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Seasonal animal movement among disparate habitats is a fundamental mechanism by which energy, nutrients, and biomass are transported across ecotones. A dramatic example of such exchange is the annual emergence of mayfly swarms from freshwater benthic habitats, but their characterization at macroscales has remained impossible. We analyzed radar observations of mayfly emergence flights to quantify long-term changes in annual biomass transport along the Upper Mississippi River and Western Lake Erie Basin. A single emergence event can produce 87.9 billion mayflies, releasing 3,078.6 tons of biomass into the airspace over several hours, but in recent years, production across both waterways has declined by over 50%. As a primary prey source in aquatic and terrestrial ecosystems, these declines will impact higher trophic levels and environmental nutrient cycling.

Urbanisation is an important global driver of biodiversity change, negatively impacting some species groups whilst providing opportunities for others. Yet its impact on ecosystem services is poorly investigated. Here, using a replicated experimental design, we test how Central European cities impact flying insects and the ecosystem service of pollination. City sites have lower insect species richness, particularly of Diptera and Lepidoptera, than neighbouring rural sites. In contrast, Hymenoptera, especially bees, show higher species richness and flower visitation rates in cities, where our experimentally derived measure of pollination is correspondingly higher. As well as revealing facets of biodiversity (e.g. phylogenetic diversity) that correlate well with pollination, we also find that ecotones in insect-friendly green cover surrounding both urban and rural sites boost pollination. Appropriately managed cities could enhance the conservation of Hymenoptera and thereby act as hotspots for pollination services that bees provide to wild flowers and crops grown in urban settings. Pollinators can persist in urban areas despite little natural habitat. Here the authors compare insect pollinators and pollination inside and outside of German cities, showing that urban areas have high diversity of bees but not other insects, and high pollination provisioning, relative to rural sites.

Understanding controls on net primary production (NPP) has been a long-standing goal in ecology. Climate is a well-known control on NPP, although the temporal differences among years within a site are often weaker than the spatial pattern of differences across sites. Climate sensitivity functions describe the relationship between an ecological response (e.g., NPP) and both the mean and variance of its climate driver (e.g., aridity index), providing a novel framework for understanding how climate trends in both mean and variance vary with NPP over time. Nonlinearities in these functions predict whether an increase in climate variance will have a positive effect (convex nonlinearity) or negative effect (concave nonlinearity) on NPP. The influence of climate variance may be particularly intense at ecosystem transition zones, if species reach physiological thresholds that create nonlinearities at these ecotones. Long-term data collected at the confluence of three dryland ecosystems in central New Mexico revealed that each ecosystem exhibited a unique climate sensitivity function that was consistent with long-term vegetation change occurring at their ecotones. Our analysis suggests that rising temperatures in drylands could alter the nonlinearities that determine the relative costs and benefits of variance in precipitation for primary production.

A freely available dataset produced from three million Landsat satellite images reveals substantial changes in the distribution of global surface water over the past 32 years and their causes, from climate change to human actions. A moving picture of Earth's surface waters The distribution of surface water has been mapped globally, and local-to-regional studies have tracked changes over time. But to date, there has been no global and methodologically consistent quantification of changes in surface water over time. Jean-François Pekel and colleagues have analysed more than three million Landsat images to quantify month-to-month changes in surface water at a resolution of 30 metres and over a 32-year period. They find that surface waters have declined by almost 90,000 square kilometres—largely in the Middle East and Central Asia—but that surface waters equivalent to about twice that area have been created elsewhere. Drought, reservoir creation and water extraction appear to have driven most of the changes in surface water over the past decades. The location and persistence of surface water (inland and coastal) is both affected by climate and human activity 1 and affects climate 2 , 3 , biological diversity 4 and human wellbeing 5 , 6 . Global data sets documenting surface water location and seasonality have been produced from inventories and national descriptions 7 , statistical extrapolation of regional data 8 and satellite imagery 9 , 10 , 11 , 12 , but measuring long-term changes at high resolution remains a challenge. Here, using three million Landsat satellite images 13 , we quantify changes in global surface water over the past 32 years at 30-metre resolution. We record the months and years when water was present, where occurrence changed and what form changes took in terms of seasonality and persistence. Between 1984 and 2015 permanent surface water has disappeared from an area of almost 90,000 square kilometres, roughly equivalent to that of Lake Superior, though new permanent bodies of surface water covering 184,000 square kilometres have formed elsewhere. All continental regions show a net increase in permanent water, except Oceania, which has a fractional (one per cent) net loss. Much of the increase is from reservoir filling, although climate change 14 is also implicated. Loss is more geographically concentrated than gain. Over 70 per cent of global net permanent water loss occurred in the Middle East and Central Asia, linked to drought and human actions including river diversion or damming and unregulated withdrawal 15 , 16 . Losses in Australia 17 and the USA 18 linked to long-term droughts are also evident. This globally consistent, validated data set shows that impacts of climate change and climate oscillations on surface water occurrence can be measured and that evidence can be gathered to show how surface water is altered by human activities. We anticipate that this freely available data will improve the modelling of surface forcing, provide evidence of state and change in wetland ecotones (the transition areas between biomes), and inform water-management decision-making.

Aim Climate change causes major shifts in species distributions, reshuffling community composition and favouring warm‐adapted species (“thermophilization”). The tree community response is likely to be affected by major disturbances, such as fire and harvest. Here, we quantify the relative contributions of climate change and disturbances to temporal shifts in tree composition over the last decades and evaluate whether disturbances accelerate community thermophilization. Location Québec, Canada. Time period 1970–2016. Taxa studied Trees. Methods Using 6,281 forest inventory plots, we quantified temporal changes in species composition between a historical (1970–1980) and a contemporary period (2000–2016) by measuring temporal β‐diversity, gains and losses. The effects of climate and disturbances on temporal β‐diversity were quantified using multiple regressions and variation partitioning. We compared how community indices of species temperature preference (CTI) and shade tolerance (CSI) changed for forests that experienced different levels of disturbance. We quantified the contribution of species gains and losses to change in CTI. Results Temporal β‐diversity was mainly driven by disturbances, with historical harvesting as the most important predictor. Despite the prevailing influence of disturbances, we revealed a significant thermophilization (ΔCTI = +.03 °C/decade) throughout forests in Québec. However, this shift in community composition was weakly explained by climate change and considerably slower than the rate of warming (+.14 °C/decade). Importantly, thermophilization was amplified by moderate disturbances (+.044 °C/decade), almost a threefold increase compared with minor disturbances (+.015 °C/decade). The gains and losses of a few tree species contributed to this community‐level shift. Conclusions Our study provides evidence that disturbances can strongly modify tree community responses to climate change. Moderate disturbances, such as harvesting, might reduce competition and facilitate gains of warm‐adapted species, which then accelerate thermophilization of tree communities under climate change. Although accelerated by disturbances, community thermophilization was driven by the gains and losses of a small number of species, notably gains of maples.

1. NDVI analysis and repeated aerial photographs have revealed significant shrub expansion in many subarctic regions. While the recent increase in temperature is usually considered to be the main driver of this phenomenon at regional scales, very little is known about the local heterogeneity of shrub responses across the landscape. 2. In this study, we aim to identify the climatic factors controlling the growth of the largely distributed shrub species Betula glandulosa in three types of environments (terrace, hilltop and snowbed). We also aim to evaluate the relationship between B. glandulosa growth and the NDVI data for the Boniface River region, in north-western Québec, where the study took place. 3. In the field, we harvested 180 B. glandulosa individuals (20 per site, 3 sites per type of environment). We constructed specific growth-ring width chronologies and mean axial growth rate chronologies for each site and used them for dendroclimatic analysis (response functions). We also used linear regressions to evaluate the relative influence of dwarf birch growth on the NDVI trend. 4. We found a sharp increase in B. glandulosa radial growth in the 1990s followed by a sharp decreasing trend from 2002 on terraces and hilltops, while growth remained high in snowbeds. Betula glandulosa growth was positively correlated with summer temperatures on terraces and hilltops, whereas winter precipitation promoted growth on snowbeds. The NDVI trend was largely correlated to B. glandulosa growth on terraces and hilltops for the period between 1986 and 2002 (71—80% explained variance). 5. Synthesis. Our results suggest that topography plays a major role in B. glandulosa growth and therefore in shrub community dynamics. Because terraces and hilltops represent 70% of the land surface, the sharp B. glandulosa growth increase at these sites promoted an important overall expansion of the shrub community in the region. However, the decline in B. glandulosa growth observed after 2002 suggests that the expansion could be slowed down in the near future, therefore limiting shrub growth contribution to the regional NDVI signal.

The climate change-induced expansion of mangroves into salt marshes could significantly alter the carbon (C) storage capacity of coastal wetlands, which have the highest average C storage per land area among unmanaged terrestrial ecosystems. Mangrove range expansion is occurring globally, but little is known about how these rapid climate-driven shifts may alter ecosystem C storage. Here, we quantify current C stocks in ecotonal wetlands across gradients of marsh- to mangrove-dominance, and use unique chronological maps of vegetation cover to estimate C stock changes from 2003 to 2010 in a 567-km² wildlife refuge in the mangrove-salt marsh ecotone. We report that over the 7-yr. period, total wetland C stocks increased 22 % due to mangrove encroachment into salt marshes. Newly established mangrove stands stored twice as much C on a per area basis as salt marsh primarily due to differences in aboveground biomass, and mangrove cover increased by 69 % during this short time interval. Wetland C storage within the wildlife refuge increased at a rate of 2.7 Mg C ha⁻¹ yr.⁻¹, more than doubling the naturally high coastal wetland C sequestration rates. Mangrove expansion could account for a globally significant increase of terrestrial C storage, which may exert a considerable negative feedback on warming.

1. Climate change and extreme events, such as drought, threaten ecosystems world-wide and in particular mountain ecosystems, where species often live at their environmental tolerance limits. In the European Alps, plant communities are also influenced by land-use abandonment leading to woody encroachment of subalpine and alpine grasslands. 2. In this study, we explored how the forest-grassland ecotone of Alpine tree lines will respond to gradual climate warming, drought events and land-use change in terms of forest expansion rates, taxonomic diversity and functional composition. We used a previously validated dynamic vegetation model, FATE-HD, parameterized for plant communities in the Ecrins National Park in the French Alps. 3. Our results showed that intense drought counteracted the forest expansion at higher elevations driven by land-use abandonment and climate change, especially when combined with high drought frequency (occurring every 2 or less than 2 years). 4. Furthermore, intense and frequent drought accelerated the rates of taxonomic change and resulted in overall higher taxonomic spatial heterogeneity of the ecotone than would be expected under gradual climate and land-use changes only. 5. Synthesis and applications. The results from our model show that intense and frequent drought counteracts forest expansion driven by climate and land-use changes in the forestgrassland ecotone of Alpine tree lines. We argue that land-use planning must consider the effects of extreme events, such as drought, as well as climate and land-use changes, since extreme events might interfere with trends predicted under gradual climate warming and agricultural abandonment.

ContextEcotones are boundary zones formed where overlap between neighboring ecosystems creates an intermediate ecosystem with unique ecological characteristics. Dynamic ecotones change position along a boundary over time and can be further categorized as either shifting, where the adjacent ecosystems alternatively drive movement of the ecotone but maintain the same relative location over time, or directional, where one system encroaches into the other and the ecotone moves laterally.ObjectivesThe purpose of this work was to examine how climate change alters movement dynamics of both directional and shifting ecotones.MethodsIn three ecosystem case studies, we examine the effects of climate change on landscape-scale ecotone movement across the marine, terrestrial, and interfacing environments.ResultsShifts in local and global climate drive changes in ecotone patterns, increasing directional ecotone movement at both shifting and directional ecotones. Specifically, unidirectional changes in climate patterns disrupt dynamic equilibria at shifting ecosystem boundaries, thereby facilitating unidirectional movement at the previously shifting boundaries. Climate changes additionally accelerate pre-existing directional migration of ecotones through changes to abiotic gradients.ConclusionDirectional climate change increases directional movement in multiple types of ecotone. Future work should consider the rate and feedback mechanisms of ecotone movement and function at additional ecotones.