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Leaching – the release of elements from organic matter through dissolution in water – plays an important role in biogeochemical cycling and ecosystem processes. However, our limited understanding of the patterns and underlying drivers of element solubility in leaves hinders accurate predictions of leaching over space and time in terrestrial ecosystems. In this study, we quantify the solubility of carbon (C), nitrogen (N) and phosphorus (P) from leaves of Betula pubescens – a widespread boreal tree species – across a post-fire retrogressive chronosequence. We then relate solubility to variation in leaf-level traits and ecosystem properties (e.g. soil chemistry, tree density and productivity) across the chronosequence to quantify micro- and macro-scale determinants of leaching. We find that P is much more soluble than C and N and is released in solution mainly in readily accessible mineral form. Solubility patterns are strongly related to foliar chemical and structural traits, particularly for green leaves. Metrics related to ecosystem properties exert a stronger influence over solubility from senesced leaf litter. Overall, our results indicate that leaching could constitute an important flux of nutrients to the soil, particularly for P. The rate and spatio-temporal pattern of this leaching flux may be predicted from foliar traits and ecosystem properties. Further application of the method should allow for rapid integration of leaching-related foliar traits into broader plant trait frameworks and models of ecosystem biogeochemical cycling.

Trees affect organic matter decomposition through allocation of recently fixed carbon belowground, but the magnitude and direction of this effect may depend on substrate type and decomposition stage. Here, we followed mass loss, chemical composition and fungal colonisation of leaf and root litters incubated in mountain birch forests over 4 years, in plots where belowground carbon allocation was severed by tree girdling or in control plots. Initially, girdling stimulated leaf and root litter mass loss by 12% and 22%, respectively, suggesting competitive release of saprotrophic decomposition when tree-mediated competition by ectomycorrhizal fungi was eliminated (Gadgil effect). After 4 years, girdling instead hampered mass loss of root litter by 30%, suggesting late-stage priming of decomposition in the presence of trees, in parallel with increased growth of shrubs and associated fungi following tree elimination. Hence, different mechanisms driving early- and late-stage litter decomposition should be considered in climate-feedback evaluations of plant–soil interactions.

High-resolution unoccupied aerial vehicle (UAVs) data have alleviated the mismatch between the scale of ecological processes and the scale of remotely sensed data, while machine learning and deep learning methods allow new avenues for quantification in ecology. Ant nests play key roles in ecosystem functioning, yet their distribution and effects on entire landscapes remain poorly understood, in part because they and their mounds are too small for satellite remote sensing. This research maps the distribution and impact of ant mounds in a 20 ha treeline ecotone. We evaluate the detectability from UAV imagery using a deep learning model for object detection and different combinations of RGB, thermal and multispectral sensor data. We were able to detect ant mounds in all imagery using manual detection and deep learning. However, the highest precision rates were achieved by deep learning using RGB data which has the highest spatial resolution (1.9 cm) at comparable UAV flight height. While multispectral data were outperformed for detection, it allows for novel insights into the ecology of ants and their spatial impact on vegetation productivity using the normalized difference vegetation index. Scaling up, this suggests that ant mounds quantifiably impact vegetation productivity for up to 4% of our study area and up to 8% of the Betula nana vegetation communities, the vegetation type with the highest abundance of ant mounds. Therefore, they could have an overlooked role in nutrient-limited tundra vegetation, and on the shrubification of this habitat. Further, we show the powerful combination UAV multi-sensor data and deep learning for efficient ecological tracking and monitoring of mound-building ants and their spatial impact.

Motivation: Freshwater ecosystems have been heavily impacted by land-use changes, but data syntheses on these impacts are still limited. Here, we compiled a global database encompassing 241 studies with species abundance data (from multiple biological groups and geographic locations) across sites with different land-use categories. This compilation will be useful for addressing questions regarding land-use change and its impact on freshwater biodiversity.

Main Types of Variables Contained: The database includes metadata of each study, sites location, sample methods, sample time, land-use category and abundance of each taxon.

Spatial Location and Grain: The database contains data from across the globe, with 85% of the sites having well-defined geographical coordinates.

Major Taxa and Level of Measurement: The database covers all major freshwater biological groups including algae, macrophytes, zooplankton, macroinvertebrates, fish and amphibians.

Salmonid repeat spawners are precious individuals for wild populations due to their high fecundity and previous spawning experience, making them important in environmental policy. However, repeat spawners rarely exist above hydropower dams in regulated rivers as the mortality of post-spawners (kelts) when passing through turbines during downstream migration is very high. To mitigate this problem, there are different technical solutions that potentially guide fish toward available fishways. Bubble barriers represent one alternative to costly physical guiding structures, but the efficiency of bubbles for guiding downstream migrating kelts has not been tested. In this study, we evaluate a 100 m long bubble barrier in guiding salmonids—both smolts and kelts—away from the main current and toward an alternative fishway in Ume River, a large regulated river in northern Sweden. We used both acoustic telemetry and sonar to measure the guiding effect of the bubble barrier for downstream migrating fish. We found that more than twice as many salmonids chose the alternative fishway when the bubble barrier was turned on. This was true both for smolts and kelts, suggesting that bubble barriers can be used to guide salmonids of different life stages in rivers with flow rates over 500 m3 s−1. Indeed, our study indicates that bubble barriers are low-cost structures that could be rapidly applied in many regulated rivers to support salmonid migration. 

Microbes decomposing leaf litter in aquatic ecosystems are exposed to two major sources of carbon (C), namely, particulate organic C (POC) and dissolved organic C (DOC). The use of DOC relative to POC during litter decomposition likely depends on the availability of DOC, which in turn is regulated by the characteristics of the surrounding landscape, although this extrinsic indirect control of DOC use remains largely unexplored. We have investigated how variations in stream physical and chemical characteristics, distribution of major landscape elements (i.e., forest, mires, and lakes), and riparian vegetation community composition (i.e., relative cover of deciduous vs. coniferous tree species) influence DOC use by leaf-associated microbes (LAM). Specifically, in a boreal stream network of ten first- to third-order streams, we related in-stream characteristics, landscape elements, and riparian vegetation community composition to DOC/POC respiration ratios (i.e., the amount of CO2 produced by LAM respiration of DOC + POC divided by the amount of leaf C mass lost through decomposition). The results showed that DOC/POC respiration ratios were > 1 in most of the study sites, indicating that LAM use a substantial amount of DOC during leaf litter decomposition. This microbial reliance on DOC varied with in-stream DOC and nutrient concentrations, proportional mire and forest cover, and riparian vegetation community composition. In particular, high mire and coniferous cover increased DOC use by LAM. As such, landscape configuration and how it is modified by land use and climate change must be considered in order to understand microbial turnover of terrestrial C in boreal streams.

Forest disturbances are expected to increase in severity with climate change and intensified land use, threatening future delivery of several ecosystem services, including the climate-mitigating potential of forests. Alleviating these consequences through adaptive forest management demands a greater understanding of what drives the impacts of disturbances on forests, which, in turn, requires collection of high-quality data through large-scale and long-term monitoring programs. The Swedish National Forest Inventory has been recording “damages” on living trees across a forest area of 230,000 km², in addition to a wide range of stand characteristics and environmental conditions. Using 15 years of these data, we investigated the frequency of different types of tree damages and the causes of these damages and modeled damage risk among tree species and across gradients in stand attributes and environmental conditions. We found that 94% of all surveyed trees had some type of damage, but for 65% of these, the underlying cause was not identified. Nevertheless, for all damage types and causes, we found that damage risk varied considerably among tree species and across gradients in tree species richness, tree height, and stand age. For a few damages, stand age or tree species richness interacted with climate to influence risks. Among identified causes of damage, “wind and snow” was most common (11.9% of surveyed trees), followed by “forestry” (6.9%). Further, for most causes of damage where stand age was significant, the risk was highest in young or the youngest stands. As such, our results indicate that there is great potential for reducing the risk of tree damages via adaptive management, such as altered tree species composition and increased rotation length. However, for a greater understanding of what is driving the frequency and magnitude of forest damages, and to be able to provide specific, useful information to stakeholders, collection of higher-quality data must be prioritized by monitoring programs.

Europe has committed to upscale ecosystems protection to include 30% of land and sea. However, due to historical overexploitation of natural assets, the available area for biodiversity protection is severely limited. Riparian zones are natural ecotones between aquatic and terrestrial ecosystems, contributing disproportionately to regional biodiversity and providing multiple ecosystem functions and services. Due to this and their branching geometry, riparian networks form a vast system of ‘blue-green arteries’ which physically and functionally connect multiple ecosystems over elevation gradients, despite covering a relatively small area of the basin. Hence, RIPARIANET argues that developing approaches able to optimise the spatial conservation of natural stream-riparian networks represent a flagship example of biodiversity protection in the EU. Although the integrity of riparian zones is fundamental for the achievement of multiple EU environmental objectives, the lack of a standardised framework for biodiversity assessment and protection across Member States has led to extensive impairment of riparian areas and frequent stakeholder conflicts.

The main objective of RIPARIANET is to leverage the increasing resolution of remote sensing information to provide practitioners with evidence-based guidance and approaches to biodiversity conservation. Key questions include: i) how can we remotely assess riparian integrity and identify areas which provide effective connectivity allowing species biodiversity and ecosystem functions to persist through meta-ecological processes? ii) how can we disentangle the influence of local- and network-scale stressors and processes on riparian biodiversity to better implement river basin management schemes? iii) to what extent do currently existing protected areas in rivers account for the geometry of riparian networks and their multifunctionality?

We will address these questions in riparian networks within six river basins in Europe, including Boreal, Continental, Alpine, Temperate and Mediterranean systems. First, we will gather local needs and interests from key stakeholders together with satellite imagery and GIS environmental data for all basins. Then, riparian and river ecosystems functions will be modelled and ecological hotspots will be identified through a GIS-based multi-criteria approach, including stakeholder inputs. Then, we will collect in situ data to assess multiple biodiversity and stressors at the local scale and, subsequently, scale-up this information to the network scale using geostatistical tools and advanced modelling. This knowledge will be conveyed to managers at local and EU scales in the form of decision-support tools allowing decision-makers to identify protection gaps and ecological hotspots along riparian networks, based on multiple biodiversity, functional and connectivity criteria.

1. Most stream networks are characterised by spatial and temporal variability in the physico-chemical conditions that regulate microbial processing of particulate organic matter. How these patterns control the turnover of particulate organic matter via altered activity of leaf-associated microbes has rarely been studied in high-latitude landscapes, particularly throughout long (i.e., up to 6 months) ice- and snow-covered periods.
2. We investigated development of fungal biomass, enzyme activity, microbial respiration, and birch leaf litter decomposition from autumn to early summer in 11 nested streams in a boreal catchment that encompass a gradient in wetland (mire) cover.
3. We observed relatively low variability in decomposition rates across the network, despite differences in key physical and chemical variables (e.g. temperature, pH, and dissolved organic carbon [DOC] concentrations) over time and space.
4. Microbial enzymatic activity and respiration were positively related to leaf litter decomposition rates during early stages of decomposition (i.e., up to c. 30% loss of initial ash-free dry mass). Thereafter, variation in microbial activity and respiration was decoupled from leaf litter mass loss, as enzymatic activity and respiration instead became positively related to DOC concentrations and upstream mire (wetland) cover among streams.
5. Our results suggest that leaf-associated microbes increase their reliance on external sources of energy over time. This switch in resource use was more evident in streams with higher DOC concentration, which in boreal landscapes is largely determined by mire cover. Hence, variation in DOC concentration, linked to landscape configuration, or from intensified land use and climate change, could affect how different carbon sources are used by stream microbial communities, with consequences for overall carbon cycling in boreal headwaters.

Structures for guiding fish around migration barriers are frequently used for maintaining connectivity in regulated riverine systems. However, for non-physical barriers, experimental studies providing direct and detailed observations of fish–barrier interactions in rivers are largely lacking. In this study, we quantify the efficiency of bubble barriers (alone or in combination with light stimuli, and in both daylight and darkness) for diverting downstream migrating Atlantic salmon (Salmo salar). Both a laboratory-based migration experiment and a large-scale field experiment in a regulated river were used to evaluate efficiency of bubble barriers. In the latter, we used acoustic telemetry to provide in situ measurements of how downstream migrating Atlantic salmon smolts interact with bubble barriers. We show that bubbles divert smolts with high efficiency in both a laboratory flume (95%) and in natural settings (90%). This latter efficiency is higher compared to an already present physical barrier (46%) covering the upper two meters of the water column in the large river. The bubble barrier did not affect flume migration in darkness, suggesting that visual cues are crucial for the observed repelling effect of bubbles. We conclude that bubble barriers can be effective, largely maintenance free and low-cost alternatives to physical structures currently used to divert salmon away from high-mortality passages.