Parent tree distance-dependent recruitment limitation of native and exotic invasive seedlings in urban forests

Urban Ecosystems - Urban forests are more vulnerable to exotic species invasions than natural forests and are often a pathway for exotic invasions into natural areas. Investigating the mechanisms...     

Vulnerability of native and exotic urban birds to housing densification and changing gardening and landscaping trends

Variation in densities of native and exotic urban-adapted birds across suburban habitats may reveal levels of adaptation that predict vulnerability to habitat modification over time. We investigated the densities of the eight most common exotic and native birds in a southern hemisphere city across suburbs of varying housing density, vegetative cover and garden vegetation characteristics to determine whether avian population densities are maintained across variations in habitat structure that mirror current temporal trends in land use and landscaping/gardening preferences. We also tested whether densities of birds in residential areas bordering undeveloped patches were higher due to spill-over from patches. Densities of all four native species were highest in undeveloped patches and these species were largely absent from high density housing areas. While densities of two exotic species (blackbird, song thrush) were slightly higher in suburbs with greater vegetation complexity, they were still present in higher density housing suburbs in significant numbers. Common starlings were similarly abundant across all residential habitats and house sparrow density increased in higher density housing areas. Blackbirds appeared least vulnerable to housing densification and landscaping and gardening trends because they were abundant across all habitats, including undeveloped patches. Densities of native birds were higher in residential areas bordering undeveloped patches indicating spill-over was occurring and emphasising the role that patches could play in boosting city-wide native bird abundances. Native birds are vulnerable to reductions in garden size and vegetation complexity that should have little or positive effects on populations of common exotic species.     

Urban biodiversity: comparison of insect assemblages on native and non-native trees

Trees are thought to be important for supporting urban biodiversity. However tree species differ considerably in the numbers of invertebrates they support, with potential consequences for higher trophic groups such as birds. In this study the influence of native and non-native trees on the abundance of insects (Hemiptera) and the incidence of insectivorous birds (Paridae) were investigated in the southern English town of Bracknell. The number and species of tree were recorded from each of 17 roundabout and parkland sites. Tree beating was used to sample arboreal Hemiptera and Paridae were recorded either with point counts and transect walks, depending on the size of the site. Due to the great variation between tree species, there was no overall significant difference in species richness or abundance of Hemiptera between native and non-native tree species. However, individual native trees had more species and individuals than non-natives. The proportion of native trees at Bracknell sites was positively related to the abundance of both Hemiptera and the number of Paridae observed. The consequences of vegetation type for insect abundance indicates that in order to sustain and enhance urban biodiversity, careful consideration needs to be given to species of trees present in urban areas.     

Interactions between birds, fruit bats and exotic plants in urban Hong Kong, South China

I observed the use of exotic plant species by native birds and bats in 8 km² of urban Hong Kong. Twenty-nine plant taxa were used repeatedly. Five species accounted for most interactions with birds: Cinnamomum camphora (10 bird species), Ficus religiosa (6), Livistona chinensis (7) and Pyracantha crenulata (6) provided fruits, while Bombax ceiba (6) supplied nectar. Panicum maximum (2) and C. camphora (1) provided seeds for granivorous birds and Leucaena leucocephala is host to a psyllid consumed by small insectivores in winter. Most trophic interactions between exotics and fruit bats involved the fruits or flowers of Syzygium jambos, while Livistona chinensis provided roosting sites for Cynopterus sphinx. The fruiting phenologies of the exotic species differed from the local flora, with fruit of some species available for the majority of the year. Fruit characteristics for the most commonly eaten species are within the range for native fruit species, although most are larger and have a lower seed load than the medians for native species. Seed dispersal by birds and/or fruit bats is a necessary, but not sufficient, condition for the naturalization of fleshy-fruited plants in Hong Kong, but S. jambos is the only naturalizing exotic species that needs vertebrates for pollination.     

If you plant it,they will come: quantifying attractiveness of exotic plants for winter-active flower visitors in community gardens

Urban community gardens are potentially important sites for urban pollinator conservation because of their high density, diversity of flowering plants, and low pesticide use (relative to agricultural spaces). Selective planting of attractive crop plants is a simple and cost-effective strategy for attracting flower visitors to urban green spaces, however, there is limited empirical data about which plants are most attractive. Here, we identified key plant species that were important for supporting flower visitors using a network-based approach that combined metrics of flower visitor abundance and diversity on different crop species. We included a metric of ‘popularity’ which assessed how frequently a particular plant appeared within community gardens. We also determined the impact of garden characteristics such as size, flower species richness, and flower species density on the abundance and diversity of flower visitors. Two plant species, Brassica rapa and Ocimum basilicum were identified as being particularly important species for supporting flower visitor populations. Flower species richness had a strong positive effect on both the abundance and diversity of flower visitors. We suggest that gardeners can maximise the conservation value of their gardens by planting a wide variety of flowering plants including attractive plants such as B. rapa and O. basilicum.

     

Bee-friendly community gardens: Impact of environmental variables on the richness and abundance of exotic and native bees

With their abundant floral resources, urban community gardens have the potential to play an important role in pollinator conservation. At the same time, the gardens themselves are dependent upon the pollination services provided by insects. Thus, understanding the variables that can increase bee richness or abundance in community gardens can contribute to both urban agriculture and pollinator conservation. Here we examine the impact of several environmental variables on bee abundance and diversity in urban community gardens in Sydney, Australia. We used hand netting and trap nests to sample bees in 27 community gardens ranging from inner city gardens with limited surrounding green space, to suburban gardens located next to national parks. We did not find strong support for an impact of any of our variables on bee species richness, abundance or diversity. We found high abundance of a recently introduced non-native bee: the African carder bee, Afranthidium repetitum (Schulz 1906). The abundance of African carder bees was negatively correlated with the amount of surrounding green space and positively correlated with native bee abundance/species richness. Our results highlight the seemingly rapid increase in African carder bee populations in inner city Sydney, and we call for more research into this bee’s potential environmental impacts. Our results also suggest that hard-to-change environmental factors such as garden size and distance to remnant forests may not have a strong influence on native bee diversity and abundance in highly urbanized area.     

Urban park area and age determine the richness of native and exotic plants in parks of a Latin American city: Santiago as a case study

Plant diversity and composition in urban parks is determined by socio-economics, environmental, and ecological drivers. These drivers give rise to urban spaces with unique compositions of flora, consisting of planted and spontaneous species. The present study aimed to determine the contribution of native and exotic species in urban parks of a Latin American city, and to assess the related role of park area, age and socio-economic status. We also evaluated administration type (public or private) and the effect of environmental factors on plant richness. We hypothesized that the composition of park vegetation differs according to urban-rural gradient. To determine flora composition, two transects (100 m long by 1–3 m wide) per park were selected in 49 parks. In each of these, we identified all the vascular plants found (woody and herbs, planted and spontaneous), which were then classified as native or exotic. We conducted ANCOVAs in order to determine the effect of five independent variables and one factor, on native and exotic plant richness. Of 550 recorded species, 16.2% were native and 83.8% exotic. Number of plant species per park varied between 42 and 146. The parks are known urban habitats containing the highest planted and spontaneously occurring exotic diversity in the city of Santiago, contrasting with other types of habitats. Likewise, parks in Santiago are habitats with low levels of planted and spontaneously occurring native diversity, compared to the parks of Europe, America North and Asia. Ours results show that park area and age affected native plant richness, while exotic plant richness was determined only by park age. We rejected all other possible drivers. Finally, according to the low frequency of native species, we propose that Santiago’s parks could be gradually reoriented towards ex-situ conservation of native plants.     

Comparing the transpirational and shading effects of two contrasting urban tree species

Urban Ecosystems - Urban trees are getting increasing attention as a tool to mitigate urban heat island effects. A more functional and quantitative view of transpirational and shading effect,...     

Effects of habitat and landscape quality on amphibian assemblages of urban stormwater ponds

Urbanisation is one of the most severe drivers of current global biodiversity loss and has contributed to severe declines in many amphibian species. The aim of this study was to determine whether artificial stormwater ponds, designed to control water flow, can act as refuges for amphibians in urban areas. Moreover, we analysed the influence of habitat and landscape quality on amphibian species richness of 46 stormwater ponds (STOPON) in comparison to 46 control ponds (CONTROL).Our study revealed that environmental conditions clearly varied between STOPON and CONTROL. The most pronounced differences were that STOPON were larger, shallower, sunnier, more isolated by streets and had a greater cover of built-up area and lower cover of arable land surrounding them. Nevertheless, the amphibian assemblages of STOPON and CONTROL were very similar. All nine amphibian species (including three threatened species) detected in this study were found in both pond types. Moreover, species richness (2.8 ± 0.2 vs. 2.3 ± 0.2) and the frequency of each species did not differ between STOPON and CONTROL. The only exception was Pelophylax spp., which occurred more regularly in STOPON. Both habitat and landscape quality affected amphibian species richness; however, the explanatory power of the habitat models was about twice as high as those of the landscape models.In conclusion, stormwater ponds play an important role for amphibians in urban areas. In comparison to CONTROL, the low landscape quality in the surroundings of STOPON seemed to be compensated by a higher habitat quality due to regular management.     

Influence of human population size and the built environment on avian assemblages in urban green spaces

While studies of how habitat patch dynamics structures avian communities in urban environments has received some attention, there is considerably less known of how the built environment and human population size may influence the structuring of urban bird communities. We investigated bird populations in Pittsburgh, Pennsylvania (U.S.A.) through replicated point count surveys of breeding birds in 50 parks and cemeteries of varying sizes. We counted 4,435 individual birds in 441 counts. Of the 61 species detected, 27 were rare (detected at <8 points). Migratory species accounted for 46.1 % of all individuals, while 23.2 % of all individuals were of introduced species. Species richness increased significantly with green area size, as did the number of rare species. Species diversity decreased significantly with an increase in the proportion of individuals of introduced species; in particular, cavity nesters were less abundant when introduced species were present. Elements of the built urban environment including commercial development and transportation corridors were associated with significant reductions in park-wide species richness, mean number of species per point, and mean number of individual birds recorded per point. Human population size was positively related to increased numbers of individuals of introduced species, but a lower mean number of species per point. Ours is among the first to identify specific relationships between avian population characteristics and human population size, as few other studies have specifically incorporated human population size into a local, fine grain study design. Our data suggest that human population size is an important parameter that can be measured independently of characteristics of the built environment and the physical characteristics of the park itself as a correlate of avian diversity and abundance. Our study points to a variety of trade-offs needed to manage habitat for birds in urban settings.     

Effects of fragmentation and trampling on carabid beetle assemblages in urban woodlands in Helsinki, Finland

We studied the effects of fragmentation (edge effects and patch size) and trampling (path cover) on carabid beetle assemblages in urban woodland patches in Helsinki, Finland. We expected that (1) open habitat and generalist species would benefit and forest species would suffer from increased woodland fragmentation, and (2) most carabid species would respond negatively to increased levels of trampling. A total of 2088 carabid individuals representing 37 species were collected. A cluster analysis distinguished sites in the interior of large woodland patches, with low or moderate path cover, from the other sites. The other sites did not cluster meaningfully, suggesting increased variation in the carabid fauna with increasing human impact. All species and ecological species-groups decreased with increasing distance from the edge toward the woodland interior and with increasing patch size. This pattern is in accordance with our expectation for open habitat and generalist species but opposite to what we expected for forest species. The reason for these surprising results may be that (1) the species we collected are not true forest interior species, (2) urban woodland edges are optimal habitats for many forest carabids, or (3) edges are actually sub-optimal, and high catches simply reflect increased activity of beetles moving away from the edge. Trampling did not have an overall negative effect on carabids as hypothesized. Species associated with moist forest habitat responded as predicted: they decreased in abundance with increasing path cover. Furthermore, open habitat species decreased with increasing path cover but more straightforward than we had predicted. Model elaboration, by dropping the highly trampled sites from the analyses, suggested that our data of high trampling may be too scarce: the results without these sites were more in accordance with our predictions than with the full dataset.     

Using macroinvertebrate assemblages and multiple stressors to infer urban stream system condition: a case study in the central US

Characterizing the impacts of hydrologic alterations, pollutants, and habitat degradation on macroinvertebrate species assemblages is of critical value for managers wishing to categorize stream ecosystem condition. A combination of approaches including trait-based metrics and traditional bioassessments provides greater information, particularly in anthropogenic stream ecosystems where traditional approaches can be confounded by variously interacting land use impacts. Macroinvertebrates were collected from two rural and three urban nested study sites in central Missouri, USA during the spring and fall seasons of 2011. Land use responses of conventional taxonomic and trait-based metrics were compared to streamflow indices, physical habitat metrics, and water quality indices. Results show that biotic index was significantly different (p?<?0.05) between sites with differences detected in 54 % of trait-based metrics. The most consistent response to urbanization was observed in size metrics, with significantly (p?<?0.05) fewer small bodied organisms. Increases in fine streambed sediment, decreased submerged woody rootmats, significantly higher winter Chloride concentrations, and decreased mean suspended sediment particle size in lower urban stream reaches also influenced macroinvertebrate assemblages. Riffle habitats in urban reaches contained 21 % more (p?=?0.03) multivoltine organisms, which was positively correlated to the magnitude of peak flows (r ²?=?0.91, p?=?0.012) suggesting that high flow events may serve as a disturbance in those areas. Results support the use of macroinvertebrate assemblages and multiple stressors to characterize urban stream system condition and highlight the need to better understand the complex interactions of trait-based metrics and anthropogenic aquatic ecosystem stressors.     

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...     

Native and exotic species in the urban landscape of the city of Rio de Janeiro,Brazil: density,richness, and arboreal deficit

Shaped by European influences, the Brazilian urban landscape was marked by the predominant use of exotic species in planted areas. In the 19th century along the city streets of Rio de Janeiro, trees were planted at a standard distance from each other. With time, native species began to be used in the urban landscape. Our purpose was to evaluate the utilization of exotic plant species in the urban landscape of Rio de Janeiro, evaluate the city’s arboreal deficit, and relate its neighborhood arboreal density to its economic index. Arboreal deficit represents the negative difference between the total number of expected trees and the observed number in the streets based in the standard distance used in the past. Twenty native and 40 exotic species were found in the 1701 streets sampled. A high percent of streets did not have any planted trees and the number of trees was greater in wealthier neighborhoods. The strong prevalence of exotic species is indicative of the negative impact of human activity on the biota. Since the municipality of Rio de Janeiro harbors forested areas, the risk for dissemination of exotic species is high.     

Nested patterns in urban butterfly species assemblages: respective roles of plot management,park layout and landscape features

Increasing numbers of cities are currently developing sustainable policies aimed at promoting urban biodiversity and ecological dynamics through the planning of green networks and the implementation of more sustainable management practices. These human activities can strongly influence environmental factors on which the organization of ecological communities at different scales depends. Thus, it is of fundamental importance to understand the relative impact of local management, green space design and landscape features on the distribution and the abundance of species in urban areas. On the basis of 2 years of butterfly surveys in urban public parks within an extensive Mediterranean metropolitan area, Marseille (South-East France), the aim of this paper is to provide a better understanding of the effect of these three environmental scales (plot, park, landscape) on the composition and organization of species assemblages. Using variation partitioning and nestedness analysis on ecological data aggregated at plot-level and park-level respectively, we demonstrate the preponderant effect of landscape scale features on urban butterfly assemblages. Our results also highlight an important co-variation of plot management, park layout and urban landscape features, in their interaction with the community structure of urban butterflies. Although there is no significant species-area relationship, significantly nested patterns arise in species composition. Selective colonization appears as a driving force constraining the constitution of species assemblages within the city. However, a prospective study on adjacent more natural areas suggests that biotic limitations, interspecific competition and habitat filtering may play an important role if a larger portion of the urbanization gradient is explored, which remains to be investigated.     

The role of dispersal and local environment in urban land snail assemblages: an example of three cities in Central Italy

Ecologists increasingly appreciate the central role that urban biodiversity plays in ecosystems, however much urban biodiversity is neglected, especially some very diverse groups of invertebrates. For the first time in southern Europe, land snail communities are analysed in four urban habitats along a geographical gradient of three cities, using quantitative methods and assessing the relative roles of local environmental conditions (“distance from sea”, “distance from city centre”, “vegetation cover”) and spatial effects by principal coordinate analysis of neighbour matrices, redundancy analysis and variation partitioning. A total of 53 species was recorded, a richness similar to that of natural areas. At habitat level, species richness did not show a clear increasing trend from more to less urbanized habitats, but rather a homogeneous pattern. At city level, study areas hosted rather heterogeneous species assemblages and biotic homogenization did not seem to have any impact; indeed, only three species could be considered alien. Variation partitioning showed that land snail communities were mostly structured by environmental factors, even when spatial structures independent of measured environmental variables were included: “vegetation cover” and “distance from city centre” were the environmental variables that explained most of the variation in species composition. The lack of strong spatial structure also unexpectedly suggested that transport by humans aids dispersal of organisms with low mobility, which are usually limited by spatial constraints in natural environments. These results provide ecological and conservation implications for other invertebrate groups, suggesting to set priorities in management strategies that include habitat conservation at local scale.     

The effect of artificial light at night on the biomass of caterpillars feeding in urban tree canopies

Urban Ecosystems - Alternation of day and night is the oldest cycle on Earth, which is increasingly disturbed by the accelerating rate of urbanization and technological development. Despite the...     

Diversity patterns of alien and native plant species in Trieste port area: exploring the role of urban habitats in biodiversity conservation

Nowadays, urban areas play a crucial role in biodiversity conservation and habitat protection despite the constant pressures on which these habitats are subjected. They may even host relatively new plant communities due to the peculiar ecosystem where they vegetate. The port of Trieste (NE Italy) is characterized by a mixed mosaic of intensely human impacted areas (where commercial activities are still ongoing) flanked by abandoned areas where vegetation persists or has spontaneously recovered. In this study, we sampled the whole port area through a stratified random sampling by placing multiscalar nested plots in four different habitats (strata) previously identified by photo-interpretation. Plant species richness and abundance were assessed in each plot. Each species was then classified as native or alien and patterns of species richness and complementarity were compared among habitats. Results show that there is a significant difference in species richness patterns among habitats, while observed patterns are likely to vary at different spatial scales. As expected, urban plots account for most of the alien species in the sampling, while wooded plots cope better with invasion, accounting for a lower alien/native ratio. These results highlight how habitat diversity enhances biodiversity in urban areas and how it could provide an effective filtering effect able to reduce the spread of alien species. In addition, we provide further evidence for the use of multi-scale approaches in order to study the complex relationships between spatial heterogeneity and plant species richness.     

Indigenous internationalism: native rights and the UN

Abstract

Since 1982, with the creation of the Working Group on Indigenous Populations, the UN has taken steps toward addressing the violations of indigenous human rights around the globe that have characterized the colonization of indigenous peoples by western nations since the 15th century. This article explores the question of whether actions taken by the WGIP and other UN bodies promise to relieve this legacy; or whether the UN, as the proper overseer of international law concerning human rights today, continues that legacy in revised form, as some analysts have claimed. A brief overview of positions taken by key figures in the history of international law concerning indigenous peoples since the early 16th century provides a background against which to compare the work of the UN. My conclusion is that while the UN has in some ways sustained the inherited order of neglect of indigenous rights, it has, more importantly, created openings which make it possible for indigenous peoples to assert their claims. While this is not a story of continuous progress, it does suggest that there is reason to respect the UN's efforts in this relentlessly neglected area of human rights.     

Diversity in flowering plants and their characteristics: integrating humans as a driver of urban floral resources

Urban neighborhoods vary in development intensity and in the life style and demographics of their residents. Decisions made by urban residents affect plant communities, their functional characteristics, and the floral resources they provide. We recorded flowers in front-facing yards in 58 neighborhoods in Chicago, IL (USA) and examined patterns in community composition and species turnover between neighborhoods. We investigated how species richness and plant characteristics, including origin, cultivation intent, and life cycle, are affected by neighborhood socioeconomic factors. Urban plant species tended to be perennial, ornamental, and non-native. White clover had the broadest distribution and the highest floral abundance but was not present in several of the highest-income neighborhoods. Although we found 144 morpho-species across neighborhoods, most occurred infrequently. Species turnover was highest for ornamental species and lowest for weedy species, suggesting that intentional plantings are driving beta diversity across the landscape. We found the highest species richness in neighborhoods with intermediate numbers of Hispanic and white residents and with intermediate number of residential lots; neighborhoods with racially or ethnically homogenous populations had fewer plant species. The high frequency of weeds in low-income neighborhoods, the occurrence of certain ornamental plant species in whiter, wealthier communities, and high turnover of species from one neighborhood to another, all suggest a disparity in plant-related ecosystem services across cities. Complexity in urban plantings may be influenced by the suite of perspectives that residents bring towards habitat management. Cultivation sustains a diversity of plants and creates a disparity in plant traits by neighborhood socioeconomics.