Tree species effects on herb layer development in post-agricultural forests

The forest cover in Flanders and many similar lowland regions has been subjected to many land use changes in previous centuries. Especially on fertile loam and sand loam soils, the forest cover has been declining rather continuously. Only in the last decades, fertile agricultural land has been afforested for biodiversity conservation and other objectives. These so called post-agricultural forests have, however, strongly altered soil characteristics, especially elevated phosphorus (P) levels. The elevated P concentrations cause a strong increase in growth of competitive species, like Urtica dioica L.. While, stress tolerant species like many forest plant species, show only a limited response in growth. Many forest plant species, so called ancient forest species (AFS), are predominantly present in sites with a long and continuous forest land use due to their limited colonisation capacity of recent forest. It concerns a large group of species and consequently they are important for the functional and taxonomic biodiversity of the herb layer of forests. The colonisation of AFS in post-agricultural forests can thus be considered as a bottleneck for forest restoration. In this thesis, tree species effects on the colonisation of AFS are studied in post-agricultural forests. Tree species are known to have a strong impact on soil characteristics, light transmittance and understory vegetation. It is hypothesized that increased shade levels will suppress competitors and facilitate the colonisation of AFS while acidifying tree species will strongly limit the survival of many AFS. The thesis comprises an observational vegetation study and four different experiments focusing on tree species effects on AFS. The vegetation study showed a diverging vegetation development in a chronosequence with two contrasting tree species, i.e. poplar and oak. This is explained by the quick soil acidification under oak compared to stable near neutral pH under poplar. No difference was found in the cover of forest plants, but oak had mainly acid tolerant forest plants while poplars had more acid intolerant forest plants. For the first experiment six AFS were introduced under eight different tree species in a common garden. The survival of the introduced AFS was limited by soil acidifying tree species while growth of these AFS was higher under tree species with low light levels. Temporary canopy gaps promoted the establishment of AFS. In a sowing experiment, germination and recruitment of both acid tolerant and intolerant species was higher under tree species with higher soil pH. However, competitive species from the seed bank also germinated more numerously by higher pH. In another sowing experiment, recruitment showed to be independent for early and late leafing out shrub species. However, four out of seven species showed higher recruitment in shaded versus non shaded treatment. In a final experiment, tree species induced soil acidification is linked to decreasing plant Ca and P concentrations and increasing Mg and Al shoot/root ratios, likely explained by Al antagonism. A potential interaction between light availability and soil acidification effects was not found in the various experiments. The results lead to the conclusion that tree species are indeed important drivers of the understory development in post-agricultural forests. This tree species effect can be explained by their impact on soil acidification and understory light availability. Dark stands suppress the competitors and facilitate the vegetative colonisation of many AFS. Temporary canopy gaps seem to facilitate recruitment of AFS. However, it is important that gaps close quickly enough to prevent competitors from establishing. The recruitment and survival of acid intolerant AFS is strongly limited to moderately acidifying tree species. In the concluding chapter, a simple framework is proposed to evaluate tree species effects based on light transmittance and soil acidity. It is concluded that topsoil is best kept clearly above pH-H2O 4.2 and light transmittance below 8% of the open field for the optimal recovery of AFS

Reappearance of old growth elements in lowland woodlands in northern Belgium : do the associated species follow?

The forest cover of the western European lowland plain has been very low for centuries. Remaining forests were intensively managed, and old-growth elements like veteran trees and coarse woody debris became virtually absent. Only over the last decades have these old-growth elements progressively redeveloped in parks, lanes and forests, and have now reached their highest level over the last 500-1000 years. Biodiversity associated with these old-growth elements makes up an important part of overall forest biodiversity. The ability of species to recolonise the newly available habitat is strongly determined by limitations in their dispersal and establishment. We analyse the current status and development of old-growth elements in Flanders (northern Belgium) and the process of recolonisation by means of specific cases, focussing on saproxylic fungi and saproxylic beetles. Our results show that 'hotspots' of secondary old growth, even isolated small patches, may have more potential for specialised biodiversity than expected, and may provide important new strongholds for recovery and recolonisation of an important share of old-growth related species

Phylogeographic structure and ecological niche modelling reveal signals of isolation and postglacial colonisation in the European stag beetle

Lucanus cervus (L.), the stag beetle, is a saproxylic beetle species distributed widely across Europe. Throughout its distribution the species has exhibited pronounced declines and is widely considered threatened. Conservation efforts may be hindered by the lack of population genetic data and understanding of the spatial scale of population connectivity. To address this knowledge gap this research details the first broad scale phylogeographic study of L. cervus based on mitochondrial DNA (mtDNA) sequencing and microsatellite analysis of samples collected from 121 localities across Europe. Genetic data were complemented by palaeo-distribution models of spatial occupancy during the Last Glacial Maximum to strengthen inferences of refugial areas. A salient feature of the mtDNA was the identification of two lineages. Lineage I was widespread across Europe while lineage II was confined to Greece. Microsatellites supported the differentiation of the Greek samples and alongside palaeo-distribution models indicated this area was a glacial refuge. The genetic endemism of the Greek samples, and demographic results compatible with no signatures of spatial expansion likely reflects restricted dispersal into and out of the area. Lineage I exhibited a shallow star like phylogeny compatible with rapid population expansion across Europe. Demographic analysis indicated such expansions occurred after the Last Glacial Maximum. Nuclear diversity and hindcast species distribution models indicated a central Italian refuge for lineage I. Palaeo-distribution modelling results also suggested a western refuge in northern Iberia and south-west France. In conclusion the results provide evidence of glacial divergence in stag beetle while also suggesting high, at least on evolutionary timescales, gene flow across most of Europe. The data also provide a neutral genetic framework against which patterns of phenotypic variation may be assessed.</div

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

A protection strategy for the stag beetle (Lucanus cervus, (L., 1758), Lucanidae) based on habitat requirements and colonisation capacity

Some of the threatened Belgian populations of the stag beetle are found in a suburban context near Brussels. In this study, a protection strategy is selected based on modelling of the capacity to colonise habitat patches. The habitat requirements were studied and we found that the stag beetle inhabits open woody habitat on steep south-exposed slopes. Two different maps, one with suitable and one with potential habitat were created based on these requirements. Colonisation of habitat patches was modelled to detect best practice for creating corridors between isolated populations and nearby forests. Our results showed that stag beetle colonisation over a period of about 30 years does not exceed a radius of about 1 km. This means that a strategy is required which focuses on in situ protection and the creation of suitable habitat in nearby receptor sites, such as parks

Applying species distribution modelling for the conservation of the threatened saproxylic stag beetle (Lucanus cervus)

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Distribution of Lucanus cervus (Coleoptera: Lucanidae) in Belgium: surviving in a changing landscape

This paper describes results updating the former and present distribution of the stag beetle in Belgium. Based on these data, modelling of the distribution was conducted through land use, climatic and topographic parameters in order to identify areas corresponding to the requirements of the species. The habitat and ecological needs of the species in Belgium are described and discussed