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A Tale of Two Cities

Urban landscapes record in their structures accumulated changes in the biological, social, and engineered environments; the history of their development, use, and abuse. In a very real way, a tale of any two cities is a tale of two ecosystems. With attention and observation, there is much to learn from simple walking tours, “comparative hiking,” in the great cities of the world. For example, consider two cities in the same landscape of northwestern Europe: Amsterdam and The Hague in The Netherlands. Amsterdam is far larger geographically and in human population, of course. But the urban cores of both are densely inhabited and intensely built. Their settlement histories are similar. Common features include the ubiquitous canals that drain and dry the city streets that were once muddy flatlands, wetlands, and waterways. In Amsterdam, the canals are lined with vertical bulkheads and the walls of buildings. Canal “banks” are concrete walkways, curbs, and stoops. In The Hague, canals are situated in strips of green, narrow riparian gardens and parks. The banks are vegetated and overgrown, mud and loam instead of steel and concrete. The differences are substantive. Canals in Amsterdam are components of the built environment. In The Hague, they are networks of nature in the urban matrix, attractive, certainly, and interesting as design features. But do they have any functional significance? Indeed they do. Ecosystems have emergent properties, functions of the whole system that do not accrue from component parts. Resistance (tendency to retain conformation) and resilience (ability to recover from forced change) provide a kind of homeostasis. Connectedness gives the whole system the ability to function at its maximum extent. Energy flux and material cycling allow the whole system to maintain its own environment and develop at a self-controlled pace. The more “complete” a system is, the more its emergent properties are expressed, and the more effectively its components can function. Places like The Hague, with ecosystems embedded in the urban landscape, are inherently more active ecologically than places like Amsterdam. But that is not all. Human beings, notwithstanding our collective tendency to ignore or misconstrue, are biological entities and thus unavoidably linked to the ecosystem. Healthier and more complete ecosystems support healthier human populations. Green spaces in urban environments allow us to realize this principle in stark relief. Habitat for predatory spiders and birds helps resist the population fluctuations of insects and mites that are vectors of human disease organisms. Habitat buffers reduce the contact between humans and mammalian parasites like those that produced Medieval plague pandemics. Microclimate amelioration helps reduce the