Urban spatial patchiness as represented by the HERCULES land cover classification. Urban areas include much fine-scale heterogeneity, which may be important for how the system functions socially and ecologically. In particular, spatial patchiness may control the effects of social processes and built covers on ecosystem functions. This false color infrared aerial photo of the Glyndon area of Baltimore County, MD, shows healthy vegetation in red. Impervious surfaces such as roofs, streets and parking lots, show up as other colors and can be distinguished by a computer algorithm or a human investigator. The patches in this image are differentiated on the basis of how much cover is contributed by trees, by grass, by pavement, by bare ground, and by buildings of different types. Even patches that would be classified as residential by the traditional classification differ based on several of the major contrasts in cover.
Credit: Baltimore Ecosystem Study LTER Photo. For details see Cadenasso et al. (2007).
A new classification of urban lands exposes relationships between socially-determined structure and ecological function better than the traditional classification. Nitrate yield from urban watersheds (in terms of Kg N per hectare per year) is of interest because it is a pollutant of ground water and shallow coastal estuaries, such as the Chesapeake Bay. In the left hand panel, the relationship of nitrate yield to the percent residential cover in parts of the Gwynns Falls watershed in metropolitan Baltimore, MD is shown. There is a very low correlation of nitrate to percent residential cover, and the correlation is not statistically significant. In the right hand panel, the relationship of nitrate yield to covers in HERCULES that correspond to most closely to the residential categories in the traditional system are correlated with nitrate yield. The correlation between HERCULES patches and nitrate yield is high (r2 = .81) and statistically significant (P = 0.03).
Redrawn from Cadenasso et al. (2007).
