Drivers of soil carbon in residential ‘pure lawns’ in Auburn,Alabama

Urban land area is expanding worldwide and may contribute to long-term carbon (C) storage; however, little is known about potential drivers of soil C in urban areas. Residential areas are one of the largest urban land use zones and lawns can provide stable chronosequences for studying soil C dynamics. In residential lawns containing no trees (n?=?23), the relationships between soil C and four potential drivers [home age (1–51 years), yard maintenance practices (fertilization, irrigation, and bagging or mulching lawn clippings), soil nitrogen (N) and soil texture] were investigated. Soil C increased with home age at 0–15 cm depth by 0.026 kg C m^?2?yr^?1, declined by ?0.011 kg C m^?2?yr^?1 at 15–30 cm depth, and was stable at 30–50 cm depth. Soil C had a positive relationship with soil N (R ²?=?0.55) at the 0–15 cm depth. Soil C and N were not related to yard maintenance practices or soil texture. The low soil C sequestration rate and limited relationships between soil C and home age, yard maintenance, soil N and soil texture may have resulted from the positive influence of Auburn’s humid, subtropical climate on residue decomposition.     

Nitrogen retention and loss in unfertilized lawns across a light gradient

A desirable function for terrestrial urban ecosystems is the mitigation of nitrogen (N) pollution associated with cities and suburbs. To assist in maximizing this function, identifying locations of sources and sinks of N in the urban environment is crucial to inform management strategies. Lawns are an extensive land cover in urbanized landscapes, and in general, they have demonstrated the capacity to function as a sink for N inputs. How N is cycled by lawns, however, is likely not uniform across the physical heterogeneity or management activities that exist in lawns. We investigated the influence of heterogeneity in light availability on N cycling in lawns that were irrigated but not fertilized. Light availability is affected by tree canopy and built structures and is, therefore, heterogeneous both within individual lawns and among lawns. Light is expected to control N retention and loss through effects on primary productivity. We experimentally examined N regulation over one calendar year by measuring net primary production (NPP), N retention using an isotopic tracer, and N leaching in existing unfertilized lawns under heterogeneous light conditions. We used a budgetary approach to estimate gaseous N loss which we assume is primarily via denitrification. Light functioned as a limiting resource for primary productivity. From low to high light conditions, annual NPP increased 177 to 430 g C?m^?2?y^?1 and retention of N isotope tracer increased from 50 to 65% as a result of increased retention in plants. Nitrate leaching losses were low overall and were not affected by light levels. Light availability regulated the fate of N inputs and unfertilized lawns may function as substantial sinks for reactive N through storage in the terrestrial system and N loss by denitrification. However, whether or not denitrification is generally an N sink will depend on the ratio of non-reactive (i.e., N₂) to reactive (i.e., N₂O, NO) denitrification products. Overall, we find that effective strategies for managing N sources and sinks in cities will likely need to consider light availability, particularly in systems receiving water subsidies via irrigation.     

Potential nitrogen mineralization responses of urban and rural forest soils to elevated temperature in Louisville,KY

Soil nitrogen (N) mineralization is an important process determining terrestrial N availability, and evidence suggests elevated temperatures will enhance N mineralization rates. Along a 40 km urban-rural gradient of chestnut oak forest stands in Louisville, KY, we expected N mineralization rates would be higher in urban than in rural forests in part due to increased temperatures caused by the urban heat island. However, a 12-month field study along this Louisville gradient showed that annual N mineralization rates were lower in urban than in rural stands. Since variation in precipitation inputs and other factors across this land-use gradient may be influencing soil N mineralization rates, we conducted a three-month soil incubation experiment in the lab to determine the extent to which a + 2 °C temperature difference could affect soil N mineralization in urban and rural soils. Across the range of temperatures tested, rural soils mineralized N at twice the rate of urban soils under base (7.86 vs. 3.65 mg N kg^?1 AFDW soil d^?1) and elevated (9.08 vs. 4.76 mg N kg^?1 AFDW soil d^?1) temperatures (p < 0.01). A 2 °C temperature difference, did not significantly alter total inorganic N production in urban (p = 0.272) or rural soils (p = 0.293). The proportion of nitrate produced was lower in the urban (15.1 %) than in the rural soils (72.3 %; p < 0.01). These results suggest that differences in soil organic matter quality and potentially decomposer community composition are the primary explanatory factors for forests along this Louisville gradient.     

Estimating urban lawn cover in space and time: Case studies in three Swedish cities

Lawns are considered monocultures and lesser contributors to sustainability than diverse nature but are still a dominating green area feature and an important cultural phenomenon in cities. Lawns have esthetical values, provide playground, are potential habitat for species, contribute to carbon sequestration and water infiltration, but also increase pesticides, fertilization, are monocultures and costly to manage at the same time. To evaluate the potential impact of lawns, whether positive or negative, it is of interest to estimate the total lawn cover in cities and its change over time. This is not a straightforward process, e.g., because many lawns are small and covered by trees. In this study we review the existing literature of lawn cover in cities and the different methodologies used for cover estimation. We found both pros and cons with NDVI and LiDAR data as well as manually interpreted aerial photos. The total cover of lawns in three case study cities was estimated to 22.5%. By extrapolating these percentages to all Swedish cities lawn cover was estimated to 2589 km² (0.6% of the terrestrial surface). The approximated total municipal management cost of lawns in all Swedish cities was 910,000,000 USD/ year. During 50 years lawn area almost doubled in relative cover and 56% of them were continuously managed. Since lawns constitute large parts of the urban greenery and are costly to manage it is highly relevant to consider their social, ecological and cultural value compared to alternatives, e.g., meadows with less intensive management.     

The effects of landscape cover on surface soils in a low density residential neighborhood in Baltimore,Maryland

Previous studies at the scale of a city have shown that surface soil nutrients, pH, and soil organic matter (SOM) can vary by land cover, land use, and management. This study was conducted in Baltimore County, Maryland, to quantify the differences in characteristics of soil in a residential neighborhood and adjacent forest patch sampling at a fine scale. The first objective was to compare soil characteristics in a residential neighborhood among ecotope types of forest, lawn, and planting beds that were underlain by the same parent material and thus only differed in plant cover. Another objective was to examine differences in soil properties of lawn soils that differed in age by 10 years. The final objective was to quantify the variation of these residential and forest soils. Composite soil samples from the surface to a depth of 5 cm were taken from planting beds and lawns from 50 residences and an adjacent forest patch. Results showed that the forest soil had 30 % more SOM and was more acidic than lawn soil. Conversely, Mg, P, K, and Ca were 47 to 67 % lower in forest compared to lawn soils even though both soils developed from similar parent materials. For the residential lawns, the older development had significantly higher concentration of soil P. There was also a difference between front and back lawns where front lawns had 26 and 10 % higher concentrations of Ca and Mg, respectively, and a higher pH than the back lawns. Finally, the variation of soil characteristics of all areas sampled, from lowest to highest was pH < SOM < K < Mg < Ca < P. Results of this study suggest that anthropogenic factors appear to overwhelm natural soil forming factors in suburban residential areas in the Baltimore metropolitan area and these differences appear to increase with time.     

Water,sediment, and nutrient runoff from urban lawns established on disturbed subsoil or topsoil and managed with inorganic or organic fertilizers

Urban runoff has become an increasingly important environmental concern in recent years. With increasing urbanization, turfgrass area has substantially expanded in North America, and these lawns are often established on subsoil stripped of topsoil. In this study, 24 turfgrass-type tall fescue (Festuca arundinacea) plots were established on subsoil or topsoil, and managed with inorganic fertilizer (Scott’s Turf Builder®), organic fertilizer (Nature’s Touch® with enzymes), or no fertilizer (control). A one-hour simulated rainfall at 8.9 cm/hour was applied to the plots, and the time to runoff initiation and total runoff volume were measured. Runoff water samples were analyzed to quantify the amounts of sediment, N (NH₄-N), P, K, and S losses. The results indicated that runoff initiation time was almost half in subsoil lawns (12.5 min) than in topsoil lawns (23 min). The total runoff volume and sediment loss were significantly larger in subsoil lawns (11,900 ml and 3,700 mg, respectively) than in topsoil lawns (2,200 ml and 900 mg, respectively). Although the N, P, K, and S losses in runoff were low, they were significantly higher from the subsoil-based than topsoil-based lawns, and were higher from inorganic fertilizer treated lawns than those treated with organic fertilizer. These results highlight the significance of topsoil preservation in city planning and urban development with respect to urban run-off and water quality and show distinct benefits of organic lawn management practices over the conventional inorganic practices for maintaining urban water quality.     

Groundwater denitrification capacity and nitrous oxide flux of former fringing salt marshes filled with human-transported materials

While former salt marsh sites filled with human transported material (HTM) have altered the surface marsh ecosystem, if artificial drainage is absent, subsurface conditions may continue favorable for denitrification, a microbial process reducing nitrogen (N) export to estuaries. We used piezometer networks to evaluate the in situ groundwater denitrification capacity and nitrous oxide (N₂O) flux (with ¹⁵N-enriched nitrate-N via the push-pull method) in four former fringing salt marshes topped by HTM along the Rhode Island coast, U.S.A. Groundwater at these sites commonly interacted with the buried marsh horizon and the HTM. In situ groundwater denitrification capacity site means ranged from 15.2 to 71.7 μg?N?kg^?1d^?1 with no significant differences between sites due to high intrasite variability. The site with the highest and most consistent denitrification capacity also had HTM of the finest texture and highest soluble organic carbon. Three of four sites had minimal N₂O flux [mean N₂O:(N₂O + N₂)?=?0.082] while the final site had N₂O generation rates up to 52.5 μg?N?kg^?1?d^?1. The site with the highest N₂O contributions also had the lowest ambient groundwater nitrate-N indicating lack of priming for N₂O reduction to N₂. Former salt marshes with HTM deposits may still have the capacity for substantial groundwater denitrification capacity, similar to that observed in undisturbed salt marshes, but may also contribute substantially to global N₂O emissions. For both salt marsh restoration and greenhouse gas mitigation efforts, attention should be given to ensuring that a tidally-driven, fluctuating water table regularly intercepts the buried organic horizons of the filled salt marsh.     

Ecology of urban lawns under three common management programs

Turfgrass lawns are a central part of urban and suburban landscapes throughout North America and are often managed using repeated applications of chemical fertilizers and pesticides. These inputs are expensive and may negatively affect ecological processes in lawns. Therefore, we evaluated the influence of three most common lawn care programs on ecological characteristics of turfgrass lawns. Twenty-eight home lawns, separated into 3 groups based on the lawn care program (professional, do-it-yourself [DIY], and no-input), were studied. Data on lawn quality, weed and insect infestation, disease incidence, soil nematode community, soil nitrogen pools, microbial biomass (MBN), and soil organic matter (SOM) were collected. Results indicated that professional lawn care resulted in the highest aesthetic lawn quality mainly due to better weed control, compared to DIY and no-input programs. However, professional and DIY programs negatively affected MBN and SOM pools and enhanced disease (rust) severity. No significant differences in soil nematode population and nematode community indices across the three programs were found, indicating no differences in net ecosystem productivity among the three programs. Overall, soil nematode food web in turfgrass lawns represented a disturbed food web compared to natural grasslands and forest ecosystems, irrespective of the lawn care program used.     

Soil-atmosphere exchange of carbon dioxide,methane and nitrous oxide in urban garden systems: impact of irrigation,fertiliser and mulch

Urban green spaces provide important ecosystem services, such as amenity, biodiversity, productivity, climate amelioration, hydrological and biogeochemical cycling. Intensively managed urban gardens can sequester carbon through vegetation growth and soil C increase, but may experience nitrous oxide (N₂O) emissions and reduced soil methane (CH₄) uptake from irrigation and fertiliser use. Soil atmosphere exchange of N₂O, CH₄ and carbon dioxide (CO₂) was measured in lawn and wood chip mulched garden areas in Melbourne, Australia in winter, spring and summer under various water and fertiliser regimes. Gas exchange before and after lawn fertiliser application was measured continuously for three weeks using an automated chamber system. Applying fertiliser led to a peak N₂O emission of >60 μg N m⁻² h⁻¹, but overall only weekly irrigation (10 mm) significantly increased mean soil N₂O emissions above that in other treatments. Under mulch, mean soil N₂O emissions (14.0 μg N m⁻² h⁻¹) were significantly smaller than from irrigated lawn (27.9 μg N m⁻² h⁻¹), whereas mean soil CH₄ uptake under mulch (−30.7 μg C m⁻² h⁻¹) was significantly greater (p < 0.01) than in any lawn treatment. Lawns were either a weak CH₄ sink or source. Soil C density (0–25 cm) under mulch (12.5 kg C m⁻²) was greater that under lawn (8.0 kg C m⁻²). On a carbon dioxide equivalent (CO₂-e) basis, soil N₂O emissions offset the benefits of soil CH₄ uptake. Mulched garden areas provide greatest C sequestration potential in soil and vegetation and the smallest non-CO₂ emissions, as soil CH₄ uptake offsets a large fraction of soil N₂O emissions. Results of this study suggest that reducing the irrigation and fertiliser application to lawns can help mitigate GHG emissions from urban garden systems, and increasing the area of mulched perennial garden beds can also provide net GHG benefits; however, this needs to be tested in other garden systems with different soil types and environmental conditions.     

Establishing turf grass increases soil greenhouse gas emissions in peri-urban environments

Urbanization is becoming increasingly important in terms of climate change and ecosystem functionality worldwide. We are only beginning to understand how the processes of urbanization influence ecosystem dynamics and how peri-urban environments contribute to climate change. Brisbane in South East Queensland (SEQ) currently has the most extensive urban sprawl of all Australian cities. This leads to substantial land use changes in urban and peri-urban environments and the subsequent gaseous emissions from soils are to date neglected for IPCC climate change estimations. This research examines how land use change effects methane (CH₄) and nitrous oxide (N₂O) fluxes from peri-urban soils and consequently influences the Global Warming Potential (GWP) of rural ecosystems in agricultural use undergoing urbanization. Therefore, manual and fully automated static chamber measurements determined soil gas fluxes over a full year and an intensive sampling campaign of 80 days after land use change. Turf grass, as the major peri-urban land cover, increased the GWP by 415 kg CO₂-e ha^?1 over the first 80 days after conversion from a well-established pasture. This results principally from increased daily average N₂O emissions of 0.5 g N₂O ha^?1 d^?1 from the pasture to 18.3 g N₂O ha^?1 d^?1 from the turf grass due to fertilizer application during conversion. Compared to the native dry sclerophyll eucalypt forest, turf grass establishment increases the GWP by another 30 kg CO₂-e ha^?1. The results presented in this study clearly indicate the substantial impact of urbanization on soil-atmosphere gas exchange in form of non-CO₂ greenhouse gas emissions particularly after turf grass establishment.     

Influence of aboveground tree biomass,home age,and yard maintenance on soil carbon levels in residential yards

With the rapid urbanization of natural lands, researchers have begun to examine the capacity of urban soils to store carbon (C), with recent attention to residential yards. We performed a case study to examine four potential influences on soil C levels in residential yards. In 67 yards containing trees, we examined the relationship of soil C (kg m^?2) to tree aboveground biomass, home age (3–87 years), yard maintenance (fertilization, irrigation, mulching or bagging lawn clippings), and soil texture (% clay, % sand, % silt), at three depths (0–15 cm, 15–30 cm, and 30–50 cm). Six tree aboveground biomass data sets were developed: 1) biomass, 2) biomass*(1/distance from tree), 3) biomass?≤?15 m from sample site, 4) biomass?≤?10 m, 5) biomass?≤?5 m, and 6) biomass?≤?4 m. Biomass?≤?5 m and biomass?≤?4 m had the greatest explanatory power for soil C at 30–50 cm depth (P?=?0.001, R²?=?0.28; P?=?0.05 R²?=?0.39, respectively). The relationship between soil C and home age was positive at 0–15 cm (P?=?0.0003, R²?=?0.19), but constant at the two lower depths. Yard maintenance had no significant influence on soil C levels across home age. At 0–15 cm, soil C increased with % silt (P?=?0.006, R²?=?0.12). Overall, trees in turfgrass yards may have a stabilizing effect on soil C levels below 15 cm but minimal influence above 15 cm.     

Management mitigates the impact of urbanization on meadow vegetation

Urban regions often contain remnants of ecologically valuable habitats. Whilst meadow habitats have been recognized as ecologically important and much studied, little attention has been given to meadow assemblages of urban locations. We studied the effects of meadow type, urbanization level, and management on vascular plant species richness, field layer diversity and soil chemistry in 18 grassland sites in the Helsinki Metropolitan Area (60°E, 25°N), on the southern coast of Finland during the summer of 2007. We recorded a total of 252 species, though the average number of species per m² was only 12.6. The negative effects of urbanization on forbs seemed to result in particular from increased soil nitrate (NO₃^- -N) concentration. The highest NO₃^- -N and Fe concentrations and ratios of total inorganic nitrogen (N_tot) to phosphorus (P) and potassium (K), were recorded from the soils of urban rocky meadows. Management by mowing decreased soil NO₃^- -N and Fe concentrations, ratios of N_tot:P and N_tot:K, and increased species richness and diversity. Elevated NO_x deposition is considered as a major driver of urbanization effects on vegetation, though changes in soil pH and metal concentrations, such as zinc (Zn), may also negatively affect the frequency of both forbs and grasses. This study shows that regular management by mowing and removal of hay mitigates these effects. We also recommend increasing the provision of dry meadows and maintaining more areas of supplementary semi-natural grassland habitats in urban green space as concrete measures for the conservation of dry meadow assemblages and urban biodiversity.     

Implementing integrated pest management in professional lawn care: a case study

Human choices regarding land cover management practices may influence ecosystem services provided by urban green spaces. We conducted a 2-year study to compare biological (weed, insect, and disease), aesthetic (lawn quality), and economic (lawn care program cost) attributes of an integrated pest management (IPM) program, in which pesticides are applied on the basis of treatment thresholds, with a standard program, in which pesticides are applied on a calendar basis without pest monitoring. Both programs were managed by a professional lawn care operator. Although weed incidence was low, the IPM program had significantly more lawns with weed presence than the standard program during 2005 and 2006. However, only 21% of the IPM lawns required herbicide applications in 2005, and none exceeded the treatment threshold (5% weed cover) in 2006 as compared to 100% of the standard program lawns being treated for weeds in both years. The IPM program also had significantly more lawns with insect damage than the standard program during June 2005 and August 2005, but not September 2005 and throughout 2006. Only 28% of the IPM lawns required insecticide applications in 2005 and none exceeded the threshold (5% insect damage) in 2006 whereas all of the lawns in the standard program received insecticide treatments in both years. Rhizoctonia blight was present on some of the lawns, but was not a common problem. Although lawn quality was high for both programs (>8, on a scale of 1–9), it was significantly higher for standard than for IPM program lawns during 2005, and June 2006 and September 2006, but not August 2006. The annual lawn management costs were lower for the IPM (281.50) than the standard program (281.50) than the standard program (458.06). Thirty one percent of the IPM program customers who continued with the study in 2006 did so because they were satisfied with the IPM program. Among those who did not continue with the program, 33% cited weed or insect problems, while 33% expected better results. The implications of these findings for implementation of IPM in professional lawn care are further discussed.     

Variations in carbon dioxide fluxes within a city landscape: Identifying a vehicular influence

To date, studies examining carbon dioxide (CO₂) fluxes in urban areas have been limited compared to those in rural environments. The objectives of our study were to examine the relationship between traffic volume and CO₂ fluxes. We demonstrated that CO₂ fluxes were strongly linked with surrounding land use, specifically impervious surfaces and traffic volume. A site near downtown Syracuse in New York State (USA) had relatively constant positive fluxes (source: +39 μmol CO₂ m^?2 s^?1) throughout the year as a result of strong vehicular traffic influence from two nearby interstate highways. There was a strong positive relationship between traffic and CO₂ fluxes (r²?=?0.93, p?<?0.0001) with marked differences between the weekend days versus the workweek days. In contrast, a residential site in Syracuse was dominated by vegetative influences during the leaf-on period due to CO₂ uptake by photosynthesis, reaching a maximum negative mean diurnal flux of ?11 μmol CO₂ m^?2 s^?1 around midday (sink). The spatial variations of CO₂ fluxes identify the critical role played by local traffic volumes in affecting the CO₂ dynamics of urban environments. Understanding the dynamic fluxes of CO₂ in urban environments has important implications for local, regional and global evaluations of CO₂ budgets and inventories, and carbon cycle and climate modeling.     

Photosynthetic CO<Subscript>2</Subscript> uptake and carbon sequestration potential of deciduous and evergreen tree species in an urban environment

Urban tree planting programmes are increasingly promoted as a way to reduce atmospheric carbon dioxide (CO₂) mixing ratios. However, few studies have investigated the photosynthetic CO₂ uptake potential of different urban tree species across seasons. In particular little is known about photosynthetic CO₂ uptake in cities with a subtropical, oceanic climate where evergreen species are dominant. We addressed this shortcoming by measuring net photosynthetic rates of ten native and exotic tree species during different seasons and times of the day in Auckland, New Zealand. We also assessed the potential of leaf nitrogen (N) concentration as a proxy for net photosynthetic capacities of urban trees, which is of particular importance to upscale leaf-level photosynthetic CO₂ uptake to local and regional scales. In addition, we compared measured net photosynthetic capacities (light-saturated net photosynthetic rates) with carbon (C) sequestration rates estimated using tree growth measurements and allometric equations. Mean net photosynthetic capacities ranged between 2.37 and 10.48 μmol m^?2 s^?1 across all seasons and were closely related to tree C sequestration rates, suggesting that increased photosynthesis enhances growth rates and therefore tree C sequestration rates. Given that winter net photosynthetic capacities remained high in evergreen species (3.38–13.96 μmol m^?2 s^?1), with almost 50% higher mean net photosynthetic capacity compared to summer across all species, we suggest that tree planting programmes for CO₂ mitigation should favour long living evergreen tree species with high basal area increments (BAI). Leaf N explained 43% and 57% of the variability of photosynthetic capacities across species in summer and winter, respectively. These results indicate that leaf N may be used as a proxy for net photosynthetic capacities of commonly planted urban trees in Auckland. However, further research is required to provide robust models that may be used to estimate photosynthetic CO₂ uptake at a local and urban scale.     

Urbanisation factors impacting on ant (Hymenoptera: Formicidae) biodiversity in the Perth metropolitan area, Western Australia: Two case studies

Two synchronous projects undertaken in 2011 examined the likely impact of increasing urban densification on invertebrate populations within urban settlement in Perth, Western Australia. One project analysed the ant fauna found in 20 gardens and lawns in small to very small properties (these having a bungalow or duplex (semi-detached) as the main residential building, and a lawn or garden area of 43 m²–332 m²) east, south, north and west of the Central Business District (CBD). The other project examined the ant fauna at 14 sites, principally in native regrowth along the Kwinana Freeway, a major artery that runs north to south through Perth’s suburbs. The gardens and lawns produced a very depauperate fauna of 26 ant species, of which a maximum of 20 were native and at least six species were exotic. The ant fauna from regrowth adjacent to the Kwinana Freeway and at two additional sites (one a bush control) was more than twice as rich, the 56 species collected including only two exotics. In the garden project, ant richness, evenness and abundance were not significantly correlated with size of the garden area. The same applied even when the exotic Pheidole megacephala-dominated gardens were removed from the analysis. Ordination analysis combining the two sets of data revealed a distinct clustering of most of the regrowth sites, whereas the bush control stood alone and garden or lawn sites exhibited a much looser pattern of association. We suggest that increasing the density of Perth suburbs is resulting in drastic loss of native invertebrate fauna, of which ants are a useful bioindicator. However, native vegetation regrowth along major arterial roads could act as a reservoir for invertebrate species that might otherwise disappear entirely from the Perth metropolitan area.     

Baseline biodiversity surveys of the soil macrofauna of London’s green spaces

A serious barrier to our understanding of urban ecosystems is a lack of information on the ecology of soils organisms of green spaces within large cities. This study addresses this gap by providing baseline survey data on the biodiversity of soil macrofauna in urban parks and domestic gardens of London, UK. In April and June 2004, the soil macrofauna were handsorted from soil cores in eleven parks and gardens of various sizes in central London. Five taxa were identified to species (Lumbricidae, Isopoda, Diplopoda, Chilopoda and Formicidae). The biodiversity value of the two main habitats (horticultural borders and mown grass lawns) was assessed and the influence of a range of environmental factors on species density (number of species per unit area) examined. The species densities of the studied soil invertebrates in the urban gardens were comparable with those found in natural ecosystems, although plant borders contained significantly more species than lawns. Borders had higher levels of plant nutrients, higher floristic diversity and lower levels of micronutrients and heavy metals than lawns. Significant predictor variables of species densities in the plant borders were the percentage of leaf litter cover, sampling month and soil pH. Species densities in the lawns were significantly correlated with the distance of the samples from the edge of the lawn.     

Changes through time in soil Collembola communities exposed to urbanization

The study aimed to assess if long-term exposure to urbanization changes the structure and composition of soil collembolan communities in urban green components (street lawns and park lawns) and in all urban green. Species diversity metrics, rarefaction, species richness estimators (Chao 1 and ACE) and multivariate analysis were used for the comparison of changes in community structure and diversity pattern over ca 30 years’ time span. Our results clearly demonstrate a shift, through time, in Collembola community composition and structure in an urban ecosystem and confirm that there is a linkage between long-term exposure to urbanization and changes in collembolan communities. Long-term urbanization led to erosion in species diversity and the formation of species-poor communities, species replacement, loss of specialized forms and promoted the invasion of exotic species. However, we show that the time span considered produced significant differences in diversity attribute values for the collembolan communities from street lawns and insignificant differences in park lawns, also we noted lack of significant differences in collembolan abundance across the two urban green components. The observed temporal changes in collembolan communities indicate that their response to disturbances in urban settings and selecting species is shaped by multiple processes. We conclude that more resistant collembolan communities were found over time in less stressed urban greening components such as park lawn soils compared to street lawn soils.     

Carbon fluxes and nitrogen availability along an urban–rural gradient in a desert landscape

Urbanization is increasing in arid and semi-arid regions of the world and impacting native ecosystems through disturbance, climatic modification, and pollution deposition. Arid ecosystems often exhibit a mosaic of shrub/tree canopy covered and non-canopy covered patches that differ in elemental pools and processes. We measured belowground ecosystem attributes and processes in native Larrea tridentata {(D.C.) Cov} dominated communities along an urban–rural gradient in Phoenix, Arizona. Organic carbon (C), total nitrogen (N), and nitrate levels were significantly greater in the urban locations, but soil respiration rates (R_s) were higher at the rural sites. Urban sites exhibited no difference in R_s and N between the canopy and interplant patches while both the rural and suburban sites had significantly greater N and higher R_s under the canopy than in the interplant spaces. Soil respiration rates at the urban locations were not correlated with either soil moisture or temperature individually. These data suggest that urbanization has caused a disconnect of ecological pattern and processes in L. tridentata ecosystems within the urban setting such that water and N limitations no longer explain expected spatial R_s patterns, or elemental pools.     

Gross primary productivity of a large metropolitan region in midsummer using high spatial resolution satellite imagery

Although gross primary productivity (GPP) is estimated with remote sensing over large regions of Earth, urban areas are usually excluded due to the lack of light use efficiency (LUE) parameters for urban vegetation and the spatial heterogeneity of urban land cover. Here, we estimated midsummer GPP, both within and among vegetation and land-use types, across the Minneapolis-Saint Paul, Minnesota metropolitan region. We derived LUE parameters for urban vegetation types using estimates of GPP from tree sap flow and eddy covariance CO₂ flux observations, and from fraction of absorbed photosynthetically active radiation based on 2 m resolution WorldView-2 satellite imagery. Mean GPP per unit land area (including vegetation, impervious surfaces, and soil) was 2.64 g C m^?2 d^?1, and was 4.45 g C m^?2 d^?1 per unit vegetated area. Mapped GPP estimates were within 11.4% of estimates from independent tall tower eddy covariance measurements. Turf grass GPP had a larger coefficient of variation (0.18) than other vegetation classes (~0.10). Vegetation composition was largely consistent across the study area. Excluding golf courses, mean land-use GPP for the total study area varied more by percent vegetation cover (R²?=?0.98, p?<?0.001) than by variability within vegetation classes (R²?=?0.21, p?=?0.19). Urban GPP in general was less than half that of natural forests and grasslands in the same climate zone.