Mitchell Pavao-Zuckerman

Debates—Perspectives on socio‐hydrology: Socio‐hydrologic modeling: Tradeoffs, hypothesis testing, and validation

Socio-hydrology focuses on studying the dynamics and co-evolution of coupled human and water systems. Recently, several new socio-hydrologic models have been published that explore these dynamics, and these models offer unique opportunities to better understand these coupled systems and to understand how water problems evolve similarly in different regions. These models also offer challenges, as decisions need to be made by the modeler on trade-offs between generality, precision, and realism. In addition, traditional hydrologic model validation techniques, such as evaluating simulated streamflow, are insufficient, and new techniques must be developed. As socio-hydrology progresses, these models offer a robust, invaluable tool to test hypotheses about the relationships between aspects of coupled human-water systems. They will allow us to explore multiple working hypotheses to greatly expand insights and understanding of coupled socio-hydrologic systems.

Decomposition of chestnut oak (Quercus prinus) leaves and nitrogen mineralization in an urban environment

We studied soil processes along an urban to rural gradient. To determine the ecosystem response to the urban soil environment, we measured (1) leaf litter decomposition rates using a reference leaf litter, and (2) net N-mineralization and net nitrification rates using paired in situ soil cores. A significant trend toward slower litter decomposition rates toward the urban end of the gradient was observed. In addition, percent ash-free dry mass remaining of the litter was significantly higher during the course of the study but was not statistically significant at the final sampling date. Litter C:N ratio had a complex response with respect to degree of urban land use, and litter % N did not differ between land-use types. Litter decomposition rates were not significantly correlated with observed soil physicochemical and biological characteristics but were influenced by soil moisture and soil organic matter. Net N-mineralization rates were higher in urban soils. Net nitrification rates did not differ with land-use type. Net N-mineralization rates were positively correlated with soil temperature, indicating a response to the urban heat island effect. Net N-mineralization rates were negatively correlated with the numbers of higher trophic level nematodes.

Woody plant encroachment impacts on soil carbon and microbial processes: results from a hierarchical Bayesian analysis of soil incubation data

Belowground processes and associated plant–microbial interactions play a critical role in how ecosystems respond to environmental change. However, the mechanisms and factors controlling processes such as soil carbon turnover can be difficult to quantify due to methodological or logistical constraints. Soil incubation experiments have the potential to greatly improve our understanding of belowground carbon dynamics, but relating results from laboratory-based incubations to processes measured in the field is challenging. This study has two goals: (1) development of a hierarchical Bayesian (HB) model for analyzing soil incubation data and complementary field data to gain a more mechanistic understanding of soil carbon turnover; (2) application of the approach to soil incubation data collected from a semi-arid riparian grassland experiencing encroachment by nitrogen-fixing shrubs (mesquite). Soil was collected from several depths beneath large-sized shrubs, medium-sized shrubs, grass, and bare ground—the four primary microsite-types found in this ecosystem. We measured respiration rates from substrate-induced incubations, which were accompanied by measurements of soil microbial biomass, soil carbon, and soil nitrogen. Soils under large shrubs had higher respiration rates and support 2.0, 1.9, and 2.6 times greater soil carbon, microbial biomass, and microbial carbon-use efficiency, respectively, compared to soils in grass microsites. The effect of large shrubs on these components is most pronounced near the soil surface where microbial carbon-use efficiency is high because of enhanced litter quality. Grass microsites were very similar to bare ground in many aspects (carbon content, microbial biomass, etc.). Encroachment of mesquite shrubs into this semi-arid grassland may enhance carbon and nutrient cycling and increase the spatial heterogeneity of soil resource pools and fluxes. The HB approach allowed us to synthesize diverse data sources to identify the potential mechanisms of soil carbon and microbial change associated with shrub encroachment.

Urban and agricultural soils: conflicts and trade-offs in the optimization of ecosystem services

On-going human population growth and changing patterns of resource consumption are increasing global demand for ecosystem services, many of which are provided by soils. Some of these ecosystem services are linearly related to the surface area of pervious soil, whereas others show non-linear relationships, making ecosystem service optimization a complex task. As limited land availability creates conflicting demands among various types of land use, a central challenge is how to weigh these conflicting interests and how to achieve the best solutions possible from a perspective of sustainable societal development. These conflicting interests become most apparent in soils that are the most heavily used by humans for specific purposes: urban soils used for green spaces, housing, and other infrastructure and agricultural soils for producing food, fibres and biofuels. We argue that, despite their seemingly divergent uses of land, agricultural and urban soils share common features with regards to interactions between ecosystem services, and that the trade-offs associated with decision-making, while scale- and context-dependent, can be surprisingly similar between the two systems. We propose that the trade-offs within land use types and their soil-related ecosystems services are often disproportional, and quantifying these will enable ecologists and soil scientists to help policy makers optimizing management decisions when confronted with demands for multiple services under limited land availability.

Urban ecology: advancing science and society

Urban ecology has quickly become established as a central part of ecological thinking. As cities continue to grow in size and number, two questions serve to unify this broad and multidisciplinary research landscape: (1) how can urban ecology contribute to the science of ecology, and (2) how can urban ecology be applied to make cities more livable and sustainable? In spite of the advances made thus far, there are many unexplored ways of integrating the science and application of urban ecology. Although scientists assess and make predictions regarding the connections between environmental and socioeconomic processes, practitioners involved in real-world application deal with urban planning and with designing ecosystem services to improve living conditions for all urban inhabitants and to make cities more sustainable. Research in urban ecosystems can be developed from many different perspectives, and we suggest that each perspective has something to offer both society and the science of ecology. We present s...

Scratching the surface and digging deeper: exploring ecological theories in urban soils

Humans have altered the Earth more extensively during the past 50 years than at any other time in history (Millennium Assessment 2003). A significant part of this global change is the conversion of land covers from native ecosystems to those dominated by human activities (Kareiva et al. 2007; Ellis and Ramankutty 2008). Although agricultural needs have historically been the dominant driver of land cover change (Millennium Assessment 2003), urbanization is now emerging as a primary process of land cover transformations around the world. As a result, urban ecology has emerged as an important research focus because of the increasing spatial extent of, and human population sizes in, urbanized ecosystems (Grimm et al. 2008a). Similarly to urbanized ecosystems, over the past several decades soils have been receiving increasing research attention due, in part, to growing appreciation of their linkages with aboveground ecosystems (Wardle et al. 2004; Wall et al. 2005) and global biogeochemical cycles (Schlesinger and Andrews 2000), and their roles in providing and regulating essential ecosystem services (Wall 2004). Yaalon (2007) recently pointed out that, although often underappreciated, soils are greatly impacted by human-mediated land cover changes and that greater understanding and mitigation of the impacts is needed to ensure the future sustainability of societies. Anthropogenic impacts on soils are perhaps most dramatic in urbanized ecosystems where humans remove, reconfigure, and pollute them to a greater degree than in other contexts (DeKimpe and Morel 2000). In this special issue of Urban Ecosystems, the two topics of urbanized ecosystems and soils are integrated Urban Ecosyst (2009) 12:9–20 DOI 10.1007/s11252-008-0078-3

Mapping the Design Process for Urban Ecology Researchers

The integration of research into the design process is an opportunity to build ecologically informed urban design solutions. To date, designers have traditionally relied on environmental consultants to provide the best available science; however, serious gaps in our understanding of urban ecosystems remain. To evaluate ecosystem processes and services for sustainable urban design and to further advance our understanding of social-ecological processes within the urban context, we need to integrate primary research into the urban design process. In this article, we develop a road map for such a synthesis. Supporting our proposals by case studies, we identify strategic entry points at which urban ecology researchers can integrate their work into the design process.

F. R. Adler and C. J. Tanner: Urban Ecosystems: Ecological Principles for the Built Environment

Jane Jacobs (1961) closes her book The Death and Life of Great American Cities with a reflection on what type of question a city poses. Her response is one that indicates that cities are complex systems, analogous to biological systems, requiring a set of perspectives and approaches appropriate for the type of question. The development of the field of urban ecology over the past two decades has been in a way a similar response to Jacobs’ question, one that frames the city as a complex ecosystem. Urban ecology emerged from roots and connections to landscape ecology and patch dynamics, drawing on connections to geography, environmental planning, engineering, economics, and a host of other disciplines. Following a recent explosion in the number of research publications and programs, several books have been released to synthesize the recent focus in urban ecology. Adler and Tanner’s Urban Ecosystems provides such synthesis of this new discipline, reflecting the development of a discipline that offers an ecological response to the Jacobs question about the nature of cities. The authors focus on a few key themes: the way urban areas transform habitats, how cities concentrate resources and amplify environmental fluxes, and the unintended consequences of these transformations. Adler and Tanner preface Urban Ecosystems by saying it is structured like a play. The book unfolds over a series of acts, introducing the setting (the built environment) and protagonists (urban organisms) before building tension and describing the challenges the protagonists face, describing the fate of the different protagonists, and finally giving resolution by exploring the fate of humans as urban organisms. This metaphor is useful, and the structure of the book and chapters within follow this general approach of describing for a specific example how the built environment produces unintended processes, patterns, and challenges. The book loosely follows the framework used by many urban ecologists; that urban ecology is a study of ecology in the city and ecology of the city (Pickett et al. 1997; Grimm et al. 2000). Some chapters describe how cities function as ecosystems while others describe ecological patterns and processes within cities. Chapter 1 gives a foundation for thinking about cities as ecosystems and what makes them different from other ecosystems. It includes a general overview of cities as engineered ecosystems, the types of habitats, and the implications for the organisms you might find there, setting up the rest of the book. Chapter 1 also gives a comprehensive primer on the science of ecology, spelling out the process/drivers and principles that Adler and Tanner think are relevant for thinking about for ecosystem, community, population, behavioral, physiological, and evolutionary ecology, again road-mapping the domain M. Pavao-Zuckerman (&) Biosphere 2, University of Arizona, Tucson, AZ 85721, USA e-mail: mzucker@email.arizona.edu