High Levels Of Environmental Stress Research Articles

A Framework Analyzing Climate Change, Air Quality and Greenery to Unveil Environmental Stress Risk Hotspots

Rapid urbanization has resulted in increased environmental challenges, compounding worries about deteriorating air quality and rising temperatures. As cities become hubs of human activity, understanding the complex interplay of numerous environmental elements is critical for developing effective mitigation solutions. Recognizing this urgency, a framework to highlight the hotspots with critical environmental issues emerges as a comprehensive approach that incorporates key criteria such as the surface urban heat island intensity (SUHII), heat index (HI) and air quality index (AQI) to assess and address the complex web of environmental stressors that grip urban landscapes. Employing the multicriteria decision analysis approach, the proposed framework, named the environmental risk hotspot mapping framework (ERHMF), innovatively applies the analytic hierarchy process at a sub-criteria level, considering long-term heat island trends with recent fluctuations in the HI and AQI. Climate change impact has been symbolized through rising temperatures, as reflected by surface urban heat island intensity trends over two decades. The robustness and correctness of the weights have been assessed by computing the consistency ratio, which came out as 0.046, 0.065 and 0.044 for the sub-criteria of the SUHII, AQI and HI, respectively. Furthermore, the framework delves into the nexus between environmental stressors and vegetation cover, elucidating the role of green spaces in mitigating urban environmental risks. Augmented by spatial and demographic data, the ERHMF adeptly discerns high-risk areas where environmental stress converges with urban development, vulnerable population concentrations and critical vegetation status, thereby facilitating targeted risk management interventions. The framework’s effectiveness has been demonstrated in a regional case study in Italy, underscoring its ability to pinpoint risk hotspots and inform specific policy interventions. The quantitative study undertaken at the sub-administrative level revealed that approximately 6,000,000 m2 of land in Bologna are classified as being under high to extremely high environmental stress, with over 4,000,000 m2 lying only within the extremely high stress group (90–100). Similarly, 1,000,000 m2 of land in Piacenza and Modena have high levels of environmental stress (80–90). In conclusion, the ERHMF presents a holistic methodology for delineating high-risk urban hotspots, providing essential insights for policymakers, urban planners and stakeholders, with the potential to enhance overall urban resilience and foster sustainable development efforts.

Anthropogenic Pressure and Climate Change Could Severely Hamper the Avian Metacommunity of the Sicilian Wetlands

Our study shows that the current levels of anthropogenic exploitation of the Sicilian wetlands (Italy), combined with the likely exacerbation of climate-driven variables, are unsustainable and could soon exclude many bird species from this metacommunity. Sicily is the largest island in the Mediterranean Sea, and its wetlands represent a network of unreplaceable stopover sites that allow waterbirds to rest and refuel during migratory journeys along the central-eastern Mediterranean bird flyway. During the summer period, these species experience higher levels of environmental stress as water scarcity and anthropogenic pressure are at their peak. Through field surveys, geoprocessing and statistical analyses, we investigated: (a) the structure of the avian metacommunity of the largest Sicilian wetlands during July–September and (b) the effects of 10 (geographic, hydrological and anthropogenic) wetland attributes on avian diversity. We sampled 73 bird species, of which 30 are listed in annex I of the Birds Directive. The avian metacommunity was significantly nested and non-modular; in addition, it presented elevated beta diversity and random species assemblage. Environmental filtering superseded biotic interactions in determining species composition. Avian diversity was significantly favored by higher water levels, water-level fluctuations and water discharges, and disfavored by water diversion, salinity and tourism pressure. The knowledge concerning the particular structure of the avian metacommunity of the Sicilian wetlands can facilitate the implementation of conservation policies that could mitigate and compensate the effects of short- and mid-term risks.

Parrotfish corallivory on stress-tolerant corals in the Anthropocene

Cumulative anthropogenic stressors on tropical reefs are modifying the physical and community structure of coral assemblages, altering the rich biological communities that depend on this critical habitat. As a consequence, new reef configurations are often characterized by low coral cover and a shift in coral species towards massive and encrusting corals. Given that coral numbers are dwindling in these new reef systems, it is important to evaluate the potential influence of coral predation on these remaining corals. We examined the effect of a key group of coral predators (parrotfishes) on one of the emerging dominant coral taxa on Anthropocene reefs, massive Porites. Specifically, we evaluate whether the intensity of parrotfish predation on this key reef-building coral has changed in response to severe coral reef degradation. We found evidence that coral predation rates may have decreased, despite only minor changes in parrotfish abundance. However, higher scar densities on small Porites colonies, compared to large colonies, suggests that the observed decrease in scarring rates may be a reflection of colony-size specific rates of feeding scars. Reduced parrotfish corallivory may reflect the loss of small Porites colonies, or changing foraging opportunities for parrotfishes. The reduction in scar density on massive Porites suggests that the remaining stress-tolerant corals may have passed the vulnerable small colony stage. These results highlight the potential for shifts in ecological functions on ecosystems facing high levels of environmental stress.

The Draft Genome of Kochia scoparia and the Mechanism of Glyphosate Resistance via Transposon-Mediated EPSPS Tandem Gene Duplication.

Increased copy number of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene confers resistance to glyphosate, the world’s most-used herbicide. There are typically three to eight EPSPS copies arranged in tandem in glyphosate-resistant populations of the weed kochia (Kochia scoparia). Here, we report a draft genome assembly from a glyphosate-susceptible kochia individual. Additionally, we assembled the EPSPS locus from a glyphosate-resistant kochia plant by sequencing select bacterial artificial chromosomes from a kochia bacterial artificial chromosome library. Comparing the resistant and susceptible EPSPS locus allowed us to reconstruct the history of duplication in the structurally complex EPSPS locus and uncover the genes that are coduplicated with EPSPS, several of which have a corresponding change in transcription. The comparison between the susceptible and resistant assemblies revealed two dominant repeat types. Additionally, we discovered a mobile genetic element with a FHY3/FAR1-like gene predicted in its sequence that is associated with the duplicated EPSPS gene copies in the resistant line. We present a hypothetical model based on unequal crossing over that implicates this mobile element as responsible for the origin of the EPSPS gene duplication event and the evolution of herbicide resistance in this system. These findings add to our understanding of stress resistance evolution and provide an example of rapid resistance evolution to high levels of environmental stress.

Developmental stability and environmental stress: A geometric morphometrics analysis of asymmetry in the human femur.

The evaluation of developmental stability (DS) by measuring fluctuating asymmetry (FA), a bioindicator of general cumulative stress, is an approach that has often been used to characterize health status in past populations. New techniques of geometric morphometrics now enable a better appreciation of FA than before, with a more refined quantification of variation. The aim of our study is to determine the effectiveness of geometric morphometrics analyses of asymmetry in the human femur for the study of individual DS and inferring health status of human populations. We conducted a comparative analysis between two diachronic populations of distinct and known health status. Two samples of 70 pairs of adult femurs from individuals of comparable age range and sex were selected and CT-scanned. For each 3D reconstruction, two sets of 27 landmarks were digitized to quantify and minimize the effect of measurement error on the evaluation of FA. While the measurement of FA in femoral centroid size seemed comparable between the samples, the amount of FA in femoral shape differed. Individuals who experienced high levels of environmental stress presented higher intra-individual variation. In parallel, results did not reveal any significant differences in DS between sexes or age groups. The geometric morphometrics analysis of femoral asymmetry was effective for distinguishing two populations. After considering various factors of influence, genetics and biomechanics seem to have a limited impact on the results. Expressing FA appears to be normal but dependent on the disturbances of DS produced by environmental stress.

Stomatal traits in Iberian populations of Osmunda regalis (Osmundaceae, Polypodiopsida) and its relationship with bioclimatic variables

Stomata are very conservative structures in plants, which allows and control the gas exchange. This ecophysiological fact appear to be critical in the ecology and adaptation of plants to environment. Plant individuals can, among other issues, adjust size and density of the stomata to adapt themselves to hydric, thermic and light regimes. In turn, this led to the reduction of transpiration and control of water losses, which is crucial in areas with Mediterranean climate. The fern Osmunda regalis have populations in both biogeographical regions of the Iberian Peninsula (Eurosiberian and Mediterranean regions), but when locations are highly continental the populations are scarce and isolated. The objective of this study is to characterize the stomatal morphological traits in both regions, to detect possible adaptations in individuals occurring in Mediterranean locations. 26 individuals of 17 different populations were sampled. Applying microscopic techniques, 4447 observations of length and width, and 234 of density and PCI were done. The sampling spots were characterized by two bioclimatic indices of Emberger and Gorzynski, and also mean maximum and minimum temperature values were obtained. All the information was included in a dataset that was statistically analyzed with the software SPSS. Our results show that Osmunda regalis fronds have higher PCI and density values in the Eurosiberian region, as expected. Gorczynski continentality index (K), and the mean maximum and minimum annual temperatures influences over stomatal traits. This is clearly informing that in the Mediterranean region, the temperature is an important factor that triggers stomatal adaptations of O. regalis to continental locations with higher levels of environmental stress. On the contrary, Emberger pluviometric index (Q) seems to be less explicative by its own. Perhaps this is related with the habitat of O. regalis in soils with high freatic level, fact which could lead to a more independent stomata from rainfall

Stomatal traits in Iberian populations of Osmunda regalis (Osmundaceae, Polypodiopsida) and its relationship with bioclimatic variables

Stomata are very conserved structures in plants, which allows and control the gas exchange. This ecophysiological fact appears to be critical in the ecology and adaptation of plants to environment. Plant individuals can, among other issues, adjust size and density of the stomata to adapt themselves to hydric, thermic and light regimes. In turn, this led to the reduction of transpiration and control of water losses, which is crucial in areas with Mediterranean climate. The fern Osmunda regalis has populations in both biogeographical regions of the Iberian Peninsula (Eurosiberian and Mediterranean regions), but when locations are highly continental the populations are scarce and isolated. The objective of this study is to characterize the stomatal morphological traits in both regions, to detect possible adaptations in individuals occurring in Mediterranean locations. 26 individuals of 17 different populations were sampled. Applying microscopic techniques, 4447 observations of length and width, and 234 of density and PCI were done. The sampling spots were characterized by two bioclimatic indices of Emberger and Gorzynski, and also mean maximum and minimum temperature values were obtained. All the information was included in a dataset that was statistically analyzed with the software SPSS. Our results show that Osmunda regalis fronds have higher PCI and density values in the Eurosiberian region, as expected. Gorczynski continentality index (K), and the mean maximum and minimum annual temperatures influences over stomatal traits. This is clearly informing that in the Mediterranean region, the temperature is an important factor that triggers stomatal adaptations of O. regalis to continental locations with higher levels of environmental stress. On the contrary, Emberger pluviometric index (Q) seems to be less explicative by its own. Perhaps this is related with the habitat of O. regalis in soils with high freatic level, fact which could lead to a more independent stomata from rainfall.

Changes in Perceived Levels of Environmental Stress Before and After a Suicide Attempt in Black American Adolescents: A 14-Year Longitudinal Study

A growing interest in factors that may explain suicidality rates in the United States is fueled in part by the increased rates of suicide behaviors in Black American adolescents, primarily male adolescents. The present longitudinal study investigates the extent to which environmental adversity or stress may relate to the course of suicide attempts in Black American adolescents living in extreme poverty (N = 457). We also consider how age and gender affect the longitudinal relations among the study variables (i.e., environmental stress and suicidality). Results indicate that suicide attempts increase over time, and environmental stress decreases over time. Furthermore, when examined in conjunction with environmental stress and gender, suicide attempts increase to a greater extent among adolescents with higher levels of environmental stress, and this effect is greater for older adolescents than for younger adolescents. Also, when baseline levels of environmental stress, suicide attempts, and gender are considered, different trajectories are found between adolescents with low baseline environmental stress levels and adolescents with high baseline environmental stress levels. Gender was significantly related to outcomes for those participants who self-reported high levels of environmental stress at baseline, but not for those who reported low levels of environmental stress at baseline. We discuss implications for future research and for culturally tailored, systems-focused suicide prevention and intervention efforts.

Neural effects of social environmental stress - an activation likelihood estimation meta-analysis.

Social environmental stress, including childhood abuse and deprivation, is associated with increased rates of psychiatric disorders such as schizophrenia and depression. However, the neural mechanisms mediating risk are not completely understood. Functional magnetic resonance imaging (MRI) studies have reported effects of social environmental stress on a variety of brain regions, but interpretation of results is complicated by the variety of environmental risk factors examined and different methods employed. We examined brain regions consistently showing differences in blood oxygen level-dependent (BOLD) response in individuals exposed to higher levels of environmental stress by performing a coordinate-based meta-analysis on 54 functional MRI studies using activation likelihood estimation (ALE), including an overall sample of 3044 participants. We performed separate ALE analyses on studies examining adults (mean age ⩾18 years) and children/adolescents (mean age <18 years) and a contrast analysis comparing the two types of study. Across both adult and children/adolescent studies, ALE meta-analysis revealed several clusters in which differences in BOLD response were associated with social environmental stress across multiple studies. These clusters incorporated several brain regions, among which the right amygdala was most frequently implicated. These findings suggest that a variety of social environmental stressors is associated with differences in the BOLD response of specific brain regions such as the right amygdala in both children/adolescents and adults. What remains unknown is whether these environmental stressors have differential effects on treatment response in these brain regions.

Creeping Bentgrass Putting Green Response to Combined Mowing, Rolling, and Foot Traffic Under Environmental Stress

Creeping bentgrass (Agrostis stolonifera L.) putting greens in the transition zone experience high levels of environmental stress during summer months. The interaction of common management practices combined with foot traffic can exacerbate environmental stress. The objective of this study was to determine the effect of management practices combined with foot traffic during high environmental stress in the transition zone. Creeping bentgrass cultivars, SR 1020 and Penn G2, were managed with various mowing heights (2.5, 3.2, or 4.0 mm), rolling frequencies (0, 3, or 6 d per week), and foot traffic. As environmental stress became prominent during summer months, bentgrass maintained at the lowest mowing heights exhibited poorer turf quality, coverage, and wear tolerance compared to the highest mowing height. SR 1020 quality was reduced below acceptable levels in July when mowed at the lowest mowing height in 2011 and 2012. Penn G2 maintained acceptable quality at all mowing heights in 2011, but severe heat and drought stress reduced turf quality regardless of mowing height in 2012. Daily rolling significantly increased wear on both cultivars during high environmental stress that resulted in decreased turf quality and coverage compared to the non‐rolled treatments. The combination of wear from mechanical stress and foot traffic increased wear injury on both cultivars. Under reduced daylengths and optimal air temperatures in September of each year, all response variables improved to similar levels.

The evolution of self-organizing communication networks in high-risk social-ecological systems

Recently published research shows that members of regional communication networks form links based on how risky their exchanges with others may be: low-risk situations favor the creation of bridging structures that solve coordination problems, whereas high-risk situations lead to the establishment of bonding structures that make detection and punishment of defection more likely. This basic expectation has been tested in low-risk regional arenas, where indeed more bridging structures formed in time (Berardo and Scholz 2010). However, no empirical evidence on the formation of networks has been produced yet in high-risk social-ecological systems (HRSES). In this article, I study the network of communication among stakeholders in a small river basin in Argentina that has been subject to high levels of environmental stress over the last decades and empirically test whether more bonding structures tend to form in this high-risk SE system. Findings show that actors in the network have a tendency to create more triadic bonding structures, as expected. However, complementary results offer a more nuanced picture of how networks look like in highly-risky regional settings and caution against an overly optimistic view linking bonding in networks to the solution of collective action problems of a regional scale.

Stress‐tolerator leaf traits determine population dynamics in the endangered New Caledonian conifer Araucaria muelleri

AbstractDemographic and ecophysiological data for the endangered New Caledonian conifer, Araucaria muelleri (Araucariaceae), were analysed to: (i) evaluate population viability in relation to site conditions and human impacts; and (ii) advance our understanding of how stress‐tolerator plant functional traits affect the population dynamic behaviour and conservation requirements of long‐lived tree species. Growth, survivorship and recruitment in four A. muelleri populations were monitored across 9 years. Demographic rates were analysed using stage‐based transition matrices. Leaf δ13C, %N and photosystem II stress (Fv/Fm) were measured for seedlings, saplings and trees, and leaf mass per area (LMA) for trees, and correlations among ecophysiological and demographic variables explored. Seedling, sapling and tree stem growth were among the slowest, and annual survivorship among the highest, reported for any tree. Transition matrix analyses yielded stable estimated population growth rates, λ, not significantly different from 1.0 for all populations. Leaf δ13C was positively correlated with seedling and sapling height growth, while daytime photosystem II stress (Fv/Fm) was high in seedlings, but low in saplings and trees. Ecophysiological measures suggest that individuals transition from moisture‐limited growth at the seedling stage to nutrient‐limited growth as adults. High levels of environmental stress result in slow stand dynamics, characterized by low recruitment and growth rates counterbalanced by equally low mortality rates. These dynamics result in populations with limited capacity to increase in size quickly, but potentially highly vulnerable to decline should the rate of adult mortality increase. This combination of traits is likely typical of extreme stress‐tolerator woody species and suggests a conservation focus on the preservation of mature individuals.

Marine ecosystem health status assessment through integrative biomarker indices: a comparative study after the Prestige oil spill “Mussel Watch”

Five integrative biomarker indices are compared: Bioeffects Assessment Index (BAI), Health Status Index (HSI), integrated biological response (IBR), ecosystem health condition chart (EHCC) and Integrative Biomarker Index (IBI). They were calculated on the basis of selected biomarker data collected in the framework of the Prestige oil spill (POS) Mussel Watch monitoring (2003–2006) carried out in Galicia and the Bay of Biscay. According to the BAI, the health status of mussels was severely affected by POS and signals of recovery were evidenced in Galicia after April-04 and in Biscay Bay after April-05. The HSI (computed by an expert system) revealed high levels of environmental stress in 2003 and a recovery trend from April-04 to April-05. In July-05, the health status of mussels worsened but in October-05 and April-06 healthy condition was again recorded in almost all localities. IBR/n and IBI indicated that mussel health was severely affected in 2003 and improved from 2004 onwards. EHCC reflected a deleterious environmental condition in 2003 and a recovery trend after April-04, although a healthy ecosystem condition was not achieved in April-06 yet. Whereas BAI and HSI provide a basic indication of the ecosystem health status, star plots accompanying IBR/n and IBI provide complementary information concerning the mechanisms of biological response to environmental insult. Overall, although the integrative indices based on biomarkers show different sensitivity, resolution and informative output, all of them provide coherent information, useful to simplify the interpretation of biological effects of pollution in marine pollution monitoring. Each others’ advantages, disadvantages and applicability for ecosystem health assessment are discussed.

Epigenetics and the Social Work Imperative

Epigenesis is the biochemical process through which some genes are expressed and others remain silent, and it reinforces and explains the powerful impact that the environment has on human development. Epigenetic effects occur not only through diet, chemical exposure, and high levels of environmental stress, but also through chronic poverty and racism. Epigenesis provides a mandate for social workers to intervene at the policy level, both for today's children and for those in future generations.

Limited phenotypic plasticity in range‐edge populations: a comparison of co‐occurring populations of two Agrimonia species with different geographical distributions

Increased importance of genetic drift and selection for stress resistance have been predicted to lead to a reduction in the degree of phenotypic plasticity in populations at margins of a species' geographical range, relative to those in the centre. We examined the effect of population positioning within the species range on degree of active morphological plasticity to vegetation shade. Importantly, we discriminated between active, size-independent morphological adjustments in response to shade and passive changes in morphology caused by the dependence of morphological traits on plant size, as only the former are considered to be adaptive. Two closely related and ecologically similar Agrimonia species were examined in the same geographical location, where one species reaches the edge of its distribution (Agrimonia pilosa) and the other does not (A. eupatoria). Plasticity to light availability is likely to be advantageous for both species as they occupy habitats with variable light conditions. However, we hypothesised that high levels of environmental stress should lead to reduced active plasticity in marginal compared with more central populations. Agrimonia eupatoria exhibited active adjustments in leaf morphology in response to tree shade, and in elongation of stems and inflorescences in response to herbaceous shade. In contrast, A. pilosa exhibited very limited active plasticity. High active plasticity allowed A. eupatoria to retain constant shoot growth in a wide range of light conditions, while the lack of active plasticity in A. pilosa resulted in a strong dependence of shoot growth on light availability. We propose that high levels of environmental stress in marginal areas of a species' range may lead to a significant reduction in the degree of active plasticity. Our results clearly indicate that discrimination between active and passive plasticity is crucial for reaching valid conclusions about differences in adaptive plasticity between marginal and non-marginal populations.

Resilience in intertidal rocky shore assemblages across the stress gradient created by emersion times

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 390:55-65 (2009) - DOI: https://doi.org/10.3354/meps08171 Resilience in intertidal rocky shore assemblages across the stress gradient created by emersion times Rosa M. Viejo* Departamento de Biología y Geología, Universidad Rey Juan Carlos, 28933 Móstoles, Madrid, Spain *Email: rosa.viejo@urjc.es ABSTRACT: A key feature of intertidal marine systems is the well-defined gradient of environmental stress generated by tides. In this study, resilience, i.e. the speed of recovery along this gradient, was explored in a temperate rocky shore system. The purpose was to test whether there was a negative relationship between environmental stress and resilience, as suggested by some previous empirical studies. The rate of recovery of macroalgal assemblages following disturbance was assessed by comparing cleared and control plots at 4 different tidal heights at 3 sampling times. The results indicated that resilience was greater at higher levels of environmental stress, contrary to previously documented patterns. The number of potential colonisers also decreased at more stressful elevations. This difference in the size of the available pool of species could in itself make re-assembly simpler and faster at higher, harsher elevations. The influence of environmental stress on resilience is possibly dependent on the degree and characteristics of the stress factors and the traits of the particular species pool. During the course of this study, dramatic changes in control assemblages were detected, with occasional local extinctions of canopy-forming species. Even when naturally species-poor assemblages (such as those from higher tidal elevations in rocky shores) may show high resilience, impoverished systems feasibly exhibit a different behaviour. An insightful approach for future research would be to test the effect of non-random extinctions in assemblages naturally varying in the richness of potential colonisers. KEY WORDS: Disturbance · Resilience · Environmental stress · Species pool · Rocky shores Full text in pdf format PreviousNextCite this article as: Viejo RM (2009) Resilience in intertidal rocky shore assemblages across the stress gradient created by emersion times. Mar Ecol Prog Ser 390:55-65. https://doi.org/10.3354/meps08171 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 390. Online publication date: September 18, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

VULNERABILITY AND ENVIRONMENTAL STRESS OF OLDER ADULTS IN DEPRIVED NEIGHBOURHOODS IN THE NETHERLANDS

ABSTRACTRecent policy rests on the assumption that it is better for older people to live independently within the community for as long as possible. A related assumption is that the local community forms a supportive context for vulnerable older people; the environment can compensate the limitations resulting from growing old. However, Lawton's ‘environmental docility hypothesis’, in which the interaction between characteristics of the environment and a person's competence is described, forms a reason to be more careful with this assumption. In a survey of 1,939 Dutch older adults carried out in 2002–2003 this hypothesis is explored for older people living in deprived and non‐deprived neighbourhoods. The results of the analysis seem to be in line with Lawton's hypothesis. In non‐deprived neighbourhoods, no differences in environmental stress are found between vulnerable and non‐vulnerable older adults, while in deprived neighbourhoods vulnerable older adults experience significantly higher levels of environmental stress than non‐vulnerable older adults.

Developmental rates and morphological properties of fibres in two eucalypt clones at sites differing in water availability

One of the ways in which the global forestry industry can remain competitive is to improve the predictability of properties of fibres produced, particularly in plantations. Since the properties of the fibres are determined by growth and developmental processes, it is of importance to understand these processes and how they are affected by changing environmental conditions. Using two Eucalyptus spp. clones growing at sites contrasting in available water, this study measured the rates of fibre production, fibre transverse radial enlargement and fibre secondary thickening and the duration of the cell cycle, as well as the duration for which the processes of fibre enlargement and wall thickening continued. Samples were taken from the cambial zone in late summer (February–March) and in winter (May–June). The study found that season had the greatest effects on characteristics of the developmental zones as well as on developmental rates and durations, although there were significant effects of both site and clone. This was complicated by significant interactions that occur between genotype, site-type and short-term variations in environmental conditions. It was found, however, that dry sites, where trees are experiencing comparatively high levels of environmental stress, can be expected to experience greater extremes in developmental processes between seasons, or over relatively short periods, generally, than wetter sites. These sorts of fluctuations will also translate into greater wood quality variation, and hence different site-types should be managed accordingly. Results from this work will contribute to the development of models of xylogenesis which are currently in development.

Suicide Attempts Among Depressed Adolescents in Primary Care

Although depression is strongly associated with suicide attempts and suicide deaths, most depressed youth do not make an attempt, indicating the need to identify additional risk factors. We examined suicide attempts among 451 depressed primary care patients, 13 to 21 years of age. In bivariate analyses, youth classified as suicide attempters showed elevated levels of psychopathology, specifically depressive symptoms, externalizing behaviors, anxiety, substance use, mania, and posttraumatic stress disorder symptoms. Externalizing behaviors and depression severity uniquely contributed to the prediction of suicide attempts in multivariate analyses. High levels of environmental stress as well as a few key stressful events were associated with suicide attempts; a recent romantic breakup or being assaulted added to suicide attempt risk, beyond the effects of psychopathology. Implications of results for primary care preventive services and suicide attempt prevention are discussed.

Invasiveness, invasibility and the role of environmental stress in the spread of non-native plants

Invasion ecology, the study of how organisms spread in habitats to which they are not native, asks both about the invasiveness of species and the invasibility of habitats: Which species are most likely to become invasive? Which habitats are most susceptible to invasion? To set the stage for considering these questions with regard to plants, we offer a two-way classification of nativeness and invasiveness that distinguishes natives, non-invasive non-natives and invasive non-natives. We then consider the current state of knowledge about invasiveness and invasibility. Despite much investigation, it has proven difficult to identify traits that consistently predict invasiveness. This may be largely because different traits favour invasiveness in different habitats. It has proven easier to identify types of habitats that are relatively invasible, such as islands and riverbanks. Factors thought to render habitats invasible include low intensities of competition, altered disturbance regimes and low levels of environmental stress, especially high resource availability. These factors probably often interact; the combination of altered disturbance with high resource availability may particularly promote invasibility. When biotic factors control invasibility, non-natives that are unlike native species may prove more invasive; the converse may also be true. We end with a simple conceptual model for cases in which high levels of environmental stress should and should not reduce invasibility. In some cases, it may be possible to manipulate stress to control biological invasions by plants.