De Levende Natuur nummer 3 van 2004 (English summary)


DLN 2004-3

Nature development in the Sliedrechtse Biesbosch

Boudewijn, T.J., E.M. van Dam & R.P. de Ridder

Two farmland polders in the Sliedrechtse Biesbosch offered the opportunity to realise 300 hectare fresh water tidal area by combining clay winning and nature development. Attention has been paid to conserve morphological and historical values as well as to realise the optimum situation for the development of new fresh water tidal areas. In the western polder clay winning has been restricted to digging new tidal channels to maximise the tidal area. In the eastern polder clay winning could be more intensive due to a higher ground level in the polder. Attention has been paid to the connection of the polders to the adjacent tidal waters to increase the tidal range. At the moment the Sliedrechtse Biesbosch has high botanical and ornithological values. Research has been carried out to ensure that the connection of the polders will not result in the loss of these values. First the polluted sediment in the tidal channels in the Sliedrechtse Biesbosch has to be removed, otherwise the sediment can be deposited in the new polders. After the removal of the polluted sediment the polders will be connected with the tidal channels in the Sliedrechtse Biesbosch and 300 ha fresh water tidal area will be realised.

Slow species in fast landscapes: recovery of forest herbs in recent forests

Verheyen, K., S. van der Veken & M. Hermy

In this paper the main findings of an integrated study of the processes involved in the recovery of forest herbs in recent forests are discussed. Results from both observational and experimental research confirmed that the habitat quality of recent forests is generally sufficient to sustain populations of forest herbs and that primarily seed availability limits the colonization of recent forest instead. A literature-survey as well as a simple colonization model indicated that the limited seed availability is caused by the interaction of different life-history traits such as low seed production, long generation times, specific germination requirements and a lack of adaptations for long-distance dispersal. Therefore, special attention should be paid to the location of newly created forests. Preferably, they are situated in landscapes where there is at least 10 to 15% cover of ancient forests and in which the total forest cover amounts at least to 30 or 40%. To promote dispersal, interactions between the patches should be enhanced. Finally, to maximize establishment chances in recent forests, litter accumulation and vigorous growth of competitive, light-demanding species should be avoided by means of an appropriate tree species choice.

The Landscape Atlas of Flanders as basis for landscape protection

Antrop, M. & L.V. van Eetvelde

In the densely populated Flemish region of Belgium, landscape protection and management is a slow and difficult process. Since the first law on the protection of monuments, sites and landscapes, only 2.7 % of the territory became legally protected. Most of the areas protected as landscape were selected for their natural qualities. In many cases, the cultural, historical and aesthetic qualities were added complementary. The procedure for landscape protection is too slow and the regulations for the management of valuable landscapes in the law of physical planning are too soft to oppose the hard economic demands. Meanwhile, devastating changes happened at an accelerating speed. Since 1995 an important change in policy occurred and placed the integrated landscape management as an objective. Simultaneously, the cultural, historical and aesthetic qualities of the traditional cultural landscapes were revalorized and attention grew also for the ordinary landscapes. This resulted in the Landscape Atlas of Flanders describing different types of relics of the traditional cultural landscapes. It shows 515 selected relic zones, covering 530.000 ha or 39% of Flanders. Also, 381 anchor places were recognized which represent ensembles of very high natural, cultural, historical or aesthetical value and cover 221.051 ha or 16,3% of Flanders’ territory. Finally, 461 line elements and 4.606 point elements have been selected as characteristic elements or landmarks in the landscape. Each of these were described and evaluated and integrated in a GIS database that is made available to all concerned. The results of the survey stimulated a new legislation that aims a more integrated management of the whole landscape as suggested also in the European Landscape Convention.

A botanical evaluation of road-side verges after a period of 15 years

Kalwij, J.M., K.V. Sykora & P.J. Keizer

Road-side verges can fulfil an important function both as a connecting element between scattered areas and as an asylum for threatened species (plants and animals). The road-side verges of highways are maintained by Rijkswaterstaat (the department for maintenance of dikes, roads, bridges and the navigability of canals). The ecological management conducted by this department is aimed at an increase of the natural values of road-side verges. This paper evaluates the changes in flora and vegetation along state-managed road-side verges in the Netherlands after a period of 15 years of ecological management. A total number of 501 relevés, first investigated in the period 1986-1988, were re-examined in 2001. The data were analysed floristically for changes in number of species, rarity of species, Red List species and syntaxonomical species groups. Besides, changes were evaluated phytosociologically, using the deductive method of Kopecký and Hejný (1978). This method proved to be a very useful tool for the evaluation of vegetation changes. After 13 to 15 years the management policy resulted in both negative and positive trends. The different directions in change are counterbalancing one another, resulting in an unchanged mean vegetation value. A negative symptom is the decrease of rare and threatened species, the increase of shrub encroachment and nitrophilous tall herb communities and the decrease of vegetation from relatively nutrient poor conditions. The considerable increase of saturated, species rich communities of the Arrhenatheretum is a positive phenomenon. Possible causes of negative trends are discussed. Probably as a result of negligence, false or lack of field management, many areas of state-managed road-side verges along highways have decreased in botanical value. Local successes have proven that a good ecological construction and accurate management of road-side verges can considerably improve their botanical value, and with these the natural value of these ecological areas. To achieve this aim, a good construction and management plan, followed by proper monitoring, evaluation and adjustments in management is required.

Platform Ecological Risk Assessment for soil pollution; an aid for soil sanitation

Waarde, J.J. van der, D. Boels & M.C.G. Hopman

Soil pollution is widely spread in The Netherlands and hampers nature restoration plans by its direct adverse eco-toxicological effects and high costs of remediation. Nowadays a risk based soil sanitation policy has been adopted which offers the possibility to counteract the pollution through managerial means. Site specific actual ecological risk assessment, using the TRIAD approach, is better suited to identify the need of remediation of contaminated lands. The Platform Ecological Risk Assessment (PERISCOOP) has facilitated the risk assessment and has made an inventory of suitable managerial solutions. The implementation of the TRIAD approach and specific soil management options will decrease the costs of soil sanitation and, moreover, will facilitate more sites to be remediated at a faster rate.