Corinna Gries

Socioeconomics drive urban plant diversity

Spatial variation in plant diversity has been attributed to heterogeneity in resource availability for many ecosystems. However, urbanization has resulted in entire landscapes that are now occupied by plant communities wholly created by humans, in which diversity may reflect social, economic, and cultural influences in addition to those recognized by traditional ecological theory. Here we use data from a probability-based survey to explore the variation in plant diversity across a large metropolitan area using spatial statistical analyses that incorporate biotic, abiotic, and human variables. Our prediction for the city was that land use, along with distance from urban center, would replace the dominantly geomorphic controls on spatial variation in plant diversity in the surrounding undeveloped Sonoran desert. However, in addition to elevation and current and former land use, family income and housing age best explained the observed variation in plant diversity across the city. We conclude that a functional relationship, which we term the “luxury effect,” may link human resource abundance (wealth) and plant diversity in urban ecosystems. This connection may be influenced by education, institutional control, and culture, and merits further study.

Effects of urbanization on plant species diversity in central Arizona

Modern urban development provides an excellent laboratory for examining the interplay among socioecological relationships. We analyzed how the rapidly urbanizing Phoenix, Arizona metropolis has affected plant species diversity and community composition at a regional scale. Species diversity and plant density probably result from abiotic sorting in undeveloped desert sites, but not in urban sites. We found that species richness at the plot scale was higher for desert as opposed to urban sites; however, the estimated total species pool in the urban ecosystem is higher than that in the desert, as a result of the increased importation of introduced species through the nursery trade. Ordination of plant communities suggests three unique groupings of species based on land-use type of the site (desert, urban, and agriculture) and two unique groupings of urban sites based on landscaping aesthetics (mesic or xeric). We therefore recognize both bottom-up and top-down controls of plant biodiversity within the urban ...

A global database of lake surface temperatures collected by in situ and satellite methods from 1985–2009

Global environmental change has influenced lake surface temperatures, a key driver of ecosystem structure and function. Recent studies have suggested significant warming of water temperatures in individual lakes across many different regions around the world. However, the spatial and temporal coherence associated with the magnitude of these trends remains unclear. Thus, a global data set of water temperature is required to understand and synthesize global, long-term trends in surface water temperatures of inland bodies of water. We assembled a database of summer lake surface temperatures for 291 lakes collected in situ and/or by satellites for the period 1985–2009. In addition, corresponding climatic drivers (air temperatures, solar radiation, and cloud cover) and geomorphometric characteristics (latitude, longitude, elevation, lake surface area, maximum depth, mean depth, and volume) that influence lake surface temperatures were compiled for each lake. This unique dataset offers an invaluable baseline perspective on global-scale lake thermal conditions as environmental change continues.

Preliminary assessment of arbuscular mycorrhizal fungal diversity and community structure in an urban ecosystem.

Arbuscular mycorrhizal fungal (AMF) species richness, composition, spore density and diversity indices were evaluated in the Phoenix metropolitan area, Arizona, USA at 20 sampling sites selected to represent the four predominant land-use types found in the greater urban area: urban-residential, urban non-residential, agriculture and desert. AMF spores were extracted and identified from soil samples and from trap cultures established using soil collected at each site. Data were analyzed according to land use, land-use history, soil chemistry and vegetation characteristics at each site. Current agricultural sites were associated with decreased spore densities and historically agricultural sites with decreased species richness. Overall species composition was similar to that previously reported for the Sonoran desert, but composition at each sampling site was influenced by the vegetation from which samples were collected. Sites with the highest degrees of similarity in AMF species composition were also similar to each other in native plants or land use. Conversely, sites with the lowest similarity in AMF composition were those from which the majority of samples were collected from non-mycorrhizal plants, predominately ectomycorrhizal plants or bare soil. Spores of Glomus microggregatum were most abundant in urban sites, while those of G. eburneum were most abundant in desert and agricultural sites. Further studies are needed to determine the functional implications of shifts in AMF communities in urban ecosystems, including effects on plant primary productivity.

The Tao of open science for ecology

The field of ecology is poised to take advantage of emerging technologies that facilitate the gathering, analyzing, and sharing of data, methods, and results. The concept of transparency at all stages of the research process, coupled with free and open access to data, code, and papers, constitutes “open science.” Despite the many benefits of an open approach to science, a number of barriers to entry exist that may prevent researchers from embracing openness in their own work. Here we describe several key shifts in mindset that underpin the transition to more open science. These shifts in mindset include thinking about data stewardship rather than data ownership, embracing transparency throughout the data life-cycle and project duration, and accepting critique in public. Though foreign and perhaps frightening at first, these changes in thinking stand to benefit the field of ecology by fostering collegiality and broadening access to data and findings. We present an overview of tools and best practices that ...

Land use and land cover mapping from diverse data sources for an arid urban environments

Accurate and up-to-date data describing land use and land cover change support studies of urban growth such as quantifying the amount of rural to urban change and identifying change trajectories. This paper compares three methods for identifying urban land use/land cover, based on aerial photography, satellite imagery, and ground observations. While it might be natural to assume that classification based on ground observations would be the most accurate, this may not always be the case. Here we aim to quantify to what degree these three different classification approaches agree or contradict each other and to understand why. Land use/land cover data derived from these three sources were compared for the Phoenix metropolitan area, an arid urban region undergoing rapid urbanization. Our results show that satellite data are well suited to classify land use/land cover where land use categories are associated with homogeneous land cover at the subpixel level, but that for land use categories with subpixel land cover complexity, aerial photographs or ground observations are needed to aid in the classification.

Historical and current atmospheric deposition to the epilithic lichen Xanthoparmelia in Maricopa County, Arizona

Spatial patterns of atmospheric deposition of trace elements to an epilithic lichen were assessed using a spatial grid of 28 field sites in 1998 throughout Maricopa County, Arizona, USA. In addition, samples of Xanthoparmelia spp. from Arizona State University lichen herbarium material (1975-1976) was utilized for a limited number of sites in order to explore temporal trends. The lichen material was cleaned, wet digested and analyzed by ICP-MS for a suite of elemental concentrations [antimony (Sb), cadmium (Cd), cerium (Ce), chromium (Cr), cobalt (Co), copper (Cu), dysprosium (Dy), europium (Eu), gadolinium (Gd), gold (Au), holmium (Ho), lead (Pb), lutetium (Lu), neodymium (Nd), nickel (Ni), palladium (Pd), platinum (Pt), praseodymium (Pr), samarium (Sm), scandium (Sc), silver (Ag), terbium (Tb), thulium (Tm), tin (Sn), uranium (U), ytterbium (Yb), yttrium (Y), and zinc (Zn)]. Cluster analysis and principal component analysis suggest three major factors, which, depending on regional aerosol fractionation, explain most of the variation in elemental signatures: (1) a group of widely distributed rare earth elements (2) a highly homogenous Co, Cr, Ni, and Sc component representing the influence of mafic rocks, and (3) anthropogenic emissions. Elemental concentrations in Maricopa County lichens were generally comparable to those reported for relatively unpolluted areas. Only highly urbanized regions, such as the greater Phoenix Metropolitan Area and the NW corner of the county, exhibited elevated concentrations for Zn, Cu, Pb, and Cd. Lead levels in lichens have fallen over the last 30 years by 71%, while Zn concentrations for some regions have increased by as much as 245%. From the spatial pattern of elemental deposition for Cd, Cu, Ni, Pr, Pb, and Cu, we infer that agriculture, mining, industrial activities, and traffic probably are the major air pollutant sources in Maricopa County.

Soil Characteristics and the Accumulation of Inorganic Nitrogen in an Arid Urban Ecosystem

Urbanization represents the extreme case of human influence on an ecosystem. Biogeochemical cycling of nitrogen (N) in cities is very different from that of non-urban landscapes due to the large input of reactive forms of N and the heterogeneous distribution of various land uses that alters landscape connections. To quantify the likely effects of human activities on soil N and other soil properties in urban ecosystems, we conducted a probability-based study to sample 203 plots randomly distributed over the 6,400 km2 Central Arizona-Phoenix Long-Term Ecological Research (CAP LTER) area, which encompasses metropolitan Phoenix with its 3.5 million inhabitants. Soil inorganic N concentrations were significantly higher in urban residential, non-residential, agricultural, transportation, and mixed sites than in the desert sites. Soil water content and organic matter were both significantly higher under urban and agricultural land uses, whereas bulk density was lower compared to undeveloped desert. We calculated that farming and urbanization on average had caused an accumulation of 7.23 g m−2 in soil inorganic N across the CAP study area. Average soil inorganic N of the sampled desert sites (3.23 g m−2) was much higher than the natural background level reported in the literature. Laboratory incubation studies showed that many urban soils exhibited net immobilization of inorganic N, whereas desert and agricultural soils showed small, but positive, net N mineralization. The large accumulation of inorganic N in soils (mostly as nitrate) was highly unusual in terrestrial ecosystems, suggesting that in this arid urban ecosystem, N is likely no longer the primary limiting resource affecting plants, but instead poses a threat to surface and groundwater contamination, and influences other N cycling processes such as denitrification.

Drivers of Spatial Variation in Plant Diversity Across the Central Arizona-Phoenix Ecosystem

ABSTRACT We examined how growth of the Phoenix urban landscape has changed spatial patterns in native Sonoran desert plant diversity. Combining data from the U.S. Census with a probability-based field inventory, we used spatial and multivariate statistics to show how plant diversity across the region is influenced by human actions. Spatial variations in plant diversity among sites were best explained by current and former land use, income, housing age, and elevation. Despite similar average diversity in perennial plant genera between desert and urban sites, numerous imported exotics have significantly increased variation in plant generic composition among urban sites, with a “luxury effect” of higher plant diversity at sites in wealthier neighborhoods. We conclude that controls on natural spatially autocorrelated desert plant diversity are replaced by a variable suite of site-specific human factors and legacy effects, which require an integration of ecology and social science to be fully understood.

Estimating vegetation cover in an urban environment based on Landsat ETM imagery: A case study in Phoenix, USA

Studies of urban ecological systems can be greatly enhanced by combining ecosystem modelling and remote sensing which often requires establishing statistical relationships between field and remote sensing data. At the Central Arizona–Phoenix Long‐Term Ecological Research (CAPLTER) site in the south‐western USA, we estimated vegetation abundance from Landsat ETM+ acquired at three dates by computing vegetation indices (NDVI and SAVI) and conducting linear spectral mixture analysis (SMA). Our analyses were stratified by three major land use/land covers—urban, agricultural, and desert. SMA, which provides direct measures of vegetation end member fraction for each pixel, was directly compared with field data and with the independent accuracy assessment dataset constructed from air photos. Vegetation index images with highest correlation with field data were used to construct regression models whose predictions were validated with the accuracy assessment dataset. We also investigated alternative regression methods, recognizing the inadequacy of traditional Ordinary Least Squares (OLS) in biophysical remote sensing. Symmetrical regressions—reduced major axis (RMA) and bisector ordinary least squares (OLSbisector)—were evaluated and compared with OLS. Our results indicated that SMA was a more accurate approach to vegetation quantification in urban and agricultural land uses, but had a poor accuracy when applied to desert vegetation. Potential sources of errors and some improvement recommendations are discussed.