Roadside verges in densely populated areas are often a significant addition to the total semi-natural area and as such may contribute to the conservation of biodiversity. Furthermore, they can enhance the ecological cohesion of a region, especially when the existing nature reserves are small and/or highly fragmented. We investigated the occurrence of ground beetles and spiders in six highway verges with grey hair-grass vegetation in the Veluwe region, The Netherlands. Total species number in the verges was similar to the values found in nearby nature reserves with comparable vegetation, but the ground beetles tended to be more abundant in the reserves. Many stenotopic species were present in the verges, confirming the significant conservation value of this habitat. However, compared with the nature reserves, there were fewer species of stenotopic ground beetles and the stenotopic spiders were less abundant in the verges. From our knowledge of the biology and ecology of the species captured it seems likely that this is attributable to differences in "habitat quality". In the verges, species preferring bare sand are scarcer, and the weighted mean body length of ground beetles is shorter than in nature reserves. This suggests that the sward in the road verges is too dense and the suitable vegetation too patchy to sustain some of the stenotopic species. Habitat analyses support this contention: Compared with the nature reserves, the verges had proportionally less bare sand, more herb and tree cover and the vegetation patches were smaller. The strategy suggested to promote stenotopic species entails removing encroaching trees and shrubs from the verges in order to expand the nutrient-poor zone and (re-)create pioneer conditions. Subsequent management should aim at further improving the road verges as extensions of nutrient-poor habitat.
This paper investigates and evaluates the effects of ecological management on the vegetation of roadside verges in the Netherlands, conducted by the Ministry of Transport (PublicWorks Department). A total of 545 relevés, made between 1986 and 1988, were re-examined in 2001. Data were analysed for changes in number of species, rarity of species, red list (endangered) species and syntaxonomical species groups. The total number of species almost did not change. Common species increased while rare species decreased. The red list species declined by 40%. Species from shrub and woodland, from fertile, wet soils and from nitrophilous fringes increased, while species characteristic of relatively open and nutrient-poor habitats and some pioneer communities decreased. Plant communities were valued, and phytosociological changes were evaluated, using the deductive method of Kopecký and Hejný and knowledge about vulnerability, rarity and replaceability. In 44.5% of the 465 evaluated relevés, the vegetation value remained unchanged, in 23.0% it decreased and in 32.5% it increased. The different trends tended to counterbalance one another, resulting in an unchanged mean vegetation value. The increase in vegetation value is mainly due to the increase in relevés containing species rich Arrhenatheretum-subassociations. The decrease is mainly due to a decrease in moist heath, dry sandy pioneer communities and grasslands on relatively poor soils, and the increase of species-poor nitrophilous tall herb communities and woody vegetation. In some of the verges studied, the vegetation value decreased as a result of inappropriate management and construction. Suggestions for improvement are given. Local successes indicate that appropriate management can considerably improve the botanical value of roadside verges, and consequently their value for other life forms.