RIPARIAN

In Collserola, the riparian environment is well represented by the Sant Medir creek and the streams in that basin, the Vallvidrera creek and La Rierada stream, and the Sant Iscle and Sant Cugat creeks.
We can distinguish different types of plant formations found around water: willow plantation, willow groves, ash groves, poplar groves and hazel woods.
The shrub layer is well represented in generally, featuring such species as common hawthorn (Crataegus monogyna), redoul (Coriaria myrtifolia) and dogwood (Cornus sanguinea). The most interesting plants in the herb layer include gromwell (Lithospermum purpurocaeruleum), wood spurge (Euphorbia amygdaloides), arum (Arum italicum), rushes (Juncus sp.), yellow cress (Rorippa sp.), leopard’s bane (Doronicum pardalianches) and the aforementioned sedges. Beside the paths that follow the course of the water grows a highly toxic nitrophilous plant, dwarf elder (Sambucus ebulus), which is often confused with common elder due to the similarity of their inflorescences. However, dwarf elder is distinguished by the fact that this is an annual herbaceous plant with a less aromatic smell than common elder.

Fauna can hide easily and find places for their dens in these brambly riverside habitats.
 

Riparian environments are especially vulnerable to anthropisation and the establishment of invasive species. For this reason, regrettably, we also find more degraded spots in Collserola, with such introduced species as black locust (Robinia pseudoacacia), tree of heaven (Ailanthus altissima), plane (Platanus hispanica) and sycamore (Acer pseudoplatanus).

 

Willow plantations
 

Willow plantations (Carici-Salicetum catalaunicae) are narrow strips of vegetation located right beside water. Beneath the willows (Salix atrocinerea ssp. catalaunicae) grows the rather exuberant herb layer, in which the predominant species are great horsetail (Equisetum telmateia) and sedge (Carex sp.). Exceptionally, at certain points along the creek, we may still find some stands of black alder (Alnus glutinosa).

Willow, ash and poplar groves
 

Further from the water, though still following its course, we find various plant formations featuring different species of willow (Salix sp.), ash (Fraxinus angustifolia and F. excelsior), white poplar (Populus alba) and black poplar (Populus nigra) and a few elms (Ulmus minor), which are re-emerging strongly at points less affected by Dutch elm disease. Also to be seen are bay (Laurus nobilis), elder (Sambucus nigra), wild cherry (Prunus avium) and a few service trees (Sorbus sp.).

Hazel woods
 

At certain points in gullies and hollows, on the damper, shadier sides, we find hazel woods with ferns (Polysticho-Coryletum). The common hazel (Corylus avellana) is accompanied by a large fern, the soft shield fern (Polystichum setiferum) and by other rather rare species in the Serra, such as sanicle (Sanicula europaea).