Kirsten Schwarz

Spatial heterogeneity in urban ecosystems: reconceptualizing land cover and a framework for classification

Urban areas are heterogeneous. Transitions in architecture and building density, vegetation, economic activity, and culture can occur at the scale of city blocks. Ecologists have been criticized for treating the city as homogeneous and urbanization as one-dimensional. To develop ecological understanding of integrated human–natural systems, the fine-scale heterogeneity of their built and natural components must be quantified. There have been calls for the integration of the biophysical and human components of systems, but here we provide a new tool to quantify this integrated heterogeneity by reconceptualizing urban land-use and land-cover classification approaches. This new tool, High Ecological Resolution Classification for Urban Landscapes and Environmental Systems (HERCULES), balances detail and efficiency and is flexible, allowing it to be used for interdisciplinary research, with ancillary datasets, and across urban systems.

Data and Methods Comparing Social Structure and Vegetation Structure of Urban Neighborhoods in Baltimore, Maryland

ABSTRACT Recent advances in remote sensing and the adoption of geographic information systems (GIS) have greatly increased the availability of high-resolution spatial and attribute data for examining the relationship between social and vegetation structure in urban areas. There are several motivations for understanding this relationship. First, the United States has experienced a significant increase in the extent of urbanized land. Second, urban foresters increasingly recognize their need for data about urban forestry types, owners and property regimes, and associated social goods, benefits, and services. Third, previous research has focused primarily on the distribution of vegetation cover or diversity. However, little is known about (1) whether vegetation structure varies among urban neighborhoods and (2) whether the motivations, pathways, and capacities for vegetation management vary among households and communities. In this article, we describe novel data and methods from Baltimore, MD, and the Baltimore Ecosystem Study (BES) to address these two questions.

Landscape, vegetation characteristics, and group identity in an urban and suburban watershed: why the 60s matter

As highly managed ecosystems, urban areas should reflect the social characteristics of their managers, who are primarily residents. Since landscape features develop over time, we hypothesize that present-day vegetation should also reflect social characteristics of past residents. Using an urban-to-suburban watershed in the Baltimore Metropolitan Region, this paper examines the relationship between demographics, housing characteristics, and lifestyle clusters from 1960 and 2000 with areas of high woody and herbaceous vegetation cover in 1999. We find that 1960 demographics and age of housing are better predictors of high woody or tree coverage in 1999 than demographics and housing characteristics from 2000. Key variables from 1960 are percent in professional occupations (+), percent of pre-WWI housing (−), percent of post-WWII housing (+), and population density (−). Past and present demographic and housing variables are poor predictors of high herbaceous cover in 1999. Lifestyle clusters for 2000 are very good predictors of high herbaceous coverage in 1999, but lifestyle clusters from 1960 and 2000 are poor predictors of high woody vegetation coverage. These findings suggest that herbaceous or grassy areas, typically lawns, are good reflections of contemporary lifestyle characteristics of residents while neighborhoods with heavy tree canopies have largely inherited the preferred landscapes of past residents and communities. Biological growth time scales of trees and woody vegetation means that such vegetation may outlast the original inhabitants who designed, purchased, and planted them. The landscapes we see today are therefore legacies of past consumption patterns.

Trees grow on money: Urban tree canopy cover and environmental justice

This study examines the distributional equity of urban tree canopy (UTC) cover for Baltimore, MD, Los Angeles, CA, New York, NY, Philadelphia, PA, Raleigh, NC, Sacramento, CA, and Washington, D.C. using high spatial resolution land cover data and census data. Data are analyzed at the Census Block Group levels using Spearman’s correlation, ordinary least squares regression (OLS), and a spatial autoregressive model (SAR). Across all cities there is a strong positive correlation between UTC cover and median household income. Negative correlations between race and UTC cover exist in bivariate models for some cities, but they are generally not observed using multivariate regressions that include additional variables on income, education, and housing age. SAR models result in higher r-square values compared to the OLS models across all cities, suggesting that spatial autocorrelation is an important feature of our data. Similarities among cities can be found based on shared characteristics of climate, race/ethnicity, and size. Our findings suggest that a suite of variables, including income, contribute to the distribution of UTC cover. These findings can help target simultaneous strategies for UTC goals and environmental justice concerns.

The role of interface organizations in science communication and understanding

“Interface” organizations are groups created to foster the use of science in environmental policy, management, and education. Here we compare interface organizations that differ in spatial scale, modes of operation, and intended audience to illustrate their diversity and importance in promoting the application of science to environmental issues. There has been exciting recent growth in the nature and extent of activities by interface organizations and in new methods for science communication and engagement. These developments can help scientists – who face personal and institutional challenges when attempting to convey the results of their research to various audiences – interact with society on specific issues in specific places, and with a wide range of non-traditional audiences. The ongoing mission for these organizations should be to move beyond simply increasing awareness of environmental problems to the creation of solutions that result in genuine environmental improvements.

Quantifying Spatial Heterogeneity in Urban Landscapes: Integrating Visual Interpretation and Object-Based Classification

Describing and quantifying the spatial heterogeneity of land cover in urban systems is crucial for developing an ecological understanding of cities. This paper presents a new approach to quantifying the fine-scale heterogeneity in urban landscapes that capitalizes on the strengths of two commonly used approaches—visual interpretation and object-based image analysis. This new approach integrates the ability of humans to detect pattern with an object-based image analysis that accurately and efficiently quantifies the components that give rise to that pattern. Patches that contain a mix of built and natural land cover features were first delineated through visual interpretation. These patches served as pre-defined boundaries for finer-scale segmentation and classification of within-patch land cover features which were classified using object-based image analysis. Patches were then classified based on the within-patch proportion cover of features. We applied this approach to the Gwynns Falls watershed in Baltimore, Maryland, USA. The object-based classification approach proved to be effective for classifying within-patch land cover features. The overall accuracy of the classification maps of 1999 and 2004 were 92.3% and 93.7%, respectively. This exercise demonstrates that by integrating visual interpretation with object-based classification, the fine-scale spatial heterogeneity in urban landscapes and land cover change can be described and quantified in a more efficient and ecologically meaningful way than either purely automated or visual methods alone. This new approach provides a tool that allows us to quantify the structure of the urban landscape including both built and non-built components that will better accommodate ecological research linking system structure to ecological processes.

Mapping urban landscape heterogeneity: agreement between visual interpretation and digital classification approaches

Visual interpretation of remotely sensed imagery has long been used for landscape pattern analysis. Few studies, however, have investigated human variation in estimates of within-patch composition for classification of those patches, particularly in urban settings. This paper compares the agreement of two approaches—visual interpretation and object-based—to estimate the proportion cover of landscape features within delineated patches, and investigates the spatial patterns of patches with large disagreement between the two approaches. The two approaches were compared for the Gwynns Falls watershed, Maryland, USA. Three methods were used to assess agreement: a traditional error matrix based procedure and two fuzzy methods, a plus-one modification of the traditional procedure, and a fuzzy set theory method. We found that while visual interpretation does not work effectively when patches contain a mix of different types of features, accuracy increases with patches that are either dominated by a specific feature, or do not contain a specific feature. The overall accuracies of estimates by visual interpretation also vary by features, ranging from 63.3% for pavement to 93.8% for bare soil. Patches with large disagreement between the two approaches cluster spatially at locations where the urban landscape is more structurally complex, suggesting the accuracy of visual interpretation may be affected by patch shape complexity, and the spatial configuration of the landscape features within the patches. These results provide important insights into the accuracy of thematic maps based on visual interpretation, not only for ecologists and managers who are using the maps, but also for those who produce the maps.

Legacies of Lead in Charm City's Soil: Lessons from the Baltimore Ecosystem Study.

Understanding the spatial distribution of soil lead has been a focus of the Baltimore Ecosystem Study since its inception in 1997. Through multiple research projects that span spatial scales and use different methodologies, three overarching patterns have been identified: (1) soil lead concentrations often exceed state and federal regulatory limits; (2) the variability of soil lead concentrations is high; and (3) despite multiple sources and the highly heterogeneous and patchy nature of soil lead, discernable patterns do exist. Specifically, housing age, the distance to built structures, and the distance to a major roadway are strong predictors of soil lead concentrations. Understanding what drives the spatial distribution of soil lead can inform the transition of underutilized urban space into gardens and other desirable land uses while protecting human health. A framework for management is proposed that considers three factors: (1) the level of contamination; (2) the desired land use; and (3) the community’s preference in implementing the desired land use. The goal of the framework is to promote dialogue and resultant policy changes that support consistent and clear regulatory guidelines for soil lead, without which urban communities will continue to be subject to the potential for lead exposure.

Effects of seasonal variation and land cover on riparian denitrification along a mid-sized river

Urban areas contribute disproportional nitrogen (N) loads to downstream aquatic ecosystems resulting in potential hypoxic ‘dead’ zones. Riparian areas along streams and rivers reduce inorganic N concentrations through denitrification, an anaerobic microbial process. Our study objective was to investigate the denitrification potential of riparian areas with differing land cover composition along the Licking River in Kentucky, USA – a tributary of the Ohio River. For one year we collected monthly samples from four sites along a 60 km reach of the Licking River. We experienced substantial drought conditions in the first half of our study period followed by record precipitation and flooding in the second half of our study period. Land cover surrounding the sample sites was classified into distinct classes hypothesized to contribute to N loads. We found flooding increased denitrification potential, water nitrate concentration, and soil organic matter, while drought conditions increased soil ammonium concentrations. Our site with the greatest impervious surface had the highest denitrification potential, and soil and water ammonium concentrations. However, we determined that denitrification potential was mostly driven by soil organic matter content and only slightly by soil nitrate among all study sites. Our data demonstrate that riparian zones of mid-sized rivers in urban areas can be integral in removing excess N during flood events and can do so year-round provided sufficient N and carbon resources are present.

Moving dirt: soil, lead, and the dynamic spatial politics of urban gardening

ABSTRACT Urban gardens are often heralded as places for building social, physical, and environmental health. Yet they are also sites of significant conflict based on competing political, economic, and ecological projects. These projects range from radical re-envisionings of liberatory urban spaces, reformist aesthetic and sanitary improvement programmes, to underwriting the production of the neo-liberal city. These projects are based on divergent visions of the garden ground itself, in particular, whether this is soil (the fertile and living source for growing food and social values) or dirt (an inert and even problematic substrate to be removed or built upon for development purposes). These are not fixed or mutually exclusive categories, but are unstable as soil/dirt moves in discursive and material ways over time and space. Contaminants such as lead in the soil contribute to this instability, reframing fertile soil as dangerous dirt. To understand this discursive and material movement of soil/dirt over time and space, a dynamic spatial politics framework is needed that encompasses three scalar concepts: location, duration, and interconnection. This paper applies this dynamic spatial politics framework to interpret the 30-year conflict over the fate of an urban garden in Sacramento, California, that began as a countercultural space and was eventually transformed into a manicured amenity for a gentrifying neighbourhood, and the role of soil lead contamination in this narrative.