Puay Yok Tan

Perception Studies of Vertical Greenery Systems in Singapore

The objective is to discover the current perception of vertical greenery systems and barriers to their widespread adoption in Singapore. It can be concluded that the energy saving property of vertical greenery systems make them suitable for the local conditions as Singapore depends heavily on air conditioning. In addition, vertical greenery systems will also enhance the aesthetic of a building. Moreover, the installation of vertical greenery system is part of the effort to reduce the increasing serious air and noise pollution. Lastly, vertical greenery system is able to bring nature closer to humans. As with all greenery, constant clearing of the residue of dead leaves as well as periodical replacement and trimming cannot be avoided. These may become a barrier in convincing building owners to adopt vertical greenery systems. Furthermore, there is a lack of technical information, maintenance instructions, and information on plants suitable for vertical greenery systems locally. Lastly, there is lack of awareness of the benefits and performance of vertical greenery systems as well as a lack of grants and subsidies for implementation of vertical greenery systems.

Benefits of trees in tropical cities

In their Perspective “The natural capital of city trees” (28 April, p. [374][1]), K. J. Willis and G. Petrokofsky draw attention to the many benefits that urban trees provide to people. However, they neglect tropical cities. The omission is not surprising, given that most relevant research has

Photosynthetically active radiation and comparison of methods for its estimation in equatorial Singapore

Photosynthetically active radiation (PAR) is an important input variable for urban climate, crop modelling and ecosystem services studies. Despite its importance, only a few empirical studies have been conducted on PAR, its relationship to global solar radiation and sky conditions and its estimation in the tropics. We report in this study, the characterisation of PAR in Singapore through direct measurements and development of models for its estimation using input variables of global solar radiation (H), photometric radiation (L), clearness index (kt) and sky view factor (SVF). Daily PAR showed a good correlation with daily H and had a comparatively small seasonal variation in PAR due to Singapores equatorial position. The ratio of PAR to H (PAR/H) showed a slight depression in midyear from May to August, which correlated well with seasonal patterns in rainfall over the study period. Hourly PAR/H increased throughout the day. Three empirical models developed in this study were able to predict daily PAR satisfactorily, with the most accurate model being one which included both H and kt as independent variables. A regression model for estimation of PAR under shaded conditions using SVF produced satisfactory estimation of daily PAR but was prone to high mean percentage error at low PAR levels.

Stability of containerized urban street trees

Trees are usually grown in containers in the nursery until they reach a certain size, whereupon they are transplanted to a permanent location. Infrastructure development has often led to the removal of large trees. To maintain lush foliage and trees of a size that benefit urban ecology, trees can be grown in containers. Containerized trees can be moved from one location to another, and this relocation does not require root pruning or crown-size reduction. The drawback to having trees in containers is the small and confined volume of the container, which limits tree root development and thus affects containerized tree stability. The objective of this study was to understand the failure mechanisms for and the effect of the root dimensions on the stability of containerized trees. Therefore, small-scale stability model tests were conducted which were verified using numerical and analytical models. The results identified two failure modes that were likely to occur: tree overturning and container overturning. The mode of failure was dependent on the root dimensions. When the trees had extended their roots deep into the container, the whole container would overturn in the event of failure due to increased root confinement and shear resistance of the soil. On the other hand, the main failure mechanism when there was shallow root development was the uplifting of the tree from the container while the container remained upright. The results from numerical and analytical models were consistent with those obtained during the small-scale model stability tests.

Urban Ecological Networks for Biodiversity Conservation in Cities

Triggered by concerns of global biodiversity loss, cities are increasingly called upon to play an increased role in biodiversity conservation, leading to a surge in interest in urban biodiversity conservation. In playing this role, greening of cities needs to move beyond mere provision of amenities or ecosystem services to one of providing habitats for native biodiversity. This chapter describes one of the approaches for enhancing urban biodiversity conservation through the ecological network approach. The concept of ecological networks is not new in the field of ecology. However, its application to cities, both in conceptual and operational forms, is highly limited. As a high-rise, high-density city in which biodiversity conservation is threatened by other competing land uses, Singapore is used as an example to illustrate the development and application of the ecological network approach. The ecological network is built on the concept of network, spatial and landscape cohesions. Using methods in landscape ecology, remote sensing, biodiversity conservation and the Analytic Hierarchy Process, this chapter describes how a toolkit for ecological network can be developed, as well as the efficacy of its use for biodiversity management. The toolkit is categorized into monitoring tools, mapping tools, and communication and decision making tools. The learning outcomes gleaned from the research are presented as the 5-multis: multispecies, multiscalar, multilevel, multifunctionality, and multidisciplinarity.

Sustainability Matters: Environmental and Climate Changes in the Asia-Pacific

Harmful algal blooms (HAB) are a yearly event in the waters of Manila Bay, Philippines. The very first major bloom was caused by a toxic dinoflagellate species, Pyrodinium bahamense var. compressum, which is known to cause Paralytic Shellfish Poisoning (PSP). This chapter reviews HAB episodes in the bay recorded from the 1980s to 1990s, and compares them with the more recent events in the 21st century. Pyrodinium blooms occurred for almost a decade from 1988 until 1998, before being succeeded by a non-toxic species, Noctiluca scintillans, that was first recorded in the year 2001. No PSP cases were recorded between then and the year 2010. More recent bloom episodes, however, were caused by another toxic dinoflagellate species, Alexandrium minutum. The numbers of recorded PSP cases were higher in the 1980s and 1990s bloom events compared to the more recent toxic blooms. The decrease in incidences of PSP do not necessarily mean that the ecological health of the bay has improved, but instead could be due to changes in the physico-chemical properties of the water favouring one phytoplankton species over another. Even though sea surface temperatures and rainfall are known to be associated to HABs, the present study found no significant correlations among the variables tested. Due to the complexity of the environmental issues identified in Manila Bay, it is essential to conduct more comprehensive studies on the biological, physical, and chemical components of the bay to facilitate a clearer understanding of HAB episodes.