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Because of its serious large-scale effects on ecosystems and its transboundary nature, acid rain received for a few decades at the end of the last century wide scientific and public interest, leading to coordinated policy actions in Europe and North America. Through these actions, in particular those under the UNECE Convention on Long-range Transboundary Air Pollution, air emissions were substantially reduced, and ecosystem impacts decreased. Widespread scientific research, long-term monitoring, and integrated assessment modelling formed the basis for the policy agreements. In this paper, which is based on an international symposium organised to commemorate 50 years of successful integration of air pollution research and policy, we briefly describe the scientific findings that provided the foundation for the policy development. We also discuss important characteristics of the science–policy interactions, such as the critical loads concept and the large-scale ecosystem field studies. Finally, acid rain and air pollution are set in the context of future societal developments and needs, e.g. the UN's Sustainable Development Goals. We also highlight the need to maintain and develop supporting scientific infrastructures. [ABSTRACT FROM AUTHOR]

Trembling aspen (Populus tremuloides) is arguably the most important deciduous tree species in the Intermountain West of North America. There, as elsewhere in its range, aspen exhibits remarkable genetic variation in observable traits such as morphology and phenology. In contrast to Great Lakes populations, however, relatively little is known about phytochemical variation in western aspen. This survey of phytochemistry in western aspen was undertaken to assess how chemical expression varies among genotypes, cytotypes (diploid vs. triploid), and populations, and in response to development and mammalian browsing. We measured levels of foliar nitrogen, salicinoid phenolic glycosides (SPGs) and condensed tannins (CTs), as those constituents influence organismal interactions and ecosystem processes. Results revealed striking genotypic variation and considerable population variation, but minimal cytotype variation, in phytochemistry of western aspen. Levels of SPGs and nitrogen declined, whereas levels of CTs increased, with tree age. Browsed ramets had much higher levels of SPGs, and lower levels of CTs, than unbrowsed ramets of the same genotype. We then evaluated how composite chemical profiles of western aspen differ from those of Great Lakes aspen (assessed in earlier research). Interestingly, mature western aspen trees maintain much higher levels of SPGs, and lower levels of CTs, than Great Lakes aspen. Phenotypic variation in chemical composition of aspen – a foundation species – in the Intermountain West likely has important consequences for organismal interactions and forest ecosystem dynamics. Moreover, those consequences likely play out over spatial and temporal scales somewhat differently than have been documented for Great Lakes aspen. [ABSTRACT FROM AUTHOR]

The chemical pollution crisis severely threatens human and environmental health globally. To tackle this challenge the establishment of an overarching international science–policy body has recently been suggested. We strongly support this initiative based on the awareness that humanity has already likely left the safe operating space within planetary boundaries for novel entities including chemical pollution. Immediate action is essential and needs to be informed by sound scientific knowledge and data compiled and critically evaluated by an overarching science–policy interface body. Major challenges for such a body are (i) to foster global knowledge production on exposure, impacts and governance going beyond data-rich regions (e.g., Europe and North America), (ii) to cover the entirety of hazardous chemicals, mixtures and wastes, (iii) to follow a one-health perspective considering the risks posed by chemicals and waste on ecosystem and human health, and (iv) to strive for solution-oriented assessments based on systems thinking. Based on multiple evidence on urgent action on a global scale, we call scientists and practitioners to mobilize their scientific networks and to intensify science–policy interaction with national governments to support the negotiations on the establishment of an intergovernmental body based on scientific knowledge explaining the anticipated benefit for human and environmental health. [ABSTRACT FROM AUTHOR]

Seasonal rounds are deliberative articulations of a community's sociocultural relations with their ecological system. The process of visualizing seasonal rounds informs transdisciplinary research. We present a methodological approach for communities of enquiry to engage communities of practice through context-specific sociocultural and ecological relations driven by seasonal change. We first discuss historical précis of the concept of seasonal rounds that we apply to assess the spatial and temporal communal migrations and then describe current international research among Indigenous and rural communities in North America and Central Asia by the creation of a common vocabulary through mutual respect for multiple ways of knowing, validation of co-generated knowledge, and insights into seasonal change. By investigating the relationship between specific biophysical indicators and livelihoods of local communities, we demonstrate that seasonal rounds are an inclusive and participatory methodology that brings together diverse Indigenous and rural voices to anticipate anthropogenic climate change. [ABSTRACT FROM AUTHOR]

In recent decades, climate change has disrupted forest functioning by promoting large-scale mortality events, declines in productivity and reduced regeneration. Understanding the temporal dynamics and spatial extent of these changes is critical given the essential ecosystem services provided by forests. As the most widespread tree species in North America, quaking aspen (Populus tremuloides) is well suited for studying the dynamics of tree populations during a period of unprecedented climate change. Synthesizing continent-wide data, we show that mortality rates of mature aspen stems have increased over the past two-to-three decades, while relative gains in aspen basal area have decreased during the same period. Patterns were pervasive across multiple stand size classes and composition types in western North America biomes, suggesting that trends in demographic rates were not simply a reflection of stand development and succession. Our review of the literature revealed that increased aspen mortality and reduced growth rates were most often associated with hotter, drier conditions, whereas reduced recruitment was most often associated with herbivory. Furthermore, interactions between climate and competition, as well as climate and insect herbivory, had important, context-dependent effects on mortality and growth, respectively. Our analyses of aspen across its entire geographic range indicate that this important tree species is experiencing substantial increases in mortality and decreases in population growth rates across multiple biomes. If such trends are not accompanied by increased recruitment, we expect that the reduced dominance of aspen in forests will lead to major declines in the many essential ecosystem services it provides. [ABSTRACT FROM AUTHOR]

The presence of many pathogens varies in a predictable manner with latitude, with infections decreasing from the equator towards the poles. We investigated the geographic trends of pathogens infecting a widely distributed carnivore: the gray wolf (Canis lupus). Specifically, we investigated which variables best explain and predict geographic trends in seroprevalence across North American wolf populations and the implications of the underlying mechanisms. We compiled a large serological dataset of nearly 2000 wolves from 17 study areas, spanning 80° longitude and 50° latitude. Generalized linear mixed models were constructed to predict the probability of seropositivity of four important pathogens: canine adenovirus, herpesvirus, parvovirus, and distemper virus—and two parasites: Neospora caninum and Toxoplasma gondii. Canine adenovirus and herpesvirus were the most widely distributed pathogens, whereas N. caninum was relatively uncommon. Canine parvovirus and distemper had high annual variation, with western populations experiencing more frequent outbreaks than eastern populations. Seroprevalence of all infections increased as wolves aged, and denser wolf populations had a greater risk of exposure. Probability of exposure was positively correlated with human density, suggesting that dogs and synanthropic animals may be important pathogen reservoirs. Pathogen exposure did not appear to follow a latitudinal gradient, with the exception of N. caninum. Instead, clustered study areas were more similar: wolves from the Great Lakes region had lower odds of exposure to the viruses, but higher odds of exposure to N. caninum and T. gondii; the opposite was true for wolves from the central Rocky Mountains. Overall, mechanistic predictors were more informative of seroprevalence trends than latitude and longitude. Individual host characteristics as well as inherent features of ecosystems determined pathogen exposure risk on a large scale. This work emphasizes the importance of biogeographic wildlife surveillance, and we expound upon avenues of future research of cross-species transmission, spillover, and spatial variation in pathogen infection. [ABSTRACT FROM AUTHOR]

Context: Anthropogenic changes (e.g., climate change, land-use change, species introductions, etc.) are reshaping ecosystems processes and patterns and causing an intense reorganization of the Earth's biotic systems. As a result, unprecedented combinations of species are emerging, forming "novel ecosystems". Objectives: The goals of this work are: (1) to examine the history and relevance of the novel ecosystems concept in non-urban and urban contexts, and (2) to evaluate what has been the focus of the research about the novel ecosystems concept in non-urban and urban contexts. Methods: Through an extensive systematic review, we collected 548 records published between 1997 and 2018. After applying inclusion/exclusion criteria the final database comprised 255 relevant records that were further examined and classified according to the scope of this review. Results: Our results demonstrated that research referring to the novel ecosystems concept has been mainly focused on non-urban areas. Still, there is a growing interest in exploring this concept in the urban domain. The definition and criteria used to describe novel ecosystems have been transforming over the years. Research has been mainly targeted on multiple taxonomic groups and plants, on terrestrial ecosystems, and conducted in North America. Overall, restoration ecology, conservation, biodiversity, ecosystem services, and climate change have been the most discussed topics in the novel ecosystems' literature. Conclusions: Our review confirms that the application of the novel ecosystems concept to urban areas is pertinent and auspicious. Future research should seek to understand the limits and differences of novel ecosystems in non-urban and urban contexts. [ABSTRACT FROM AUTHOR]

We synthesized an expert review of climate change implications for hydroecological and terrestrial ecological systems in the northern coastal temperate rainforest of North America. Our synthesis is based on an analysis of projected temperature, precipitation, and snowfall stratified by eight biogeoclimatic provinces and three vegetation zones. Five IPCC CMIP5 global climate models (GCMs) and two representative concentration pathways (RCPs) are the basis for projections of mean annual temperature increasing from a current average (1961-1990) of 3.2 °C to 4.9-6.9 °C (5 GCM range; RCP4.5 scenario) or 6.4-8.7 °C (RCP8.5), mean annual precipitation increasing from 3130 mm to 3210-3400 mm (3-9 % increase) or 3320-3690 mm (6-18 % increase), and total precipitation as snow decreasing from 1200 mm to 940-720 mm (22-40 % decrease) or 720-500 mm (40-58 % decrease) by the 2080s (2071-2100; 30-year normal period). These projected changes are anticipated to result in a cascade of ecosystem-level effects including: increased frequency of flooding and rain-on-snow events; an elevated snowline and reduced snowpack; changes in the timing and magnitude of stream flow, freshwater thermal regimes, and riverine nutrient exports; shrinking alpine habitats; altitudinal and latitudinal expansion of lowland and subalpine forest types; shifts in suitable habitat boundaries for vegetation and wildlife communities; adverse effects on species with rare ecological niches or limited dispersibility; and shifts in anadromous salmon distribution and productivity. Our collaborative synthesis of potential impacts highlights the coupling of social and ecological systems that characterize the region as well as a number of major information gaps to help guide assessments of future conditions and adaptive capacity. [ABSTRACT FROM AUTHOR]

The warm-temperate regions of the globe characterized by dry summers and wet winters (Mediterranean climate; MED) are especially vulnerable to climate change. The potential impact on water resources, ecosystems and human livelihood requires a detailed picture of the future changes in this unique climate zone. Here we apply a probabilistic approach to quantitatively address how and why the geographic distribution of MED will change based on the latest-available climate projections for the 21st century. Our analysis provides, for the first time, a robust assessment of significant northward and eastward future expansions of MED over both the Euro-Mediterranean and western North America. Concurrently, we show a significant 21st century replacement of the equatorward MED margins by the arid climate type. Moreover, future winters will become wetter and summers drier in both the old and newly established MED zones. Should these projections be realized, living conditions in some of the most densely populated regions in the world will be seriously jeopardized. [ABSTRACT FROM AUTHOR]