I used to think that both urban and urban ecology are well outlined, clear concepts and that there are straightforward definitions describing the two terms. Urban was simply a complete opposite of the natural ecosystems, which is normally void of people, built structures, and where interactions between and among organisms and between organisms and their environment occur seemingly without any human interference and influence. In contrast, the understanding of urbanized areas as human-dominated, high density – of population, buildings, traffic – systems, made them appear detached from the natural ecosystems, despite the fact that biogeophysical processes taking place in both urban and non-urban areas are essentially the same and there is no true isolation between the two. Although without a doubt impermeable built surfaces and people’s socio-economic activities define the cities, with learning more about the urban system it has become clear that it is the effect these two major components have on the ecological and environmental processes that makes urban ecosystems unique and effectively different from natural environments. As a result these modified processes and ecosystem functions may be used as a novel way to describe the cities. In other words, even though we do not see signs of human activity it does not mean that natural ecosystems are not affected by it; equally, while urban scene are dominated by passers-by and concrete and glass surfaces of the buildings we can be sure that multiple ecological processes are happening in the background and that they are affected in one way or another by the human activities and structures.
Unfortunately, there is another side of urban areas that comes up all too often – the negative impact cities have on the well-being of its human and non-human inhabitants, as well as the status of non-living environment. Due to fast expanding urban area and more importantly urban population, cities’ ecological footprint has increased significantly – the land area that the city extracts its resources from is much larger than the area of the city itself. While urban areas have been sources of pollution and contaminants throughout most of their history, more recently the spatial and temporal scales of their effect on the quality of water, soil and atmosphere has been much greater. Industry and transportation, activities in urban households all have great impacts on global climate and global cycles of matter and energy, which in turn have wide ranging effects from organisms’ distribution and abundance both within and outside the urban areas to the magnitude of primary production to changing phenology etc.
In urban ecology class we were provided with definition of urban ecology which stated that it is a scientific study of ecology but in the urban setting. This seems obvious and straightforward, however, similarly to ecology, urban ecology is a science of systems, it is multifaceted, integrated discipline, spanning across different spatial and temporal scales, and therefore hard to study, while addressing all of the involved components is rarely possible or sensible. Urban ecology is not just ecology in the city, which is an important field of study nonetheless, but it is also ecology of the city – it analyzes the relationships between different components of the urban system, the integration of social, economic and ecological within urban system, also how ecological processes are affected by urban structures and urban land cover, and how energy and matter move through the urban system. Two concepts, those of scale and spatial heterogeneity, have appeared to be especially important. Image above shows heterogeneous urban landscape as determined by different land covers, i.e. both fine and coarse vegetation, and buildings and paved surfaces. This particular configuration, as well as the richness and frequency of the patches definitely influence the ecological processes occurring in this system, for example, thermoregulation, water runoff, carbon and nitrogen cycling, and others. Consider thermoregulation: urban heat island effect is commonly experienced by urban areas as a result of huge heat storage capacity of concrete and asphalt surfaces; the greater the extent of impervious surfaces and the taller and more clustered the buildings are, the greater the heating is of the urban area in comparison with nearby rural areas. In this image the paved surfaces and large buildings without a doubt contribute to the urban heat island effect, however, the white-painted roofs have high albedo (i.e. they reflect large proportion of incoming shortwave radiation) and the extensive tree cover cools the surrounding area by shading and through evapotranspiration. Any modification of ecological processes due to particular urban structures and land cover has a complicated effect on the urban ecosystem functioning and thus needs to be addressed by both urban planners and researchers. In the case of urban heat island, its consequences are both ecological and economic – shifts in microclimate towards higher temperatures result in phenological changes in various organisms; rising temperatures in urban areas are associated with increased tropospheric ozone production, which has negative health impacts; and increased costs and energy requirements of cooling the buildings. The constructors of the building on the left in the image have addressed the latter by installing panels above its south-facing windows which reduce the heating up of the inside of the building and thus reduce the need of air conditioning.
At a smaller – e.g. household – scale, however, such considerations of ecological processes and impacts of our activities on the environment are rare. Consider lawn sprinklers: these often end up watering surfaces that are not planted such as sidewalk and ground covered in litter; water washes away various pollutants that have settled on the sidewalk as well as nutrients from the soil and eventually carries it to the nearest river or stream thus polluting the aquatic ecosystem as well. This resonates well with other issues and concepts discussed above – the interaction of social and ecological aspects is the backbone of the urban systems, and our activities do impact ecological processes and functions and vice versa.
In my opinion, appreciation of the complexity and multidimensionality of urban systems as well as consideration of relationships between physical structure of urban systems and ecological processes (not to mention all being influenced by social aspects) would be the major take-home messages. The image of Segundo Community Garden before taking urban ecology class virtually summarized my understanding of it – something green, people are involved, can be suitable habitat for many beneficial species. Due to very small scale of the garden, supporting and regulatory ecosystem services might not have a great effect on the surrounding environment while harvest is too small for there to be any substantial provisioning services; it is cultural services, however, which are the most important outcome of the garden together with promotion of sustainable development (sustainable food production in the urban setting) and addressing of some aspects of the environmental injustice. However, for what was once just a very abstract, obscure idea has crystallized into something more meaningful: this community garden can be said to represent a system where social concepts and ecological processes come together and have an impact on the community – just as it is in a large urban system.
NB Adapted from an essay written as part of PLS162 Urban Ecology, Winter Quarter 2012 at UC Davis