The authors have declared that no competing interests exist.
Conceived and designed the experiments: CR JB. Performed the experiments: CR. Analyzed the data: CR. Wrote the paper: CR JB.
Informal urban green-space (IGS) such as vacant lots, brownfields and street or railway verges is receiving growing attention from urban scholars. Research has shown IGS can provide recreational space for residents and habitat for flora and fauna, yet we know little about the quantity, spatial distribution, vegetation structure or accessibility of IGS. We also lack a commonly accepted definition of IGS and a method that can be used for its rapid quantitative assessment. This paper advances a definition and typology of IGS that has potential for global application. Based on this definition, IGS land use percentage in central Brisbane, Australia and Sapporo, Japan was systematically surveyed in a 10×10 km grid containing 121 sampling sites of 2,500 m2 per city, drawing on data recorded in the field and aerial photography. Spatial distribution, vegetation structure and accessibility of IGS were also analyzed. We found approximately 6.3% of the surveyed urban area in Brisbane and 4.8% in Sapporo consisted of IGS, a non-significant difference. The street verge IGS type (80.4% of all IGS) dominated in Brisbane, while lots (42.2%) and gaps (19.2%) were the two largest IGS types in Sapporo. IGS was widely distributed throughout both survey areas. Vegetation structure showed higher tree cover in Brisbane, but higher herb cover in Sapporo. In both cities over 80% of IGS was accessible or partly accessible. The amount of IGS we found suggests it could play a more important role than previously assumed for residents' recreation and nature experience as well as for fauna and flora, because it substantially increased the amount of potentially available greenspace in addition to parks and conservation greenspace. We argue that IGS has potential for recreation and conservation, but poses some challenges to urban planning. To address these challenges, we propose some directions for future research.
Dunn et al. argue that global conservation efforts depend on the interest people have in nature conservation, an interest formed largely through experiencing nature within the cities that people inhabit
This paper reports the results of a study that asked the following four research questions: (1) how does the land use proportion of total IGS and individual IGS subtypes differ between urban core areas in two cities? (2) how do the characteristics (distribution, vegetation structure, accessibility) of IGS differ between urban core areas in two cities? (3) does distance from the city center influence IGS quantity, and (4) how accurate is the IGS land use proportion survey method employed for estimating potential IGS quantity? This study contributes new knowledge in two ways. Our study has for the first time examined how much land likely consists of a wide variety of IGS types in an urban core. Second, it represents the first comprehensive examination comparing IGS quantity and type within the urban core area of two cities, potentially allowing scholars to examine IGS composition and quantity in other geographical settings.
Cities consist of a patchwork of different spaces, from densely built areas to green space such as urban forests or parklands. But besides these exist also more ambiguous, ‘liminal’ vegetated spaces, that Jorgensen and Tylecote refer to as ‘ambivalent landscapes’
This liminality presents a challenge for quantitatively surveying such spaces, which we aim to address by proposing a provisional, non-exclusive definition and typology of a form of liminal green spaces we term ‘informal urban green space’ (IGS). For the purpose of this study, we have defined IGS as an explicitly socio-ecological entity, rather than a solely biological or cultural object. IGS consists of any urban space with a history of strong anthropogenic disturbance that is covered at least partly with non-remnant, spontaneous vegetation
IGSs differ in their management (e.g. access, vegetation removal, stewardship), land use and site history, their scale and shape, soil characteristics and local urban context. For example, a small brownfield may be similar to a vacant lot in appearance and size, but their different land use history, vegetation removal periods, and urban context distinguish them. We identified nine potentially different subtypes of IGS: street verge, lot, gap, railway, brownfield, waterside, structural, microsite and power line IGS (
Street verges: A) Spontaneous herbal vegetation on sidewalk (Sapporo, Japan), B) Unused, highly maintained nature strip with mix of planted and spontaneous vegetation (Brisbane, Australia), C) Spont. herbal vegetation between street and sidewalk (Sapporo). Lots: D) Former residential vacant lot, remains of garden structure still present (Sapporo), E) Long-term vacant lot in residential area (Brisbane), F) Former residential, long-term vacant lot, “no trespassing” sign (Nagoya, Japan). Gap: G) Space with spontaneous herbal vegetation between two buildings, informal storage use (Sapporo), H) Gap with rudimentarily blocked access in front of building (Sapporo), I) Vegetated gap in sealed surface around fence in industrial zone (Brisbane). Railway: J) Annual grass in verge between rail track and street (Sapporo), K) Vegetated cliff next to rail track (Brisbane), L) Vegetated verge and inter-track space (Sapporo). Brownfield: M) Publicly-owned, large vacant tract with grassland and single trees (Sapporo), N) Old city quarter, overgrown former ceramics factory lot (Tokoname, Japan), O) Vegetated area on municipal land for disaster preparation material storage in urban fringe (Sapporo).
Waterside: A) Vegetation on soil deposits in concreted river bed (Nagoya), B) Spontaneous vegetation and informal agricultural use of flood-protection stream banks (Sapporo), C) Spontaneously vegetated anthropogenic river banks (Sapporo). Structural: D) Creeping vines on industrial building (Nagoya), E) Overgrown bridge (Nagoya), F) Concrete soil retention wall completely covered in ivy (Sapporo). Microsite: G) Vegetated crack in asphalt on parking lot (Sapporo), H) Vegetation between two sidewalk plates (Brisbane), I) Plant growing out of degraded traffic cone remains (Nagoya). Powerline: J) Powerline reserve in industrial zone (Brisbane), K) Vegetated area around powerline pylon (near Osaka, Japan), L) Vegetated area around powerline pylon (Sapporo).
IGS | Examples | Description | Management | Form | Substrates |
Roadside verges, roundabouts, tree rings, informal trails and footpaths | Vegetated area within 5 m from street not in another IGS category; mostly maintained to prevent high and dense vegetation growth other than street trees; public access unrestricted, use restricted. | Regular vegetation removal (> = once per month); governmental and private stewardship | Small: <100 m2, linear | Soil, gravel, stone, concrete, asphalt | |
Vacant lots, abandoned lots | Vegetated lot presently not used for residential or commercial purposes; if maintained, usually vegetation removed to ground cover; public access and use restricted. | Irregular veg. removal, medium to long removal intervals; private stewardship | Small-medium: <1 ha, block | Soil, gravel, bricks | |
Gap between walls or fences | Vegetated area between two walls, fences or at their base; maintenance can be absent or intense; public access and use often restricted. | Irregular veg. removal; variable removal intervals; private stewardship | Small: <100 m2, linear | Soil, gravel | |
Rail tracks, verges, stations | Vegetated area within 10 m adjacent to railway tracks not in another IGS category; usually herbicide maintenance to prevent vegetation encroachment on tracks; public access and use mostly restricted. | Regular veg. removal (monthly to yearly); corporate or governmental stewardship | Medium-large: >1 ha, linear | Soil, gravel, stone | |
Landfill, post-use factory grounds, industrial park | Vegetated area presently not used for industrial or commercial purposes; usually no or very infrequent vegetation removal and maintenance; public access and use mostly restricted. | Irregular veg. removal, long removal intervals; corporate and governmental stewardship | Medium-large: >1 ha, block | Soil, gravel, concrete, asphalt | |
Rivers, canals, water reservoir edges | Vegetated area within 10 m of water body not in another IGS category; occasional removal of vegetation to maintain flood protection and structural integrity; public access and use often possible with some restrictions. | Irregular veg. removal, long removal intervals; governmental stewardship | Small-large: >10 m2 to >1 ha, linear | Soil, stone, concrete, bricks | |
Walls, fences, roofs, buildings | Overgrown human artifacts; often vertical; occasional removal of vegetation to maintain structural integrity; public access and use mostly restricted. | Irregular veg. removal, medium to long removal intervals; varying stewardship | Small: <100 m2, block | Soil, stone, gravel, wood, metal | |
Vegetation in cracks or holes | Vegetation assemblages in cracks, may develop into structural IGS; maintenance can be absent or intense | Irregular veg. removal, variable removal intervals; variable stewardship | Very small: <1 m2, point | Deposits, soil, stone, concrete | |
Power line rights of way | Vegetated corridor under and within 25 m of power lines not in another IGS category; vegetation removed periodically to prevent high growth; public access and use mostly unrestricted. | Regular veg. removal (less than yearly); utility or governmental stewardship | Medium-large: >1 ha, linear | Soil |
Brisbane (Queensland, Australia) and Sapporo (Hokkaidō, Japan) were chosen as case study cities, because research that examines IGS outside of Europe and the USA is relatively scarce. The two case study cities have similarities and differences that lend them well to comparison (
Characteristics | City of Brisbane (LGA) | Sapporo |
Founded | 1824, city status 1902 | 1868, city status 1922 |
Population | 1,089,743 (2011) (2031: 1,27 million) | 1,936,189 (2013) (2030: 1,87 million) |
Area | 1,338 km2 | 1,121.12 km2 |
Pop. density | 814/km2 | 1,699/km2 |
Peak density | >5,000/km2 | >8,000/km2 |
Climate | Humid subtropical (Cfa) | Humid continental (Dfa) |
Industry | Tourism, resources, retail, financial services, agriculture hub, education | Tourism, retail, IT, agriculture hub, resources, education |
Greenspace | Local parks: 3,290 ha (32 m2/capita) | Parks: 2,345 ha (12.3 m2/capita) |
All parks: 11840 ha (115 m2/capita) | All greenspace: 5,508 ha (28.9 m2/capita) | |
Park area planned | 40 m2/capita, minimum 20 m2/capita | “No greenspace loss, park renovation” |
Sources:
While Sapporo has seen rapid growth throughout the second half of the 20th century and now has a population of about 1.9 million, its population is now stagnating and is predicted to decline in the future. In contrast, Brisbane has a population of around 1 million but is still growing quickly (
In both cities, formal greenspace consists of networks of over 2,000 public parks, most of them small local parks. Brisbane has 3,290 ha of local parkland (32 m2/capita), whereas Sapporo has 2,345 ha (12.3 m2/capita) (
To be able to measure the proportion of land use consisting of IGS and compare it between the survey areas in Brisbane and Sapporo, we used a systematic grid sampling design
We used a three-step process to measure the percentage of IGS and other land uses. First, we created a geographic information system (GIS) layer with site locations and projected it on publicly available high-resolution aerial photography data (Google Earth in Brisbane, see
For the final step, we individually estimated percentages on paper in each 10×10 m sub-site for each land use category present in the sub-site. One percent of land use in each of those sub-sites equals one square meter. For complex sites, additional support lines were drawn across the aerial photo, dividing each sub-site into four 5×5 m sites that each represented 25%. Where necessary, these were further divided into 12.5% or 6.25% blocks. To improve the quality of percentage estimates we used non-GIS-compatible high-resolution aerial photography by NearMap (Brisbane, see
For all IGS types, we visually estimated (with the help of measuring tape) vegetation cover percentage of four different vegetation strata (
We assessed how accessible IGS areas were on a three-level scale derived from prior research into vacant lot accessibility
Example photographs: a) IGS inaccessible due to height and missing ladder; b) IGS completely fenced off; c) IGS access restricted by physical (wire) and symbolic barriers (sign).
We used SPSS (v. 21 and 22, OS X) and R (v. 3.02, OS X) to perform descriptive and inferential statistical analyses. Frequency tables were used to describe quantity of IGS, quantity of IGS types, and IGS characteristics (vegetation structure, accessibility). Initial analysis indicated that the sample data was not normally distributed (P-P plots, skewness and kurtosis tests). We therefore used non-parametric tests, namely a Mann-Whitney U test to test for differences in IGS proportion, and a PERMANOVA test with Euclidean distance matrix to test for differences in IGS type proportions between the two survey areas (using R function
To test how accurate the IGS and land use survey method used in this paper was, we compared the results to land use data from GIS data sets supplied by the local city governments. For this purpose, we first combined the geographic features (e.g. polygons representing residential or green space land use) in the city-supplied data sets (ArcGIS 10, UNION), then removed all features outside the smallest possible square containing all sampling sites (ArcGIS 10, CLIP) to calculate the total land use of the features we wanted to compare. In Brisbane, we compared total combined land use percentages of parks (FGSPK), conservation areas (FGSCN), and sports and recreation areas (FGSSR) from our survey with the total greenspace land use percentage from two Brisbane council greenspace data sets (see
To check for an accumulation curve and observe the change in land use percentage as sample size increased, we plotted the land use percentage over the number of sites surveyed. Additionally, we plotted the deviation of our land use percentage results from city-supplied datasets (formal greenspace and residential land use in Brisbane, formal greenspace in Sapporo) against the number of sites surveyed. This allowed us to observe what sample size is necessary to achieve a certain level of deviation from the city-supplied datasets.
The surveyed area in Brisbane consisted of 6.3% (19,027 m2) IGS (
IGS Type | N |
Quantity (m2) | Mean size (m2) | Proportion/area (%) | Proportion/IGS (%) |
Lot | 32 | 1,433 | 44.78 | 0.47 | 7.53 |
Gap | 22 | 117 | 5.32 | 0.04 | 0.61 |
Street verge | 643 | 15,300 | 23.79 | 5.06 | 80.41 |
Brownfield | 15 | 967 | 64.47 | 0.32 | 5.08 |
Waterside | 7 | 125 | 17.86 | 0.04 | 0.66 |
Waterside/verge | – | – | – | – | – |
Structural | 38 | 126 | 3.32 | 0.04 | 0.66 |
Street verge/gap | – | – | – | – | – |
Railway | 28 | 959 | 34.25 | 0.32 | 5.04 |
Lot/street verge | – | – | – | – | – |
Powerline | – | – | – | – | – |
Total | 785 | 19,027 | 6.29 | ||
Extrapolated |
6,353,057 | 6.29 |
*N = number of IGS as recorded in all 3,025 sub-sites.
**Extrapolated to reflect the area of the smallest possible square containing all sampling sites (total square area 101,002,500 m2).
IGS Type | N |
Quantity (m2) | Mean size (m2) | Proportion/area (%) | Proportion/IGS (%) |
Lot | 159 | 6144 | 38.64 | 2.03 | 42.20 |
Gap | 386 | 2796 | 7.24 | 0.92 | 19.20 |
Street verge | 284 | 2351 | 8.28 | 0.78 | 16.15 |
Brownfield | 22 | 1458 | 66.27 | 0.48 | 10.01 |
Waterside | 27 | 1417 | 52.48 | 0.47 | 9.73 |
Waterside/verge | 5 | 179 | 35.80 | 0.06 | 1.23 |
Structural | 30 | 93 | 3.10 | 0.03 | 0.64 |
Street verge/gap | 16 | 68 | 4.25 | 0.02 | 0.47 |
Railway | 7 | 43 | 6.14 | 0.01 | 0.30 |
Lot/street verge | 1 | 7 | 7.00 | 0.00 | 0.05 |
Powerline | 2 | 3 | 1.50 | 0.00 | 0.02 |
Total | 939 | 14559 | 4.81 | ||
Extrapolated |
4858220 | 4.81 |
*N = number of IGS as recorded in all 3,025 sub-sites.
*Extrapolated to reflect the area of the smallest possible square containing all sampling sites (total square area 101,002,500 m2).
City | Brisbane survey area | Sapporo survey area | ||
Greenspace type | Area (m2) | Area (%) | Area (m2) | Area (%) |
19027 | 6.29 | 14559 | 4.81 | |
Parks | 16146 | 5.34 | 9493 | 3.14 |
Sports and recreation | 10164 | 3.36 | 4423 | 1.46 |
Conservation | 7641 | 2.53 | 32208 | 10.65 |
Planted verges | 1085 | 0.36 | 441 | 0.15 |
35036 | 11.58 | 46565 | 15.39 | |
Gardens | 62599 | 20.69 | 26193 | 8.66 |
Shared greenspace | 8434 | 2.79 | 5052 | 1.67 |
Community land | 11592 | 3.83 | 13210 | 4.37 |
Commercial and industrial | 387 | 0.13 | 776 | 0.26 |
83010 | 27.44 | 45231 | 14.95 | |
137073 | 45.31 | 106355 | 35.16 |
We found IGS was present in most of the sampling sites in both cities (
City | Brisbane survey area | Sapporo survey area | ||||||||||
IGS Type | N |
Tree (%) | Bush (%) | Herb (%) | Ground (%) | HG (%) |
N |
Tree (%) | Bush (%) | Herb (%) | Ground (%) | HG (%) |
Brownfield | 15 | 0.0 | 0.0 | 51.3 | 34.0 | 85.3 | 22 | 0.0 | 95.0 | 100.0 | 0.0 | 100.0 |
Gap | 22 | 0.0 | 2.3 | 57.0 | 21.6 | 78.6 | 386 | 3.2 | 6.2 | 45.3 | 44.4 | 89.7 |
Lot | 32 | 23.6 | 12.5 | 79.4 | 11.7 | 91.1 | 159 | 7.6 | 8.3 | 36.1 | 37.7 | 73.8 |
Lot/street verge | – | – | – | – | – | 1 | 0.0 | 0.0 | 100.0 | 0.0 | 100.0 | |
Powerline | – | – | – | – | – | 2 | 0.0 | 0.0 | 0.0 | 100.0 | 100.0 | |
Railway | 28 | 1.8 | 6.6 | 76.8 | 4.1 | 80.9 | 7 | 0.0 | 0.0 | 75.7 | 12.9 | 88.6 |
Street verge | 643 | 31.7 | 7.8 | 10.2 | 85.3 | 95.5 | 284 | 11.7 | 2.9 | 34.4 | 58.9 | 93.3 |
Street verge/gap | – | – | – | – | – | 16 | 0.0 | 0.6 | 49.4 | 43.1 | 92.5 | |
Structural | 38 | 10.5 | 9.7 | 73.2 | 21.3 | 94.5 | 30 | 0.0 | 6.2 | 26.3 | 70.7 | 97.0 |
Waterside | 7 | 35.7 | 21.4 | 92.9 | 0.0 | 92.9 | 27 | 0.7 | 11.9 | 93.0 | 7.0 | 100.0 |
Waterside/verge | – | – | – | – | – | 5 | 64.0 | 46.0 | 100.0 | 0.0 | 100.0 | |
*N = number of IGS as recorded in all 3,025 sub-sites.
**HG = combined percentage of herb and ground cover. Herb and ground cover strata add up to 100% minus ground not covered by vegetation.
Survey area | Accessibility | Lot | Gap | Street verge | Brownfield | Waterside | WS/SV |
Structural | SV/GP |
Railway | LT/SV |
Powerline | Total IGS |
Total (N) | 32 | 22 | 643 | 15 | 7 | 0 | 38 | 0 | 28 | 0 | 0 | ||
Total (m2) | 1433 | 117 | 15300 | 967 | 125 | 0 | 126 | 0 | 959 | 0 | 0 | ||
Yes (N) | 7 | 3 | 622 | 0 | 7 | – | 16 | – | 0 | – | – | ||
Yes (N%) | 22 | 14 | 97 | 0 | 100 | – | 42 | – | 0 | – | – | ||
Yes (m2) | 231 | 10 | 14433 | 0 | 125 | – | 50 | – | 0 | – | – | ||
Yes (% of area) | 16 | 9 | 94 | 0 | 100 | – | 40 | – | 0 | – | – | ||
Partial (N) | 12 | 6 | 13 | 0 | 0 | – | 8 | – | 0 | – | – | ||
Partial (N%) | 38 | 27 | 2 | 0 | 0 | – | 21 | – | 0 | – | – | ||
Partial (m2) | 661 | 23 | 655 | 0 | 0 | – | 28 | – | 0 | – | – | ||
Partial (% of area) | 46 | 20 | 4 | 0 | 0 | – | 22 | – | 0 | – | – | ||
No (N) | 13 | 13 | 8 | 15 | 0 | – | 14 | – | 28 | – | – | ||
No (N%) | 41 | 59 | 1 | 100 | 0 | – | 37 | – | 100 | – | – | ||
No (m2) | 541 | 84 | 212 | 967 | 0 | – | 48 | – | 959 | – | – | ||
No (% of area) | 38 | 72 | 1 | 100 | 0 | – | 38 | – | 100 | – | – | ||
Total (N) | 159 | 386 | 284 | 22 | 27 | 5 | 30 | 16 | 7 | 1 | 2 | ||
Total (m2) | 6144 | 2796 | 2351 | 1458 | 1417 | 179 | 93 | 68 | 43 | 7 | 3 | ||
Yes (N) | 131 | 178 | 265 | 11 | 15 | 0 | 19 | 12 | 0 | 1 | 2 | ||
Yes (N%) | 82 | 46 | 93 | 50 | 56 | 0 | 63 | 75 | 0 | 100 | 100 | ||
Yes (m2) | 5032 | 1154 | 1800 | 761 | 1007 | 0 | 73 | 50 | 43 | 7 | 3 | ||
Yes (% of area) | 82 | 41 | 77 | 52 | 71 | 0 | 78 | 74 | 100 | 100 | 100 | ||
Partial (N) | 17 | 111 | 15 | 11 | 3 | 5 | 7 | 4 | 0 | 0 | 0 | ||
Partial (%) | 11 | 29 | 5 | 50 | 11 | 100 | 23 | 25 | 0 | 0 | 0 | ||
Partial (m2) | 714 | 924 | 441 | 697 | 130 | 179 | 16 | 18 | 0 | 0 | 0 | ||
Partial (% of area) | 12 | 33 | 19 | 48 | 9 | 100 | 17 | 26 | 0 | 0 | 0 | ||
No (N) | 11 | 97 | 4 | 0 | 9 | 0 | 4 | 0 | 7 | 0 | 0 | ||
No (%) | 7 | 25 | 1 | 0 | 33 | 0 | 13 | 0 | 100 | 0 | 0 | ||
No (m2) | 398 | 718 | 110 | 0 | 280 | 0 | 4 | 0 | 0 | 0 | 0 | ||
No (% of area) | 6 | 26 | 5 | 0 | 20 | 0 | 4 | 0 | 0 | 0 | 0 |
*WS/SV = waterside/street verge, SV/GP = street verge/gap, LT/SV = lot/street verge.
When measuring the accuracy of our land use survey method, we found the combined percentage of parks, conservation and sports and recreation land use in our survey (11.2%) deviated 8.4% from the combined greenspace land use percentage in Brisbane Council datasets (10.4%). The combined percentage of residential, garden and private shared greenspace in our survey (39.5%) deviated -4.2% from the residential land use percentage in the Brisbane Council dataset (41.3%). In Sapporo, the combined percentage of non-conservation greenspace in our survey (4.8%) deviated −6.9% from the non-conservation greenspace percentage in the Sapporo City dataset (5.1%). As a result, the accuracy of our method was over 90% in both cities when comparing land use percentages of around 5% or more with those of official datasets. A visualization of the change in land use percentage with increasing sample size showed that for a common land use type (residential), good accuracy was reached at a sample size of around 70, while for the rare land use types a sample size of around 90 was necessary (
This study has found similar proportions of IGS in both survey areas. While this could indicate other urban areas may contain a similar percentage of IGS, the conclusions we can draw are limited by the sampling design used. The similarity of the study cases (e.g. age and spatial structures of the cities, size and shape of the survey areas; see Methods) may be partly responsible for the similarity in IGS proportions, so results may vary across survey areas with different characteristics. The survey areas we compared differ in their population density (
The sampling design used in this study has limitations that make it unsuitable for assessing factors of importance to urban conservation, such as the size of individual IGS or the distribution of IGS sizes. Such information is valuable and has been recorded by prior research into roundabouts
Most prior research on IGS has pointed out its potential without knowing what proportion of cities consists of IGS. Having this knowledge allows us to identify some potential policy implications that IGS has for recreational use and conservation, by considering its area compared to other greenspace types. IGS accounts for about 14% of total greenspace in the survey areas (
The results also have implications for urban conservation. Research has shown IGS plays a role in providing habitat to fauna and flora
The potential importance of IGS for urban recreational use and urban conservation has implications for urban and environmental planning. Planners may need to re-think their negative view of ‘vacancy’ in the urban landscape
The results of our study emphasize more research on IGS is needed to unlock its full potential. Examining how IGS is influenced by its socio-ecological context would be a valuable starting point for future studies. A quantitative examination of how residents use and perceive IGS could provide into the social aspects. A cross-cultural comparison seems particularly promising, as concepts such as public space may be interpreted differently depending on the cultural context
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We are deeply grateful to Yumi Nakagawa for her invaluable support with data collection and data entry. We thank Jennifer Garden and Jean-Marc Hero for their advice on research design, Alex Lo for helpful comments on the manuscript, Mariola Rafanowicz for assistance in GIS analysis and obtaining data sets, and two anonymous reviewers for their detailed and helpful comments. We also thank the Brisbane City Council and Sapporo City Department of Environment Section Greenspace for providing green space and land use data sets.