Grasslands

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Grasslands are often an important element of urban parks and woodlands, and therefore specific attention is given to them here. Even lawns are often essential elements. However, lawns that are not frequently used, apart from the edges along paths, should be replaced by meadows. These are mown once or - in case of heavily fertilized soils - twice a year during summer and a third time around October. A properly managed meadow flowers, apart from a short period after mowing, almost continuously from spring to autumn (Ash et al. 1992). As hay or freshly cut grass is removed, the regeneration niche and ultimately the coexistence of many plant species is assured (cf. Grime et al. 1988). To reach greater amenity values naturalized - originally non-native - plant species may be used (often geophytes, e.g., Narcissus spp., Camassia spp., Crocus spp.). Excellent examples include the meadows of Great Dixter in Sussex, England (Hobhouse 1997). In order to replace species poor grassland on nutrient-rich soils litter should always be removed and no fertilizing is allowed. Through mowing with litter removal the number of more stress-tolerant species increases gradually, allowing for greater coexistence of a large number of plant species (Grime et al. 1988). Haymaking is preferred to the immediate removal of the litter as it enables larger seed dissemination, although direct removal of litter may be less expensive. The application of this mowing regime will also reduce the annual biomass production considerably and thus will reduce the cost.

Particularly around the edges of forested parts - as described among the most important and rich parts of the urban forest system - it can be essential to mow the grassland only once every 2-5 years. This will allow for the development of specific woodland edge vegetation, creating valuable habitats for plants but also for butterflies and other invertebrates. Structurally this approach created a more gradual transition towards forest habitats and thus a gradual environmental gradient, where light intensity but also air humidity and other factors slowly change. In order to enhance the spring value of meadows naturalized plants with bulbs or tubers may be introduced. These may constitute spectacular displays highly appreciated by visitors. As these require no further specific management cost upon introduction, they are an integral part of sustainable urban park management. Most of these spring flowering species are to be found on richer soils, so for a sustainable result selection should follow local environmental conditions. For comprehensive reviews of habitat requirements of plant species we refer to Ellenberg et al. (1992) and Hansen and Stahl (1993).

In this concept lawns are limited to gardens, to the edge of paths or to places frequently used by visitors for activities such as picnicking and playing. Along paths lawns make gradients of height more gradual. But even on lawns spontaneous processes of germination and establishment may occur. If lawns are mown regularly, litter is removed each time and no fertilization is applied, gradually more species and particularly more herbs such as Bellis perennis, Veronica filiformis, Trifolium repens, and Hypochoeris radicata will establish.

More competitive species occur along the edges of forests; in the transition from grassland to woodland; on open, not frequently managed areas; and along ditches, rivers and ponds. Often vegetation with large herbaceous plant species is flower-rich (e.g., Hypericum perforatum and Teucrium scorodonia on nutrient-poor and dryer sites). Through their structure, these more competitive species are highly significant for wildlife: as nectar or food source for many insect species, as refuge for small animals, hibernation sites for invertebrates, as food sources for singing birds, and so forth. Non-wanted species may be of great importance for invertebrates. Urtica dioica is an important food plant for butterfly species such as Vanessa atalanta, Inachis io, Araschnia levana, Polygona c-album and Aglais urticae. In order to maintain tall herb vegetation it must be mown once every 2-5 years. Mowing intensity is lowest on poor soils. Most of the tall herb species - all related to the competitive plant strategy - are not well adapted to annual mowing regimes, at least during summer. When they are mown annually with removal of litter, grasses and other smaller plant species will take over (cf. Grime et al. 1988) and plant species diversity will increase. Mowing within urban parks is best distributed in time and space. This will yield seasonal peaks and an outdrawn flowing season to enjoy, through various phases of re-growth, and thus also shelter and food for a variety of wildlife.

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