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.     

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.     

The synanthropic flora in the Mendoza (Argentina) urban area

The synanthropic flora in the Mendoza urban area was studied in terms of its three most relevant sub-environments: house and school gardens, parks and borders of narrow ditches used to irrigate the whole city. The current synanthropic flora comprises 487 species, 8 native and 479 alien species. Neophytes include 282 genera and 104 families, with the dominant families being Fabaceae, comprising 41 species, Myrthaceae (38 spp), Rosaceae and Oleaceae (24 spp), all of which together represent 26% of the total richness recorded. Ephemerophytes, non-naturalized plants, represent 25.4% of the urban flora. Xenoergasiophytes and ergasiophytes are dominant in gardens and parks, whereas xenophytes grow in irrigation ditches across the city. Considering life forms, nanophaerophytes are prevalent in all three sub-environments, but succulents and therophytes are absent from ditches. The number of non-native plant species is increasing in the urban area of Mendoza, especially in the suburbs, and many of them at times become invasive.     

Seasonal dynamics of bird communities in urban forests of a Mediterranean city (Montpellier,Southern France)

We evaluated the richness, composition and abundance of bird communities in three urban forests of Mediterranean France during winter and spring. The urban forests differed in size, composition, structure, age of vegetation, and location relative to the city centre. Estimated species richness across all three urban forest parks was 45 species. Twenty six (26) species were recorded in both winter and spring, whereas ten species were recorded only in spring, and six were recorded only in winter. Distribution, turnover, and type of bird foraging guild were related to characteristics of each urban forest and season. During spring migration, more species were recorded in sampling units (250?×?250 m) within the largest and most natural urban forest located in the outskirts of Montpellier, whereas during winter, more species were recorded in the most urbanized park (i.e., a botanical garden dominated by exotic vegetation), which was located in the city centre. Insectivorous birds were more abundant in winter, whereas seedeaters associated with wooded habitats were recorded more frequently in spring. Our results suggested that different kinds of urban forests are important modulators of urban bird communities and they are necessary to maintain the diversity of migratory and resident birds as well as increasing the environmental quality of urban areas.     

Mammal conservation in a changing world: can urban gardens play a role?

Urbanisation threatens biodiversity globally, yet some animal populations persist within urban landscapes. Conservation of urban wildlife has prioritised parks and remnant bushland as critical habitat and neglected the role that residential gardens offer for conservation. We explored the potential for residential gardens to assist the conservation of mammals using an online questionnaire administered to residents of two case study cities in Australia to identify how widespread mammals in cities can be, which garden features promote mammal presence, and if the features varied among species with different habitat requirements. From 649 responses we found that three mammal species with different habitat requirements occurred in residential gardens throughout the city landscape. Garden features promoting mammal presence were consistent with broad ecological and habitat requirements of each species, but differed among both species and regions. Our study demonstrates that residential gardens offer a valuable habitat for mammals, and that garden features could be manipulated to promote use of gardens by these species. By considering gardens in urban planning and management actions aimed at conserving urban wildlife, residential gardens offer additional habitat to parks, roadside vegetation and urban bushland, and can play a significant role in biodiversity conservation.

     

Composition and conservation value of bird assemblages of urban ‘habitat islands’: Do pedestrian traffic and landscape variables exert an influence?

Urban forest fragments can potentially be ‘habitat islands’ for native birds, but pedestrian traffic could influence the composition and conservation value of their bird assemblages by reducing the representation of disturbance-sensitive species. Winter bird assemblages and pedestrian traffic rates were documented in twelve forested parks in suburban Melbourne, Australia. Native birds comprised 87% of sightings, but two exotic species were common. Bird species' distribution among the parks was significantly nested. However, park rank orders for bird assemblage nestedness and mean pedestrian traffic rate were not correlated and only one species' distribution was nested with respect to this variable. The observed correlation between park area and bird assemblage nestedness may have been partly due to passive sampling. Degree of isolation of parks influenced nestedness less than park area. Forested parks provided habitat for species that occur at intermediate to low densities in other suburban habitats and for ecological specialists otherwise rare in suburbia. Larger parks contained more species than, and many of the native species found in, smaller parks. However, smaller parks each had 25% of the native bird species inhabiting the suite of fragments and thus had both aesthetic value and some potential to enhance city-dwellers' awareness about biodiversity conservation.     

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.     

Vegetation composition and structure of woody plant communities along urban interstate corridors in Louisville,KY, U.S.A.

Urban forests adjacent to interstate corridors are understudied ecosystems across cities. Despite their small area, these forests may be strategically located to provide large ecosystem services due to their ability to act as a barrier against air pollutants and noise as well as to provide flood control. The woody vegetation composition and structure of forests adjacent to urban interstates is an important determinant of their ability to provide these services. However, these forest communities may be particularly susceptible to the introduction of exotic invasive species via the interstate and the surrounding city that can potentially alter current and future forest composition. The purpose of this study was to investigate the distribution of native and exotic woody vegetation and tree regeneration in forests along three interstate corridors in Louisville, KY, and to determine potential factors (e.g., traffic density) that are correlated with patterns in the woody vegetation community. We found the most important determinants of vegetation composition along these interstate corridors were the distance from the city center and the presence of an exotic invasive shrub, Amur honeysuckle (Lonicera maackii). Compared with forested plots within 10 km of the city center, plots further from the city center had 81% lower stem density of Amur honeysuckle, 96% higher tree seedling regeneration, and 51% greater woody plant species richness. The primarily native species composition of adult trees in forests alongside urban interstates in Louisville and the regeneration of native tree species provide optimism that these forests can maintain native species while experiencing multiple impacts from the interstate as well as from the surrounding city, emphasizing their important potential for maintaining natural forest functions across the urban landscape.     

Urbanization impacts on land snail community composition

Urbanization has tremendous impacts on most native species. This is especially true in land snails, which are surprisingly understudied organisms. Due to their low mobility and dispersal potential, land snails are valuable indicators of ecosystem disturbance. For this study, land snails were collected in 54 city parks along an urban gradient to understand impacts of urbanization on snail communities. Sampled parks include small extensively landscaped downtown parks, neighborhood and community parks, district parks, and large nature parks, each with variable vegetation, soil characteristics, disturbance regimes, and human activities. Sampling recovered 12,153 individual snails, representing 20 families, 43 genera, and 95 species. Seven new Tennessee state and 87 new county occurrences were recorded. Five non-native and one extra-limital non-native species were found, four of which are new Tennessee state records. Results show that urbanization greatly alters land snail community structure. Nature and district parks have significantly greater species richness, species diversity and species evenness than community, neighborhood, and downtown parks. Degradation of parks, distance from the park to the commercial city center and percent of coarse woody debris accounted for most of the variation between park types. Non-metric multidimensional scaling and pairwise Jaccard indices indicate that downtown snail communities are more similar whereas snail communities in nature parks are more distinct. This suggests that urbanization promotes homogenization among land snail communities. We also show that this homogenization is thus far driven mainly by synanthropic, broadly adapted native species rather than non-native snail species.     

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.     

Determining urban exploiter status of a termite using genetic analysis

Urban ecosystems are characterized by “urban exploiters”: species that thrive in the modified environment of cities. Few insects have been categorized as such, in part because they are usually considered as pests first, in part because many studies do not identify to species, and in part because many insects can survive in small vegetated areas within the urban matrix. Some termites may be prime examples of urban exploiters; Coptotermes species are rare in natural forests, but are abundant and major pests in urban areas. We investigated the genetic structure of the South East Asian species Coptotermes gestroi in the urban nation of Singapore. There was a panmictic population across the city, yet all 29 colonies were genetically distinct, and many had expanded from recent bottlenecks. There were no significant differences between colonies in vegetated areas (forests and parks), and those in urban habitats. The genetic pattern is similar to some other urban exploiter species in comparable environments, thus confirming C. gestroi is a native species that has become an urban exploiter, the first termite to be considered as such.     

City dwelling wild bees: how communal gardens promote species richness

Urban areas consist of wide expanses of impervious surfaces which are known to negatively affect insect biodiversity in general, but green spaces within cities have the potential to provide necessary habitat and foraging resources. Although, communal gardens were primarily intended to provide fresh, regional food to denizens, these green islands also host a surprisingly high number of wild bee species.

The gardens were characterized based on structural elements such as flower frequency, the relative percentage of lawn, trees, shrubs, planted crops and infrastructure (e.g. seating possibilities or garden houses). Further, the effects of different landscape structures surrounding the gardens and distance to the city center were analyzed on the total wild bee species richness and functional traits. Focusing on these putative influencing factors, statistical analyses calculating random decision forests along with generalized linear mixed models were applied. With 113 observed wild bee species, communal gardens provide habitat for a quarter of all known species in Vienna. In conclusion, results revealed that only elements within the gardens had an effect on species richness, with flower frequency as the major positive driver. The examined communal gardens promote and conserve wild bees independent from the location within the city or garden size. Furthermore, these green patches are important sanctuaries, hosting rare and threatened species as well as remarkably special wild bee communities.

     

Plant-pollinator networks in Australian urban bushland remnants are not structurally equivalent to those in residential gardens

Urbanisation is a prominent and increasing form of land-use change, with the potential to disrupt the interactions between pollinators such as bees and the flowering plants that they visit. This in turn may cause cascading local extinctions and have consequences for pollination services. Network approaches go beyond simple metrics of abundance and species richness, enabling understanding of how the structure of plant-pollinator communities are affected by urbanisation. Here we compared pollination networks between native vegetation (bushland) remnants and residential gardens in the urbanised region of the southwest Australian biodiversity hotspot. Across fourteen sites, seven per habitat, plant-bee visitor networks were created from surveys conducted monthly during the spring-summer period over two years. Extinction slope (a measure of how extinctions cascade through the network), and network robustness and nestedness were higher for bushland remnants, suggesting that networks in bushland remnants had greater functional integrity, but if disrupted, more cascading extinctions could occur. In contrast, niche overlap between pollinators was higher in residential gardens, suggesting greater competition for resources. Most species-level properties did not differ between habitats, except for normalised degree, which was higher in bushland remnants. In conclusion, it appears that pollination networks in managed residential gardens are not structurally equivalent with those in bushland remnants. This has implications for conservation of wild bee assemblages in this biodiversity hotspot, and suggests removal of remnant native vegetation for residential development could disrupt the integrity of plant-pollinator assemblages.

     

Predicting tree species richness in urban forests

There has been an increasing interest in urban forests and the levels of biodiversity they contain. Currently there are no spatially explicit maps of tree species richness in urban areas. This research tests and identifies GIS and remote sensing metrics (climate, area, productivity, three-dimensional structure) hypothesized to be associated with species richness in native forests and identifies methods that can be applied to predict and map tree species richness in cities. We quantified tree species richness, floristic composition, and structure in 28 1-ha plots in the city of Los Angeles. Climate and remote sensing metrics from high-resolution aerial imagery (10 cm), QuickBird (60 cm), Landsat (30 m), MODIS (250 m), and airborne lidar (2 m) were collected for each plot. There were 1208 individual stems and 108 trees identified to species. Species richness ranged from 2 to 31 species per ha and averaged 17 species per ha. Tree canopy cover from QuickBird explained the highest portion of variance (54%) in tree species richness followed by NDVI from Landsat (42%). Tree species richness can be higher in residential urban forests than native forests in the United States. Spatially explicit species richness maps at 1 ha can be created and tested for cities in order to identify both hotspots and coldspots of tree species richness and changes in species richness over time.     

Vegetation on and around large-scale buildings positively influences native tropical bird abundance and bird species richness

High population growth in the tropics is driving urbanisation, removing diverse natural ecosystems. This is causing native species to suffer while introduced synanthropes flourish. City planners are developing urban greenspace networks, in part trying to address this issue. Architects contribute to these greenspace networks by designing elevated and ground level green spaces on large-scale buildings. However, little evidence is available on whether building green spaces support native fauna. This is true for birds in tropical Singapore that support important ecosystem services and have existence value. Therefore, in this study, we conducted bird surveys and statistical analyses to determine, if and how vegetation on three building green space types (ground gardens, roof gardens and green walls) have a positive impact on native or introduced bird species. We found that elevated greenery (roof gardens and green walls) on large-scale buildings supported a higher richness of birds and abundance of urban native birds than control roofs and walls without vegetation. Ground gardens supported similar levels of native species as roof gardens but also a larger proportion of generalist synanthropes. However, we found no tropical forest habitat specialists across any space type. Therefore, we recommend roof gardens and ground gardens as a potential space for urban natives outside of a less competitive ground-level urban environment. Our study also found certain building design elements (height of elevated space, presence of specific plants) supported different species groups. Therefore, we suggest that these ecological requirements for different species groups are considered when designing a building’s green space.

     

Tree diversity,distribution, history and change in urban parks: studies in Bangalore,India

Urban parks constitute critical biodiversity hotspots in crowded, concrete-dominated city environments. Despite the importance, they remain little researched. This paper assesses the biodiversity and distribution of trees in urban parks in the southern Indian city of Bangalore. 127 plots were used to survey tree distribution in parks across the city. The distribution is largely dominated by a few common species. The proportion of exotic species was very high, with 77% of trees belonging to introduced species. Park history had an impact on distribution. Old parks had fewer but larger trees, and greater species diversity compared to recently established parks. Old parks also differed in species composition, having a greater proportion of large canopy trees compared to young parks. Examination of size distributions revealed that large canopied species were gradually being phased out, and replaced by narrow and medium sized tree species which are easier to maintain, but which may not provide the same environmental and ecological benefits. Greater attention requires to be paid to the selection of trees in cities, not just with a view to easy maintenance as is currently the case, but to select an appropriate mix of trees that supports biodiversity and maximizes environmental and ecosystem services.     

Three categories of urban green areas and the effect of their different management on the communities of ants,spiders and harvestmen

Urban green areas have become an important tool for biodiversity conservation in cities. However, land use and the different management practices applied to these areas determine their effectiveness as biodiversity refuges within cities. In our study, we compare the biodiversity of three bioindicator groups of arthropods (ants, spiders and harvestmen) found in eleven urban green sites in Warsaw (Poland). The studied sites represent three categories of management: botanical gardens, public parks and urban woodlands. Our aim was to determine the effect of the type of management (as urban green categories) on arthropod communities in urban areas.

     

Alien plant species do have a clear preference for different land uses within urban environments

Since neophytes can become invasive in the future, untangling their ecological preferences is of paramount importance, especially in urban areas where they represent a substantial proportion of the local flora. Studies exploring alien species assemblages in urban environments are however scarce. This study aims to unravel alien plant species preferences for five urban land uses (densely built-up areas, open built-up areas, industrial areas, broadleaved urban forests, and agricultural areas and small landscape elements). We took the city of Brussels as a model, in which we recorded all vascular species growing spontaneously in grid cells of 1 km². We tested two different ways of classifying the 1-km² cells: (1) We simply associated each cell with its dominant land cover; (2) We used a fuzzy approach for which the degree of association of a given cell to a given land cover depended on the proportion of that land cover within the cell. For both classification methods, we calculated the indicator species of the resulting land cover types based on alien species only. The crisp and fuzzy classifications identified 33 and 49 species, respectively, with a clear preference for some urban land use types (from a total of 129 alien plant species analyzed). Results showed that urban land use types having apparently similar environmental conditions can actually harbor different neophyte assemblages. Fine-tuning the categorization of urban environments in future ecological studies is therefore important for understanding spatial patterns of alien species occurrence.     

The influence of urban park characteristics on ant (Hymenoptera, Formicidae) communities

As rapid urbanization continues, existing natural areas within urban zones will play a critical role in safeguarding remaining biodiversity. Ants are an integral part of almost every terrestrial ecosystem, including urban environments, and understanding which environmental characteristics influence their persistence is critical. In this study, 24 protected natural areas within urban parks including mosaic, scrub, herbaceous and forest habitats were surveyed for ants with 563 pitfall traps. The data provide insights into the distribution and abundance of ant fauna in San Francisco natural areas, as well as which characteristics of parks have the most influence on ant community composition. A total of 2,068 ant individuals representing 15 species were collected. A regression analysis revealed that urban forests reduced ant richness and abundance and that there was little or no impact of the Argentine ant on native ants. Natural area size and shape were not important in explaining variations in overall ant species richness and abundance, with many smaller natural areas harboring ant populations that are just as diverse and robust as larger areas.     

Demography of a ground nesting bird in an urban system: are populations self-sustaining?

Urbanization poses threats to earth’s biota, and retention of remnant native habitat in protected areas within expanding urban boundaries may help alleviate threats to wildlife. However, it is unclear for nearly all nonsynanthropic (i.e., not benefiting from an association with humans) species whether vital rates in urban habitats can sustain populations or if populations persist only through immigration from outside the urban boundary. We conducted a three-year study of spotted towhees (Aves: Pipilo maculatus) breeding in four undeveloped parks in Portland, OR, USA, to measure park-specific seasonal reproductive output (F) and annual adult survival (S_A). We developed a stochastic model that combined F and S_A with an estimate of first-year survival to measure population growth rate (λ) in all parks assumed to be closed to immigration. F differed among parks but S_A did not. Relatively high F was possible because many pairs raised >1 brood/season. When combined with empirical estimates of survival through the 30-day period of post-fledging parental care (S_D = 0.645), only 2 of 4 parks were self-sustaining (i.e., λ > 1.0). However, S_D reflected substantial loss of fledglings to domestic cats (Felis catus). Assuming no loss to cats and either partial compensatory or additive mortality of fledglings substantially improved prospects of population persistence for declining (sink) populations. Moreover, allowing low levels of immigration to sinks reversed population declines in most parks even when vital rates were insufficient to maintain populations. Our results suggest that nonsynanthropic bird species can persist in urban landscapes, but also that offspring mortality in the post-fledging period may be a critical determinant of population viability.