The distylous plant Primula veris has long served as a model species for studying heterostyly, that is the occurrence of multiple floral morphs within a population to ensure outcrossing. Habitat loss, reduced plant population sizes, and climate change have raised concerns about the impact of these factors on morph ratios and the related consequences on fitness of heterostylous species. We studied the deviation of floral morphs of P. veris from isoplethy (i.e. equal frequency) in response to plant population size, landscape context and climatic factors, based on a pan-European citizen science campaign involving observations from 28 countries. In addition, we examined the relative frequency of morphs to determine whether landscape and climatic factors disrupt morph frequencies or whether a specific morph has an advantage over the other. Theory predicts equal frequencies of short-styled S-morphs and long-styled L-morphs in populations at equilibrium. However, data from >3000 populations showed a substantial morph deviation from isoplethy and a significant excess of S-morphs (9% higher compared to L-morphs). Deviation of morph frequency from equilibrium was substantially stronger in smaller populations and was not affected by morph identity. Higher summer precipitation and land use intensity were associated with an increased prevalence of S-morphs. Five populations containing individuals exhibiting short homostyle phenotypes (with the style and anthers in low positions) were found. Genotyping of the individuals at CYP734A50 gene of the S locus, which determines the length of the style and the position of anthers of P. veris, revealed no mutations in this region. Our results based on an unprecedented geographic sampling suggest that changes in land use and climate may be responsible for non-equilibrium morph frequencies. This large-scale citizen science initiative sets foundations for future studies to clarify whether the unexpected excess of S-morphs is due to partial intra-morph compatibility, disruption of heterostyly or survival advantage of S-morphs. Synthesis. Human-induced environmental change may affect biodiversity indirectly through altering reproductive traits, which can also lead to reduced fitness and genetic diversity. Further research should consider the possible role of pollinators in mediating the ecological and evolutionary consequences of recent landscape and climatic shifts on plant reproductive traits.

Large solitary trees (LSTs) represent important wood volumes and carbon stocks outside forests. However, quantification remains difficult as most allometric relationships have been developed using trees in forests. Here, we explore the volumetric assessment of aboveground woody biomass of LSTs outside forests and compare them to forest trees. Using terrestrial laser scanning, we captured detailed 3D point clouds of 215 solitary trees for three widely distributed species, i.e. Quercus robur, Tilia sp. & Fraxinus excelsior, across nine cities in temperate Europe. Leaf-off lidar point clouds were processed using a quantitative structure model (QSM) to estimate the aboveground volumes and develop new species-specific allometric volume equations for solitary trees. Our findings show that the woody volumes of LSTs estimated by QSMs are, on average, 83 % higher than those predicted by species-specific allometric equations tailored to forest trees of similar height and diameter at breast height. To validate this discrepancy, we applied the same laser scanning and modeling methods to both LSTs and forest trees. Regression analysis confirmed that LSTs have significantly greater woody volumes than forest trees. However, this difference diminishes with increasing height, resulting in converging volumes in the tallest height class. Our results highlight the substantial carbon storage and wood volume potential of LSTs in both urban and rural areas, and underpin the urgent need for dedicated allometric volume equations tailored specifically to large solitary trees.

Habitat fragmentation increases the proportion of forest borders in the landscape and many forest borders lose their structural complexity due to modern forestry practices. However, remnants of structurally complex deciduous forests can remain as ecotones between plantations and agricultural fields. In this study we used terrestrial laser scanning to measure structural complexity of different forest borders, measured microclimate, and surveyed bats and macro-moths to understand how these taxa are affected. Our aim is to disentangle the main drivers, direct or indirect, that influence bat and moth assemblages. We studied 79 forest borders, and surrounding landscapes and compared them with adjacent agricultural fields and coniferous plantations. Overall, we found less bat activity and lower macro-moth diversity in simple compared to complex borders. Using structural equation modelling, we show the contrasting responses of forest-specialist bats and moths to structural complexity; with bats responding positively and moths negatively. We found similar divergent results in relation to understorey openness; with increasing forest-specialist bat activity but a lower diversity of forest-specialist moths in more open borders. Understorey vegetation also appears to regulate microclimate with more open borders being warmer and less humid. This has a potential knock-on effect for bats as they favoured borders that were warmer and more humid. Surrounding land-cover was more important than structural complexity for generalist species; with increasing generalist bat activity due to a higher proportion of local deciduous forest cover and increasing generalist moth diversity in landscapes with more forest borders. Overall, these complex relationships between forest structure, microclimate and landscape factors, coupled with divergent responses of both taxa highlight their diverse ecological needs. Therefore, we highlight the importance of managing forest borders to retain complexity and connectivity within multifunctional landscapes.

Sympatric bat species can co-exist and avoid interspecific competition via niche differentiation e.g. diet. Detecting dietary differences can be achieved by comparing dietary niches of sympatric and allopatric populations. If dietary overlap is higher in sympatry versus allopatry, co-occurrence may be altering the dietary niche of the species. Our study region offers an excellent opportunity to investigate this because two species, Eptesicus nilssonii and Pipistrellus pygmaeus, occur sympatrically across southern Sweden and E. nilssonii occurs allopatrically in the north. We analysed droppings from 19 roosts during two months: six P. pygmaeus, seven E. nilssonii located in the known distribution of P. pygmaeus (sympatric) and six roosts located outside the known range of P. pygmaeus (allopatric). We used DNA metabarcoding to assess dietary overlap and dietary niche breadth in both species. We found a high dietary overlap between E. nilssonii and P. pygmaeus at all taxonomic levels of prey. The dominant prey orders in the three bat populations were Ephemeroptera (mayflies) and one Diptera species (cranefly); five species from these orders accounted for > 70% of all reads. When using quantitative relative read abundance data at the species level interspecific overlap was higher than intraspecific overlap. We find a consistent but not significant pattern that E. nilssonii populations co-occurring with P. pygmaeus have the narrowest dietary niche breadth. This could indicate that the co-occurrence with P. pygmaeus is having an impact on prey selection for sympatric E. nilssonii populations. However, confirming competition between these species would require sampling of the insect population near to the colonies. Both bat species' diets are also heavily dominated by only five species. These are all currently common insect species and most likely indicates opportunistic foraging on abundant insect populations.

As droughts become longer and more intense, impacts on terrestrial primary productivity are expected to increase progressively. Yet, some ecosystems appear to acclimate to multiyear drought, with constant or diminishing reductions in productivity as drought duration increases. We quantified the combined effects of drought duration and intensity on aboveground productivity in 74 grasslands and shrublands distributed globally. Ecosystem acclimation with multiyear drought was observed overall, except when droughts were extreme (i.e., ≤1-in-100-year likelihood of occurrence). Productivity losses after four consecutive years of extreme drought increased by ~2.5-fold compared with those of the first year. These results portend a foundational shift in ecosystem behavior if drought duration and intensity increase, from maintenance of reduced functioning over time to progressive and profound losses of productivity when droughts are extreme.

Prolonged drought is a major stressor for grassland ecosystems. In addition to decreasing plant productivity, it can affect soil microbial activities and thus destabilize nutrient cycling and carbon (C) sequestration. Soil organic amendments (OAs), such as compost, can be used to enhance soil fertility and mitigate drought effects. In this study, we evaluated the responses of fungal and bacterial communities to a 3-year-long experimental drought and compost treatment across four soil depths in two Swedish grasslands and at an upper and a lower topographic position. Results showed that while drought reduced soil moisture and compost amendment increased C content in the topsoil,the effects on microbial abundance and community composition within this time frame were weak, and detectable only in the topsoil. Fungal abundance increased with compost addition, which also affected community composition, while fungal communities were resistant to drought. Bacterial communities were not significantly affected by any of the treatments. This suggests that microbial ecosystem functions were resistant to the experimentally reduced precipitation. Overall, variation between sampling sites was more important for microbial community composition than treatments, highlighting the need for a better understanding of small-spatial-scale environmental controls on soil microbial and plant communities and their ecosystem functions.

Soils are the largest terrestrial carbon (C) pool on the planet, and targeted grassland management has the potential to increase grassland C sequestration. Appropriate land management strategies, such as organic matter addition, can increase soil C stocks and improve grasslands' resilience to drought by improving soil water retention and infiltration. However, soil carbon dynamics are closely tied to vegetation responses to management and climatic changes, which affect roots and shoots differently. This study presents findings from a 3-year field experiment on two Swedish grasslands that assessed the impact of compost amendment and experimental drought on plant biomass and soil C to a depth of 45 cm. Aboveground biomass and soil C content (% C) increased compared with untreated controls in compost-amended plots; however, because bulk density decreased, there was no significant effect on soil C stocks. Experimental drought did not significantly reduce plant biomass compared to control plots, but it stunted the increase in aboveground biomass in compost-treated plots and led to changes in root traits. These results highlight the complexity of ecosystem C dynamics and the importance of considering multiple biotic and abiotic factors across spatial scales when developing land management strategies to enhance C sequestration.

Most insect pollinators are ectothermic and rely on external heat sources for temperature regulation. Forests, with their diverse canopy structures and sunlight penetration levels, create a mosaic of microclimates influencing these insects' behaviour. This study examined how macro- and microclimatic temperatures, precipitation, forest structure, and flower resources affect pollinator activity in the understory of two Swedish mixed forests using a combination of artificial flower stations, time-lapse pictures, and high-resolution climate data. Diptera was the most abundant order of flower visitors, with Muscidae, Phoridae and Syrphidae being the most recorded families. Our results show that macroclimate was the main driver of flower visitation rates, while microclimatic conditions better predicted foraging time. Based on our models, forest fly pollinators increase their flower visitation rates within a narrow temperature window. Thus, we anticipate that the effects of rising temperatures due to climate change on flower visitation rates by insects will largely depend on baseline temperature. Additionally, temperature appears more important than changes in other macroclimatic variables such as rain. Precipitation reduced pollinator visits, and pollinators increased their activity with time since the last rainfall. Forest density negatively impacted pollinator presence, with effects varying by pollinator group and species, but suggesting that increasing canopy openness could enhance pollinator habitats and support biodiversity. Higher flower species richness decreased visitation rates but extended pollinator foraging time in some cases. Conversely, abundant wildflowers increased pollinator visitation rates but reduced their overall foraging time, probably due to competition. Our study highlights the complex relationships that occur between forest structure, climate, flower resources, and pollinator activity. Understanding species-specific responses to forest composition and understory vegetation can guide tree species selection in afforestation or reforestation projects to support diverse pollinator communities, ultimately informing effective conservation and forest management practices to maintain healthy pollinator populations and ecosystem resilience under a changing climate.

1. Urban areas can support diverse communities of plants and animals. Yet, urbanisation can affect functionally important species traits, potentially impacting population dynamics.
2. The saproxylic beetle Elater ferrugineus L. is associated with large trees and is often used as an indicator of species-rich saproxylic communities. It is an important target for conservation and it is listed as a near-threatened species on the European Red List.
3. Few studies have quantified the impact of urbanisation on the ecology and intraspecific variation in functional traits of arthropods, other than pollinators.
4. We studied how the local abundance of E. ferrugineus and functionally important response traits (e.g., width of the pronotum, length of the elytron and wing, wing area, body mass and wingload) changed along urbanisation gradients in eight European cities using pheromone traps installed on large solitary trees.
5. We analysed the effects of the surrounding built-up area and tree cover on our response variables while accounting for potential confounding effects due to tree size and the availability of microhabitats.
6. Urbanisation had a strong negative effect on the local abundance of E. ferrugineus, while the amount of tree cover had a positive influence.
7. We found no significant impact of urbanisation on the functional traits of this species, except for a significantly higher wingload in city centres.
8. Our results provide a better understanding of the ecological processes impacting this saproxylic beetle and underpin the importance of future research on urbanisation's impact on arthropods.

Anthropogenic biodiversity decline threatens the functioning of ecosystems and the many benefits they provide to humanity. As well as causing species losses in directly affected locations, human influence might also reduce biodiversity in relatively unmodified vegetation if far-reaching anthropogenic effects trigger local extinctions and hinder recolonization. Here we show that local plant diversity is globally negatively related to the level of anthropogenic activity in the surrounding region. Impoverishment of natural vegetation was evident only when we considered community completeness: the proportion of all suitable species in the region that are present at a site. To estimate community completeness, we compared the number of recorded species with the dark diversity—ecologically suitable species that are absent from a site but present in the surrounding region2. In the sampled regions with a minimal human footprint index, an average of 35% of suitable plant species were present locally, compared with less than 20% in highly affected regions. Besides having the potential to uncover overlooked threats to biodiversity, dark diversity also provides guidance for nature conservation. Species in the dark diversity remain regionally present, and their local populations might be restored through measures that improve connectivity between natural vegetation fragments and reduce threats to population persistence.