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Luxembourg Kirchberg Arboretum

Volume 3 Number 5 - December 2000

Thierry Helminger

The Kirchberg Arboretum Project was initiated in 1994 in the newly created public parks of the Kirchberg quarter. This part of Luxembourg City is situated on the sandstone plateau across the river Alzette, only half a kilometre to the east of the City Centre. The 360 ha, (890 acres) were traditionally used as farmland and were not really accessible from the City until the Pont Grand Duchess Charlotte commonly called the ‘Red Bridge’ was built in 1963.

The construction of the ‘Red Bridge’ has allowed the development of the Kirchberg plateau to provide the administrative buildings of the emerging European institutions. The area is reached by a tree-lined road, the buildings are concentrated together, a new concept of rainwater treatment is integrated in the landscape planning and some 65 ha (60 acres) of green lands are reserved for public parks. The idea of creating an Arboretum in parts of these green zones was first discussed in 1991 by the Fonds d’Urbanisation et d’Aménagement du Plateau de Kirchberg, the public fund created in 1961 to develop and urbanize the Kirchberg plateau.

The Arboretum Sites

According to the plans of Prof. Peter Latz from Munich, Germany, the creation of an arboretum could link the urban green zones to the surrounding woods, which would enhance their value and create another attraction for the new quarter. The Arboretum consists of three main sites extending like a green backbone across the Kirchberg Plateau. Both Park Réimerwee and Central Park extend along the remains of the ancient roman road that led from Reims to Trier. Park Réimerwee is a light woodland with grassy openings.

The Central Park in between the National Sports Centre and two school buildings is more of a leisure park and displays a collection of ornamental Rosaceae trees. A small hill, Little Kirchberg in the Central Park offers a view to both sides of the roman road, with Central Park on one side and Parc Réimerwee on the other side. The Park Klosegroendchen is a landscaped park with modeled sand dunes and three large spiral-formed holding basins to keep the rainwater from flowing downhill all at the same time.

Rainwater Treatment

An important part of the new urbanizing and landscaping concept is the treatment of superficial rainwater. In the past water used to drain directly into the underground sewage and the wastewater channels. Now, on the plateau of Kirchberg these waters are used above ground as an attractive element to enhance the landscape. In the new European school in the Central Park, the water is led through open ditches, planted with attractive marshland plants, where it is partly cleared into holding ponds. These ponds, are made water tight with bentonite mats, are permanently filled and have a large surrounding area which only becomes flooded in heavy rains.

Scientific Support and Theme of Collections

For scientific assistance for the Arboretum project, collaboration with the Museé National d’Histoire Naturelle has been sought from the beginning. The Museum will manage the arboretum collections in the long term, lead research projects and develop educational activities in the Arboretum. With Luxembourg being a European Capital, and the Kirchberg housing the administrative buildings of the European institutions, it was only natural to give the Kirchberg Arboretum a European focus. Thus the theme of the collections is Trees and shrubs of Europe and adjacent regions, including the wild-relatives of domesticated trees and shrubs.

Multilingual Labeling

To further enhance the European focus and as Luxembourg is a multilingual country, the labelling is in four languages, apart from the scientific name, the family and the distribution in the wild; our labels show the name in Luxembourgish, German, French and English.

The Collections

The collections only include species hardy in the open ground. A list of more than 650 species has been compiled. At present, there are 382 taxa from 109 genera and 53 families in the collections. The most represented genera are Fagus, Juniperus, Quercus, Brooms (Cytisus, Genista, Ulex, Spartium) Salix and Rosa.

The aim is to acquire a collection of plants of known wild origin. About 55% of the accessions are of known wild or garden provenence obtained through seed exchange with other gardens. However, less than 10 % of the plants have a known provenence (other than the nursery which provided the plants) because the large newly created Arboretum had to be planted quickly (the outside slope for noise protection has some 12,000 plants) to give the parks a structure, whereas the propagation of plants from seed of known provenence has given rise to only a few plants.

There have been 1059 attempts at propagation from 1995 to 1999. Of these some 40 % were successful, which resulted in 4155 plants. To keep track of the plants and the related data on provenence, planting and care the relational database BG-BASE is used.

Park Réimerwee

Park Réimerwee consists of wooded blocks of oak, beech and pine, separated by openings of grassland with solitary oaks and beeches. The original planting of the area dates from the 1960s when the grounds were still managed by the forestry department. Considering the existing beech and three oak species, a Fagaceae collection was started, which has increased to some 23 oak taxa and four beech species as well as 26 variations of the common beech. In order to show different growth forms, some of the oaks have been planted both as solitary trees and as block plantings.

Park Klosegroendchen

The sand dunes of park Klosegroendchen have been modeled with the excavations from the building of the eastern ring motorway of Luxembourg City. The material was used as it was, a mixture of sand, stones and sometimes clay from the deeper layers. There has been no amelioration of the substrate. The vegetation concept of the sand dunes is to obtain a steppe-like grassland with intermittent ‘islands’ of appropriate shrubs and trees. In order to fix the slopes, an initial sowing was done with Italian Ryegrass. Into this was sown a seed mix with Corynephorus canescens and Festuca ovina together with some flowering plants. On the northern slopes of the dunes the collections of junipers, brooms and others have been planted in diagonal rows. On the two largest dunes the shrubs are associated according to a natural phytosociological association of sandy soils.

Another attractive part of the Klosegroendchen Park consists of the three spiral-formed holding basins. They have been planted in the marsh zone with sedges, lilies and other marshland plants. Along the drains joining the basins stands a collection of different willow species. Terraces with wild fruit trees cut the slope along the bordering road.

Central Park

The Central Park, which is still under construction, also has its own holding basin with a water curtain (see illustration). In order to increase the oxygenation of the water, it is pumped to a higher basin and comes flowing back through the pipe you see hanging above the basin. This pipe has overflow holes at regular distances. The whole thing looks like a shower and makes a curtain, bordered by an open air amphitheatre. Due to the closeness of the sports and educational institutions, the park consists mostly of open meadows with larger trees. One of these meadows has been planted with more than 200 over 30-year-old trees that had been on the construction area. Other meadows hold a collection of ornamental Rosaceae trees and an Ailanthus square.

Rare and Threatened Shrubs of Luxembourg

The Arboretum has a research and conservation project on the rare and endangered trees and shrubs of Luxembourg. The aim of this project is to gather up-to-date information on the conservation status of these plants, to contribute to the seed bank of endangered plant species, create an ex situ conservation collection and make an active contribution to the in situ conservation of indigenous trees and shrubs. The Red Data Book of vascular plants of Luxembourg (Colling & Reichling, last update Apr. 1999) lists 24 tree and shrub species (revised IUCN categories (1994): (EW - extinct in the wild (1), CR - critically endangered (10), EN – endangered (5), VU – vulnerable (2), LRlc – Lower Risk least concern (3), R - extremely rare (3). The status of 8 more species, which until now have not been considered endangered, should be revised. Unfortunately we have very little current field data on many of these species. Most of the recorded observations date from the fifties and sixties. The first step will be to check these ancient sites in order to update the distribution maps, starting with the most endangered categories (CR and EN).

Seed Bank

The second step, which can be started simultaneously, will be to collect seed from existing populations. These seeds will be conserved in the seed bank of endangered plants, which has been started at the Natural History Museum. Some of the seed will be propagated in the nursery using different methods of propagation to obtain optimum results. A common threat to some populations of threatened species is their being over-aged e.g. Juniperus, a situation that according to literature is widespread throughout Europe. So the aim of propagation will not only be to get some original Luxembourgish plants for our collections, but to provide young plants that can be reintroduced in their original location.