De Levende Natuur nummer 4 van 2012 (English summary)


DLN 2012-4

Repair of road margins with botanic value in the North East Polder

L. van Kemenade, P. Bremer, E. de Boer & T. van Veen

The roadside verges in the eastern part of the North East Polder, in the region Flevoland in The Netherlands, used to have a high botanical value from 1950 up to the 1980’s. The soil in the roadside verges consists of fine sand that is calcium-rich due to the presence of shells. These circumstances are rare in The Netherlands and allowed rare dune valley species like Grass of Parnassus (Parnassia palustris), Marsh Helleborine (Epipactis palustris) and Allseed (Radiola linoides) to grow alongside the road. Until late in the 1980’s large parts of the road margins in the project area were covered with vegetations rich in flowers, such as Yellow Rattle (Rhinanthus minor), Fairy Flax (Linum catharticum), en Eyebright (Euphrasia stricta).

In the 1990’s most of this botanic wealth had faded. This was due to the fact that after 1990 the local farmers were no longer obligated to mow the roadside verges adjacent to their fields and to remove the cut grass. As a result the cut grass and slush from the ditches were left to decay on the roadside verges, or they weren’t cut at all.  Several of the roadside verges were raised with a layer of clay. All this resulted in a high productive and species-poor vegetation.

In 1999 Landschapsbeheer Flevoland, a NGO in countryside and urban nature management, started a project to repair the damage and reclaim the former valuable vegetation. The nutrient-rich topsoil was removed, and the vegetation was cut twice a year and the cut grass removed. Soon, the road margins started to regain their botanical value. The first plants that reappeared after the topsoil had been removed were species such as Knotted Pearlwort (Sagina nodosa) and Lesser Centaury (Centaurium pulchellum). This was followed by the return of several dune valley species such as Fairy Flax, Eyebright en Yellow Rattle. Other interesting species that appeared were Narrow small-reed (Calamagrostis stricta), Distant sedge (Carex distans), Little green sedge (Carex oederi ssp oederi), Lesser tussock-sedge (Carex diandra) and Bee orchid (Ophrys apifera). Also, several rare mushroom species can now be found in the roadside verges.

When the present management will be continued we expect a further botanical development. Within 10 years from now the road margins may turn pink for miles in June, because of the massive flowering of the Southern Marsh-orchid (Dactylorhiza majalis ssp praetermissa).

The effect of blown-in sand on lichen-rich coastal dunes in the Wadden district

All over the island of Terschelling (The Netherlands), high lichen diversity was found on the fixed, Grey hairgrass (Corynephorus canescens) dominated 'grey dunes' (Natura 2000 habitat). Many Cladonia species and lichens that usually occur as epiphytes, occurred terrestrially on bare sand or moss carpets. However, since the 1980s encroachment with graminoids (Ammophila arenaria and Carex arenaria) and the neophytic moss Campylopus introflexus had changed most of the central dunes. Within the Monitoring program 1995-2005 (extended to 2010) permanent plots (PQ's) were used to study the succession in vegetation composition and soil quality.

Ecological gradients on a slope on the Brunssummerheide

G. van Dijk, A.J.P. Smolders, C. Fritz, A.P. Grootjans, N. Straathof & G.J. van Duinen

This article describes the biogeochemical and ecohydrological functioning of a groundwater fed mire situated on the Brunssummerheide area in the Province of Limburg. This peatland is a sloping fen which has been formed in a small valley surrounded by dry mineral poor sandy soils. The mire is fed by groundwater from local and supra-local sources which creates gradients in water quantity and water quality. The occurrence of small-scale gradients gave rise to a large diversity of plant and aquatic invertebrate species. Small changes in the hydrology can negatively affect all species depending on these small-scale gradients. The mire is fed by both supra-local groundwater and local groundwater with differences in ionic composition. Areas fed by supra-local groundwater are relatively rich in nitrate, whereas areas fed by local groundwater are relatively poor in nutrients. The peatland is rich in sulphur, which comprise pyrite and sulphur deposits, which probably originate from pyrite-rich brown coal deposits in deeper aquifers. Nitrate-rich groundwater in these aquifers may be responsible for the release of these sulphur compounds into the mire. Management measures should be focussed on preventing further lowering of hydraulic heads of local and supra-local groundwater, decreasing the input of nutrients and reducing pollution of the groundwater. Options are to cut down a large proportion of surrounding pine forests and decreasing nitrogen input in the surrounding agricultural fields. These measures will increase the local groundwater input and decrease the nitrogen and sulphur deposition. This research enlarges the knowledge on the functioning of the mire, and the proposed measures can help to conserve the beautiful gradients and the rich biodiversity of the mire.

Sixty years of forest development in the Robbenoordbos en Dijkgatbos (Wieringermeer)

H.E. Wondergem & P.C. Schipper

The forests Robbenoordbos and Dijkgatbos (670 ha) are situated in the Wieringermeer, a polder in the north of the province Noord-Holland. The forests are isolated from other forests. The forests were one of the first afforestations on the former seabottom of the Zuiderzee in the 1930’s. After inundation in the Second World War the area was reafforestated. The soil is sandy with a clay layer of variable thickness. The forest is young (60 years), the canopy is mostly closed and in the aggradation phase. Despite the young age, the variation and appearance of the forest is impressive due to the species that have been planted initially, such as Ash (Fraxinus excelsior), Sycamore (Acer pseudoplatanus), Beech (Fagus sylvatica) and Pendunculate oak (Quercus robur).

The development of the forest is illustrated on information based on standard forest inventories (1998 and 2009), vegetation mapping 1999, two breeding bird surveys (1997 and 2009) and several recordings of flora and mosses. The forest inventories show changes in tree composition and structure of the woodland. These are the result of the forest management, but also the influence of salt seepage water.

Flora development is illustrated by grouping them by their dispersion mechanism. Specific forests species with a low colonisation rate (M, B, An3) have been introduced by commercial Snowdrop (Galanthus nivalis) culture in the 1960’s. The dispersion of these species is still very local. Species with a more dynamic dispersion (An1, En and Ep) have a much broader dispersion within the forests.

Bryophytes are grouped conform Siebel (2005) by their preferential substrate within forests, i.e. living trees and CWD (trees), forest bottom, shaded steep edges and open, mineral, humid soil . Also a group of non-preferential species have been added because their more than frequent appearance in forests. The bryophyte flora shows a distinct increment after 55 years indicating a further forest development.

To visualise the colonisation of the forests by birds, these are grouped in forest structure specific groups (Sierdsema 1995), i.e. understory, forest edge, mature forest birds, cavity-nesting birds, conifer specific birds and woodlandraports. In the first decade of the forest the bird community was restricted to the understory and forest edge groups, after three decades the cavity-nesting group was established with more common species. In the forth decade the raptors colonised the woods. Isolation of the area is the main problem for the colonisation of non-migratory forest species.

The development of the Robbenoord- and Dijkgatbos shows its own signature. Vegetation, flora, breeding bird community show each its own character of the forest.