Landscape design approaches to enhance human–wildlife interactions in a compact tropical city

Abstract

Urban landscapes have the potential to conserve wildlife. Despite increasing recognition of this potential, there are few collaborative efforts to integrate ecology and conservation principles into context-dependent, spatial and actionable design strategies. To address this issue and to encourage multi-disciplinary research on urban human–wildlife interactions, we ask the following questions. To what extent should design and planning actions be aligned with urban ecology in the context of a compact city? How can wildlife conservation meet the seemingly conflictual demands of urban development and public preference? To answer these questions, we refer to the relevant literature and a number of design projects. Using the compact tropical city of Singapore as a case study, we propose 12 design strategies. We encourage designers and planners to strengthen the links between wildlife and urban dwellers and promote wildlife conservation within cities.

Background

The rate of global wildlife extinctions has accelerated over recent decades (Ceballos et al. 2015). There are, however, huge opportunities to conserve wildlife in cities where urban ecosystems could become an essential component of habitat enhancement for some species (Muller, Werner, and Kelcey 2010; Kowarik 2013). Concomitantly, there is a greater understanding today of the socio-cultural co-benefits achieved from harmonious coexistence with nature, such as human health, well-being, and opportunities for childhood education (Fuller et al. 2007; Lee and Maheswaran 2011). These co-benefits support the notion of developing ‘more-than-human cities’ (Steele, Wiesel, and Maller 2019). For this to be a reality, urban green spaces in cities need to be carefully planned and designed, so that human–wildlife interactions, as well as the city’s liveability, can be enhanced.

Implementing human–wildlife interactions systematically in planning and design is not yet common practice, as decision makers are confronted with several major challenges. First, land scarcity is a major concern for many modern and compact cities (Richter and Behnisch 2019). Cities prioritise anthropocentric developments and regard wildlife as belonging to, and necessarily conserved in, dedicated nature reserve areas. Second, design considerations are typically limited within the project site scale while biodiversity planning and design goes beyond site scale, and must consider the large scale of connectivity across a city. Third, wildlife in urban environments can evoke mixed feedback, with some residents perceiving animals (e.g. long-tailed macaques Macaca fascicularis and wild boars Sus scrofa) as a public nuisance (Tan 2017b). Furthermore, the public may fear being close to wild animals, and public acceptance of the presence of wild animals may remain blocked by certain socio-cultural barriers (Jorgensen, Hitchmough, and Dunnett 2007). In addition, the recent pandemic of coronavirus disease 2019 has amplified negative perceptions of some animals (e.g. bats), as these have been labelled potential vectors of zoonotic diseases (Jamal 2020). Finally, there is limited guidance for designers who are looking for sources of necessary information (McDonnell 2015). This is compounded by a lack of clarity on how to translate ecological knowledge and data into appropriate spatial and temporal scales on the ground (Gandy, 2015).

Situated 1° north of the equator, Singapore is a biodiversity hotspot, with more than 2100 native vascular plant species, 390 bird species, 334 butterfly species, 140 reptile and amphibian species, 60 mammal species and over 50 species of freshwater fish despite its small size of ∼725 km² (Ng, Corlett, and Tan 2011; NParks 2020b). As the city has embarked on the next step in its greening initiative, ‘City in Nature’, with the overall aim of restoring nature in urban landscapes, designers have arguably an obligation to redefine the essence of the city as a place for wildlife (NParks 2020c). Several recently completed well-known landscape projects have moved in this direction, with ecological sensitivity integrated into the planning and design efforts.

The purpose of this article is to propose design approaches that may lead to wildlife-inclusive cities by responding to opportunities when they are presented. Our research questions are the following. (i) What aspects of ecological knowledge of urban wildlife should be integrated into urban planning and design? (ii) Which design and planning actions should be aligned with wildlife conservation, fulfilling the demands of urban development whilst simultaneously addressing public preferences? We synthesise relevant knowledge from multiple sources: a review of the literature on tropical ecology and wildlife biology, a review of design projects developed in academic studios, and a review of built works in Singapore. First, we catalogue items considered to respond to species and socio-ecological contexts; second, we list design strategies for practical implementation to enhance human–wildlife interactions. Most cases come from Singapore—a modern compact tropical city—but the discussion has broader relevance to the design of urban green spaces worldwide.

Design approaches

Species and site considerations

Species

Target flora and fauna species.

The term ‘target species’ refers to a variety of representative groups of wildlife (e.g. plants, invertebrates and arboreal/ground/aquatic animals, including birds, reptiles and amphibians) that can be suitable targets to occupy a site. Invisible species (e.g. soil microorganisms), although ecologically important, tend to be difficult to address in design and are, therefore, not addressed in this article. Information on the regional pool of visible species is available in a variety of sources, ranging from books [e.g. Singapore’s Red Data Book (Davison, Ng, and Ho 2008), biodiversity encyclopaedia (Ng et al. 2011), peer-reviewed journal articles on the long-term quantitative monitoring of wildlife populations and community dynamics (Chong et al. 2012; Jain, Lim, and Webb 2017) and biodiversity information portals of government agencies (e.g. NParks BIOME, flora and fauna web). Spatially explicit occurrences of wildlife in urban vegetated patches surrounding the design site can be acquired from geo-referenced map sources, available through online citizen science datasets (e.g. iNaturalist, eBird), global biodiversity information facilities (Global Biodiversity Information Facility (GBIF), Integrated Biodiversity Assessment Tool (IBAT)), conservation non-government organisations, and universities [e.g. NSS Wild Animals of Singapore, NUS Digital Nature Archive (DNA), wildsingapore’s fact sheets].

Characteristics of target species.

Various characteristics can be used to classify target species (Apfelbeck et al. 2019), including: (i) diet (e.g. omnivorous, frugivorous, insectivorous); (ii) habitat requirements (e.g. for nesting, breeding, and roosting) and associated landscape characteristics (e.g. proximity to water bodies); (iii) tolerance level for human disturbance, environmental stresses and species competition (e.g. human traffic, urban heat, flooding, predator–prey dynamics); (iv) behaviours (e.g. diurnal/nocturnal, migratory patterns); (v) contribution to ecological functions (e.g. pollination and seed dispersal); (vi) dispersal limitations (e.g. mobility, home range sizes and ability to disperse) and (vii) conservation value (e.g. status in global and/or national IUCN red list status).

It is crucial to translate such characteristics into vertical and horizontal spatial landscape components of habitats that can be directly linked to the design and planning of urban green spaces. It is also important to select urban adaptors as target species for a fully functional landscape design. These are species tolerant of urban microclimates, noise and edge effects and who are able to move and disperse in an urban matrix. Such species tend to be habitat generalists, and therefore, common and widely established in urban landscapes. Increasing generalists and common species is valuable because they are responsible in providing the bulk of ecosystem services in a landscape (Banerd 2018).

Socio-cultural perceptions of species.

Wild animals in urban areas often draw mixed responses and elicit contradictory attitudes (Yeo and Neo 2010; Chan 2017). Positive attitudes stem from the enjoyment of seeing wildlife or simply knowing certain iconic species (e.g. otters, hornbills) or taxonomic groups (e.g. butterflies) exist in the city. Negative attitudes are often associated with certain species perceived to be a public nuisance (Soulsbury and White 2015; Tan 2017b). Greater public awareness is needed to preclude a fear of wildlife in urban areas.

When selecting target species in the design and planning of spaces, designers should consider principles facilitating the avoidance or mitigation of human–animal conflict. One Health, a global research organisation, provides a transdisciplinary platform that recommends strategies in landscape management and planning to prevent disease spill-over whilst recognising risks and benefits at the human–wildlife interface (Kelly et al. 2017). Several resources attempt to educate the general public on proper reactions to wildlife. For example, the animal encounter webpage of Singapore’s biodiversity agency NParks (NParks 2020a) explains how members of the community should react if they come across certain creatures in order to minimise conflicts. People are advised to not feed monkeys, e.g. as this helps monkeys return to the forest and regain their natural foraging behaviours. People living near conflict areas can take a highly effective ‘Monkey Guards’ training course teaching them how to alter macaque movements away from human habitations through assertive but non-aggressive behaviours (Jabbar 2018). Certain socio-demographic factors may impact human–wildlife interactions as well, and these should be investigated on a context-by-context basis [e.g. females view coexistence of humans and animals as more fundamental than males in Denmark; see (Gamborg and Jensen, 2016)].

Site context

Spatial conditions of design sites.

The site should be assessed from a wildlife perspective. First, the configuration of and proximity to ‘source areas’, such as nature reserves and nature areas, large water bodies, existing corridors, gardens and parks (Hathaway et al. 2017), should be assessed. This can help inform the overall biodiversity potential of the site and identify alignment with city level biodiversity masterplans. The next step is to map the existing vegetated patches (‘patch’ refers to an area of unfragmented habitat of a single vegetation type) present at the site. A minimum patch size can be defined as a threshold (e.g. 100 m² for a site that is tens of hectares in size), above which all patches are mapped. Next, the patches should be classified according to dominant habitat types (e.g. forest, freshwater swamp, marsh, managed vegetation, unmanaged grass patch), vegetation density, presence of mature trees, canopy coverage, edge condition, microclimate and food sources for fauna. Vegetated patches can be further classified based on the shape and size, connectedness (based on distance between patches), and the proportion of suitable habitats for target species. When deciding which patches to retain or selecting a shape for new patches, circular patches are generally preferred over elongated or linear shapes because the former allows fauna to establish a defendable territory in the centre core/undisturbed area more easily. Rounder patches also have fewer edge effects. It has also been shown that fewer large patches generally support higher species diversity over several small patches (see SLOSS debate; Jain, Lim, and Webb 2017). As a rule of thumb, in the Singaporean context, patches > 100 m wide are generally large enough to support a relatively healthy fauna movement comprising a mix of urban adapted edge (e.g., wild boar) and core species (e.g. Sunda pangolin Manis javanica). Patches 50–100 m wide are large enough for medium-sized mammals (e.g. common palm civet Paradoxurus hermaphroditus), whereas a 20–50 m width is suitable for small mammals (e.g. plantain squirrel Callosciurus notatus) and large birds (e.g. Oriental Pied Hornbill Anthracoceros albirostris), and a 5–20 m width is acceptable for small birds and insects. Patches < 5 m wide tend to support transient wildlife and may only be able to act as stepping stones (A.J. pers. obs; Banerd 2018). The understanding of a site’s potential as a part of an ecological network at the city scale using connectivity approaches, such as least cost path analysis (Hamid and Tan 2017), provides a useful basis to evaluate the extent to which the site can accommodate, connect and nurture targeted faunal communities.

Ecosystem service potential of sites.

The ecosystem service potential of a site should be evaluated during the planning and design stage, as the degree and type of ecosystem service performance, urban biodiversity and human well-being tend to be positively correlated (Tratalos et al. 2007). Several software tools and frameworks (e.g. Ecosystem Services Identification & Inventory (ESII); Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST); Storm Water Management Model (SWMM)) can be used to characterise sites’ capacity for saving water run-off, stormwater management, erosion control, nutrient cycling, heat mitigation, and noise abatement. The quantified ecosystem services can be directly translated to cost and carbon emission savings, as they replace mechanical systems. Building consensus on which ecological benefits and services to prioritise at a site (air, water, soil etc.) can be a good way to engage the community about greenery in urban environments.

Physical barriers of sites.

Barriers refer to structures or infrastructure in urban areas that interrupt the movement of fauna (Moretto and Francis 2017), and these are influenced by the building density, size of built structures and infrastructure (Wang et al. 2017), permeability, noise level and human traffic load (Weitowitz et al. 2019). Changes to water flows can cause a huge disturbance to movements of aquatic animals and may facilitate the spread of non-native species (Liew, Tan, and Yeo 2016). Mapping barriers by degree/intensity, as well as their impacts on target taxa, is an essential step in the design stage to determine how to remove or soften such barriers.

Socio-economic demands of site development.

Designers should be aware of the contexts determining public preferences for certain flora and/or fauna groups. These may include aesthetic perceptions, recreational demands of residents/users, alignment with land development plans (e.g. Singapore’s Urban Redevelopment Authority’s 5-year master plan), conservation/management measures from private/government agencies/non-governmental organisations and transboundary laws. For example, residents in Singapore may be happy to watch primates (e.g. long-tailed macaques) in a forested area, but may not want them at close proximity, such as in their own backyards. In a recent online survey of a community in eastern Singapore (Pasir Ris), residents were supportive of wild chickens but had mixed feelings about wild boars and stray dogs in their neighbourhoods (Begum 2020). More public or resident surveys would be useful to ascertain site-specific opportunities and challenges (e.g. houses near the forest edge versus distanced forest viewable from windows in high-rise buildings) although conducting surveys requires funding with substantial time and efforts.

Design strategies to enhance human and wildlife interactions

Based the preceding discussion of species and site considerations, we propose 12 actionable and contextualised design strategies to enhance interactions between urban dwellers and wildlife and contribute to habitat enhancement in the city. We group these strategies into four essential urban ecological principles: maintain heterogeneity, accommodate dynamism, interweave social and ecological processes and recognise urban landscapes as functioning ecosystems at nested scales. These principles are synthesised from published articles (Zipperer et al. 2000; Pickett et al. 2001; Cadenasso and Pickett 2008; Spirn 2014) and exemplified in relevant design projects recently developed in Singapore (Fig. 1).

Maintain heterogeneity

Heterogeneity in this article refers to fine-scale habitat diversity affecting both species richness or composition and diverse forms and structure of vegetated areas. Affiliated heterogeneity strategies include the following sections.

Increase, retain or restore wild nature and integrate it in landscape planning.

It is essential to improve the quality and size of vegetated patches by increasing, retaining or restoring natural greenery as a reservoir and refuge for wildlife in the overall landscape development plan. A good example is Thomson Nature Park, located to the east of the central catchment nature reserve in Singapore. This 50 ha park was recently converted from state-reserved lands and a former village into a buffer park. Visitor trails and amenities have been curated to preserve a variety of wild flora and for a wide variety of animals to thrive. The species found there include rare and globally threatened fauna like the Raffles’ banded langur (Presbytis femoralis), lesser mousedeer (Tragulus kanchil) and the straw-headed bulbul (Pycnonotus zeylanicus). A freshwater stream within the park that has been retained forms a habitat for a range of native aquatic species, including the near-threatened spotted tree frog (Nyctixalus pictus) and the Malayan box terrapin (Cuora amboinensis) (Youjin, 2019). Another example is the 75 ha Windsor Nature Park, a green buffer protecting the central catchment reserve against the heavy traffic along the Upper Thomson Road. Design efforts include the following: improving marsh and freshwater swamp habitat; adding structural and functional diversity through multi-layered plantings to increase habitat complexity, which, in turn, will support a wide variety of native fauna, such as the Sunda Pangolin; placing a sub-canopy walk to observe fauna whilst minimising the impact on sensitive habitats (Chan and Toh, 2017).

Insert diverse microhabitats in the design site.

Appropriate microhabitats and flora species based on the range of target species can be provided to enhance the site’s diversity. A Singaporean example is the creation of diverse butterfly habitats along a 4 km butterfly trail in Orchard Road (Jain et al. 2012). Suitable microhabitats for target species (e.g. urban adapted butterfly species present in the surrounding natural areas) were created which included feeding, resting, puddling and hill-topping areas, caterpillar host and nectar plants were added on ground and trellises based on the species’ habitat preferences. The interventions naturally attracted 62 butterfly species over 2 years which is remarkable for a busy urban district. In other Singaporean examples, Nature Ways have been planted with fruit canopy trees and multi-layered shrubs for frugivorous animals (NParks 2020f); and nesting boxes for birds have been provided in Pulau Ubin (Teo 2011). A common misconception is that birds survive solely by living in trees and flying between them. However, planting a heterogeneous shrub and herb cover can greatly enhance bird diversity because many Southeast Asian birds spend a considerable amount of time in the understorey layer and on the ground. Clustered trees are preferred over linear strips as the former provide refuge by saving birds’ energy in flight and allow them to establish territories (Hails and Kavanagh 2013). Finally, Kampung Admiralty is a 0.9 ha public housing building that uses vertical structures of the building, roof garden, and community farm as multi-layered habitats. In this diverse planting palette, the habitats are stacked on different floors to create the impression of a continuous hill-like planting typology (Fig. 3). The habitats provide fruit and nectar and attract a wide range of birds and insects (see Banerd 2018).

Diversify types of landscape management.

A less controlled management regime can not only save maintenance cost or resources (Ignatieva and Hedblom 2018), but also promote animal diversity (Rupprecht et al. 2015; Rupprecht 2017). Certain vegetated patches on land or near water streams can be zoned for no or less human disturbance to facilitate ecological processes. For example, Singapore Botanic Gardens reuse leaf litter as mulch or composting so that detritivores may return to eat leaf litter and dead wood. Biological pest control in the Enabling Village project showcases a minimised use of pesticides against small insects and supports the breeding of populations of dragonflies. The Enabling Village project also features collaborative efforts by landscape architects, managers and clients to develop flexible management regimes for avian-attractive landscapes, pruning particular trees to increase visibility of a pond for birds, for instance. The community farm at the top of the Kampung Admiralty building is not sprayed with insecticide (typically done to prevent mosquito breeding) and thereby attracts a higher diversity of animals than other larger habitats that are sprayed regularly (A. J. unpublished data). Studies are ongoing at Jurong Lake Gardens in Singapore to understand how waterbodies landscaped to attract dragonflies can naturally control mosquito populations (Fig. 3).

Accommodate dynamism

Tropical plant community succession provides a unique opportunity to accommodate wildlife dynamics at spatial and temporal scales. Affiliated succession strategies include the following.

Allow spontaneous growth of urban green spaces as habitats.

Natural succession of managed green spaces could harbour more dynamic wildlife habitats over time. For example, on a 600 m² tropical lawn on a university campus in Singapore, grass cutting activities were halted for a couple of years; over time, the wildlife community increased (69 fauna species in total) starting with common birds and insects in the initial months and evolving towards the inclusion of frugivorous bats, pollinators, medium-size reptiles and mammals found in forest edges and an iconic visitor—the nationally critically endangered spotted wood owl (Hwang, Yue, and Patil 2019). Over the last decade, since a concrete drainage channel was converted into a 3 km naturalised waterway, Bishan Ang Mo Kio Park has seen a substantial growth of shrubby areas and waterside greenery (Fig. 3). The vegetation changes have attracted many distinctive water birds, like the migratory Asian Openbill Storks (Anastomus oscitans) and a colony of nesting Purple Herons (Ardea purpurea). Populations of aquatic animals including smooth-coated otters (Lutrogale perspicillata) have also increased (A. J. unpublished data; An, Chen, and Li 2020).

Propose incremental habitat enhancement plans to build a stable foundation to maximise the persistence of wildlife populations and diversity in the long run.

The first phase of habitat enhancement involves optimising the site’s abiotic elements, such as water and air flows, for ideal animal movement, to establish healthy nutrient fluxes (Naeem, Duffy, and Zavaleta 2012). Abundant fallen woody material on the ground builds a strong foundation for higher fungal and insect richness, and this interconnects with higher avian richness. This strategy has been applied across several managed spaces in Singapore through the introduction of log piles, including at Dairy Farm Nature Park. Such spaces need to be left undisturbed and unmanicured to allow food webs to be re-established. The second phase involves thoughtful structural interventions, including plant selection to stimulate plant–animal interactions, such as active seed dispersal by herbivores (Berzaghi et al. 2018), and higher breeding success rate by planting preferred nesting trees for birds. Fauna-attractive landscape elements, such as bird perches, water ponds and bug hotels, can be inserted in this phase. Jurong Lake Gardens is an exemplary case: the Gardens use existing natural resources (soil, existing trees, and water flows) and attempt to restore original habitats (freshwater swamp forest) to create a foundation for the restoration of wildlife populations. New habitat features have been added, such as Alstonia Island (comprising swamp-adapted Alstonia trees), riverine and marshy areas, woodlands and dry grasslands, so that the Gardens can become a food source and nesting ground for resident and migratory wildlife populations (Low 2020). Despite these features, a hindrance to maximising wildlife populations in the Gardens is that the habitat features are frequently manicured; this leads to disturbance and lack of woody debris for insect diversity and food web establishment.

Introduce pre-emptive planning interventions to avoid the sudden and complete erasure of habitats.

A pre-emptive planning strategy will strive to maintain the ecological equilibrium of remaining green spaces in compact cities, whilst meeting the needs of human development. For example, if unprotected forests need to be developed, planners should commission a pre-development survey. Environmental safeguards, such as stringent and transparent Environmental Impact Assessments (EIAs), need to be put in place to identify important flora (e.g. plants of conservation value, heritage trees), fauna-supporting natural resources (e.g., top-soils, plant materials, fallen tree trunks and tree cavities), and important faunal areas for conservation purposes. After years of civil society campaigns to make the EIA process more stringent in Singapore (NatureSociety 2016), policies around the EIA framework have been finally amended. Future development projects in Singapore are expected to be more sensitive to wildlife (Tan 2020). For example, the Bidadari new town development plan is slated to replace a mature woodland that was formerly a haven for migratory birds with a high-dense public housing development. To mitigate the impact on wildlife, a large park retaining 350 mature trees and terrains is to be maintained around the housing units. New parks, wetland, and marsh will be created to increase habitat diversity. The hope is that these interventions will maintain the site’s function as a haven for migratory birds (Lin 2019).

Intertwine social and ecological processes

One metre-long monitor lizards and long-tailed macaques are commonly spotted in tropical cities such as Singapore. Yet, such astonishing creatures are not widely appreciated and seldom regarded as a part of urban dwelling. To address this issue, design strategies should include the following.

Minimise wildlife conflicts by maintaining a ‘preferred’/’safe’ distance from wild animals.

Several techniques can minimise stress, fearful reactions, and conflict between humans and wildlife. For instance, for a forest edge adjacent to houses, a Ha-ha wall (a recessed turf area creating a vertical barrier whilst preserving an uninterrupted view of the landscape beyond, see Fig. 2) may be a useful landscape element against wildlife access whilst maintaining visual connection. Similar to the Bidadari public housing in Singapore and high-rise residential buildings in Hong Kong (Jim and Chen 2006), the creation of photography spots allowing observers to establish connections with wild animals through window views may be a socially acceptable design strategy for the community. ‘Socially’ preferable settings, by which we mean human tolerance levels of certain species, and acceptable densities of each fauna group could be further studied in site-specific contexts. For example, designers may suggest manicured turfs as a buffer for dense grass habitats that might contain snakes and vermin, like those implemented at Tampines Eco Green (NParks 2020h). In another example, a sub-canopy walkway in Windsor Park allows users to observe fauna whilst minimising the impact on the sensitive on-ground habitats.

Align cultural, ecological and recreational use.

A good designer knows how to introduce aesthetically pleasing landscape scenes with visually attractive combinations of flora, fauna, and supportive landscape features (e.g. artificial nest boxes, bird feeders, water pots). It would be ideal if such combinations were associated with restorative planning and ecological functions, so that the pleasant human experience could contribute to increasingly favourable attitudes to wildlife in the designed spaces. Over and above the habitat creation features at Jurong Lakeside Gardens (see Accommodate dynamism section), the Gardens have sensitively developed a number of recreational areas for users to have a favourable view of wildlife: one of the playgrounds emulates the movement of animals who inhabit a freshwater swamp forest; long grass hills provide uninterrupted views of the expansive landscape and serve as a popular photo-taking spot; and a meandering boardwalk brings visitors closer to freshwater swamp forest and wetland habitat suitable for feeding and foraging water birds (NParks, 2019).

Create educational opportunities to increase public awareness of wildlife in cities.

Many studies (Gobster et al. 2007; Straka, Kendal, and van der Ree 2016; Ngo, Hosaka, and Numata 2019) have found educational programmes tailored to local contexts (e.g. historical, ecological and cultural significance of particular fauna species, such as hornbills in Borneo) are essential for people to become attached to and appreciate nature. Synergies can be identified if such programmes include playful engagement activities for childhood development (Louv 2010), involvement of community members in wildlife gardening and photography groups (Mumaw, Maller, and Bekessy 2017), and, to some extent, utilitarian functions (e.g. harvesting honey from a bee hive). Learning Forest in Singapore Botanic Gardens (NParks 2020e) and Community in Nature Schools Award schemes (NParks 2020d) in Singapore include many educational programmes, such as fauna observation tips, rescue wildlife programs, and the creation of butterfly gardens. The Windsor and Tagore neighbourhoods adjacent to Windsor and Thomson nature parks that expect a ‘spill over’ effect (Brudvig et al. 2009) should be prime targets to develop public awareness about wildlife in the surrounding areas (see Maintain heterogeneity section). Awareness programmes can be accompanied by citizen-science projects to enable citizens to participate in and support ecological data collection (e.g. Every Singaporean a Naturalist, Garden Bird Watch). This can lead to better long-term monitoring and planning of wildlife and ecosystems.

Functioning ecosystems connected at nested scales

As a highly urbanised island city-state, the green and grey infrastructure in Singapore is highly interconnected. It is important to understand the relationship between the biological (e.g. fauna movement patterns), biophysical (e.g. water flow) and social (e.g. movement of people and traffic) flows of the city (Lewis et al. 2019; Egerer and Anderson 2020). Armed with this understanding, designers can identify synergies and reduce conflicts between these flows, both within sites and in the larger surrounding context. This could be achieved by applying three strategies.

Increase landscape connectivity to enhance faunal movement.

Connectivity is an important issue in urban landscapes, as urban habitat edges have harsh limits for landscape elements and the urban matrix generally constrains faunal movement (Jain et al. 2020). Design actions can link fragmented animal populations as a part of a larger biological network using multiple approaches, such as visibly connected tree canopies, tree-top overpasses for birds and arboreal fauna, and overhead bridges above highways. For example, two elevated bridge crossings in Singapore are solely designed for wildlife. These are the 62 m Eco-link@BKE connecting the Bukit Timah and Central Catchment nature reserves (Fig. 3) and the 140 m Mandai Ecolink (Tan 2017a) linking the north western part of the central reserves. These crossings have multi-tiered forest canopy layers; thus, over time, critically endangered animals, such as the Sunda pangolin, mouse deer and another terrestrial species have used the crossings as a temporary refuge and stepping stones. Well-designed vegetation strips on the ground (e.g. Nature Ways) could work for burrowing animals and relatively immobile reptiles and amphibians or riparian corridors. Corridors should be designed keeping in mind the dispersal distances of target fauna species. For instance, in Singapore, the Crimson Sunbird Aethopyga siparaja has a maximum dispersal distance between habitat patches of ∼200 m (Weir and Corlett, 2007; Hamid, 2015). Integrating vegetation in buildings (e.g. Skyrise Greenery Awards schemes; NParks 2020g) could be extensively applied in a compact city, particularly for flying animals (e.g. insects, birds, and bats). At Thomson Nature Park, the National Parks Board of Singapore added rope bridges for the threatened Raffles Banded Langurs to cross the approaching Old Upper Thomson Road. Culverts have been installed for small mammals such as pangolins and porcupines. A Roadway Animal Detection System has been installed which uses video analytics to detect animals when they are near the road and alters incoming motorists to their presence through flashing road signs. Wooded streets and/or canals with naturalised edges can increase urban landscape connectivity by providing an alternative habitat for feeding and nesting, whereas remaining mindful that human traffic and the limited width of a vegetated strip negatively affect biodiversity (Plante, Jaeger, and Desrochers 2019). These connecting strips can be further enhanced for biodiversity if designated spaces are left unmanaged or minimally managed.

Reduce or remove barriers blocking faunal movement.

The strategy includes modifying traffic flows to minimise incompatible flows (e.g. partially pedestrianised existing roads), increasing the permeability of the urban matrix (e.g. reducing the use of impervious surfaces, promoting underpasses and viaducts below elevated highways or culverts for wildlife crossings), and aggregating green spaces to ensure minimal animal crossing of habitat edges and reduced edge effects. Such actions could enhance movement for visible species, as well as the many invisible organisms that cannot disperse across the landscape in the absence of a continuous corridor. Several wildlife culverts have been created in Jurong Lake Gardens; these allow freshwater fauna to cross via small streams and water channels running below small roads and trails (Fig. 3). Neglected spaces under viaducts located in the southern part of the Central Catchment nature reserve could offer a safe haven for animals by fostering terrestrial habitats, as these areas are typically less disturbed by human presence. The shaded conditions could become a positive opportunity to attract bat species, and viaduct edges could become nesting spaces for cliff and mud nesting birds, such as swifts and swallows. Possible design strategies for spaces under viaducts include the following: improve soil fertility so the growth of microorganisms as food sources for small insects can thrive, and the space can ultimately attract a diverse group of animals; provide a shaded softscape to facilitate the movement of reptiles and ground animals; form an airflow and then reconfigure planting to assist seed dispersal, plant reproduction and movement of pollination from CCNR, as shown in the ‘Rewilding Singapore’ design studio (Hwang, Endo, and Lum 2020).

Retrofit existing green spaces and infrastructure to mitigate biophysical impacts of urbanization.

Green spaces that minimise light and noise pollution can increase wildlife in urban areas. For example, using dark-sky lighting principles such as minimising the area of illumination by using light fixtures and long-wavelength lights can make urban green areas friendlier to nocturnal wildlife. Similarly, quieter environments with denser and wider multi-layered planting areas can greatly reduce the impact of urban traffic noise, so that birds don’t have to vocalise louder or raise their minimum frequency of vocalisations to communicate and expend an increased amount of energy to singing in noisy urban environments (Hu and Cardoso 2010).

In addition, the replacement of typical wayside plantings with fauna-supporting species and more complex vertical structures able to support a variety of animals, including mammals birds and insects. Another intervention could be reducing the mowing frequency on road verges, as this tends to enhance invertebrate biodiversity (O’Sullivan et al. 2017). Bishan Ang Mo Kio Park and Sungei Api Api mangrove restoration projects in Singapore showcase the transformation of concretised canals/drainage into naturalised waterways (Fig. 3). Such examples are able to not only support aquatic animal movements but also reduce runoff and improve water quality.

Key takeaways from the design approaches

There is increasing recognition of the importance of collaboration between ecologists and designers to build urban resilience and sustainability in research and practice (Felson, Bradford, and Terway 2013; Grose 2014). Yet ways to fill information and practice gaps between these fields require exploration. The proposed approaches suggest contexts and possible strategies to engage with the complex dynamics of urban ecology in design and planning, to link data and design, and to integrate knowledge-driven science into site-specific, spatial and actionable design strategies that could be implemented in the real world.

Compact cities like Singapore face trade-offs between landscape development and conservation of wildlife and are typically confronted by a reduction of green spaces which, in turn, will reduce wildlife in the city. The pressures of urban growth encourage designers to explore the optimum use of urban nature by maximising and densifying ecological functions and increasing multi-functionality and resource efficiency to create an ecological equilibrium. The proposed approaches include ways to explore human coexistence with non-human animals, despite high urban density within a finite land area.

Many landscape design projects in Singapore partially respond to and support these proposed design strategies. Although most projects do not focus on human–wildlife interactions, they bring people closer to nature. The potential for design outcomes may be more significant if designers explicitly recognise the socio-ecological functions of target species and include the systemic assessment of sites as critical parameters in their designs. Designers’ ability to reconcile the conflict between anthropocentric and ecocentric development thus becomes imperative.

The key to wildlife-inclusive cities goes beyond simply designing spaces for animals to thrive. Success also depends on public acceptance of wildlife in the urban context. Thus, the social perspectives of human–wildlife interactions require more study. We hope our suggestions will boost design and planning efforts in that direction, strengthening links between wildlife and urban dwellers and having a positive impact on the pursuit of conservation beyond cities and towards a biodiverse planet.

Conflict of interest statement. None declared.

References