e urban green volume — how to calculate Clemens Deilmann, Guenter Arlt, Iris Lehmann Leibniz Institute of Ecological and Regional Development, Germany e urban environmental quality depends very much on the ecological performance of urban green. Key factor for the microclimatic situation of cities is the green ‘volume’. e volume can be diﬀerentiated into three basic layers of green which are of importance to urban planning. For example low vegetation (lawns) does have good assimilation values. High vegetation (trees) is favorable to improving air-temperature and moisture. Parks, where all layers of vegetation exist, do have high bioclimatic impact for the overall city balance. e Leibniz Institute of Ecological and Regional Development (IOER) analyzed empirically 116 cities in Germany to discover relations between urban green and the diﬀerent land use categories. is was done with help of GIS-tools (feature recognition). Important factors for the green volume situation of cities as a whole are sealed surfaces, forest, water and minimizing areas. e results are cause-eﬀect relations and models for urban green. ese models can be helpful to develop planning strategies and management tools. It was possible to identify 5 characteristic clusters of cities within the 116 cases. e ecological quality and quantity of green volume and connectivity could be linked to the 5 clusters with average values and indicators. e clusters take into account the land use structure, the land use density, the green volume and its spatial distribution. e information does support decisions in urban planning especially when it comes to deciding on how and where to use brown ﬁeld areas. Keywords: cluster-analyses, environmental quality, green volume 1 Context and Goal of the Study Urban greenery is a quality factor in the ecology of cities. In particular, the supply of urban green spaces strongly influences climatic conditions and air hygiene. e type, level, and spatial distribution of urban vegetation are determined by the uses to which land is put. Land-use structures interact with ecological production, living-environment, and regulatory functions. Knowledge about causes and eﬀects is required if land-use patterns are to shape ecological quality in the city. Urban ecological quality is part of environmental quality. It is a measure of the extent to which the status of the urban environment deviates from the environmental protection and nature conservation targets set by society. Green space in cities exhibits various spatial patterns. Its positive ecological impact depends largely on how much of the urban territory it occupies, its spatial distribution, and the biomass of total vegetation (vegetation or “green” volume). e study investigated the proportion of green space and vegetation volume, which, together with ground sealing, interconnectivity, and ecological quality levels, providing a basis for ensuring the diﬀerentiated internal development of urban ecological quality. Within cities, the findings permit conclusions to be drawn about deficiencies in the supply of green spaces at the district or neighbourhood level. 2 Urban Green Space as Indicator of Ecosystem services Ecosystem services refer to the degree to which functions are performed in the context of land use (Arlt et al. 2001). e supply of urban vegetation influences ecosystem services. It is thus also an indicator of certain environmental situations. Fig. 1: Indicator function of urban green space for selected ecological functions (source: Arlt et al. 2005 after Baeseler et al.1974) Basically, the type and extent of landcover influences ecological performance. To quantify the impact of various types of landcover on the environment, selected ecological land functions and landcover types of sealed, unsealed vegetation-free areas and unsealed vegetated areas were analysed and assessed (Heber, Lehmann 1996). e assessment procedure assigned dimensionless ecological performance parameters to types of landcover. e ecological performance of an area is assessed on an ordinal scale from 0 (no ecological performance) and 1 (very high ecological performance). e functions climatic compensation, dust filtration, pollutant retention, porosity and permeability, groundwater replenishment, rainwater infiltration, and biotope formation were assessed for lawn, meadow, and perennial cover as well as trees and shrubs and open ground as vegetationless land. Low to high ecological performance was recorded for all vegetated areas and open ground areas. Vegetated areas are most eﬃcient in climatic compensation, porosity and permeability of the soil, rainwater infiltration, pollutant retention, and biotope formation (except for lawn surfaces). Lawn, meadow, and perennial cover showed low to medium performance in binding dust and replenishing groundwater. Areas with tree and shrub cover contribute least to groundwater intake but are the most eﬃcient when it comes to dust filtration. 3 Empirical Studies 3. 1 Subject of Study A research project at the Leibniz Institute of Ecological and Regional Development addressed the empirical-deductive determination and assessment of green space and volume in cities and urban regions. e basis was a GIS vegetation structure analysis of 116 urban districts and selected surrounding communities. e empirical investigation focused on an impact analysis of relations between land use structure and the proportion of green space and area-specific vegetation volume. Regional statistical procedures were used. e fundamental methodological tool was the comparative city study. It addressed ordinal scaled measurement of vegetation levels (low, medium, and high) on the basis of the proportion of green space and area-specific green volume. is involved urban typology studies on the basis of cluster analysis with the aim of identifying city types. Cities belonging to the same type show comparable proportions of green space and area-specific vegetation volume, which can be interpreted as ecosystem services and quality levels. ey have largely similar use structures (for example, in settlement and traﬃc infrastructure, settlement density, area per inhabitant). 3. 2 Spatial Levels and Data Base e vegetation structure analysis of 116 German cities addressed three spatial levels: the core city, the urban region, and open space. e term core city refers to the city within its administrative boundaries. e urban region includes the core city and selected surrounding communities. e data base for determining vegetation structure in German urban districts is generated by the 1993 and 1999 Dresden urban biotope type maps, the 1997 urban structure type maps of the 116 urban districts, and land cover maps. Fig. 2: Mapping of urban structure types, open space and surface water bodies. The example of the Stuttgart urban region (source: Arlt et al. 2005) 3. 3 Method for Determining Green Space and Vegetation Volume Of key importance in determining the proportion of green space and vegetation volume in German urban districts and urban regions are the urban biotope type and urban structure type approaches. For practical planning purposes, they enable a workable definition of vegetation structures and their assessment by type (classified units of public and private green space), dimensions (size and geometry of green spaces), and location (compactness and interconnectivity of green spaces). From a biological point of view, the city consists of a mosaic-like multiplicity of biotopes. As a rule, they are clearly demarcated and internally relatively homogeneous. Urban biotope mapping provides a good overview of the biotope types and vegetation structures in a city. Vegetation structures were analysed and vegetation patterns determined on the basis of the urban biotope mapping of Dresden. 52 biotope types were identified, on the basis of which vegetation structures and volumes were assessed. Fig. 3: Matrix of vegetation structure: example of the urban biotope type 1 (residential development, mixed uses, industrial, commercial and special purpose areas)and schematic flowchart of vegetation structural analysis (Arlt, et al., 2002) e vegetation structure of urban biotope types was analysed in representative areas, analysis including the physiognomic identification of areas with low (≤ 1m), medium (≥ 1m to ≤ 3m), high vegetation levels ((> 3m), and vegetation less areas (built-up land, other sealed and open ground, water bodies). 4 Results of the Study of 116 German urban districts and their regions In the context of the empirical studies, the vegetation structure analysis shows the proportion of green space and specific vegetation volume diﬀerentiated in terms of vegetation layer for the 116 German urban districts and their regions. e proportion of green space and specific vegetation volume are parameters which, on a medium scale (1: 25 000 to 1: 50 000), assist practical city-wide or urban regional planning. At the same time they serve to pinpoint deficiencies in the supply of green spaces at the district or neighbourhood level. In a model abstraction, green spaces and their cubature are two and three dimensional components of the physical urban space and, in interaction with sealed areas, surface water, and buildings, fundamentally aﬀect the material, energetic, and informational state of the urban living environment. Physical urban structures are influenced by land-use structures. 4.1 Proportion of Green Space and Specific Vegetation Volume e proportion of green space refers to the percentage share of vegetated areas in the core city, the urban region, the settlement area, and open spaces as a whole and diﬀerentiated by layer as “low,” “medium,” and “high.” Specific vegetation or “green” volume refers to the volume of vegetated areas in relation to given units of area (as a rule 1 m²) in the core city, urban region, settlement area, or open space. It is diﬀerentiated by vegetation layer into “low,” “medium,” and “high” and expressed in m³ per m² for the sum of vegetation layers. Data on the urban ecological parameters green space and vegetation volume diﬀerentiated by spatial level and vegetation stratification are available for 116 German urban districts and as mean values for all cities. Tab. 1: German urban districts – mean proportion of green space and specific vegetation volume diﬀerentiated by spatial level and vegetation layer (source: Arlt et al. 2005) Against a backdrop of progressive land take for settlement and transport purposes, the quality of the living environment is increasingly reflected in the type and extent of green space in settlement areas. Owing to the long period people spend in the settlement area and its relatively poor experience value, the ecological and psycho-social functions of green space in urban settlement areas are more greatly appreciated than those of open terrain. In the settlement areas of core cities, the average proportion of green space is about 25 %. e proportions by vegetation layer are 5 % (“low”), 5 % (“medium”), and 15 % (“high”). In the settlement areas of urban regions, there is a markedly higher proportion of green space, on average 60 %; 35 % with a “low” vegetation coverage, 10 % with “medium” coverage, and 15 % with “high” coverage. Vegetation volume relative to a square metre unit and the spatial units core city and urban region is not a sensitive indicator. Changes in green volume caused by urban development measures at the neighbourhood or plot level are hardly shown by city-wide or urban regional statistics, although the micro-climatic impact of such changes can be considerable. Specific vegetation volume on the medium spatial scale is rather to be seen as a basic municipal indicator which – generally in connection with soil sealing – provides a “rough” pointer of urban ecological quality. 4.2 Interaction between Urban Structure, Green Space and Vegetation Volume Impact analysis was based on regional statistics research, and selected structural and phenomenological parameters were included. Sub-studies were conducted within the circular causal connection between processes, structures, and phenomena. ey addressed interaction between urban and land-use structures and green spaces and vegetation volumes diﬀerentiated in terms of vegetation layer. Correlations were shown and incorporated in stochastic models. Relevant regional statistical methods were used in the studies on interaction between urban and land-use structures, green space and volume. e regional statistics programme was developed against a backdrop of accepted and plausible circumstances. Stochastic models were developed on the basis of factors and parameters to calculate the proportion of green space and vegetation volume in both core cities and urban regions. e high coeﬃcients of determination make the models highly relevant for planning practice. Taking the land cover data (for the 5 parameters) as input for the model will be suﬃcient to calculate the green volume and proportion of green space for any German city. It might be possible to adapt the model for other countries. Fig. 4: Analytical parameter models “proportion of green space” for core cities and “specific green volume” for urban regions (source: Arlt et al. 2005) 5 City Clusters City clusters enable complex circumstances to be structured and substance lent to complex concepts like “sustainable urban development.” rough cluster analysis as a multivariate procedure, the parent population of urban districts was divided in terms of several characteristic variables into types (clusters) in such a way as to make the similarities between cities of a given type and the diﬀerences between cities of any two types as great as possible. Such cluster analysis takes account of the proportion of green space, vegetation volume, degree of surface sealing, and the proportion of surface water bodies – use-structural parameters that relate to selected elements of the physical urban space. Apart from these statistical parameters of land-use structure, function performance and eﬃciency depend very strongly on the spatial structure of urban land. e analysis identified clusters of cities with characteristic quality standards and attribute structures. is permits land-use structures to be identified, described, and assessed from a qualitative perspective. Fig. 5: City clusters from an ecological perspective – characteristic vegetation patterns with vegetation volumes and the proportion of green space and surface water for clusters I to V (source: own processing) 6 Conclusion Green and open spaces perform ecological functions. e type and extent of green space and vegetation volume in cities and urban regions interact with land-use structures and the spatial structuration of uses. Urban vegetation volume is a highly aggregated indicator of many aspects of ecosystem services in the urban living environment (especially in bioclimatic balance and air hygiene), whose function is to be seen as providing a rough intimation of city-wide ecological quality. Cognizance of interaction within the structure of uses enables action to be taken to influence ecological performance and quality in urban settlement areas. Diﬀerentiated preferences in urban development create diﬀerences in land-use structure and thus in the characteristic ecological setting of a city. ese framework conditions require a range of strategies and the diﬀerentiated use of tools and programmes to secure and develop the supply of urban green spaces and ecological quality. 7 References Arlt, G., Fürll, L., Hennersdorf, J., Kochan, B., Lehmann, I., Mathey, J., et al. (2002). Stadtökologische Qualität und Vegetationsstrukturen städtischer Siedlungsräume (Bde. IÖR-Texte 139). (Leibniz-, ed.) Dresden. Arlt, G., Gössel, J., Heber, B., Hennersdorf, J., Lehmann, I., & inh, N. (2001). Auswir-kungen städtischer Nutzungsstrukturen auf Bodenversiegelung und Bodenpreis (Bde. IÖR-Schriften 34). (L.-I. f. e.V., ed.) Dresden. Arlt, G., Hennersdorf, J., Lehmann, I., & inh, N. (2005). Auswirkungen städtischer Nutzungsstrukturen auf Grünflächen und Grünvolumen (Bde. IÖRSchriften/Band 47). (L.-I. f. e.V., ed.) Dresden. Baeseler, H., Gelbrich, H., Greiner, J., Stefke, E., & iemann, H. (1974). Grünanlagen im Wohngebiet. Berlin: Bauakademie der DDR, Institut für Städtebau und Architektur. Bruse, M. (2003). Stadtgrün und Stadtklima. LÖBF-Mittelungen 1 , 66-70. Doetsch, P., & Rüpke, A. (1997). Revitalisierung von Altstandorten versus Inanspruchnahme von Naturflächen. Gegenüberstellung der Flächenalternativen zur gewerblichen Nutzung durch qualitative, quantitative und monetäre Bewertung der gesellschaftlichen Potentiale und Eﬀekte. Im Auftrag des Umweltbundesamtes. Finke, L. (1994). Landschaftsökologie – Das Geographische Seminar. Braunschweig. Hege, H.-P., Lausterer, H., Scheﬄer, V., & Schwarting, H. (1998/99). Verbesserung des Stadtklimas durch Grün – Wirkungen, Planung und Umsetzung Seminarpapier. Instrumente der ökologischen Planung, Stadtklima 21. Universität Kaiserslautern, Lehr- und Forschungsgebiet Ökologische Planung und UVP; WS. M. Großmann, M., Pohl, W., & H.D. Schulze, H. (9 1983). Grünvolumenzahl und Bodenfunktionszahl in der Landschafts- und Bauleitplanung. Schriften der Behörde für Bezirksangelegenheiten, Naturschutz und Umweltgestaltung . Miess, B., & Miess, M. (10 1997). Materialien zur Grünordnungsplanung – Teil 1: Siedlungs-ökologische und gestalterische Grundlagen. (L. f. Umweltschutz, ed.) Schriftenreihe Untersuchungen zur Landschaftsplanung . Nohl, W. (1993). Kommunales Grün in der ökologisch orientierten Stadterneuerung (Bd. Handbuch und Beispielsammlung. Studien). (IMU-Institut, ed.) München, 19. Schulte, W., Sukopp, H., & Werner, P.-A. ". 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WUA-News . 8 Figures and Tables Fig. 1: Indicator function of urban green space for selected ecological functions (source: Arlt et al. 2005 after Baeseler et al.1974)..................2 Fig. 2: Mapping of urban structure types, open space and surface water bodies. e example of the Stuttgart urban region (source: Arlt et al. 2005).....................................................................................................................3 Fig. 3: Matrix of vegetation structure: example of the urban biotope type 1 (residential development, mixed uses, industrial, commercial and special purpose areas)and schematic flowchart of vegetation structural analysis (Arlt, et al., 2002)..........................................................4 Fig. 4: Analytical parameter models “proportion of green space” for core cities and “specific green volume” for urban regions (source: Arlt et al. 2005).....................................................................................................................6 Fig. 5: City clusters from an ecological perspective – characteristic vegetation patterns with vegetation volumes and the proportion of green space and surface water for clusters I to V (source: own processing)...............7