Scientific research

Monitoring in the nature reserves

We carry out phytosociological studies in order to analyse the evolution of the vegetation in the nature reserves of the Sonian Forest. This is done by using sample plots (permanent plots, Braun-Blanquet relevés and related methods) and multivariate analyses.

Species mapping

The distribution of indicator plant species is mapped at a fine scale over the whole Brussels part of the Forest (1660 ha), according to a grid of 50x50m˛-grid cells (up to now more than 30,000 data over 6400 grid cells). The data are incorporated in a data bank in a GIS environmental (Arc View).

Digitising archives data

Ancient distribution maps (own data or maps of Rogister 1978) of indicator species in the Brussels Sonian Forest (1660 ha) are digitised and a data bank is built up in a GIS environment (Arc View). Up to now, we compared the actual and the former (14 years ago) distribution of some disturbance species (e.g. Carex remota, Juncus effusus, Rubus fruticosus and Urtica dioica). Chi-square tests are used to examine whether the progression or the regression of these species is significantly related to forestry parameters (stand diversity and structure).

Forest management and the herb layer

On the basis of the data bank that is currently under construction (up to now 30,000 data over 6400 grid cells), we examine if the development of the herb layer is correlated with the dominant tree species, stand diversity, stand structure and stand age.

Forest paths

The vegetation which develops around forest paths (closed to public motor vehicles) is also accurately described in the Sonian Forest. The main purposes of this investigation are: (1) to analyse how far into the forest stands, paths have an influence on the surrounding plant species composition; (2) to acquire more specific information on the particular effect of some types of surfacing materials; and (3) to assess the impact of a dense path network on nature conservation in a large peri-urban forest.

Microclimatic gradients

The vegetation and microclimatic gradients are also analysed in some clearcuts of the Sonian Forest. The objectives of this study are: (1) to investigate whether, within clearcuts, microclimate gradients are detectable; and (2) to test for correlations between plant species composition and microclimatic heterogeneity, to determine which aspects of the microclimate might influence vascular plant composition in the clearcut environment. In order to test these hypotheses, we measure the air and soil temperatures, air humidity and light intensity along transects across clearcuts. Generalised Additive Models (GAM) are used to determine the response of herb species to microclimatic variables.

Indicator species

Floristic surveys are carried out to identify indicator plant species in the herbaceous layer, which could be used as an aid within the framework of a more sustainable management of the forest. Criteria of habitat quality that have been chosen are the species richness, the rarity of the habitat, based on constitutive species, and its invasibility (vulnerability for invasion). On basis of a comparison of the value of these criteria when each considered (potential indicator) species is present or not, several species can been recognised as reliable indicators of at least one of these three criteria.

Forest fragmentation and edge effect

The plant species composition of forest patches in the Brussels area are inventoried in order to analyse the influence of the patch surface, patch shape and their spatial distribution in an urban environment. We also study the edge effect in order to understand the influence of the city-forest ecotone.

Tree health status

In the Sonian Forest, it is not rare to meet healthy beeches near more or less degraded ones, and this under apparently identical habitat conditions (soil type, topography). The health status of beech and oak is therefore very variable and spatially heterogeneous. Using only point measurements on the field will not reflect this spatial variability. For this reason we use remote sensing (hyperspectral images from the CASI sensor) which is here superior for recording the spatial distribution of tree health status throughout the 4000 ha of the forest.

Soil compaction

We also model the response of herb species to soil degradation, e.g. soil compaction. The main objectives of this research project are: (1) to develop tools in forestry; (2) to emphasise the deleterious effects of soil compaction on the species composition of the herb layer.

Invasive species

The relationships between the invasive success and the habitat type of some invasive species, such as Prunus serotina and Impatiens parviflora, are also studied in the Sonian Forest. This is done with the help of a rather big number of vegetation samples and environmental variables. The aim is to get a better understanding of the ecological behaviour of these species in order to avoid or to limit further invasions.

Seed bank

To test whether the management type has an impact on the seed bank (seeds and spores), we examine the composition, density and distribution of the buried soil seed bank under different overstory types (beech, oak and pine). The main objective is to determine which stand types are the best for an optimal conservation of valuable forest herbs.