A predictive approach to assess urban biodiversity and plan for future development scenarios
Abstract
Protecting and enhancing biodiversity in urbanized areas is recognized as an important priority. To achieve this through urban planning, there must be empirically derived tools to predict biodiversity at the appropriate spatial scales and resolutions given various options in urban designs to compare the expected biodiversity outcomes and make optimal decisions.
We demonstrate how this can be done by developing models that predict the expected species densities or ‘alpha diversity’ in urban landscapes for four animal groups: birds, butterflies, odonates and amphibians, based on assemblage data from spatiotemporally replicated surveys conducted in the tropical city of Singapore. We demonstrate two use cases for these predictive models: citywide assessment and future scenario planning.
For citywide assessment, sub-city ‘towns’ (equivalent to districts or suburbs elsewhere) were compared and benchmarked relative to all other towns, based on the average species densities as indicators of habitat value for each of the four animal groups.
For future scenario planning, four development scenarios were compared, and the compatibility of vector-type planning layers with the models was tested.
An open-source R package, biodivercity, was developed that would facilitate the use of the same workflow elsewhere: to build, apply and validate predictive models elsewhere given similar available empirical data.
Synthesis and applications: The models developed can also be examined to generate recommendations for further actions that can improve biodiversity across different spatial scales. These techniques can be incorporated into current planning practices to achieve a more quantitative and performance-based approach to enhancing biodiversity at fine spatial scales in human-dominated landscapes.
Dataset DOI: 10.5061/dryad.2fqz6131p
Description of the data and file structure
Sampling locations
Four animal groups were surveyed at six towns (as officially delimited) in the equatorial city-state of Singapore located in Southeast Asia (1.3° N, 103.8° E). For each town, surveys were conducted every two months across a one-year duration.
Point locations for surveys were randomly sampled across two land-cover strata—natural vegetation and urban cover. Before each survey year, ‘natural vegetation cover’ (forest patches) within the respective study towns was preliminarily delineated in Google Earth; large water bodies were then excluded from the remaining area to form ‘urban cover’ (which includes cultivated vegetation). The two land-cover strata were used to randomly generate sampling points at a density higher than the target of 1 point per 50 ha, to provide backup points upon inspection and on-site reconnaissance. Each sampling point was checked for accessibility and the presence of water bodies nearby. Proximity to permanent or ephemeral water bodies was required for surveys of two out of the four animal groups—odonates and amphibians. Sampling points were adjusted up to 50 m to avoid safety hazards, or to increase their proximity to water bodies to be within 20 m, owing to the relatively low chance of points being randomly generated close to water bodies. For each survey round, the number of points close to water bodies was fixed at 10 per town.
Animal surveys
Four animal groups were assessed in this study: Birds (Aves); butterflies (Insecta: Lepidoptera excluding moths); dragonflies and damselflies (Insecta: Odonata; hereafter ‘odonates’); and frogs and toads (Amphibia: Anura; hereafter ‘amphibians’). Thirty-minute surveys were conducted by two observers for each animal group. The bird and butterfly surveys were conducted at all sampling points, while the odonate and amphibian surveys were only conducted at points that were close to water bodies. Counts of each species were recorded within a fixed radius of the sampling point; the radius of observations was set at 50 m for birds, and 20 m for the other three animal groups. No animals were captured; visual and aural surveys were conducted for birds (0700–0930 hrs) and amphibians (2000–2200 hrs); and visual surveys were conducted for butterflies (0930–1200 hrs) and odonates (1400–1600 hrs). Surveys were conducted during fair weather conditions. For points close to ephemeral water bodies, the odonate and amphibian surveys were conducted within 24 hours after a rain event (recorded at the weather station nearest to the sampling point). To account for seasonal variation, surveys were repeated every two months at each sampling point, across a one-year duration (six surveys). For some survey points, there were disruptions such as commencement of construction work that meant that the full set of six surveys could not be completed; only the points with six completed surveys were used in the analysis (sample size n = 134 for birds and butterflies; n = 50 for amphibians and odonates). For each animal group, the total number of species observed across the six repeated surveys was tallied at each sampling point.
Remote sensing of landscapes
Features of the built environment (i.e., buildings, roads) were derived based on OpenStreetMap (OSM) data, downloaded using the R package osmextract, and then ground-truthed on-site during the year of the animal surveys and amended if necessary for accuracy. Sentinel-2 satellite images were downloaded using the R package sen2r , to derive classes of land cover such as vegetation and water cover at a 10-m pixel resolution. Vegetation cover was then sub-categorized into canopy (> 2 m height) and short (≤ 2 m height) vegetation cover, based on height from ground level. The height from ground level was represented by the normalized digital surface model (nDSM) at a 0.5-m pixel resolution, derived from the LiDAR-based digital surface model (DSM) and digital terrain model (DTM) obtained from the Singapore Land Authority from airborne scans conducted in 2019. Landscape patterns were then quantified for each land cover class, summarized at each sampling point. The R package landscapemetrics was used to calculate each metric at the ‘class’ level.
Files and variables
File: data.xlsx
Description: Excel file with four sheets, one for each animal group
Variables
- town: The residential town in Singapore where the point counts were conducted. BS: Bishan; JW: Jurong West; PG: Punggol; QT: Queenstown; TP: Tampines; WL: Woodlands.
- sprich: The total number of unique species encountered across the six bimonthly surveys at that point.
- r[x]m_*: Quantified within a buffer radius of x m. Followed by either osm or lsm.
- osm: From a vector layer generated from Open Street Maps. Followed by one of the following:
- *_buildingAvgLvl: The weighted average height of buildings in the area, (∑(A × L))/(∑A), where A and L are the respective areas and number of levels for each building.
- *_buildingFA_ratio: The gross floor area of buildings divided by the area of interest, (∑(A × L))/(πr^2), where A and L are the respective areas and number of levels for each building, and r is the radius of the sampling point.
- *_buildingVol_m3: The total volume of buildings within the area of interest, ∑(A × H) where A and H are the respective areas and height for each building.
- *_laneDensity: Represents the density of traffic within the area of interest, (∑(s × l))/(πr^2 ), where s and l denote the respective length and number of lanes of each road segment, and r is the radius of the sampling point.
- lsm: A landscape metric extracted from the raster layer generated from remote sensing. Followed by _:
- Land covers
- veg: all vegetation
- vegshort: short vegetation
- vegcanopy: vegetation canopy
- water: water cover
- Landscape metrics
- Land covers
| Variable Code | Name |
|---|---|
| <land cover>_ai | Aggregation index |
| <land cover>_area_mn | Patch area (mean) |
| <land cover>_circle_mn | Related circumscribing circle (mean) |
| <land cover>_clumpy | Clumpiness index |
| <land cover>_contig_mn | Contiguity index (mean) |
| <land cover>_division | Division index |
| <land cover>_ed | Edge density |
| <land cover>_enn_mn | Euclidean nearest neighbor distance (mean) |
| <land cover>_frac_mn | Fractal dimension index (mean) |
| <land cover>_gyrate_mn | Radius of gyration (mean) |
| <land cover>_lpi | Largest patch index |
| <land cover>_lsi | Landscape shape index |
| <land cover>_mesh | Effective mesh size |
| <land cover>_nlsi | Normalized landscape shape index |
| <land cover>_np | Number of patches |
| <land cover>_para_mn | Perimeter-area ratio (mean) |
| <land cover>_pd | Patch density |
| <land cover>_pladj | Percentage of like adjacencies |
| <land cover>_pland | Percentage of landscape |
Code/software
All sampling design, data processing, and analyses in this study were performed using the open-source statistical software R v. 4.1.1.
