Public Parks and Wellbeing in Urban Areas of the United States

Sustainable development efforts in urban areas often focus on understanding and managing factors that influence all aspects of health and wellbeing. Research has shown that public parks and green space provide a variety of physical, psychological, and social benefits to urban residents, but few studies have examined the influence of parks on comprehensive measures of subjective wellbeing at the city level. Using 2014 data from 44 U.S. cities, we evaluated the relationship between urban park quantity, quality, and accessibility and aggregate self-reported scores on the Gallup-Healthways Wellbeing Index (WBI), which considers five different domains of wellbeing (e.g., physical, community, social, financial, and purpose). In addition to park-related variables, our best-fitting OLS regression models selected using an information theory approach controlled for a variety of other typical geographic and socio-demographic correlates of wellbeing. Park quantity (measured as the percentage of city area covered by public parks) was among the strongest predictors of overall wellbeing, and the strength of this relationship appeared to be driven by parks’ contributions to physical and community wellbeing. Park quality (measured as per capita spending on parks) and accessibility (measured as the overall percentage of a city’s population within ½ mile of parks) were also positively associated with wellbeing, though these relationships were not significant. Results suggest that expansive park networks are linked to multiple aspects of health and wellbeing in cities and positively impact urban quality of life.     

The castor-oil plant in the United States

About 125,000,000 pounds of castor oil are annually used in the United States in the manufacture of paints and varnishes, fatty acids, sulphonated oils, soap and other important products, 95% of which is imported either as seed or expressed oil. Attempts are now being made to revive a former American industry in the growing of domestic crops.     

Mechanisms underlying the impacts of exotic plant invasions

Although the impacts of exotic plant invasions on community structure and ecosystem processes are well appreciated, the pathways or mechanisms that underlie these impacts are poorly understood. Better exploration of these processes is essential to understanding why exotic plants impact only certain systems, and why only some invaders have large impacts. Here, we review over 150 studies to evaluate the mechanisms underlying the impacts of exotic plant invasions on plant and animal community structure, nutrient cycling, hydrology and fire regimes. We find that, while numerous studies have examined the impacts of invasions on plant diversity and composition, less than 5% test whether these effects arise through competition, allelopathy, alteration of ecosystem variables or other processes. Nonetheless, competition was often hypothesized, and nearly all studies competing native and alien plants against each other found strong competitive effects of exotic species. In contrast to studies of the impacts on plant community structure and higher trophic levels, research examining impacts on nitrogen cycling, hydrology and fire regimes is generally highly mechanistic, often motivated by specific invader traits. We encourage future studies that link impacts on community structure to ecosystem processes, and relate the controls over invasibility to the controls over impact.     

Non-native earthworms alter the assembly of a meadow plant community

Non-native earthworms can alter ecosystems by modifying soil structure, depredating seeds and seedlings, and consuming soil organic matter, yet the initial responses of plant communities to earthworm invasions remain poorly understood. We assessed the effect of non-native earthworms on seedling survival during germination and after establishment using six native and six non-native plant species grown from seed in single- and multi-species experimental mesocosms. We examined the extent to which earthworms (1) influenced seedling survival, (2) selectively depredated native versus non-native plants, (3) impacted establishment based on seed size and/or root morphology, and (4) shaped community assembly. The effect of earthworms on seedling survival varied temporally and among species but inconsistently with respect to species origin. Differences in seed/seedling survival translated to changes in community assembly. Earthworms tended to reduce species abundance, richness, evenness, and diversity in multi-species mesocosms and led to the divergence of communities by treatment. In general, species with large seeds and fibrous roots dominated communities with earthworms present, whereas species with small seeds and taproots only persisted in multi-species mesocosms without earthworms. Our findings suggest that earthworms act as ecological filters in the early stages of invasion to shape community composition based on plant morphological traits.

     

Variation of cyanogenesis in some plant species of the midwestern United States

The frequency of cyanogenesis of 48 species of vascular plants was examined by testing 30 individuals from five populations of each species for release of cyanide. The rate at which cyanide was released and the amount of cyanide released varied widely among individuals of a population and among populations of a species. For many taxa, the frequency of cyanogenesis was highly variable among populations. Of the species examined, 20 have not been reported previously as being cyanogenic.     

Biological invasions as disruptors of plant reproductive mutualisms

Invasive alien species affect the composition and functioning of invaded ecosystems in many ways, altering ecological interactions that have arisen over evolutionary timescales. Specifically, disruptions to pollination and seed-dispersal mutualistic interactions are often documented, although the profound implications of such impacts are not widely recognized. Such disruptions can occur via the introduction of alien pollinators, seed dispersers, herbivores, predators or plants, and we define here the many potential outcomes of each situation. The frequency and circumstances under which each category of mechanisms operates are also poorly known. Most evidence is from population-level studies, and the implications for global biodiversity are difficult to predict. Further insights are needed on the degree of resilience in interaction networks, but the preliminary picture suggests that invasive species frequently cause profound disruptions to plant reproductive mutualisms.     

Climate change increases risk of plant invasion in the Eastern United States

Invasive plant species threaten native ecosystems, natural resources, and managed lands worldwide. Climate change may increase risk from invasive plant species as favorable climate conditions allow invaders to expand into new ranges. Here, we use bioclimatic envelope modeling to assess current climatic habitat, or lands climatically suitable for invasion, for three of the most dominant and aggressive invasive plants in the southeast United States: kudzu (Pueraria lobata), privet (Ligustrum sinense; L. vulgare), and cogongrass (Imperata cylindrica). We define climatic habitat using both the Maxent and Mahalanobis distance methodologies, and we define the best climatic predictors based on variables that best ‘constrain’ species distributions and variables that ‘release’ the most land area if excluded. We then use an ensemble of 12 atmosphere-ocean general circulation models to project changes in climatic habitat for the three invasive species by 2100. The combined methodologies, predictors, and models produce a robust assessment of invasion risk inclusive of many of the approaches typically used individually to assess climate change impacts. Current invasion risk is widespread in southeastern states for all three species, although cogongrass invasion risk is more restricted to the Gulf Coast. Climate change is likely to enable all three species to greatly expand their ranges. Risk from privet and kudzu expands north into Ohio, Pennsylvania, New York, and New England states by 2100. Risk from cogongrass expands as far north as Kentucky and Virginia. Heightened surveillance and prompt eradication of small pockets of invasion in northern states should be a management priority.     

A global comparison of plant invasions on oceanic islands

Oceanic islands have long been considered to be particularly vulnerable to biotic invasions, and much research has focused on invasive plants on oceanic islands. However, findings from individual islands have rarely been compared between islands within or between biogeographic regions. We present in this study the most comprehensive, standardized dataset to date on the global distribution of invasive plant species in natural areas of oceanic islands. We compiled lists of moderate (5–25% cover) and dominant (>25% cover) invasive plant species for 30 island groups from four oceanic regions (Atlantic, Caribbean, Pacific, and Western Indian Ocean). To assess consistency of plant behaviour across island groups, we also recorded present but not invasive species in each island group.We tested the importance of different factors discussed in the literature in predicting the number of invasive plant species per island group, including island area and isolation, habitat diversity, native species diversity, and human development. Further we investigated whether particular invasive species are consistently and predictably invasive across island archipelagos or whether island-specific factors are more important than species traits in explaining the invasion success of particular species.We found in total 383 non-native spermatophyte plants that were invasive in natural areas on at least one of the 30 studied island groups, with between 3 and 74 invaders per island group. Of these invaders about 50% (181 species) were dominants or co-dominants of a habitat in at least one island group. An extrapolation from species accumulation curves across the 30 island groups indicates that the total current flora of invasive plants on oceanic islands at latitudes between c. 35°N and 35°S may eventually consist of 500–800 spermatophyte species, with 250–350 of these being dominant invaders in at least one island group. The number of invaders per island group was well predicted by a combination of human development (measured by the gross domestic product (GDP) per capita), habitat diversity (number of habitat types), island age, and oceanic region (87% of variation explained). Island area, latitude, isolation from continents, number of present, non-native species with a known invasion history, and native species richness were not retained as significant factors in the multivariate models.Among 259 invaders present in at least five island groups, only 9 species were dominant invaders in at least 50% of island groups where they were present. Most species were invasive only in one to a few island groups although they were typically present in many more island groups. Consequently, similarity between island groups was low for invader floras but considerably higher for introduced (but not necessarily invasive) species – especially in pairs of island groups that are spatially close or similar in latitude. Hence, for invasive plants of natural areas, biotic homogenization among oceanic islands may be driven by the recurrent deliberate human introduction of the same species to different islands, while post-introduction processes during establishment and spread in natural areas tend to reduce similarity in invader composition between oceanic islands. We discuss a number of possible mechanisms, including time lags, propagule pressure, local biotic and abiotic factors, invader community assembly history, and genotypic differences that may explain the inconsistent performance of particular invasive species in different island groups.     

Landscape-scale patterns of biological invasions in shoreline plant communities

Little is known about the patterns and dynamics of exotic species invasions at landscape to regional spatial scales. We quantified the presence (identity, abundance, and richness) and characteristics of native and exotic species in estuarine strandline plant communities at 24 sites in Narragansett Bay, Rhode Island, USA. Our results do not support several fundamental predictions of invasion biology. Established exotics (79 of 147 recorded plant species) were nearly indistinguishable from the native plant species (i.e. in terms of growth form, taxonomic grouping, and patterns of spatial distribution and abundance) and essentially represent a random sub-set of the current regional species pool. The cover and richness of exotic species varied substantially among quadrats and sites but were not strongly related to any site-level physical characteristics thought to affect invasibility (i.e. the physical disturbance regime, legal status, neighboring habitat type, and substrate characteristics). Native and exotic cover or richness were not negatively related within most sites. Across sites, native and exotic richness were positively correlated and exotic cover was unrelated to native richness. The colonization and spread of exotics does not appear to have been substantially reduced at sites with high native diversity. Furthermore, despite the fact that the Rhode Island strandline system is one of the most highly-invaded natural plant communities described to date, exotic species, both individually and as a group, currently appear to pose little threat to native plant diversity. Our findings are concordant with most recent, large-scale investigations that do not support the theoretical foundation of invasion biology and generally contradict small-scale experimental work.     

Patterns of plant species richness in pasture lands of the northeast United States

Pasture lands are an important facet of land use in the northeast United States, yet little is known about their recent diversity. To answer some fundamental questions about the diversity of these pasture lands, we designed a broad survey to document plant species richness using an intensive, multi scale sampling method. We also wanted to learn whether environmental (soils or climate) or land management variables could help explain patterns of species richness. A total of 17 farms, encompassing 37 pastures, were sampled in New York, Pennsylvania, Vermont, Maryland, Massachusetts and Connecticut during July and August 1998. We positively identified a total of 161 different plant species across the study region. Species richness averaged 31.7±1.1 on pastures. Infrequent, transient species that were mostly perennial and annual forbs accounted for 90% of the species richness. Except for a subjective rating of grazing intensity, land management methods were not good predictors of species richness. Over time, it appears that grazing neither reduces nor increases species richness in pastures. Of the environmental variables measured, only soil P explained a significant amount of the variation in species richness. Soil P was inversely related to species richness at the 1m² scale. Percent SOM was positively associated with species richness at this scale, although weakly. At larger spatial scales, we suggest that patterns of species richness are best explained by the species diversity of soil seed banks, or seed rain, and stochastic recruitment of these species into existing vegetation.     

Non-native grass invasion alters native plant composition in experimental communities

Invasions of non-native species are considered to have significant impacts on native species, but few studies have quantified the direct effects of invasions on native community structure and composition. Many studies on the effects of invasions fail to distinguish between (1) differential responses of native and non-native species to environmental conditions, and (2) direct impacts of invasions on native communities. In particular, invasions may alter community assembly following disturbance and prevent recolonization of native species. To determine if invasions directly impact native communities, we established 32 experimental plots (27.5 m²) and seeded them with 12 native species. Then, we added seed of a non-native invasive grass (Microstegium vimineum) to half of the plots and compared native plant community responses between control and invaded plots. Invasion reduced native biomass by 46, 64, and 58%, respectively, over three growing seasons. After the second year of the experiment, invaded plots had 43% lower species richness and 38% lower diversity as calculated from the Shannon index. Nonmetric multidimensional scaling ordination showed a significant divergence in composition between invaded and control plots. Further, there was a strong negative relationship between invader and native plant biomass, signifying that native plants are more strongly suppressed in densely invaded areas. Our results show that a non-native invasive plant inhibits native species establishment and growth following disturbance and that native species do not gain competitive dominance after multiple growing seasons. Thus, plant invaders can alter the structure of native plant communities and reduce the success of restoration efforts.