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

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

Evaluating the effects of canine urine on urban soil microbial communities

Due to extensive areas of impermeable surfaces, combined sewer overflow (CSO) is currently a major problem in urban areas across the United States. In CSO systems, sewage can travel through underground pipes to be decontaminated in treatment facilities, or it can combine with stormwater after a precipitation event and discharge into local waterways. Many cities are implementing green infrastructure installations, which use vegetation and bioactive soil microbial communities to enhance soil water-holding capacity, thereby minimizing CSO events. Understanding the factors that structure soil microbial communities in green infrastructure will facilitate more effective management of these engineered ecosystems; however, few studies to date have evaluated ecological patterns and processes of microbes in the urban environment. Nitrogen loading is known to be a major factor structuring fungi and bacteria in non-urban soils, and since cities also contain large populations of canines, N-rich urine deposition is a potential factor that could be important for structuring soil microbes in ground-level green infrastructure installations. Our study investigated the effects of canine urine on the urban soil microbial communities in a greenhouse experiment by treating Liriope muscari, a common plant found in New York City green infrastructure, with different concentrations of canine urine for 4 weeks in an experimental setting. We found that urine application significantly decreased total soil microbial biomass and microbial richness, and increased water runoff volume. These findings indicate that canine urine may have negative consequences for soil water-holding capacity and nutrient cycling in urban green infrastructure installations by directly decreasing the abundance and richness of soil microbial communities.

     

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.

     

Spontaneous plant colonization and bird visits of tropical extensive green roof

Green roofs can contribute to enrichment and conservation of urban ecology. An experimental green roof was established in humid-tropical Hong Kong to monitor over two years its spontaneous colonization by plants and bird visits. Some 94 voluntary vascular plant species from 26 families and 76 genera were established, with propagules brought mainly by birds and wind and secondarily inherited from soil seed bank. Plant species composition changed dynamically during the study period. They fall into three groups, namely dominant ruderal (herbaceous and sub-shrub) as surrogate of early-stage local grassland ecosystem succession, arboreal (trees and shrubs), and hygrophilous herb. Progressive increase in vegetation cover was accompanied by changes in species diversity and evenness. In addition, 16 bird species from 8 families and 14 genera were recorded. Ten species were residents and the six migrant species were winter visitors. Their food preference was mainly omnivore and insectivore. Winter and the second year encountered higher species richness, diversity, and evenness. Most vegetation parameters correlated positively with avian community indexes, signifying provision of sustenance by green-roof ecosystem to birds. Vegetation coverage correlated negatively with avian abundance, due to shunning by the abundant ground-foraging Tree Sparrow. Both local common ruderal plant species and common urban bird species can successfully establish and reproduce on the extensive green roof, confirming potentials for urban ecology and biodiversity enhancement and conservation even in densely-developed urban areas. The successful nurturing of naturalistic green roof offers new opportunities for green roof design that deviates from the predominant cultivated-horticultural approach.     

The potential value of mosses for stormwater management in urban environments

Plant-based stormwater management systems such as green roofs are typically composed exclusively of vascular plants. Yet, mosses have several desirable properties that could warrant their more widespread use in green roof applications. In natural systems mosses are important primary colonizers of bare ground, and their establishment improves water storage and provides numerous soil benefits including carbon and nitrogen sequestration. Additionally, mosses often facilitate the establishment and survival of vascular plants at otherwise environmentally harsh or stressful sites. Despite their potential value, few studies have investigated the functional performance of mosses on green roofs. In this study we evaluated the establishment success and potential stormwater performance of three candidate moss species. We also directly compared the runoff and thermal characteristics of replicate moss covered green roofs to vascular planted and bare roofs. Candidate mosses had high water holding capacities, storing 8–10 times their weight in water compared to only 1.3 times for typical green roof medium. Mock-up roof sections composed of mosses and medium had delayed and reduced runoff flows relative to medium only sections, although the magnitude of these effects varied with moss species. In field trials all three mosses survived a harsh rooftop environment with limited summer irrigation, although lateral growth after one year was minimal. Green roofs planted solely with Racomitrium canescens had between 12–24% higher stormwater retention than vascular or medium only roofs. Moss cover also ameliorated temperature fluctuations on green roofs. Hourly heating rates were buffered to a similar degree (less than half that of surface temperatures) 5 cm below the surface of both moss covered and medium only roofs. In contrast, cooling under the surface of the moss roof was nearly 6 times faster than under the medium only roof. These results demonstrate the potential for mosses to be valuable components of green roofs, either in combination with vascular plants or planted exclusively.     

Elevated phosphorus: dynamics during four years of green roof development

Green roofs are emerging engineered ecosystems that provide multiple benefits, but many are constructed with nutrient-rich substrate and have been found to leach out high levels of phosphorus (P) in runoff. It is unclear, however, how long green roofs act as sources of P or what mechanisms are responsible for these net losses. We measured P concentrations in runoff water over 4 years from a 1–5 year old extensive green roof in Cincinnati, OH, USA, produced a model to predict runoff P levels into the future, and validated predictions using runoff from 2 nearby extensive green roofs. P concentrations in runoff from the focal green roof were on par with heavily fertilized agroecosystems and displayed strong seasonal dynamics and a rapid decline over the 4-year study. Runoff measurements and changes in substrate P content over a 2-year period were used to estimate a mass balance for green roof P. P loss from the substrate was substantial (4.55 ± 2.3 g P/m²/yr), but only a small portion of the loss was attributable to leaching of P in runoff (0.19–0.65 g P/m²/yr). Missing P may be attributed to a combination of plant uptake and altered P form and binding strength, but further research is needed to precisely identify the mechanisms of P depletion. Our results also suggest that these and similar extensive green roofs are likely to act as environmentally significant sources of P for 10 or more years following roof installation, highlighting the need for reductions in initial substrate P content.     

The exchangeability and leachability of metals from select green roof growth substrates

Batch extraction and leaching studies were conducted with potential green roof substrates (e.g., Axis, Arklayte, coal bottom ash, Haydite, Lassenite, lava rock, and composted pine bark). The results indicated that these materials would not likely be sources of Cr, Cu, Fe, Ni, or Zn and that Lassenite would be considered a source of Mn if the leachate concentrations were compared to USEPA drinking water standards for these elements. Lassenite would not be a source of Mn if the data was compared to a USEPA standard for Mn toxicity to aquatic life. All of the substrates tested leached Cd and/or Pb concentrations that exceeded the USEPA water quality standards at least once during the 6-month leaching study, so these materials may be potential sources of Cd and Pb in green roof storm water runoff. The leaching of Cu, Cd, Fe, Mn, Pb, and Zn was differentially influenced by time and/or the presence of a single Sedum hybridum ‘immergrauch’ plant. The leaching of Cd, Cu, and Pb displayed complex, three-way interactions between main effects (substrate type and the presence or absence of a plant) and between leaching events. For all substrates except Lassenite, the presence of a S. hybridum plant decreased the leaching of Pb over time. The leaching of Cd was generally enhanced by plants for most substrates with time. Collectively the results suggest that changes in the biogeochemical conditions within green roof systems may alter metal solubility, decreasing the leaching of some elements and increasing the leaching of others.     

The impact of mosses on the growth of neighbouring vascular plants,substrate temperature and evapotranspiration on an extensive green roof

Currently the majority of vegetation used on shallow extensive green roofs are species of Sedum, which are able to survive in the harsh green roof environment. While mosses frequently colonize green roofs in Europe, intentional planting of mosses on green roofs is less common, especially in North America. Mosses may contribute to the ecosystem services provided by green roofs, and may act as facilitators of vascular plants. This study examined the effect of three different moss species on soil temperature, water loss rates and the growth of neighbouring vascular plant species. Overall, the presence of mosses in this experiment impacted the neighbour species differently, suggesting that mosses are best used in particular species combinations. One species of grass showed a net benefit of moss neighbours, suggesting that facilitation may be operating. Mosses reduced soil temperature relative to bare substrates; net evapotranspiration of green roof modules planted with mosses varied depending on the identity of moss and neighbour species.     

Ecological and biological determination of invasion success of non-native plant species in urban woodlands with special regard to short-lived monocarps

Today’s urban green space is exposed to a constant flow of newly introduced exotic plant species, resulting from multiple, intentional and inadvertent introductions. A substantial share of introduced plant species are represented by potential invaders of plant communities, which allows considering that the risk of rapid dispersion by aggressive plant species to be today’s most serious threat to the urban biodiversity. Alien plant species with a short life span (monocarps, therophytes, annuals and biennials) are the most successful invaders across anthropogenically transformed landscapes. These species can have a significant impact on the functioning of previously disturbed ecosystems. At the same time, it is still unclear which mechanisms enable short-lived monocarps to invade under specific conditions of urban forest interiors. Therefore, I have conducted a literature analysis aiming at identifying possible biological and ecological determinants of monocarpic plants’ invasive success in urban woodlands. The analysis was made at three qualitative levels taking into account characteristics of the urban environment, those of different types of urban woodlands as well as traits of non-native monocarpic species. Considering the city level, the main ecological factors are the high level of human-induced disturbance and propagule pressure on the urban-woodland interface sites. The level of invasion as well as invasibility of urban woodlands is mainly determined by the landscape context, whereas the habitat type, species composition and spatial structure play a less important role. In the forest environment, where competition for light and nutrients is the main shaping factor of the phytocoenosis, short-lived alien species must possess a certain level of competitive ability. These findings indicate that this ability may be due to such traits as high fecundity rates, effective dispersal mechanisms, early germination, high rate of growth and the overall big size of plants, presence of autonomous pollination and high shade-tolerance.     

Horizontal and vertical island biogeography of arthropods on green roofs: a review

From an ecological perspective, urban green roofs can be viewed as green islands embedded in an urban matrix. Island biogeography theory suggests that species richness on an island is the outcome of dynamic equilibrium between immigration and extinction. Immigration is affected by the size of an island and distance of an island from a colonizing source. In the context of green roofs, building height and horizontal distance from green areas can potentially be a limiting factor for many species. Here, we considered two distance components of green roofs - vertical (building height) and horizontal (distance of building from open green areas). Based on island biogeography theory, we would expect species richness or community similarity to be negatively related to horizontal or vertical distances from colonizing sources. The green roof literature addressing such questions is currently sparse. In our review comprised of 10 studies, we were unable to identify consistent statistically significant richness-distance or community similarity-distance (vertical or horizontal) relationships. The absence of statistically significant relationships could be due in large part to low statistical power as a consequence of both the paucity of roofs and limited range of vertical distances in many of the existing studies. In addition, these roofs differ in numerous aspects (e.g. roof size, age, substrate type, plant composition and building height). The low number of replicates, combined with the lack of homogeneity among replicates combines to reduce statistical power and our ability to detect differences.     

Initial agronomic performances of Mediterranean xerophytes in simulated dry green roofs

The growing desire to make the urban environment more sustainable from an ecological point of view has stimulated research on the architectural and agronomic aspects of green roofs. The practical realisation of green roofs, is however limited by economic and ecological issues. More specifically, water availability is the most limiting factor, and is likely to be ever more so in the future in the light of climate change. For this reason, we evaluated the agronomic performance of several xerophytes in a simulated dry green roof. Seeds of 20 species were collected in typically dry habitats (abandoned quarries, rocky soils, dunes, etc.) and studied in the laboratory for germination ecology. In cases of strong dormancy, methods were tested to stimulate germination and their germination ecology was studied. The resulting seedlings were transplanted in spring 2008 in two green roof types that differ in substrate depth (150 and 200 mm) made up of lapil, pumice, zeolites and peat, resting on a drainage layer of hydroperlite. Temperature and humidity in the substrate and drainage layer were measured during the whole test period. Survival of the seedlings in both substrate depths was almost 100%, favoured by a rainy spring. Most of the tested species showed an excellent performance during the hot and dry summer months in terms of survival rates, growth, and vegetation cover dynamics, notwithstanding the difficult ecological conditions (temperatures around 50°C; hydric potential Ψ -15 bars). Furthermore, most of the species had a long flowering stage in the first year of growth. Plants in the green roof with the deeper substrate depth produced, for most of the tested taxa, a significantly higher vegetation cover and growth compared to when they were placed in the 150 mm substrate. The results of this study show that some Mediterranean xerophytes have biological characteristics suitable for their use in dry green roofs, although an irrigation system for emergency use seems advisable. To conclude, further research should focus on long term evaluation of green roof vegetation in terms of plant survival and flowering dynamics.     

Green roofs are not created equal: the hydrologic and thermal performance of six different extensive green roofs and reflective and non-reflective roofs in a sub-tropical climate

Green roofs have the potential to retain stormwater on the roof surface and lower the thermal loading on buildings. Because of this, the greatest environmental benefits from green roofs might be achieved in subtropical climates characterized by high temperatures and intense rain events. There is, however, little research to support this. In a replicated study in Texas, we compared the performance of six different extensive green roof designs vegetated with native species, to non-reflective (black) roofs, and reflective (white) roofs. Preliminary hydrologic and thermal profile data indicated not only differences between green and non-vegetated roofs, but also among green roof designs. Maximum green roof temperatures were cooler than conventional roofs by 38°C at the roof membrane and 18°C inside air temperature, with little variation among green roofs. Maximum run-off retention was 88% and 44% for medium and large rain events but some green roof types showed very limited retention characteristics. These data demonstrate indicate that: 1. Green roofs can greatly affect the roof temperature profile—cooling surface layers and internal space on warm days. 2. Green roofs can retain significant amounts of rainfall, this is dependent on the size of the rain event and design and can fail if not designed correctly. We suggest that as green roofs vary so much in their design and performance, they must be designed according to specific goals rather than relying on assumed intrinsic attributes.     

Influence of vegetation composition on runoff in two simulated green roof experiments

Despite the fact that green roofs are based upon living systems, the majority of published research literature contains little specific information on the contribution of plants to the various functions and properties of green roofs. Furthermore, there has been little investigation of the influence of the composition of vegetation on the physical properties of a green roof system. This paper reviews previously published material that throws light on the role of vegetation composition on green roof function, with particular regard to rainwater runoff. Two experiments at the University of Sheffield, UK, are considered in detail: (a) An outdoor lysimeter experiment that investigated the quantity of runoff from trays containing 100 mm of growing medium and combinations of grasses and forbs, together with bare substrate, and (b) a greenhouse experiment using simulated rainfall to estimate the amount of rainfall intercepted by different vegetation types. In both cases the vegetation ranged from simple monocultures of forbs and grasses through to complex mixtures of both. In both cases, the composition of the vegetation was found to significantly affect both the amount of water retained and released from the system.     

Effects of urbanization on plant flowering phenology: A review

Studies of flowering and leafing phenology have dramatically increased during the last few decades because changes in plant phenology can be indicative of possible effects of climate change at multiple scales. This article reviews the available literature focusing on the effects of urbanization on flowering phenology. The literature of flowering phenology in urban environments suggests that spring-blooming plants in a variety of ecosystems in North America, Europe, and China tend to bloom earlier in the city than in the surrounding un-urbanized habitat. Moreover, ephemerals, early spring bloomers, and insect-pollinated plants in these environments tend to be more sensitive than perennials, mid- or late-spring bloomers, and wind-pollinated plants. Researchers attribute advanced flowering in urban environments to the Heat Island Effect. The potential ecological consequences of changes in flowering phenology in urbanized areas are not well understood or explicitly studied. However, studies in global biology have suggested that climate change may result in a series of important ecological consequences as well as human-related problems such as earlier and extended allergy seasons. More field-based studies are needed to elucidate this issue.     

Buzzing on top: Linking wild bee diversity,abundance and traits with green roof qualities

Green roofs are potentially valuable habitats for plants and animals in urban areas. Wild bees are important pollinators for crops and wild plants and may be enhanced by anthropogenic structures, but little is known about wild bees on green roofs in cities. This study investigates the effects of green roof qualities (floral resources, substrate character and depth, roof height and age) on wild bee diversity, abundance and traits (nesting type, sociality, pollen specialisation, body size) on green roofs in Vienna. Nine green roofs were sampled monthly between March and September 2014 by a semi quantitative approach. Wild bees were collected in pre-defined sub-areas for the same amount of time and floral resources were recorded. Over all green roofs, 992 individuals belonging to 90 wild bee species were observed. Wild bee diversity and abundance was strongly positively affected by increasing forage availability and fine substrates. Wild bees on roofs were characteristically solitary, polylectic and 8.3–11.2 mm. Regarding nesting type, the percentage of above-ground nesting bees was higher compared to the common species composition in Middle Europe. Ground-nesting wild bees were mainly eusocial, smaller (6.4–9.6 mm) and positively affected by roofs with fine substrates. During June, when forage availability by wildflowers on roofs was “low” (5–15% flower coverage), flowering Sedum species were an important forage resource. We conclude that wild bee diversity and abundance on green roofs are enhanced by floral resources. Furthermore, the installations of areas with finer and deeper substrates benefit ground nesting and eusocial wild bees.     

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.

     

Non-native plants are a seasonal pollen source for native honeybees in suburban ecosystems

In urban and suburban ecosystems, biodiversity can depend on various non-native plant species, including crop plants, garden plants and weeds. Non-native plants may help to maintain biodiversity by providing a source of forage for pollinators in these ecosystems. However, the contribution of plants in urban and agricultural areas to ecosystem services has often been underestimated in biodiversity assessments. In this study, we investigated the pollen sources of native honeybees (Apis cerana) in an arboretum containing native trees and urban and agricultural plants in a suburban landscape. We surveyed the flowering tree species planted inside the arboretum, which were potential pollen sources. The number of potential pollen-source species of native trees peaked in June and July and decreased after August. We collected A. cerana pollen balls every month and identified plant species of pollen in the collected pollen balls using DNA barcoding. In total, we identified 29 plant species from A. cerana pollen balls. The probability of A. cerana using pollen from urban and agricultural plants was higher in July and August than in June. A. cerana collected pollen forages from native tree species (53%), but also gathered pollen from crop plants (13%), garden trees (19%) and native and non-native weeds (14%); the predominant pollen sources in September and October were the garden tree Ulmus parvifolia and the non-native weed Solidago altissima. We found that native honeybees used plants from a variety of habitats including non-native plants to compensate for apparent seasonal shortages of native tree sources in suburban ecosystems. Our results highlight the importance of assessments of both positive and negative roles of non-native plants in urbanized ecosystems to improve biodiversity conservation.     

Insect species composition and diversity on intensive green roofs and adjacent level-ground habitats

While it is expected that green roofs support a wider variety of insects compared with conventional roof surfaces, few studies have quantified insect diversity on green roofs. Even fewer have attempted to determine whether green roofs can support insect communities comparable to level-ground urban habitats. In this study, insect richness, abundance and diversity indices were compared between five pairs of intensive green roofs and adjacent ground-level habitat patches in downtown Halifax, Nova Scotia. Pitfall traps were set at each site, collected bi-weekly between May-October 2009 and captured insects were identified to morphospecies (except where taxonomic expertise was available). No significant differences in richness, abundance or any of the indices (S, H’, E_var) were detected in analysis, which included plant species richness, site area and sampling effort as covariables. However, richness and abundance tended to be greater at ground level for all orders (except Heteroptera), and diversity appeared to increase away from the downtown core. Insect composition differed slightly between green roof and ground-level sites; only 17 species were collected from a single site type in numbers greater than five specimens. Nevertheless, a wide variety of insects, including many uncommon species were collected from green roofs, supporting the idea that these habitats can contribute to sustaining biodiversity in cities.     

Getting to Yes or Bailing on No: The Site Selection Process of Ethanol Plants in Wisconsin

Prior studies of ethanol location rest on the assumption that ethanol producers are economic free agents—evaluating sites as if all counties are contenders for their business, weighing the availability of feedstocks along with their infrastructure needs, operating without ties to localities, and being subject to enticement from policy incentives. We analyze the political‐economic process through which ethanol plants come into communities by examining plant location decisions, plant financing, community receptivity toward the plant, local government incentives, and the dynamics of the approval process. We use case studies of ethanol plants in Wisconsin to explore the economic, social, and political dynamics of ethanol plant location. Our case studies provide evidence in support of some findings in the ethanol location literature—such as the importance of access to corn; however, they also suggest site selection criteria not adequately addressed by the literature. Furthermore, our data suggest that capital may not be as mobile as location theory assumes it to be and that location decisions are not primarily determined by consideration of profit maximization. Instead, the location of ethanol plants is greatly influenced by the extent to which the original initiators of the plant are locally embedded in its host community. Our research answers Barkley and McNamara's ( 1994 :45) call for a return to a case studies approach in order to develop “reliable insights into the location process.”     

Salt tolerance of common green roof and green wall plants

Detrimental effects of road deicing salt on vegetation are well known and have been well studied, with the exception of typical green roof plants, which could experience damage on green roofs with public access and green walls near roadways in cold climates. Two studies were conducted comparing salt tolerance of five Sedum species, two Allium species and a mixture of turf grasses when exposed to six levels of salinity applied either as foliar spray or as liquid applications to the soil. A third study compared salt tolerance when plants were placed at three distances from a major highway. Response variables measured included survival, a health score from 0 to 5, and a growth index. Allium cernuum, A. senscens and S. ellecombianum were relatively tolerant of both saline spray and soil inundation at high saline concentrations in terms of survival, mean health scores, percentage of healthy plants and growth index. Sedum reflexum was much less tolerant of saline spray at higher salinity concentrations and soil inundation regardless of salinity levels. Distance from the road had no effect on plant survival rates but plants farthest from the road had higher mean health scores and a greater percentage of healthy plants than plants closer to the highway.