Comparative Analysis of Urban Vegetation Scale and Abundance

Vegetation abundance and distribution are fundamental determinants of urban environmental conditions. Physical and ecological processes in urban environments are dependent on the distribution and scaling properties of urban vegetation. By comparing intraurban and interurban vegetation distributions in different urban settings, it is possible to quantify consistencies and variances that determine which properties may be assumed and which properties must be measured. Properties found to be consistent among and within urban settings may be assumed whereas those that are variable must be specifically measured. This paper presents a comparative analysis of vegetation abundance and spatial distribution in six diverse urban settings for the purpose of illustrating such consistencies and variances. High resolution (1-10 m) satellite imagery can detect urban vegetation down to the level of individual trees thereby providing a critical link between field observation and moderate resolution (10-100 m) imagery. Spectral Mixture Analysis and image segmentation are applied to Quickbird multispectral imagery to quantify vegetation abundance, density and patch size distributions in 6 cities. In each city, spectral mixing is found to be strongly linear and dominated by binary mixing continua between a non-reflective dark surface endmember and illuminated vegetation and high albedo substrate endmembers. These binary mixing continua illustrate the importance of fine scale (< 2.8 m) shadowing to urban reflectance in both vegetated and non-vegetated surfaces. Vegetation fraction distributions are similar in four of the six cities but differ in the two containing significant amounts of open canopy scrub vegetation. Patch size distributions are similar in all six cities with 40% to 50% of vegetated area composed of smaller patches (< 100 m equivalent diameter). These results suggest that the abundance of smaller patches of vegetation may play an important role in urban microclimat- e . While these six cities are not necessarily representative of all cities worldwide, the consistencies suggest that the combination of vegetation fraction distributions from high resolution spectral mixture analysis and patch size distributions from image segmentation could be used to characterize vegetation distributions elsewhere for comparison.