Are plant communities mainly determined by anthropogenic land cover along urban riparian corridors?

Often used as a mitigation tool to landscape fragmentation, urban riparian corridors also suffered from the effects of the urban expansion. This study explored the relationships between plant riparian communities and two major environmental variables (land cover, soil characteristics) and analyzed the floristic change along an urbanization gradient. Fifteen sites were surveyed on both riverbanks of two riparian corridors characterized by contrasting water regimes in Strasbourg, North Eastern France. Data of spontaneous species abundance was collected from 180 quadrats using (i) all plant species, (ii) herbaceous stratum and (iii) ligneous stratum (bush and tree). The diversity and compositional patterns of riparian plant species were analyzed within each corridor according to three levels of urbanization (urban, suburban, peri-urban). Relationships between riparian communities, land cover and soil chemical properties (pH, nitrogen and carbon content, moisture) were established by between-class co-inertia analyses. Land cover emerged as the main factor explaining changes in riparian communities along the rural–urban gradient while soil chemical properties discriminate water stress and fluvial dynamics of the two corridors. Similar compositional patterns were found within the most urbanized sites with the establishment of ubiquitous species. The herbaceous stratum is best linked to the level of urbanization, whereas the tree stratum is primarily correlated with corridor attributes (hydrological regime, soil properties). Although riparian species and communities are mainly determined by land cover, urban riparian corridors maintain native biodiversity up to the urban center.     

Riparian woody plant diversity and forest structure along an urban-rural gradient

Changes in riparian woody plant assemblages are anticipated in the southeastern United States due to increases in urbanization rates. Because riparian forests serve important roles in maintaining water quality and biodiversity, understanding how they respond to urbanization is crucial. The objective of this study was to examine forest structure and woody vegetation diversity indices of riparian communities in response to an urbanization gradient in West Georgia, USA. Measures of forest structure and diversity were compared to measures of urbanization and land cover. Although Liquidambar styracifluaand Quercus nigrawere dominant species in the forest stand and regeneration layer for all riparian communities, the invasive, non-native shrub Ligustrum sinense was the most dominant species observed in the regeneration layer for urban, developing, and agriculture communities. The proportion of non-native species in the forest stand and regeneration layer decreased and Shannon diversity of the regeneration layer increased with increasing distance from the urban center. Shifts in diversity indicate that anthropogenic disturbance may subdue the ability of diverse communities to resist non-native plant invasions.     

Biodiversity of ant species along a disturbance gradient in residential environments of Puerto Rico

One of the most effective ways to describe the successional gradient of an environment is by using measures of biodiversity. We investigated the biodiversity of ant communities (known tramp/structure invaders) in an environment undergoing urban succession to characterize how ant communities changed along a disturbance gradient. Ant community dynamics were examined within three Puerto Rican housing developments of different ages. Within each development, we assessed the ant community using biodiversity measures of richness, abundance, diversity and evenness. We also studied changes in biodiversity within each development over time as well as how biodiversity related to food preferences within the ant communities. In general, the biodiversity measures increased as the age of the housing development increased. Monthly changes in biodiversity indicated that month was a better predictor of biodiversity in the most recently disturbed development, while the biodiversity in the older developments was less predictable from month to month. The biodiversity measures also suggested that the ant community in the youngest development was comprised mostly of generalist feeders. However, the older sites’ ant species appeared to have more specific feeding preferences. Based on the biodiversity measures of these ant communities, our findings suggest that the housing developments of different ages represented advancing stages of secondary succession. Furthermore, this study indicated that the succession of ant species occurs rapidly (<10 years) in urban environments, resulting in a relatively diverse ant community.     

What shapes plant and animal diversity on urban golf courses?

Recent concern over increasing loss of biodiversity has prompted considerable interest in the role of urban green spaces as reservoirs of local biodiversity. This study assessed the diversity of three indicator taxa - plants, ants and birds - on golf courses spanning a wide range of environmental variation in terms of climate, elevation, course age, size and connectivity to native woodland. Species richness and community composition was further compared between contrasting on-course habitat types that reflect different management intensities. We identified a set of taxon-specific environmental correlates indicating an intricate interplay of landscape- and local-scale variables that affect local species diversity. Our results show that floristic diversity is positively associated with the amount of rainfall, whereas ant and bird diversity are related to local-scale factors, particularly the number of trees and the size of water features on a site. The amount of on-course native habitat was a strong predictor of plant and ant diversity and was also associated with the number of unique species at the site level; this reinforces the value of remnant habitat patches as local biodiversity reservoirs that represent mini hot-spots in an otherwise species-poor urban landscape. Community composition for all three taxa differed markedly between non-playing and playing areas, with boundary and remnant habitats generally having more diverse, species-rich communities. Our results suggest that local floral and faunal biodiversity on urban golf courses can be enhanced by creating woody non-playing areas and, especially, by preserving, restoring or expanding remnant habitats.     

Pollinating animals in the urban environment

Urban environments contain habitats for flowering plants and their pollinating animal species. It is, however, unclear how the urban matrix influences plant-pollinator processes. We recorded plant diversity, floral abundance, flower visitor diversity and plot visits at 89 plant patches within the city of Zürich. The urban matrix surrounding each site was analyzed for the landscape metrics edge density and the extent of green area up to 200 m radius. The correlation between edge density and bee diversity and visitation frequency varied over the entire spatial range, while the correlation for syrphid diversity and visitation frequency levelled off at 80 m radius. In contrast, the correlations with green area were more consistent, with bee diversity levelling off after 100 m, while syrphid diversity and visits continued to increase. The variation in the correlation of bee visits was partly accounted for by the large contribution of honeybees. Plant diversity significantly affected bee diversity and visits, and syrphid visits. Floral abundance had a positive effect on bee visits and bee diversity. Syrphid diversity had a negative interaction with floral abundance and green area. The extent of green area increased bee diversity and visits, and syrphid visits, while edge density reduced visitation by bees. This study showed that plant diversity and floral abundance in urban environments promote pollinating flower visitors. The extent of green area and edge density are important urban mosaic attributes that affect pollinator abundance and visitation frequency at multiple scales.     

Avian use of suburban greenways as stopover habitat

Greenways may provide stopover habitat for migrating birds in otherwise inhospitable suburban landscapes. We examined the effect of greenway forested corridor width, vegetation composition and structure, and adjacent land cover on the species richness and abundance of migrating songbirds during spring and fall migration in Raleigh and Cary, North Carolina, USA. Generally, migrating birds were more abundant in wider forest corridors during spring and fall migration. During the spring, migrants were detected more commonly in greenways with taller trees and a higher percentage of hardwood trees. In the fall, migrant richness and abundance was highest in greenways with lower canopy cover, possibly because of the increased vertical complexity of the vegetation at these sites. Forest-interior migrant richness was not correlated with corridor width in either season, but these species were more abundant in greenways bordered by less bare earth and pavement cover in the spring. No other bird groupings were correlated with adjacent land cover measures. Although migrants used greenways of all widths, forested corridors wider than 150 m should be conserved whenever possible to provide stopover habitat for forest-interior migrants. Shrub cover should be retained to maintain vegetative complexity. Habitat for the greatest diversity of migrants can be provided by constructing greenways in areas of lower development intensity and encouraging residents to retain shrubs and trees on properties bordering greenways.     

Ecological corridors also operate in an urban matrix: A test case with garden shrews

The fragmentation of landscapes, induced by the growing urbanisation, is a major cause of biodiversity loss. Ecological corridors are landscape elements that make up for the negative effects of habitat fragmentation in agricultural or natural landscapes. However, their effectiveness have been rarely assess in an urban context. To do so, we analysed shrews in woodlots, corridors and domestic gardens that are connected or disconnected from a corridor. Indeed, these mammals are very sensitive to fragmentation and could play an important ecological role even in small and isolated areas such as domestic gardens. Ninety-seven shrews, from three species were trapped. In our study, Sorex coronatus, Sorex minutus and Crocidura russula were not widely distributed and mainly occurred in woodlots, corridors and connected gardens. In gardens, shrew occurrences were mainly determined by landscape configuration with negative effects of the distance to the corridor and the distance to the woodlot, stronger for C.russula than Sorex species. At the local scale, garden management and vegetation showed a positive effect mainly for Sorex species. The quality of gardens seems good enough to permit the co-occurrence of several species of shrews and thus competition was not identified as a major process for determining the occurrence. We showed that, as in other ecosystems, ecological corridors in urban context can play an effective role for the distribution of organisms with low dispersal capabilities and should be develop in planning strategies.     

Impact of urban structure on avian diversity along the Truckee River, USA

Urban riparian habitats are potentially important resources for native birds in arid ecosystems. Most studies have assessed the value of urban riparian habitat in terms of vegetation and natural resources; however, the surrounding land use and infrastructure may determine the viability of urban habitat. We studied the impact of urban structure, the combination of land use, infrastructure and vegetation variables that work together to shape the urban environment, on avian riparian habitat in the Truckee Meadows, Nevada, USA. Land use and infrastructure explained avian species richness and abundance better than local vegetation alone, but community resemblance was more strongly correlated to vegetation. Avian species guilds responded differentially to surrounding land use, suggesting there may be a functional difference between land use types. The best models for bird diversity used urban structure (both land use and vegetation) to describe potential habitat. Urban structure describes urban habitat in ways that vegetation variables alone cannot. Studies that ignore land use and infrastructure and other socioeconomic variables are likely missing key functional differences within urban ecosystems, and may miss the potential for compatible development that encourages both biodiversity and urban growth.     

Using environmental affordances to direct people natural movement indoors

Understanding and predicting people's displacement movement is particularly important for professionals involved in planning complex buildings (e.g., hospitals, convention centers, subway stations and university campus). Some decisions taken by the visitors while choosing what route to follow can be influenced by some environmental cues which can act as a factor of attraction, influencing the wayfinding process. Therefore, the main objective of this study was to evaluate the hypotheses that, in the context of a simulated emergency egress, people prefer to move along either a wider and with more lighting corridor or to bear right. To collect the users' responses, a constant stimulus method was used, combined with a two forced choices method, involving the projection of stereoscopic images in a wall-screen. Results suggest that, in a "T-type" intersection, users randomly chose which direction to follow. However, if there is an increment in the width of the side corridor, users tend to follow the wider corridor. When light is inserted, users also prefer to choose the corridors with more lighting. In situations where the variables corridor width and existence of lighting are concurrent, the corridors with light are the most chosen by the users.     

Diversity,abundance, and species composition of ants in urban green spaces

Urbanization threatens biodiversity, yet the number and scope of studies on urban arthropod biodiversity are relatively limited. We sampled ant communities in three urban habitats (forest remnants, community gardens, vacant lots) in Detroit and Toledo, USA, to compare species richness, abundance, and species composition. We measured 24 site characteristics to examine relationships between richness and composition and habitat patch size, vegetation, and urban features. Ant richness was higher in forests (26) than in gardens (14) and intermediate in vacant lots (20). Ant richness in gardens and vacant lots negatively correlated with abundance of an exotic ant species (Tetramorium caespitum); thus this ant may affect native ant richness in urban habitats. Ant composition differed with habitat type, and abundance was lowest in forests. Site characteristics varied with habitat type: forests were larger, had more woody plants, higher woody plant richness, more branches, and leaf litter whereas lots and gardens had more concrete and buildings. Vacant lots had taller herbaceous vegetation, and gardens had higher forb richness, density, and more bare ground. Differences in vegetation did not correlate with ant richness, but several vegetation factors (e.g. patch size, number and size of trees, leaf litter, and amount of concrete and buildings) correlated with differences in ant species composition. Additional factors relating to soil, nests, or microclimatic factors may also be important for urban ant communities. Implications for biodiversity conservation in urban ecosystems are discussed.     

Can urban greening increase vector abundance in cities? The impact of mowing,local vegetation,and landscape composition on adult mosquito populations

Worldwide, cities are investing in greenspace to enhance urban quality of life and conserve biodiversity. Cities should ensure these investments do not unintentionally result in ecosystem disservices. Municipal management decisions regarding urban greenspaces, such as mowing frequency, could influence mosquito communities and public health. We examined how mowing, resultant vegetation characteristics, and landscape context influenced adult mosquito abundance in urban vacant lots. We sampled adult Culex and Aedes mosquitoes in a network of vacant lots within eight Cleveland, Ohio, USA neighborhoods in 2015 and 2016 using CO₂-baited light traps and grass-infused gravid traps. For each lot, we quantified vegetation characteristics, including plant diversity, bloom area, and biomass, as well as the surrounding landscape composition at radii of 60 and 1000 m. We found that periodic mowing did not significantly affect mosquito abundances. However, vacant lots with more diverse plant communities were associated with a greater light trap capture of both Culex and Aedes. Both mosquito genera declined in light trap catches with increased impervious surface at 60 m. Similarly, Culex (gravid trap) declined with the amount of built infrastructure at 1000 m. In contrast, Aedes (light trap) increased with the concentration of buildings in the landscape at 1000 m. Our findings indicate that reducing the frequency of mowing within vacant lots will not necessarily increase adult mosquito abundance. Nonetheless, mosquito surveillance and management should be considered when planning conservation-focused greenspaces, as vegetation design choices and the landscape context of a site do influence vector abundance and potentially disease risk.

     

Urban gradients alter the diversity,specific composition and guild distribution in tropical butterfly communities

The increasing expansion of the urban environment has been considered one of the causes of biodiversity loss. Due to the decrease of the quantity and quality of habitats, this process causes the restriction of organisms to sometimes-specific microhabitats. The patterns of variation of the biodiversity along the environmental gradients, however, are still poorly understood. This study evaluated how urban gradients affect the diversity, specific composition and frequency of guild of the community of butterflies. Butterflies were collected in three transects continuously traversing the urban, rural and preserved habitats using baited traps and by active sampling. We found that the urban gradient acts as an environmental filter in the butterfly communities, reducing the richness and frequency of guilds of frugivorous butterflies, structuring the community through turnover, but without effects in the abundance. This study shows the importance of the urban gradients approach in the butterfly community and its applicability in the management of urban areas in order to include native vegetation along the gradients, aiming at increasing environmental heterogeneity, to preserve butterflies and maintain the ecosystem services and network interactions in altered landscapes.

     

Relationships among nutrients,chloride and biological indices in urban Maryland streams

Using a spatially extensive urban database constructed from the Maryland Biological Stream Survey (MBSS), we describe the relationships of nutrients in small-order streams to eight defined categories of percent catchment urbanization, correlations between chloride and conductivity in urban streams, and relationships between nutrients and chloride with two Maryland-specific indices of biotic integrity for benthic macroinvertebrates and fish assemblages. Stream nutrients become elevated with increasing percent catchment urbanization, followed by increases in all four measured nitrogen species and total phosphorus at catchment urbanization levels greater than 10%. There was a strong collinear relationship (r ² = 0.90) between chloride and conductivity (trimeans) across all eight urbanization classes, where Cl (mg/L) = −0.397 + 0.188*conductivity (μS/cm). Critical values for all water quality parameters with the two Maryland biological indices were derived using quantile regression, with significant regressions developed for 11 of 16 water quality parameters and the two biotic indices. For nitrate (NO₃-N), the critical thresholds between fair and poor stream quality for the two Maryland biological indices were 0.83 mg/L (benthic macroinvertebrate assemblages) and 0.86 mg/L (fish assemblages). Increasing stream nutrient and chloride levels, associated with widespread catchment urbanization intensity, now affect many small streams in Maryland, with implications for decreasing water quality in major tributaries and the Chesapeake Bay.     

Urban river wall habitat and vegetation: observations from the River Thames through central London

Along heavily engineered urban rivers, river walls and embankments represent the most common habitat available to riparian vegetation. This paper presents the first study into river wall vegetation and the influence of wall surface materials on plant diversity. We were concerned with investigating the plant diversity of such wall habitats, assessing relationships between different wall surface materials and plant diversity, and determining whether river wall and embankment habitats along the River Thames through central London could support native riparian species alongside more typical urban wall flora. Fifteen sites along the River Thames through central London were surveyed to describe wall flora and establish relationships between plant diversity and wall materials. Walls were not species rich, but contained a mix of terrestrial and riparian species. Stone walls with surface fractures and heterogeneous wall surfaces were conducive to plant diversity at the local scale, while wall surface heterogeneity was also important at the landscape scale. Some stratification of vegetation was observed based on wall position relative to flow disturbance. The potential exists for walls to act as sites for habitat improvement and reconciliation ecology within urban rivers.     

Urbanization affects the trophic structure of arboreal arthropod communities

Urbanization is one of the most significant causes of habitat fragmentation on the planet, resulting in substantial losses of biodiversity and disruptions to ecological processes. We examined the effects of urbanization on the diversity and abundance of arboreal invertebrates in a dominant tree species (Angophora costata) in a highly urbanized landscape in Sydney, Australia, identifying the potential ecological consequences of shifts in diversity. We hypothesized that trophic structure would be influenced by landscape context with a greater richness and abundance of invertebrates in small remnants and edges. Canopy arthropods were sampled via beating from trees in 15 sites in three landscape contexts; five large patches of continuous vegetation, five edges of large patches and five small urban remnants. Trees in large patches supported fewer individuals compared to trees in small urban remnants and edge sites. The composition of assemblages and overall trophic structure also differed between edges and large patches, with a greater abundance of grazing insects in edges. No differences were detected between small urban remnants and edges, suggesting that observed differences might be attributed to an edge effect as opposed to an area effect per se. These changes in trophic structure, revealing a greater abundance of grazing herbivores and a reduced abundance of predators and parasitoids in edge sites, are consistent with work describing elevated levels of herbivory in edges of remnant vegetation. Future management of remnant urban vegetation and associated biodiversity requires not only an understanding of how trophic status influences the extent of responses by arboreal invertebrate communities, but also how these will affect ecosystem functioning.     

Patterns in macroinvertebrate taxonomic richness and community assembly among urban wetlands in Cape Town,South Africa: implications for wetland management

Urbanization has significantly increased globally during the last century and has far-reaching consequences for biodiversity and their associated habitats, particularly wetland ecosystems. Previous studies have focused primarily on wetlands in non-urban areas, and urban wetland biodiversity patterns are currently not well understood, particularly across Africa. Here, we investigate two highly transformed urban wetlands in Cape Town, South Africa, and determine the relative importance and influence of local environmental variables as drivers of macroinvertebrate richness and community structuring. We also determine the influence of local environmental variables for patterns of species turnover and nestedness within and among these wetlands, and provide management recommendations based on our findings. We found that few macroinvertebrate species were associated with these wetlands, yet community variation was driven by a combination of local environmental variables. Our results also indicate that the turnover component of beta diversity, rather than nestedness, was responsible for most of the variation in the overall macroinvertebrate community. We identified two major problems regarding the current ecological state of the investigated wetlands. Firstly, high nutrient loads originating from the surrounding land uses which reduced wetland biodiversity, and secondly, the transformation of these wetlands from seasonal to perennial water bodies. We recommend local and regional scale approaches to limit urban waste from entering these systems, and management of water levels simulating natural Mediterranean-type climate dynamics more closely are required to ensure that the maximum possible diversity can be supported in these wetlands.

     

Drivers of biodiversity patterns in parks of a growing South American megacity

How urban habitats contribute to biodiversity conservation is a key challenge in a rapidly urbanising world. Urban parks can provide important habitats for native species, but previous studies are geographically biased; fast growing megacities, in particular in South America, are clearly understudied. To assess habitat functions and underlying drivers in parks of Santiago de Chile, we analysed the assemblages of wild growing plant species in two ubiquitous park habitat types (grasslands, wooded areas) in 15 parks (150 plots) along an urban-rural gradient. We first used linear contrasts to compare species richness, beta diversity and the proportion of introduced species. We then tested for the explanatory value of environmental variables operating at different spatial scales (plot, park, urban matrix). Unlike in most previous studies, biodiversity patterns were not related to the position of the parks on the urban-rural gradient. Introduced species, mostly from Europe, generally dominated both habitat types (>90 %). Socio-economic (population growth or density), but not spatial, variables were retained in most models. Maintenance intensity was most influential in predicting species assemblages, complemented by park age in wooded areas. A high proportion of European grassland species indicates a trend of homogenisation in park grassland at a cross-continental scale. We conclude that habitat functions of urban parks for native species that have been mainly demonstrated for Europe cannot be generalised to South American megacities. This highlights the need for innovative and locally appropriate conservation approaches (e.g., re-introduction of native species) to foster biodiversity functions in urban parks of South American megacities.     

Impacts of traffic noise on anuran and bird communities

Anurans and birds rely on sound for a number of social behaviors. Species that use roadside habitats are exposed to traffic noise that can mask important social signals and directly affect the community diversity and composition. We evaluate the impact of traffic noise on anuran and bird species richness, species occurrence, and composition in Puerto Rico, where there is a high density of highways and cars that generate high levels of noise pollution. We compared paired forest sites near (100 m, n = 20, dB > 60) and far (>300 m, n = 20, dB < 60) from highways, with similar vegetation structure, but different levels of noise. We found that the anuran community was not affected by traffic noise. In contrast, bird species richness and occurrence were significantly lower in sites near the highway, and bird species composition also varied significantly. Bird species with low-frequency songs were only detected in sites far from highways. The differences in the ecology and communication behavior between anurans and birds could explain these results. Anurans mainly call at night, when traffic activity was low. In contrast, bird singing activity occurs during the day and overlaps with the high levels of traffic noise. In addition, in natural habitats, Puerto Rican anurans occur at high densities and form noisy choruses (>80 dB), which may allow them to tolerate high levels of anthropogenic noise.     

Relation of urbanization to stream fish assemblages and species traits in nine metropolitan areas of the United States

We examined associations of fish assemblages and fish traits with urbanization and selected environmental variables in nine major United States metropolitan areas. The strongest relations between fishes and urbanization occurred in the metropolitan areas of Atlanta, Georgia; Birmingham, Alabama; Boston, Massachusetts; and Portland, Oregon. In these areas, environmental variables with strong associations (r_s ≥ 0.70) with fish assemblages and fish traits tended to have strong associations with urbanization. Relations of urbanization with fish assemblages and fish traits were weaker in Denver, Colorado; Dallas-Fort Worth, Texas; Milwaukee-Green Bay, Wisconsin; and Raleigh, North Carolina. Environmental variables associated with fishes varied among the metropolitan areas. The metropolitan areas with poor relations may have had a limited range of possible response because of previous landscape disturbances. Given the complexities of urban landscapes in different metropolitan areas, our results indicate that caution is warranted when generalizing about biological responses to urbanization.     

Determinates of inner city butterfly and bee species richness

Although urbanization is increasing worldwide, relatively few studies have investigated patterns of urban biodiversity outside of city parks and reserves, in urban neighborhoods where people live and work. We evaluated models including local and landscape factors that might influence the bee and butterfly richness of community gardens located within densely populated neighborhoods of the Bronx and East Harlem in New York City (>10,000 people/km²). The gardens were surrounded by buildings and limited amounts of green space (3,600–17,400 building units and 10–32% green space within a 500 m radius). Contrary to our initial prediction that landscape green space might be especially influential in this heavily urbanized setting, the most highly supported models for both bee and butterfly richness (based on Akaike Information Criterion) included just the local, within-garden variables of garden floral area and sunlight availability. There was marginal support for models of bee richness including the number of building units surrounding gardens within a 500 m radius (which exhibited a negative association with bee richness). In addition, perhaps because bees are central place foragers that may nest within or near gardens, supported models of bee species richness also included total garden area, canopy cover, and the presence of wild/unmanaged area in the garden. Generally, our findings indicate that sunlight and floral abundance are the major factors limiting local pollinator diversity in this setting. This suggests that rooftop and other “open” urban habitats might be managed to increase local pollinator diversity, even if seemingly “isolated” within heavily developed neighborhoods.