The size structure of populations is crucial for predator–prey dynamics and ecosystem function. Anthropogenic pressures such as habitat alteration may affect the demography of many species. We investigated the size structure of European perch (Perca fluviatilis) populations in lakes before and after dam removal by using the planned removals of multiple dams in the outlets of boreal lakes in central Sweden as a natural experiment. In five lakes from which we had obtained data both before and after dam removal, removal resulted in a reduced abundance of small perch and an increase in body size of large, piscivorous perch, but there was no major effect on perch biomass. In a second comparison of 22 lakes where we only had access to data from either before or after removal, the effects were not as evident. We suggest that a plausible mechanism explaining a potential effect on perch demography was alterations in the predator–prey dynamics caused by changes in refuge habitat area for small fish. Specifically, dam removal caused a reduction of aquatic plant coverage. Large piscivorous fish are known to play a crucial regulatory role in controlling lake ecosystem function. Thus, we suggest that lake outlet dam removal may induce processes leading to positive effects on fish populations and ecosystem state. Moreover, our study emphasises the importance of before versus after studies to evaluate restoration measures. 

Hydropeaking causes unnatural flow and water level fluctuations in the riparian zone. Biological processes in the riparian zone,such as nutrient cycling, are affected by changes in temperature, oxygen, and moisture, which are all to some extent influencedby the water level. Here, we studied the relationship between hydropeaking and decomposition of organic matter in the riparianzone. Specifically, we measured the decomposition rate (k) and decomposition endpoint (the stabilization factor, S), and exam-ined associations between k, S, hydropeaking, and different environmental variables. Decomposition was estimated using theTea Bag Index at 33 sites in Swedish rivers and streams with different degrees of hydropeaking. Rivers and streams were sampledin the summer of 2020 (N = 26) and autumn of 2023 (N = 16), with nine sites sampled on both occasions. In summer 2020, k wasnegatively related to high hydropeaking intensity, but there was no effect of hydropeaking on S. In autumn 2023, there was noeffect of hydropeaking on k or S. Of the other environmental variables tested (substrate grain size, temperature, and length ofgrowing season), the growing season had a positive relationship with S in autumn 2023. Our findings indicate that reducing hy-dropeaking during summer, when biological activity is high, may be beneficial for maintaining riparian function.

Water is an important dispersal vector for seeds of riparian plants, but little is known on how this form of dispersal, called hydrochory, varies throughout seasons and through geomorphically different areas. Therefore, we trapped seeds in 25 x 25 Astroturf mats along a free-flowing boreal river for an entire year. Sites mirrored the full range of geomorphic variation in the area and traps were emptied before and after the annual peak flow. The traps collected 2,062 seeds before the spring flood and 16,157 during the spring flood. While most of the seeds were deposited in the summer-low water traps (from now on "water edge") before the spring flood, they were distributed more equally in the riparian traps (defined as the level 40 cm above the water edge; from now on "riparian zone") during the spring flood. We found 77 species in total, of which 71 were at least recorded during the spring flood. Species numbers were higher at the water edge than at the riparian zone before and during the spring flood. Only 6.6% of the seeds, from 26 species, were viable. Most viable seeds were found in the water edge traps and, during the spring flood, in the riparian zone traps. While species that are primarily dispersed by water were not the most abundant among the viable seeds, they were the most species-rich group. This means that hydrochory is an important dispersal mechanism for riparian vegetation and an important contributor to riparian plant diversity in free-flowing rivers, and that changes in flow regimes, such as by flow regulation, can affect riparian vegetation composition.

In light of the decline of semi-natural grasslands, road verges have become important refuges for grassland plants, benefiting from the management regimes that resemble those of traditional grasslands. However, the value of road verges for grassland plants is threatened by the presence of invasive alien plant species such as Lupinus polyphyllus. Mowing is most effective for controlling invasive plants when the shoot:root ratio is high or when below-ground reserves are exhausted but seeds have not yet matured. The aim of this study was to identify the optimal time for mowing of L. polyphyllus based on the species nutrient dynamics and phenology. We photographed and collected whole lupine plants throughout one growing season, divided them into roots, leaves, and stem + inflorescence, and analyzed each fraction for three growth-limiting, phloem-mobile nutrients (N, P and K). The nutrient contents in roots were lowest during the flowering phase, while the nutrient contents in stems + inflorescences were lowest during the early flowering phase and increased until the seed ripening phase, before declining again in the seed dispersal phase. Leaf nutrient contents showed a general decrease throughout the season. Shoot:root ratios of nutrient contents were also maximized during flowering. Our conclusion is that mowing will weaken L. polyphyllus most when carried out between phenological phases 2 (less than 50% of flowers open) and 4 (more than 50% of flowers withering), with the most optimal timing being during phase 3, i.e., when more than 50% of flowers are open. Concerning the heterogeneity within L. polyphyllus populations, the phenological assessment before management should prioritize individuals that have progressed furthest in their development.

Question

Riparian vegetation and seed banks are the foundation of functional riparian zones, yet insight in the processes that explain their composition is limited. We tested three theories fundamental to dispersal and environmental filtering of riparian seed banks and vegetation. Combining these theories, we expected hydrochory to lead to increased species richness downstream in both soil seed bank and vegetation with accumulation restarting after a lake section, and geomorphological filtering to lead to higher similarity of seed bank and vegetation composition locally and within lakes, slow-flowing sections and rapids, respectively, than between them.

Location

Svartån, a free-flowing river in central Sweden.

Methods

We surveyed riparian vegetation and conducted a germination experiment on riparian soil seed bank cores from lakes, slow-flowing sections and rapids. We combined these with trait data on seed dispersal syndromes, floating capacity of seeds and seed longevity. We analysed differences throughout the system with linear models and between process domains with Kruskal–Wallis tests and similarity in community composition with the Horn–Morisita similarity index.

Results

Our results indicated that species richness did not increase downstream and was relatively similar throughout lakes, slow-flowing sections and rapids for both riparian seed banks and vegetation. Seed floating capacity was similar throughout these river sections, too, and seed longevity was higher in seed banks than in vegetation.

Conclusions

Geomorphology and hydrochory were not as important drivers in this area for riparian seed bank and vegetation composition as expected. In the area and on the scale studied here, other local and regional environmental factors and dispersal syndromes are more likely to be determinants of riparian dynamics and composition. Continued studies of riparian seed banks can help improve our understanding of riparian composition and functioning in the future.

Regularly mown road verges are an important habitat for conservation of grassland vegetation. Disturbance and movement of seed-contaminated soil during road construction and maintenance makes road verges susceptible to the establishment of invasive alien plants such as garden lupine (Lupinus polyphyllus Lindl.). To combat spread of L. polyphyllus via seeds, we tested methods for seed destruction using heat. This study aimed at developing heat eradication methods for dry and imbibed L. polyphyllus seeds applying dry heat (88, 93, 98, 103 C at 1, 3, 5, 10 min) in a laboratory, steam (85, 90, 95 C at 3, 5, 10 min) in a test-box steaming device and (97 C at 10-17 min; dry seeds only) in a stationary soil-steaming machine (S30). In order to speed up water absorption and post-treatment germination, the imbibed seeds were manually scarified before the heat treatment and the dry seeds afterwards. Additionally, germination of two different age seed batches was tested applying dry heat (88, 98 C at 3, 5 min). The results showed that steam treatments inhibited seed germination more than dry heat in both dry and imbibed seeds. Germination dropped to < 5% when steamed at ≥ 90 C or dry-heated at > 100 C. Seed germination decreased with higher temperatures and longer exposure times. Imbibed seeds exhibited lower germination compared to dry seeds for dry and steam heat. Approximately 0.5% of dry seeds germinated when steamed using S30. 2022-collected seeds were less sensitive to dry heat th an seeds from 2020. In conclusion, hot steam is more effective in reducing L. polyphyllus seed germination than dry heat. Thus, to successfully eradicate L. polyphyllus seeds in soil masses, we recommend steaming them at 97 C for at least 10 minutes. 

Road verges can be important habitats for vascular plant communities and the organisms that, in turn, depend on them. However, the plant diversity in Swedish road verges is threatened by the invasive perennial plant Lupinus polyphyllus Lindl. Therefore, this study aimed to investigate the effects of L. polyphyllus on species richness, diversity, and biotic and abiotic characteristics of dissimilar plant communities in road verges. The study was performed in 24 road verges of high nature value (i.e. with high flowering plant diversity) in central Sweden. We selected road verges within two study areas, one dominated by forest (west) and the other by agricultural land (east). In each road verge we established a pair of 1 m2 plots. One plot was dominated by L. polyphyllus while in the other plot L. polyphyllus either had very low occurrences or was completely absent. We investigated whether species richness, effective number of species, and the probability of occurrence of species belonging to three functional groups (based on their competitive ability and affiliation to nutrient rich soil) differed between plots with vs without lupine and if responses varied between the study areas. We found that L. polyphyllus reduced species richness and diversity of plant communities in road verges. However, we found that even though the direction of the effect was similar, the magnitude was strongly dependent on the pre-existing communities. Community composition differed between the study areas. The study area in the west hosted a lower proportion of competitive species typical for nutrient poor soils compared to the east. We conclude that invasion by L. polyphyllus is a serious threat to vascular plant communities but that the response is context dependent. Communities with high abundance of vulnerable and poor competitive plant species should be prioritised for eradication and control of the invasive.

The invasive herb Lupinus polyphyllus has been focus of a number of fact sheets worldwide but a comprehensive summary of the species’ taxonomy and morphology, distribution, habitat requirements, and biology has been lacking. This paper gives a thorough account of the species’ systematic position and taxonomy, highlighting the difficulties to delimit taxa, which is related to interbreeding among members of this genus. However, L. polyphyllus var. polyphyllus is apparently the taxon that has naturalized and is regionally invasive in temperate-humid climates worldwide. We also present an updated distribution map of L. polyphyllus in the native and invaded ranges, which highlights seven regions in the world where the species has been established. We show that the climatic niche of L. polyphyllus in the invaded range shifts towards higher summer precipitation and lower isothermality, probably because the invaded range includes subcontinental regions of eastern Europe and western Siberia. The habitats of L. polyphyllus range from rather dry to wet, have moderately acidic to strongly acidic soils, and the species’ indicator values across Europe suggest that it occurs along a gradient from very nutrient poor sites to intermediate to rich sites from northern to southern Europe. The species shows high resistance to both drought and frost. In Central Europe, the species has a stronghold in alpic mountain hay meadows, abandoned meadows and pastures, low and medium altitude hay meadows, anthropogenic herb stands and temperate thickets and scrubs. In northern Europe, the species occurs in anthropogenic herb stands along roads and railroads as well as in abandoned pastures and fields. We also found some doubtful information about L. polyphyllus in the literature. This refers to its description as “rhizomatous perennial” although it lacks rhizomes; an apparently very high longevity of its seeds, which may only be true under artificial conditions in an ex situ seed repository; and a very deep rooting depth, which may not represent the average rooting depth but rather an extreme value. Knowledge about the interrelationships between the species’ future population dynamics and spread and ongoing climate warming is lacking. Finally, our review points out that there is currently no evidence-based strategy for a cost-efficient management of L. polyphyllus although it is among the most problematic non-native plant species in Europe due to its environmental and socio-economic impacts. 

Photo observations are a highly valuable but rarely used source of citizen science (CS) data. Recently, the number of publicly available photo observations has increased strongly, for example, due to the use of smartphone applications for species identification. This has enabled the raising of ecological insights in poorly studied subjects. One of the fields with the highest potential to benefit from the use of photo observations is phenology. We propose a workflow for iPhenology, the use of publicly available photo observations to track phenological events at large scales. The workflow comprises data acquisition, cleaning of observations, phenological classification and modelling spatiotemporal patterns of phenology. We explore the suitability of iPhenology to observe key phenological stages in the plant reproductive cycle of a model species and discuss limitations and future prospects of the approach using the example of an invasive species in Europe. We show that iPhenology is suitable to track key phenological events of widespread species. However, the number and quality of available observations may differ among species and phenological stages. Overall, publicly available CS photo observations are suitable to track key phenological events and can thus significantly advance the knowledge on the timing and drivers of plant phenology. In future, integrating the workflow with automated image processing and analysis may enable real-time tracking of plant phenology.

Semi-natural grasslands invaded by the legume Lupinus polyphyllus need the introduction of target species in order to promote highly endangered native target plant communities. However, which techniques are best suited to achieve both invader control and the introduction of target species at the same time? Few studies have investigated restoration techniques that support native plant communities in mountain meadows and control the invader simultaneously. We employed the restoration techniques seed bank activation and green hay transfer in combination with manual removal of the invasive L. polyphyllus on three types of grassland (Nardus grassland, mesic and wet mountain hay meadows) in the low mountain ranges of the Rhon UNESCO Biosphere Reserve in central Germany. Vegetation reacted differently to specific measures depending on the type of grassland. L. polyphyllus cover could be effectively reduced by L. polyphyllus removal in Nardus grassland and mesic hay meadow sites, but not in wet meadows. In Nardus grassland, the cover of target species was lowered by the application of green hay. The target species cover of wet mountain hay meadows declined in response to seed bank activation. When restoring mountain meadows, restoration practitioners should thus first consider the specific vegetation types. As our study indicates that target mountain meadow species may react negatively to restoration measures in the short term, the long-term effects of the application of green hay should be studied.