Effect of pavement and water deficit on biomass allocation and whole-tree transpiration in two contrasting urban tree species

Urban Ecosystems - Aiming to explore the species-specific responses of biomass allocation and whole-tree transpiration in urban trees to pavement and drought, a field manipulation experiment grew...     

Improving confidence in tree species selection for challenging urban sites: a role for leaf turgor loss

High species diversity is argued to be the most important requisite for a resilient urban forest. In spite of this, there are many cities in the northern hemisphere that have very limited species diversity within their tree population. Consequently, there is an immense risk to urban canopy cover, if these over-used species succumb to serious pests or pathogens. Recognition of this should motivate the use of less commonly used species. Analysis of plant traits, such as the leaf water potential at turgor loss (Ψ_P0), can provide useful insights into a species’ capacity to grow in warm and dry urban environments. Therefore, the aim of this study was to evaluate Ψ_P0 of 45 tree species, the majority of which are rare in urban environments. To help evaluate the potential for using Ψ_P0 data to support future decision-making, a survey of professionals engaged with establishing trees in urban environments was also used to assess the relationship between the measured Ψ_P0 and the perceived drought tolerance of selected species. This study demonstrates that Ψ_P0 gives strong evidence for a species’ capacity to tolerate dry growing conditions and is a trait that varies substantially across species. Furthermore, Ψ_P0 was shown to closely relate to the experience of professionals involved in establishing trees in urban environments, thus providing evidence of its practical significance. Use of plant traits, such as Ψ_P0, should, therefore, give those specifying trees confidence to recommend non-traditional species for challenging urban environments.     

Decomposition of labile and recalcitrant litter types under different plant communities in urban soils

Although little is known about the relationship between aboveground and belowground biota and ecosystem services in urban soils, the scarce data suggests that plant coverage has a key role in influencing the urban C and N cycles. Plant litter quality and quantity have been addressed as one the major factors determining the rate of nutrient and organic carbon cycling in urban soils. However, the land-use history of urban soils, frequency of disturbances and abiotic-biotic conditions may largely contribute to the effects of aboveground biota on decomposition process. Here we studied the decomposition process of different litter types (labile and recalcitrant litter) in two structurally and chemically divergent urban soils (landfill sandy soil and richer park soil). At both of these urban sites, a reciprocal litter placement experiment was performed to distinguish the effects between plant coverage (plant treatment) and litter type on litter decomposition processes. As hypothesized, labile litter decomposed faster than recalcitrant litter at both urban soil types. Urban soil type however, had a clear impact on degradation rate of the litter: all litter types decomposed at higher rates in park soil with higher organic matter and soil moisture content. Unexpectedly, the plant treatment did not affect the degradation rate of the litter although it did have a significant influence on the abundance of litter-inhabiting Collembola in landfill soil. Our study suggests potentially higher carbon retention in urban soils under recalcitrant litter producing plants in comparison to plant-soil systems with labile-litter producing plants.     

城市供水水质督察工作的实践与思考

从2004年初开始,天津市供水管理处在全市开展了城市供水水质督察工作,经过一年多的研究和实践,取得了很好的效果,受到了建设部城建司和天津市建委的肯定以及社会各界的好评.下面结合天津实际,谈谈我对城市供水水质督察工作的认识与体会.     

Plant-mycorrhizal fungi associations along an urbanization gradient: implications for tree seedling survival

Mycorrhizal fungi symbioses can be critical determining if established seedlings survive or not. Currently, in remnant forests, plants and their fungal symbionts are exposed to varied anthropomorphic effects related to urbanization, however, little is known about their impact on this association. We investigated the relationship between mycorrhizal fungi and tree seedling survival along an urbanization gradient. We planted three species of temperate tree seedlings (Acer rubrum, Carya ovata, and Quercus rubra) in three landscapes: urban, suburban, and rural. We measured the percent of root length colonized by mycorrhizal fungi and monitored survival during their first growing season. We analyzed mycorrhizal colonization as a function of landscape type (urban-rural) and additional variables known to contribute to mycorrhizal colonization (phosphorus, nitrogen, initial plant height). We then analyzed seedling survival as a function of the degree of mycorrhizal fungi colonization associated with the landscape gradient and of additional environmental factors (light and soil moisture). Within a species we found no changes in the levels of mycorrhizal fungi colonization across the urbanization gradient. Each species, however, had markedly different levels of colonization. Survival of A. rubrum was independent of mycorrhizal colonization, while C. ovata and Q. rubra had a significant positive response to increased mycorrhizal fungi. These findings highlight the resilience of mycorrhizal communities across the rural-urban gradient typical of this region, but they also underscore the potential sensitivity of some tree species to lower levels of mycorrhizal fungi colonization.     

Linking bird species traits to vegetation characteristics in a future urban development zone: implications for urban planning

Identifying the relationships between species traits and patch-scale vegetation characteristics in areas designated for urban development can improve our understanding of how animal communities may change with urbanization. We explored the implications of this premise to the urban planning process in a mixed-use landscape in Canberra (Australia), prior to its development into new suburbs. We used RLQ analysis to relate bird foraging, nesting and body size traits to patch-scale vegetation characteristics. Relationships between species traits and vegetation characteristics within the development zone suggest that species that forage and nest on the ground and in the understory strata, and smaller-bodied species will be most negatively affected by urbanization. Identifying the relationships between species traits and vegetation characteristics may be used by urban planners to (i) identify potentially critical habitat and species at risk from development, (ii) inform the choice of impact mitigation measures, and/or (iii) distinguish between high and low mitigation measures. Analyses conducted early in the planning process can then be used to allocate proposed land uses in an ecologically sensitive way, and to plan appropriate mitigation measures.     

Influence of water quality and habitat conditions on amphibian community metrics in rivers affected by urban activity

Urban Ecosystems - Anuran amphibians are highly dependent on aquatic ecosystems. Many amphibian species are exhibiting population declines primarily due to habitat destruction and water quality...     

Decomposition of urban atmospheric carbon in Sonoran Desert soils

Urban atmospheres can have high concentrations of particulate organic carbon (oC) but the rate and fate oC deposition in near-urban ecosystems are rarely quantified. We collected atmospheric particulate matter in Phoenix, AZ and applied these samples to Sonoran Desert soils in a series of laboratory incubation experiments. The addition of fine particulate matter (<2.5 μm aerodynamic diameter) increased microbial respiration in soils collected from the interspaces between desert shrubs. The increase in soil respiration was equivalent to 25% to 30% of the added oC. In contrast, we did not detect increases in respiration when coarse particulate matter (>2.5 μm aerodynamic diameter) was added to interspace soils, suggesting that coarse particulate oC is recalcitrant to microbial decomposition. Due to comparatively higher background levels of C mineralization, we rarely detected changes in microbial respiration when fine or coarse particulate oC was added to soils collected beneath shrub canopies. We measured total atmospheric C concentrations within and surrounding Phoenix and, using inferential methods, estimated rates of deposition that ranged from 0.02 to 0.58 mg C m⁻² d⁻¹ for fine particles and from 0 to 6.15 mg C m⁻² d⁻¹ for coarse particles. Results show that fine atmospheric particulate matter deposited at low rates downwind of Phoenix is a labile oC substrate for soil heterotrophs. In contrast, oC deposited at higher rates as coarse particulate matter may accumulate in soils due to slow microbial decomposition rates.     

Connectivity of public urban grasslands: implications for grassland conservation and restoration in cities

An important limitation of studies on the ecological value of urban habitats is the question of habitat connectivity. While connectivity allows spread and genetic exchange of species, isolation can lead to the extinction of populations through inbreeding and loss of genetic diversity. However, while practitioners already start improving urban habitat patches by means of restoration, issues of connectivity have not been taken in account although being crucial for a self-sustaining habitat network. In our study, we evaluate the connectivity of public urban grasslands such as lawns, grasslands in residential areas, playgrounds or parks in the city of Münster, Germany. Employing a graph theory approach, which uses a map (graph) of habitat patches to calculate functional connectivity measures using patch area size and patch connectivity, we studied four groups of different plant dispersal distances (2 m, 20 m, 44 m and 100 m). This approach can be recommended for planning issues due to the output of different indicator values and comparably low data demands. Our results show for the first time, that connectivity of urban grasslands is extremely low for species of short-distance dispersal but slightly increases for long-distance dispersal. Except two larger conglomerations of well-connected patches, urban grasslands were found to be mostly sparsely connected. Thus, future research should focus on options to improve connectivity and to prioritize patches for ecological improvement. The graph theory approach turned out to be a useful tool to analyse urban habitat connectivity but also to illustrate results obtained.

     

Determinants of urban tree canopy in residential neighborhoods: Household characteristics, urban form, and the geophysical landscape

The aesthetic, economic, and environmental benefits of urban trees are well recognized. Previous research has focused on understanding how a variety of social and environmental factors are related to urban vegetation. The aim is often to provide planners with information that will improve residential neighborhood design, or guide tree planting campaigns encouraging the cultivation of urban trees. In this paper we examine a broad range of factors we hypothesize are correlated to urban tree canopy heterogeneity in Salt Lake County, Utah. We use a multi-model inference approach to evaluate the relative contribution of these factors to observed heterogeneity in urban tree canopy cover, and discuss the implications of our analysis. An important contribution of this work is an explicit attempt to account for the confounding effect of neighborhood age in understanding the relationship between human and environmental factors, and urban tree canopy. We use regression analysis with interaction terms to assess the effects of 15 human and environmental variables on tree canopy abundance while holding neighborhood age constant. We demonstrate that neighborhood age is an influential covariate that affects how the human and environmental factors relate to the abundance of neighborhood tree canopy. For example, we demonstrate that in new neighborhoods a positive relationship exists between street density and residential tree canopy, but the relationship diminishes as the neighborhood ages. We conclude that to better understand the determinants of urban tree canopy in residential areas it is important to consider both human and environmental factors while accounting for neighborhood age.     

A small-scale response of urban bat activity to tree cover

Urban Ecosystems - Bats in urban areas depend on trees, and bat activity increases with tree cover. To effectively manage bat habitat in cities, it is important to know the distance to which tree...     

Rainfall interception capacity of tree species used in urban afforestation

Afforestation is inserted in the urban environment and interferes directly in the surface runoff. In order to quantify the rainfall interception by tree species, an experiment was carried out in the city of Uruaçu, Goiás, Brazil, with the four most common tree species in the urban afforestation of the region. The species chosen were the Mangifera indica (mango tree), the Caesalpinia peltophoroides (sibipiruna tree), the Pachira aquatica (munguba tree) and the Licania tomentosa (oiti). In order to register precipitation, ten pluviographs were used. They are capable of measuring precipitation over time in terms of duration, volume, and intensity. For events with a mean cumulative precipitation of 16.7 mm, the mean values of interception found in each species were: Mangifera indica - 8.0 mm; Pachira aquatica - 7.4 mm; Licania tomentosa - 7.2 mm; and Caesalpinia peltophoroides - 4.8 mm. The research confirms the importance of studies related to the identification of the species’ individual characteristics that interfere in the rainfall interception capacity and that can consequently contribute to urban drainage actions. In addition, it proves the existence of variations of rainfall interception in relation to rainfall events and during their occurrences and emphasizes the need for a careful definition of the species that will compose the urban afforestation.     

Vegetation management and benthic macroinvertebrate communities in urban stormwater ponds: implications for regional biodiversity

Urban Ecosystems - Designed ecosystems (e.g., gardens or engineered ponds) are increasingly common components of urban landscapes and contribute valuable ecosystem services. However, management of...     

Intrinsic and extrinsic drivers of yard vegetation in urban residential areas: implications for conservation planning

Residential green areas often represent a significant portion of a city’s green infrastructure which has generated great interest in studying the factors that contribute to the formation of plant associations in residential yards. This project evaluated the external factors to the household social-ecological system that influence the availability of plants for residential landscapes and how they may influence the presence of native plants in residential yards on households within the Río Piedras watershed in the metropolitan area of San Juan, Puerto Rico. The methods used included a residential survey with open and closed questions that addressed the sources of plants used in landscaping and an evaluation of ornamental plant species inventories from local nurseries. A total of 432 yards were surveyed. Yard plants in this watershed have multiple sources. Aside from obtaining plants at local nurseries, natural dispersion, exchanges among family and friends and historical plantings can be just as important sources of yard plants. Our results also suggest that the majority of residents do not know where to get native plants which could represent a challenge for the development and implementation of initiatives for natives gardening. At the same time, most commercial nurseries have a deficit of native plants in their inventories. This information is critical to species conservation strategies that seek the inclusion of urban residential areas and may help improve initiatives about the involvement of individual citizens in sustainable gardening practices at the residential scale.     

Food at home production and consumption: implications for nutrition quality and policy

The production and consumption of food at home is one of the most frequent and ubiquitous of all human activities and yet little is known about some of the basic economic constructs of this activity. Increasing our knowledge of food at home economics is important for improving the nutritional quality of diets and nutritional policies of the United States. This paper reviews the empirical literature on food at home production and consumption and food away from home consumption, demonstrates how the effectiveness of some nutrition policies depends on the magnitudes of a few key parameters, and identifies numerous areas in need of further research.     

城市轨道交通服务质量模糊综合评判

一、引言 城市轨道交通系统是构成现代城市公共交通系统的子系统之一.城市轨道交通系统对城市提供的服务状况体现在两个方面,一是交通的服务质量,二是运输质量.服务质量可以通过服务水平来表达,而运输质量则通过轨道交通客运的服务质量来描述.因此对轨道交通服务状况的评价主要体现在对轨道交通服务质量的评价上,即对轨道交通的服务水平的评价.     

Short-term impacts of urban landscape conversion on surface runoff quality

Urban Ecosystems - Given the rapid pace of urbanization and resulting pressures on water supplies in many regions, landscape water conservation has become increasingly important for many...     

Investigations of the urban street tree forest of Mendoza, Argentina

The investigation of the urban street trees was undertaken in the oasis city Mendoza, Argentina. The analysis included 1,680 urban street trees in their structure (species, age, and spatial structure), vitality and irrigation conditions. A questioning of 120 residents analysed the perception and acceptance of the urban trees by urban dwellers. Different urban structures, residential, commercial and residential mixed structures and the city centre were investigated. The results show clearly the insufficient maintenance of the trees (composition, aging, irrigation, pruning etc.) and damaged irrigation system with leads to a loss of vitality. The questioning showed that easily recognisable problems (insufficient pruning etc.) are more reflected by people than long term problems (irrigation). There is a different reflection of urban street tree problems in the different urban areas, related to status, information level and management. The maintenance and relation to urban street trees was best in the residential area. Not only better maintenance of the trees but also a clearer recognition of street tree problems by residents and by the responsible municipal institutions is urgently needed. A public-private partnership and more environmental education could help to overcome the problems.     

The influence of land use type and municipal context on urban tree species diversity

Recent research has focused on the ways urban forest patterns vary in relation to level of urbanization and socioeconomic characteristics, with most studies limited to one urban land use type or multiple non-differentiate land uses. Additionally, the majority of studies examining urban forest patterns focus on canopy cover extent, with less attention given to patterns of species diversity. This study explores how tree species diversity varies across different urban land uses and municipal boundaries to better understand the role of land use types in shaping urban forest patterns. The goal is addressed through an exploration of plot-level tree data in the urban municipalities of Peel Region located in the Greater Toronto Area (Ontario, Canada). Species composition and standard diversity metrics are calculated for eight land use types and four municipalities. Our results show that differences in diversity metrics and species composition are greater between urban land uses than municipalities. Moreover, Peel’s urban forest has relatively high alpha diversity but many species are present on only one land use type. The results suggest that different causal processes are associated with each land use type, and that urban forest managers should adopt land use-specific strategies to meet species composition goals within the urban forest.