The seed bank of a restored tidal freshwater marsh in Washington,DC

The species composition of seed banks may be a useful indicator of vegetation structure and dynamics, but seed bank studies have rarely been applied to monitoring of wetland restoration projects. We studied the seed banks and vegetation of three distinct sites within a restored tidal freshwater marsh and of two nearby natural marsh sites. Surface soil samples were collected and subjected to flooded and nonflooded conditions in a greenhouse for enumeration of emerging seedlings. Percent coverage of vegetation was estimated in permanent 1-m² plots at each soil sampling location.Species composition of the seed bank and vegetation differed considerably; only 43% of the species observed were common to both. The seed bank of restored marsh sites had higher species richness and seed density than the natural marsh sites, but both had similar species diversity. Annual species were more important in the seed bank and less important in the vegetation of restored sites than reference sites. Flooding significantly reduced the species richness, diversity, and density of emerging seedlings. Most species planted at the site were rare in the seed bank, with Leersia oryzoides being an important exception. Other species abundant in the seed bank included Cyperus odoratus, Juncus effusus, and the nonindigenous Lythrum salicaria. A possible mechanism explaining the higher densities of seeds in restored areas is that ruderal vegetation colonized the restoration site, reproduced, and set seed shortly following placement of dredge material. Perennial species subsequently colonized and were planted, and expanded to reduce the abundance of annuals in restored marsh vegetation. Our study suggests that the plant regeneration dynamics of the restored marsh sites are considerably different from those of natural marshes. Additionally, we suggest that seed bank studies are a useful technique for assessing the community structure and vegetation dynamics of restored wetlands.     

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.     

The soil seed bank and its relationship to the aboveground vegetation in deciduous forests in New York City

The soil seed bank was studied in two deciduous forests in Bronx (New York City), NY. The purpose of this study was to determine how the biotic andabiotic differences between urban and rural forests arereflected in urban forest seed banks. Soil samples werecollected in two consecutive years and monitored for emergencein the greenhouse over two years. In 1993, the mean number ofemergents ranged from 4636 to 5373 m^-2 (excluding ferns), or from 6972 to 9651 m^-2 (including ferns). In 1994, the mean number of emergents ranged from 1656 to 2013 m^-2 (excluding ferns), or from 5019 to 5992 m^-2 (including ferns). Graminoids and fernscombined accounted for approximately 70% of all emergents eachyear. Three taxa, Rubus spp., Betula lenta, and Liriodendron tulipifera, comprised 60–80% of the woody emergents and were theonly woody taxa to exhibit delayed germination. A substantialnumber of forbs, graminoids and ferns (15–50%) exhibiteddelayed germination. The nonnative woody species Ailanthusaltissima, Morus alba, and Celastrus orbiculatus were absentfrom the aboveground vegetation of some forest plots yet werepresent at low densities in the seed bank. A greater meandensity of emergents and the presence of nonnative species arethe main differences between the seed banks of these urbanforests and those reported for similar nonurban forests in thisregion.     

Provincial and cosmopolitan: floristic composition of a dryland urban river

High rates of intercontinental exchange of plant species have caused scientists to ask whether floristic areas with similar environments are undergoing global homogenization. We focused on riparian forests of the urban Salt River (Sonoran Desert, USA) to ask: (1) Is the forest dominated by cosmopolitan or provincial elements? (2) Which trees planted in the irrigated cityscape have established along the river? (3) Which types of restoration interventions have favored provincial species? We surveyed tree abundance, size and vigor in belt transects among five reaches that differed in degree of restoration, and obtained data on tree species composition of the urban landscape and pre-development riparian zone. Our results reveal the urban riparian forest to have many cosmopolitan elements, owing in part to spillover of trees from the cultivated cityscape (e.g., Acacia stenophylla, Vitex agnus-castus). Global spread of some regional (Neotropical) riparian taxa (e.g., Parkinsonia aculeata, Prosopis) also has contributed to the cosmopolitan status. Yet, the forests retain a distinct regional signature. Unintentional restoration of winter floods has allowed for regeneration of Salix gooddingii, a vernally-adapted provincial pioneer, although its long-term survivorship is restricted to limited micro-sites (storm drain outfalls). Urbanization-related changes in stream hydrogeomorphology explain increases in some regional species (e.g., Washingtonia spp.) that historically were excluded from the river.

Reaches restored by planting, weeding, watering, and geocountouring had the greatest abundance of provincial species and greatest floristic similarity to historic conditions.

     

Woody plant communities along urban,suburban, and rural streams in Louisville,Kentucky, USA

Anthropogenic changes in land use and cover (LULC) in stream catchments can alter the composition of riparian plant communities, which can affect ecosystem functions of riparian areas and streams from local to landscape scales. We conducted a study to determine if woody plant species composition and abundance along headwater streams were correlated with categorical and continuous LULC and environmental variables along an urban-to-rural gradient. These variables were calculated at different spatial scales (subcatchment level and within 0.5 and 1 km radii of plots) and used % impervious surface cover (ISC) and finer scale LULC classification levels to determine their ability to explain species composition, diversity, abundance, non-native provenance and wetland indicator status of four plant strata—canopy tree, tree sapling, tree seedling and shrub. At all scales, we found distinct riparian woody communities within land-use categories, with significant differences among shrub species. Fine-scale land-cover variables correlated with species composition of shrub, tree sapling and tree seedling strata, but not the canopy tree stratum. Celtis occidentalis and Acer negundo were ubiquitous but dominated riparian areas surrounded by development, while Asimina triloba was associated with forested rural riparian banks. Non-native shrubs, Lonicera maackii and Euonymus alatus, were indicative of areas surrounded by development, while the native shrub, Lindera benzoin, was associated with deciduous forest. Negative factor-ceiling relationships between canopy tree, sapling and tree seedling densities and % ISC were found, with abrupt declines above approximately 30 % ISC. Facultative wetland shrubs were not found above 30 % ISC. Streambank height, which was strongly negatively correlated with depth to the water table and positively correlated with cumulative catchment area, was negatively correlated with facultative wetland tree and shrub species. In addition, riparian tree sapling and seedling densities declined as the abundance of Lonicera maackii increased.     

Invasive weeds in urban riparian zones: the influence of catchment imperviousness and soil chemistry across an urbanization gradient

The riparian zones of urban waterways are frequently degraded by weed invasions. This study examined the effects of different levels of catchment imperviousness, as a surrogate for the extent and intensity of urbanisation, on invasive weeds and soil physical and chemical attributes. The study was conducted adjacent to waterways in the partly urbanised Georges River catchment in south western Sydney. Vegetation and soil sampling was undertaken in the riparian zone of 10 freshwater streams in non-urban (low imperviousness), peri-urban (moderate imperviousness) and urban (high imperviousness) sub-catchments. Soil samples were tested for a suite of physical and chemical properties (moisture, bulk density, organic matter, pH, salinity, phosphorus, potassium and calcium). Increased levels of sub-catchment imperviousness and urbanisation were associated with higher weed coverage and elevated soil geochemical attributes. One of the most interesting findings in this study was that urban soil calcium concentrations were over 2000 times greater than soils collected from non-urban catchments. The BIOENV procedure identified soil pH, salinity, calcium, organic matter, moisture and catchment imperviousness to be important environmental factors associated with variation in riparian vegetation. The single factor of soil pH was most highly correlated with variations in riparian vegetation. Soil pH was approximately 1.5 units higher in urban compared to non-urban riparian soils. We speculate that there is a link between urban concrete materials, urban soil and water contaminants and riparian weed invasion. We also recommend further study into the contribution of urban concrete materials on the geochemical contamination of riparian soils.     

The ecology of littoral zone Chironomidae in four artificial,urban, tropical Malaysian lakes

Urbanization is increasingly compromising lakes in the rapidly developing countries of tropical Southeast Asia. Greater understanding of the ecology of tropical lakes is essential in order to determine the best ways to protect and manage them. A comparison was made of the species richness, abundance and diets of Chironomidae in two forest lakes (both created by damming rivers - one in an urban forest reserve, one adjacent to an urban area) and two urban park lakes (ex- tin mine lakes) in Kuala Lumpur, Malaysia. 19 species of chironomids were recorded (10 collector-gatherers, one collector-filterer, one shredder, 3 predators and 4 predators/grazers). The most abundant species were Polypedilum leei, Tanytarsus formosanus, Zavreliella marmorata and Procladius sp.. Conductivity was highest in the urban park lakes due to pollution. Temperature was also highest in the urban park lakes due to lower riparian canopy cover and lower macrophyte abundance. Larval abundance (mostly collector-gathering Chironominae) was significantly higher in the forest lakes compared to the urban park lakes, which could be related to cleaner water and higher vegetation cover which provided more food resources (leaf litter and periphyton) and more microhabitats. Predatory tanypods were most abundant in forest lakes which also had the highest numbers of their prey (Chironominae). Four predatory species of Tanypodinae supplemented their diet with blue-green algae in two of the urban lakes. Only one collector-filterer (Corynoneura sp.) was recorded (only in the forest lakes).

     

Urban and wildland herpetofauna communities and riparian microhabitats along the Salt River, Arizona

Metropolitan areas are continually expanding, resulting in increasing impacts on ecosystems. Worldwide, riverine floodplains are among the most endangered landscapes and are often the focus of restoration activities. Amphibians and reptiles have valuable ecological roles in ecosystems, and promoting their abundance and diversity when rehabilitating riparian systems can contribute to reestablishing degraded ecosystem functions. We evaluated the herpetofauna community by measuring abundance, richness, diversity, and species-habitat relations along three reaches (wildland, urban rehabilitated, and urban disturbed reaches) varying in degree of urbanization and rehabilitation along the Salt River in central Arizona. We performed visual surveys for herpetofauna and quantified riparian microhabitat along eight transects per reach. The wildland reach had the greatest herpetofauna species richness and diversity, and had similar abundance compared to the urban rehabilitated reach. The urban disturbed reach had the lowest herpetofauna abundance and species richness, and had a similar diversity compared to the urban rehabilitated reach. Principal Component Analysis reduced 21 microhabitat variables to five factors which described habitat differences among reaches. Vegetation structural complexity, vegetation species richness, densities of Prosopis (mesquite), Salix (willow), Populus (cottonwood), and animal burrow density had a positive correlation with at least one herpetofauna community parameter, and had a positive correlation with abundance of at least one lizard species. Rehabilitation activities positively influenced herpetofauna abundance and species richness; whereas, urbanization negatively influenced herpetofauna diversity. Based on herpetofauna-microhabitat associations, we recommend urban natural resource managers increase vegetation structural complexity and woody debris to improve herpetofauna habitat when rehabilitating degraded riparian systems.     

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

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

Soil microbial community of urban green infrastructures in a polar city

Urban and technogenic landscapes in subarctic zones are not considered comfortable habitats for soil microbiota. However, green infrastructures in polar cities can provide a new niche for the development of a microbial soil community. Soil microbial biomass and the diversity of cultivable microfungi have been studied in relation to the chemical and morphological properties of urban soils in the polar city of Apatity. The quantitative indicators based on fluorescence microscopy and PCR real-time methods as well as the qualitative composition of the cultivable microfungal community were used to characterize the microbial community. Changes in the morphological and chemical composition of urban soils included a shift in pH and increased C and N content compared with forest soil. Studies have shown that the biomass of microfungi and actinomycetes in urban soils was lower than in forest soils and equals 0.12–0.19 mg/g and 0.06–0.44?×?10^?3 mg/g, respectively. Bacterial biomass, on the contrary, increased in urban soils up to 2.6?×?10^–3 – 5.6?×?10^–3 mg/g. The number of ITS gene copies of fungi in urban soils varied from 5.0?×?10⁹ to 1.45?×?10¹⁰ copies/g of soil, reaching the highest values in the courtyard. The number of rRNA gene copies of bacteria and archaea in urban soils increased compared with forest soil and amounted to 2.37?×?10¹⁰ – 9.99?×?10¹⁰ and 0.4?×?10¹⁰ – 0.8?×?10¹⁰ copies/g of soil, respectively. In urban soils, morphological changes in microfungi, including the predominance of small spores, were revealed in comparison with forest soils, where mycelium prevailed. An increase in the diversity of microfungi in urban soil and changes in the structure of their communities compared with forest soil was noted. Microfungi found in urban soils are not typical of the background soils of the region and would be expected in more southern conditions. Among them, opportunistic fungi species have been identified in humans, which increases the risk of diseases in residents of the northern region.

     

Black widow spiders in an urban desert: Population variation in an arthropod pest across metropolitan Phoenix, AZ

The effects of urban disturbance are critical to understand, as the majority of the world??s population now resides in urban centers. For example, urbanization often leads to reduced species diversity at the expense of a few urban-adapted taxa. However, it remains unclear why some taxa thrive following human disturbance whereas others do poorly. The western black widow spider, Latrodectus hesperus, thrives in disturbed, urban habitat??often forming dense aggregations (i.e., infestations) relative to typical low-density, desert populations. We examined the population dynamics of ten black widow aggregations spread across metropolitan Phoenix, AZ, during the peak of the breeding season (June?CAugust). Here we show that prey abundance, female mass, web volume and population density exhibit minimal temporal variation across the breeding season, but that prey abundance, female mass and population density show significant spatial variation across the ten urban aggregations. Our measure of prey abundance and foraging success, the number of prey carcasses found in black widow webs, shared a strong positive relationship with female mass and population density, but not with web volume. Surprisingly, female mass, web volume and population density were not correlated with each other. The abiotic variables we measured at each site did a poor job of explaining black widow population parameters, although we did find a marginal trend for more recent developments to harbor denser black widow aggregations. Our findings support the generalization that urbanization heightens spatial variation, and we suggest that local urban prey abundance is influential in promoting urban infestations full of heavy, fecund female black widows. Studies of the population ecology of urban pests are necessary to identify the mechanisms allowing some species to thrive following human disturbance while much native biodiversity is lost following urbanization.     

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.     

Bird and butterfly communities associated with two types of urban riparian areas

We examined the distribution of birds and butterflies at two types of urban riparian areas in the metropolitan area of Denver, Colorado, USA. The sites consisted of relatively natural areas containing native woody vegetation, and those that had been highly modified with trees and shrubs removed and planted with lawn grass. Species richness of both butterflies and birds differed significantly between the two types of sites. Species richness, however, was not significantly correlated between birds and butterflies. Bird abundance was similar between site types but consisted of two assemblages. Brewer's blackbirds, common grackles, bank swallows, and mourning doves were abundant at wooded sites while American robins, European starlings, house sparrows, house finches, and mallards were more abundant at lawned riparian sites. Butterfly abundance was less at lawned sites. This contrast in bird and butterfly response to habitats suggests they respond to different habitats in distinct ways. Both taxon groups, however, were important discriminators between habitat types. Overall, butterfly and bird species richness was 44% less at highly modified riparian sites.     

Bird community responses to different urban conditions in La Paz,Bolivia

Urbanization alters ecosystems worldwide, but little is known about its effects in the Neotropical region. In the present research we examined the relative influence of different levels of urbanization and of some urban development measures on bird species richness, abundance and composition. We surveyed 104 observation stations at which we collected data on the relative abundance of bird species, and also data on seven environmental variables as measures of urban development and human activity. We registered 57 native bird species. Bird species richness and bird abundance increased with lower urbanization levels. Both variables were positively related to vegetation cover and native vegetation, and negatively to built-up cover, abundance of Rock Pigeon (Columa livia), pedestrian rate and car rate. A canonical correspondence analysis produced a significant model that explained 37% of the total variation in species data. This analysis segregated bird species along two important gradients: urbanization and elevation. The most urbanized areas were dominated by a few synanthropic species tolerant to human disturbance, such as Rufous-Collared Sparrow (Zonotrichia capensis), Eared Dove (Zenaida auriculata) or Chiguanco Thrush (Turdus chiguanco). Areas with lower urbanization levels had more species typically associated with native vegetation, such as Plain-Mantled Tit-Spinetail (Leptasthenura aegitaloides) or D’Orbigny’s Chat-Tyrant (Ochthoeca oenanthoides), among others. Elevation had a significant influence in structuring bird communities, with some species restricted to higher elevations and some to lower elevations. Although changes in elevation had an important influence, urbanization had a stronger effect on structuring bird communities. This study provides valuable information and an important baseline for future studies.     

Non-native plants in the understory of riparian forests across a land use gradient in the Southeast

As urbanization expands into rural areas, an increase in the number of non-native plant species at the urban-rural interface is expected due in large part to the increased availability of propagules from ornamental plantings. A study investigating the distribution of non-native plants in the understories of riparian forests across an urban-to-rural gradient north of Columbus, GA was initiated in 2003. A significantly greater number of non-native plant species occurred at the urban sites and at one site at the urban-rural interface, where 20 to 33% of the species encountered were non-native. In contrast, at the more rural sites non-native species comprised 4–14% of the total number of species. However, the importance values of non-native species as a whole did not change significantly across the land use gradient due to the high frequency and abundance of three non-native species (Ligustrum sinense, Lonicera japonica, and Microstegium vimineum) in the majority of the watersheds. Reductions in species richness and overstory reproduction associated with these non-natives could impact long-term forest structure and ecosystem function.     

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

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

The genesis,classification, and mapping of soils in urban areas

This paper discusses the concept of soil in both urban and rural environments, and along the urban-rural land use gradient, to illustrate the obvious need to increase our understanding of urban soils. Spatial variability of the urban landscape is illustrated with "Soil series - Urban land complexes" from Baltimore County, Maryland. The World Reference Base for Soil Resources (ISSS-ISRIC-FAO, 1994) proposed Anthrosol and Regosol major soil groups are discussed to show modern approaches to soil classification and to illustrate how the classification of urban soils is essentially undeveloped. Models of soil genesis help identify the processes and functions of the soil system. A conceptual model using Jenny's (1941) state factor approach for human impact on soil formation details the "anthroposequence." The benchmark anthroposequence model may be applied to studying soil systems along urban-rural land use gradients. The process of "anthropedogenesis" is supported to quantify the role of human activity in changing the "natural" direction of soil formation. Future directions of soil research in the urban landscape should involve large scale soil mapping (e.g. 1:6000), benchmark anthroposequences, improved soil classification, and refined characterization of the role of human activities in soil formation.     

Which traits influence the frequency of plant species occurrence in urban habitat types?

Plants in cities must cope with various anthropogenic environments that differ from surrounding landscapes. Moreover, the differences in biotic and abiotic conditions among these habitats filter species with suitable traits and niche requirements. Here we aim to identify those attributes that promote species occurrence across and within urban habitat types of large cities. Species composition of spontaneously occurring vascular plant species was recorded in 1-ha plots in seven different urban habitat types in each of 32 European cities. Each species was characterized in terms of dispersal type, growth form, height, seed bank longevity, seed mass, selected leaf traits and ecological indicators including Ellenberg indicator values, Grime’s life strategies, and immigration pathways using information from available species-trait databases. For each species, total frequency of occurrence across all plots and habitat frequency of occurrence across plots of given habitat types were calculated and regression trees were used to relate them to traits and ecological indicators. The most frequently occurring species in the cities tended to be human-dispersed, nutrient-demanding plants that prefer drier to mesic soil conditions. These species do not possess the S-strategy and usually produce seeds of low mass forming short-term persistent seed banks. Habitat-specific responses were also revealed, indicating the effects of between- and within-habitat heterogeneity on trends in species performance in cities. Such patterns can be overlooked when differences in species occurrences in particular urban habitat types are not considered; thus, habitat-specific responses can resolve inconsistencies found when whole urban floras are analysed as a whole.     

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.     

Macroinvertebrate richness on flood defence walls of the tidal River Thames

The River Thames through central London has seen significant environmental recovery, particularly in regard to water quality, but a substantial barrier to further ecological improvement is the spatial restriction of riparian areas. Flood defence walls represent a potential habitat for ecological improvements to benefit biodiversity. However before restoration actions are considered, an understanding of the current biodiversity and ecological status of these structures is necessary. Physical habitat and macroinvertebrate richness of flood defence walls at 15, evenly spaced sites along a 32?Km reach in central London were evaluated. We found no longitudinal patterns in total macroinvertebrate richness among our 15 sites, but did find that richness was influenced by wall type. Specifically, we found the highest richness on brick walls and lowest richness on concrete walls. Further, wall sections with algal cover supported significantly higher numbers of macroinvertebrates than sections lacking algal cover. However, reaches of the river where the channel was constricted had fewer macroinvertebrates likely due to scouring flows. These results show that macroinvertebrates of the river walls are influenced by habitat availability (i.e., wall type) and localised river flows. This work suggests that appropriate management of river wall habitats has the potential to enhance the biodiversity of highly modified, urban rivers.