Ecological studies of terrestrial urban systems have been approached along several kinds of contrasts: ecology in as opposed to ecology of cities; biogeochemical compared to organismal perspectives, land use planning versus biological, and disciplinary versus interdisciplinary. In order to point out how urban ecological studies are poised for significant integration, we review key aspects of these disparate literatures. We emphasize an open definition of urban systems that accounts for the exchanges of material and influence between cities and surrounding landscapes. Research on ecology in urban systems highlights the nature of the physical environment, including urban climate, hydrology, and soils. Biotic research has studied flora, fauna, and vegetation, including trophic effects of wildlife and pets. Unexpected interactions among soil chemistry, leaf litter quality, and exotic invertebrates exemplify the novel kinds of interactions that can occur in urban systems. Vegetation and faunal responses suggest that the configuration of spatial heterogeneity is especially important in urban systems. This insight parallels the concern in the literature on the ecological dimensions of land use planning. The contrasting approach of ecology of cities has used a strategy of biogeochemical budgets, ecological footprints, and summaries of citywide species richness. Contemporary ecosystem approaches have begun to integrate organismal, nutrient, and energetic approaches, and to show the need for understanding the social dimensions of urban ecology. Social structure and the social allocation of natural and institutional resources are subjects that are well understood within social sciences, and that can be readily accommodated in ecosystem models of metropolitan areas. Likewise, the sophisticated understanding of spatial dimensions of social differentiation has parallels with concepts and data on patch dynamics in ecology and sets the stage for comprehensive understanding of urban ecosystems. The linkages are captured in the human ecosystem framework.

/pdf/urban-ecological-systems-linking-terrestrial-ecological-2kwkdbwzer.pdf

Urban ecological systems: linking terrestrial ecological, physical, and socioeconomic components of metropolitan areas

https://www.nrs.fs.fed.us/pubs/jrnl/2011/nrs_2011_pickett_001.pdf

Urban ecological systems: Scientific foundations and a decade of progress

Most of the global human population lives in urban areas where biogeochemical cycles are controlled by complex interactions between society and the environment. Urban ecology is an emerging discipline that seeks to understand these interactions, and one of the grand challenges for urban ecologists is to develop models that encompass the myriad influences of people on biogeochemistry. We suggest here that existing models, developed primarily in unmanaged and agricultural ecosystems, work poorly in urban ecosystems because they do not include human biogeochemical controls such as impervious surface proliferation, engineered aqueous flow paths, landscaping choices, and human demographic trends. Incorporating these human controls into biogeochemical models will advance urban ecology and will require enhanced collaborations with engineers and social scientists.

/pdf/a-distinct-urban-biogeochemistry-3osk2i3z1b.pdf

A distinct urban biogeochemistry

Although the watershed approach has long been used to study whole-ecosystem function, it has seldom been applied to study human-dominated systems, especially those dominated by urban and suburban land uses. Here we present 3 years of data on nitrogen (N) losses from one completely forested, one agricultural, and six urban/suburban watersheds, and input– output N budgets for suburban, forested, and agricultural watersheds. The work is a product of the Baltimore Ecosystem Study, a longterm study of urban and suburban ecosystems, and a component of the US National Science Foundation’s long-term ecological research (LTER) network. As expected, urban and suburban watersheds had much higher N losses than did the completely forested watershed, with N yields ranging from 2.9 to 7.9 kg N ha 1 y 1 in the urban and suburban watersheds compared with less than 1 kg N ha 1 y 1 in the completely forested watershed. Yields from urban and suburban watersheds were lower than those from an agricultural watershed (13–19.8 kg Nh a 1 y 1 ). Retention of N in the suburban watershed was surprisingly high, 75% of inputs, which were dominated by home lawn fertilizer (14.4 kg N ha 1 y 1 ) and atmospheric deposition (11.2 kg N ha 1 y 1 ). Detailed analysis of mechanisms of N retention, which must occur in the significant amounts of pervious surface present in urban and suburban watersheds, and which include storage in soils and vegetation and gaseous loss, is clearly warranted.

/pdf/nitrogen-fluxes-and-retention-in-urban-watershed-ecosystems-t7hd9e5tp4.pdf

Nitrogen Fluxes and Retention in Urban Watershed Ecosystems

Over the past decade, the urban–rural gradient approach has been effectively used to study the ecology of cities and towns around the world. These studies have focused on understanding the distribution of plants and animals as well as ecosystem processes along gradients of urbanization that run from densely urbanized inner city to more rural exurban environments. We reviewed 300 papers investigating urbanization gradients that were published in peer-reviewed journals between 1990 and May 2007. Sixty-three percent of the papers investigated the distribution of organisms along urbanization gradients. Only five papers addressed the measures used to quantify the urbanization gradient itself. Within the papers addressing the distribution of organisms, 49% investigated the responses of birds to urbanization gradients, and <10% of the papers investigated more cryptic organisms. Most of these studies utilized a variety of broad measures of urbanization, but future advances in the field will require the development of some standardized broad measures to facilitate comparisons between cities. More specific measures of urbanization can be used to gain a mechanistic understanding of species and ecosystem responses to urbanization gradients. While the gradient approach has made a significant contribution to our understanding of the ecology of cities and towns, there is now a need to address our current knowledge gaps so that the field can reach its full potential. We present two examples of research questions that demonstrate how we can enhance our understanding of urbanization gradients, and the ecological knowledge that we can obtain from them.

The use of gradient analysis studies in advancing our understanding of the ecology of urbanizing landscapes: current status and future directions

To determine the patterns of atmospheric deposition and throughfall in the vicinity of a large city, bulk deposition, oak forest throughfall, and particulate dust deposition were measured at sites along a transect within and to the north of New York City. Concentrations and fluxes of NO3-, NH4+, Ca2+, Mg2+, SO42-, and Cl- in throughfall all declined significantly with distance from the city, while hydrogen ion concentration and flux increased with distance from the city. Most of the change in concentrations and fluxes occurred within 45 km of the city. Throughfall deposition of inorganic N was twice as high in the urban sites as compared to the suburban and rural sites. Bulk deposition patterns were similar to those of throughfall, but changes along the transect were much less pronounced. The water-extractable component of dust deposition to Petri plates also was substantially higher in the urban sites for Ca2+, Mg2+, SO42-, NO3-, and Cl-. The dust particles had little alkalinity, suggesting that alkaline...

Atmospheric deposition to oak forests along an urban - rural gradient.

During the past 50 years urban and suburban areas in the United States have been expanding rapidly at the expense of agricultural land and natural ecosystems (Richards. 1990; Douglas, 1994). Between 1960 and 1990, 12.6 million ha of cropland, forest and pasture in the United States were converted to urban and suburban land (Frey, 1984; Dougherty, 1992). An additional 4.5 million ha of rural land were developed in the 5 years between 1992 and 1997 (USDA National Resources Inventory, 2000), indicating that the pace of land conversion in the United States has been accelerating. While cities and towns now cover 3.5% of the conterminous United States, their associated sprawl into adjacent counties designated as Metropolitan Areas has resulted in 24.5% of the area of the United States being categorised as urban land cover (Dwyer et at., 2000). These areas, including their natural components like forested land, are thus becoming increasingly exposed to the effects of diverse urban activities. The states that have experienced the greatest population growth per unit land area between 1990 and 1996 occur in the eastern third of the country, where human settlement is expanding mostly into forested land (Dwyer et al., 2000). These eastern rural

Ecology of Cities and Towns: Carbon and nitrogen cycling in soils of remnant forests along urban–rural gradients: case studies in the New York metropolitan area and Louisville, Kentucky

Margaret M. Carreiro

Papers

Atmospheric deposition to oak forests along an urban - rural gradient.

Ecology of Cities and Towns: Carbon and nitrogen cycling in soils of remnant forests along urban–rural gradients: case studies in the New York metropolitan area and Louisville, Kentucky