulphur that enterred the forest by wet or dry atmospheric deposition. The observed periodic acid events are a natural phenomenon in the stream system in this urban environment because of naturally acidic rainfall and granitic soils with low buffering potential. However, acid events are likely amplified in frequency and magnitude by anthropogenic pollution emissions of sulphur and nitrogen species (e.g., SO2and NOx) from local and regional sources that lower rainfall pH. Although, acid runoff events are typically short‐lived (<12–24 h), further longitudinal monitoring and experimental studies are needed to investigate the long‐term implications on sensitive taxa in the NSFC streams. Finally, understanding the flow pathways of stormflow water in the nested system was critical for deciphering the mechanisms driving stream acid events at the site.

Environmental change since the Last Glacial Maximum: palaeo‐evidence from the Nee Soon Freshwater Swamp Forest, Singapore

AbstractOur examination of pollen, microcharcoal, and sediment material in Nee Soon Freshwater Swamp Forest in Singapore revealed the following regarding its more than 20 000‐year history: (1) the pollen record supports the presence of a savanna corridor in this part of South‐East Asia during the Last Glacial Maximum (LGM); (2) a high abundance of charcoal at depths greater than 1.5 m supports the existence of a dryer climate and/or more frequent fires until about 18 000 cal bp; (3) missing sedimentary material in the upper 30–40 cm, ranging in age from 64 to 7500 cal bp, was likely removed during recent construction work in the 1950s; (4) there is evidence of sea‐level influences on the site from the presence of mangroves from 9000 cal bp to present but it is difficult to determine whether this impacted the site because of the missing sediments; and (5) the low organic carbon content throughout the stratigraphy indicates that the swamp is not a peatland. The results indicate that the forest in this protected area of Singapore developed from a grassland‐dominated landscape after the LGM as the climate warmed and became wetter, and therefore, may not be as resilient to long‐term drought conditions as previously believed. Further, the stratigraphy contains evidence that the swamp and stream system have been highly dynamic, both naturally and in response to anthropogenic disturbance.

Habitat Adaptation Mediates the Influence of Leaf Traits on Canopy Productivity: Evidence from a Tropical Freshwater Swamp Forest

Functional traits offer generalizability to the prediction of ecosystem processes such as production, and community-weighted mean trait values are increasingly used for such predictions. However, the underlying causal direction between traits and ecosystem processes are often indirect and sometimes even tenuous. In this study, we aimed to uncover underlying causal mechanisms between traits, habitat adaptation and canopy productivity. We used canopy production data estimated from leaf litter traps, and trait and habitat association data obtained from 40 permanent vegetation plots in the Nee Soon catchment in Singapore, which contains a heterogeneous mix of freshwater swamp and dry-land tropical forests. Mean canopy production across the catchment was estimated to be 768 g m−2 year−1, which is similar to other tropical dry-land forests in the region. Biweekly per-basal-area canopy production was found to be consistently lower in swamp than non-swamp plots, and positively correlated with monthly mean temperature. Structural equation models fitted to data of canopy production, leaf traits, plot type (swamp versus non-swamp), basal areas and habitat adaptations of 69 tree species–plot combinations suggested that tree species possessing leaf traits associated with more conservative resource acquisition strategies, viz. low specific leaf area, high leaf C:N ratio, and thicker leaves, are better adapted to stressful, waterlogged swamp conditions, but that this adaptation also reduces canopy—and likely total—net primary productivity. These observations suggest that the stressful conditions of waterlogged, anoxic swamp habitats significantly reduce the rate at which nutrients are cycled by communities found in such environments.

Notes on Acer laurinum (Sapindaceae) in freshwater swamp forest in Singapore

Acer laurinum Hassk. was recently recorded as both a new species and genus for Singapore from the Nee Soon swamp forest in the Central Catchment Nature Reserve, but little is known about its biology and ecology. Here, the species is described and notes on its distribution, ecology and proposed conservation status in Singapore are given.

Native and introduced fish community structure in a freshwater swamp forest: Implications for conservation and management

Abstract Freshwater swamp forests are poorly studied but highly threatened freshwater habitats, especially in Southeast Asia. Very little is known about the environmental factors associated with the assembly and spatial distribution of fish communities in these acid‐water habitats, although such knowledge is of immense importance for conservation and management. Fish assemblages in 40 stream sites throughout the Nee Soon Swamp Forest, Singapore, were surveyed using push nets from October 2013 to November 2014. The Nee Soon Swamp Forest is the last substantial remnant of freshwater swamp forest habitat in Singapore, and today it is the only refuge for many of the native forest‐specialist freshwater fish species. The overall diversity and richness of the fish community are positively correlated with depth, stream order, and canopy cover, and are negatively correlated with distance to a connected reservoir, mean velocity, and silt substrate. Observed patterns indicate that three main communities exist, each with distinct associated species and environmental parameters. One is a novel community of introduced species and non‐forest specialist native species found only at the outskirts (downstream portion) of the swamp forest, close to a reservoir connection that drains the swamp, whereas the other two communities are found in the interior of the swamp forest and harbour mostly forest‐specialist native species of restricted distribution and high conservation value. The community on the outskirts may be a potential route for introduced species to spread and establish populations deeper within the swamp forest. At present the native community within the swamp forest appears to be healthy, but constant monitoring is needed to ensure that the native community is not threatened by loss of habitat or introduced species.

Soil elemental analysis in a high conservation tropical forest in Singapore

To understand the distribution of soil elemental concentrations and their potential sources of trace metal contamination in the high-conservation Nee Soon freshwater swamp forest in Singapore, we analyzed samples from 227 surface and 35 subsurface (auger profiles) locations. Our assessment involved distribution maps, principle component analysis, cluster analysis, and correlation analysis of element concentrations determined from a mixed acid digestion and measurement on an ICP-MS. We found a distinct zonation in the distribution of several elements (Ba, Cr, Cu, Fe, Mn, Pb, Sr, Ti, V, and Zn) between the upper and lower catchment that gives an erroneous notion of widespread contamination in the lower catchment. We believe this zonation is natural, likely related to differences in the underlying geology. However, Cu, Pb, and Sb concentrations were greatly enriched by anthropogenic activities on military training lands in the lower catchment, firing ranges in particular. Barium, Sr, and Zn also appear to be enriched in the lower part of the catchment, possibly from anthropogenic activities including military activity and roads. Although soils in the catchment are not highly contaminated, isolated areas with high concentrations of Cu, Pb and Sb may warrant management attention given the sensitive nature of the urban forest, which includes the last remaining fresh water swamp forest in Singapore.

NGS barcoding reveals high resistance of a hyperdiverse chironomid (Diptera) swamp fauna against invasion from adjacent freshwater reservoirs

BackgroundMacroinvertebrates such as non-biting midges (Chironomidae: Diptera) are important components of freshwater ecosystems. However, they are often neglected in biodiversity and conservation research because invertebrate species richness is difficult and expensive to quantify with traditional methods. We here demonstrate that Next Generation Sequencing barcodes (“NGS barcodes”) can provide relief because they allow for fast and large-scale species-level sorting of large samples at low cost.ResultsWe used NGS barcoding to investigate the midge fauna of Singapore’s swamp forest remnant (Nee Soon Swamp Forest). Based on > 14.000 barcoded specimens, we find that the swamp forest maintains an exceptionally rich fauna composed of an observed number of 289 species (estimated 336 species) in a very small area (90 ha). We furthermore barcoded the chironomids from three surrounding reservoirs that are located in close proximity. Although the swamp forest remnant is much smaller than the combined size of the freshwater reservoirs in the study (90 ha vs. > 450 ha), the latter only contains 33 (estimated 61) species. We show that the resistance of the swamp forest species assemblage is high because only 8 of the 314 species are shared despite the close proximity. Moreover, shared species are not very abundant (3% of all specimens). A redundancy analysis revealed that ~ 21% of the compositional variance of midge communities within the swamp forest was explained by a range of variables with conductivity, stream order, stream width, temperature, latitude (flow direction), and year being significant factors influencing community structure. An LME analysis demonstrates that the total species richness decreased with increasing conductivity.ConclusionOur study demonstrates that midge diversity of a swamp forest can be so high that it questions global species diversity estimates for Chironomidae, which are an important component of many freshwater ecosystems. We furthermore demonstrate that small and natural habitat remnants can have high species turnover and can be very resistant to the invasion of species from neighboring reservoirs. Lastly, the study shows how NGS barcodes can be used to integrate specimen- and species-rich invertebrate taxa in biodiversity and conservation research.

Aquatic macroinvertebrate richness, abundance and distribution in the Nee Soon freshwater swamp forest, Singapore

The Nee Soon freshwater swamp forest is a vital area for biodiversity conservation in Singapore. A survey of the aquatic macroinvertebrates in the streams of the Nee Soon drainage was carried out to c

Integrated research, conservation and management of Nee Soon freshwater swamp forest, Singapore: hydrology and biodiversity

The current paper acts as an introduction to nine following papers concerning the hydrology and biodiversity of Nee Soon freshwater swamp forest. Freshwater swamp forest is a threatened and overlooked

Diversity, distribution and habitat characteristics of dragonflies in Nee Soon freshwater swamp forest, Singapore

Biodiversity baselines were established for dragonflies of Nee Soon freshwater swamp forest based on quantitative sampling across the eight sub-ctachments. Surveys were conducted from december 2014 to

Projected impacts of climate change on stream flow and groundwater of Nee Soon freshwater swamp forest, Singapore

As Singapores only remaining patch of primary freshwater swamp forest, the good management of the Nee Soon catchment is of utmost importance if a large proportion of the flora and fauna in Singapore i

Conservation outputs and recommendations for Nee Soon freshwater swamp forest, Singapore

The current paper acts as a summary to the Nee Soon Swamp Forest biodiversity and hydrology baseline studies project, including results published previously and the results from papers of the current

Diversity of terrestrial snails and slugs in Nee Soon freshwater swamp forest, Singapore

Diversity of terrestrial snails and slugs in Nee Soon freshwater swamp forest, Singapore

The hydro-geomorphic status of Nee Soon freshwater swamp forest catchment of Singapore

The hydro-geomorphic status of Nee Soon freshwater swamp forest catchment of Singapore

Rediscoveries, new records, and the floristic value of the Nee Soon freshwater swamp forest, Singapore

Rediscoveries, new records, and the floristic value of the Nee Soon freshwater swamp forest, Singapore

The biological, ecological and conservation significance of freshwater swamp forest in Singapore

The Nee Soon stream drainage in the Central Catchment Nature Reserve is virtually the last remaining fragment of primary freshwater swamp forest in Singapore. The forest type has been poorly studied i

Next-Generation identification tools for Nee Soon freshwater swamp forest, Singapore

Next-Generation identification tools for Nee Soon freshwater swamp forest, Singapore

Development and Application of an Integrated Hydrological Model for Singapore Freshwater Swamp Forest

As Singapore's only remaining patch of primary freshwater swamp forest, the conservation of the Nee Soon Swamp Forest (NSSF) is of utmost importance if a large proportion of the flora and fauna in Singapore is to be conserved. An integrated hydrological model for the NSSF is developed, with the objectives to numerically model the hydrological variations, to assess the impact of future climate change as well as to facilitate future eco-hydrology management. The numerical model considers the hydrological processes in a holistic manner, which includes the rainfall-runoff, the evapotranspiration, and the interactions between surface water and groundwater etc. Due to the constraints imposed from setting up monitoring stations in the protected forest, a combined approach is adopted to develop the numerical model which makes use of the field survey data and the alternative remote sensing data. With the climate projection inputs from the Regional Climate Model (RCM), the numerical model is applied to run future scenarios to assess the climate change impact. A few management strategies are also proposed in order to maintain favourable hydrological conditions for conserving the local ecosystem.

Cryptocarya Nitens (Lauraceae), a New Species Record for Singapore

Cryptocarya nitens (Blume) Koord. & Valeton is newly recorded for Singapore. It was discovered during surveys in Bukit Timah Nature Reserve and the Nee Soon Swamp Forest. A description is given, together with a key based mostly on vegetative characters for all Cryptocarya species occurring in Singapore. A short overview of the Lauraceae of Singapore shows that, in total, 57 species belonging to 14 genera have been recorded, of which 47 species in 13 genera are native. Cryptocarya nitens is lectotypified in addition to two of its synonyms.