Reproduction of Crassula helmsii by seed in western Europe

The amphibious plant species Crassula helmsii is a widely established and still-spreading alien in various parts of Europe, where it is considered invasive as its dense swards stress the viability of local biota. The species was considered to exclusively reproduce through vegetative means, until ex situ germination was recorded from a single locality in Belgium. We assessed whether this seed viability holds on a wider scale, by testing 16 populations from The Netherlands, Belgium, northern France, eastern England and northern Germany in a greenhouse germination experiment. Seedlings were observed from all populations but two, and from each of the five countries. Although most fruits were lacking seeds and the inferred germination percentages were overall low, germinable seed numbers are considerable given the high density of flowering stems. An in situ test revealed seeds to make it through normal winter conditions without signs of physical damage and with retention of germinability. Our results suggest that reproduction by seed is a relatively cryptic but widespread phenomenon throughout western Europe. The persistency of seed banks requires further investigation. Nonetheless, these findings already challenge the efficacy of techniques currently applied in C. helmsii control

Cabomba caroliniana Gray (Cabombaceae) invades major waterways in Belgium

Recently, unattached viable stem fragments of the invasive macrophyte Cabomba caroliniana Gray were found at several locations in two canals in northern Belgium. A subsequent survey of the canal Zuid-Willemsvaart revealed one site with rooted plants and the presence of floating stem fragments along the entire length of the canal (25 km). These findings indicate that C. caroliniana is already well established in the Zuid-Willemsvaart and probably considerably more widespread than previous records from isolated lentic water bodies indicate. We have summarised the new records and discuss the potential spread and risks associated with further establishment and spread of C. caroliniana in Belgium

A database of threat statuses and life-history traits of Red List species in Flanders (northern Belgium)

Red Lists estimate the extinction risk of species at global or regional levels and are important instruments in conservation policies. Global Red List assessments are readily available via the IUCN website (https://www.iucnredlist.org) and are regularly updated by (taxonomic) experts. Regional Red Lists, however, are not always easy to find and often use local criteria to assess the local extinction risk of species. Here, we publish a database with the outcome of 38 Red List assessments in Flanders (northern Belgium) between 1994 and 2018. In total, the database contains 6,224 records of 5,039 unique taxa pertaining to 24 different taxonomic groups. Using a quality control procedure, we evaluated the criteria used, the number of records, the temporal and spatial distribution of the data and the up-to-dateness of the Red Lists. This way, nineteen Red Lists were approved as being of sufficient high quality (i.e. validated) and nineteen others were not. Once validated, Red Lists are approved by the regional Minister of Environment and published in the Belgian Official Gazette acquiring legal status. For the validated Red Lists, we additionally compiled (life-history) traits that are applicable to a wide variety of species groups (taxonomic kingdom, environment, biotope, nutrient level, dispersal capacity, lifespan and cuddliness). The publication of this dataset allows comparison of Red List statuses with other European regions and countries and permits analyses about how certain (life-history) traits can explain the Red List status of species. The dataset will be regularly updated by adding new Red List (re)assessments and/or additional (life-history) traits

Past and present distribution of the rare aquatic plant Luronium natans (Alismataceae) in Belgium shows marked decline and bad conservation status

Background and aims – Luronium natans is a rare endemic plant of West- and Central-Europe and protected by the Habitats Directive. The present study gives a comprehensive and up-to-date overview of its past and present distribution in Belgium, which lies within the core area of Luronium natans . Methods – We assessed the distribution by consulting herbaria, literature and databases, and by additional field visits, recording the number of ramets, flowering, general site characteristics and accompanying plant species for extant populations. Key results – The core area of Luronium natans is located in the Campine phytogeographical district, a region with sandy soils in northern Belgium. Overall, it was recorded at c. 250 sites in 155 16 km 2 -squares, with 93 populations occurring since 1980. Field observations show thirty extant populations, all but one in the northern part of the country. Less than half of them are large flowering populations with a good conservation status as far as the species population characteristics are concerned; 30% are located in nature reserves and 70% in Special Areas of Conservation. The number of records decreased since 1985, especially outside the core area. This decline related well to eutrophication, but not to anthropogenic acidification. In general, populations are short-lived and population size fluctuates strongly. Population size correlates with flowering incidence. For one isolated population it appears that the species was introduced with fish. Conclusions – The number of Luronium natans records shows that the Belgian territory accounts for a significant part of its global distribution. There was however a marked decline of records since 1985, especially outside its core area. Moreover, most of the remaining populations are small and have a bad conservation status. They show little or no flowering, which is worrying, considering the alleged importance of sexual reproduction for the survival of the species

Implementing ecological potential of lakes for the Water Framework Directive-approach in Flanders (northern Belgium)

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Gray (Cabombaceae) invades major waterways in Belgium

Recently, unattached viable stem fragments of the invasive macrophyte Cabomba caroliniana Gray were found at several locations in two canals in northern Belgium. A subsequent survey of the canal Zuid-Willemsvaart revealed one site with rooted plants and the presence of floating stem fragments along the entire length of the canal (25 km). These findings indicate that C. caroliniana is already well established in the Zuid-Willemsvaart and probably considerably more widespread than previous records from isolated lentic water bodies indicate. We have summarised the new records and discuss the potential spread and risks associated with further establishment and spread of C. caroliniana in Belgium

A moderate differential effect of organic and conventional agriculture across taxonomic groups inhabiting farmland ponds

Organic agriculture is increasingly promoted as a more environmentally friendly alternative to conventional agriculture, as it restricts the use of fertilisers and synthetic pesticides. However, the impact of both farming systems on aquatic biodiversity is strongly debated. Ponds are abundant in agricultural landscapes and strongly contribute to biodiversity. They also respond strongly to land use on a very local scale. The present study assessed the effects of conventional and organic agriculture on the taxonomic diversity of multiple groups of aquatic organisms at local and regional spatial scales. We conducted a broad scale field survey to quantify the differential impact of conventional and organic agriculture on local environmental conditions in ponds, on community composition and on local, among site and regional diversity of macrophytes, cladoceran zooplankton and selected macroinvertebrates in Belgian farmland ponds (Flanders). We observed that organic agriculture was moderately positively associated with higher local species richness for shoreline vegetation, but not for other organism groups. Only minor differences were observed for among-pond variation, and these were mostly related to rare species of cladocerans and heteropterans. At the regional scale, ponds in organic showed higher species richness than in conventional farmland for shoreline vegetation, emergent vegetation, and cladoceran zooplankton, but lower for coleopterans and gastropods. There was no significant effect of agricultural type on water quality. We conclude that organic farming is associated with moderate positive effects on pond biodiversity and regional species richness of plants and zooplankton. We observed no systematic differences between the two types of agriculture in local environmental conditions in ponds. The absence of large differences in biodiversity and water quality between ponds located in organic and conventional farmland might be related to the dominance of intensive conventional farming in our study region and the history of conventional farming around ponds that are now surrounded by organic farming. Future studies should include other factors such as the structure of the landscape and the role of natural elements such as buffer strips surrounding the ponds