Biotopes. Retuerta de Pina (Spain)
Please take a look at the map of the area. General botanical description and a photo can be viewed below:
La Retuerta is situated in the central part of the Ebro valley, east of Zaragoza, in northeastern Spain. The extreme climatic conditions of the area have produced a vegetation similar to that of the North-African steppes. This climate can be summarized as follows: large annual range of minimum and maximum temperatures, oscillating from -10 oC to more than +40 oC; frequent frost in spring; prevailing winds from the NW and the SE (cold and warm, respectively), both with great desiccating power; low annual rainfall (200-400 mm); water deficit over 300 mm.
These climatic conditions are connected with a climax vegetation of Juniperus thurifera L. forests of the Juniperetum phoeniceo-thuriferae (Br.-Bl.& O.Bolós) Rivas-Martínez community, a species-poor plant community characterized by the presence of Juniperus thurifera L., Rhamnus lycioides L., Ephedra nebrodensis Tineo ex Guss. and Asparagus acutifolius L..
Nevertheless these kind of forests have been destroyed by man and the existing landscape is composed by various shrub and grass communities whose composition depends on microclimatic, altitude, exposure, and soil conditions. Taking into account their relative importance in the area, the main plant communities are:
- Agropyro-Lygeion Br.-Bl.& O.Bolós, steppe grasslands with perennial species on the deep soils found on the less steep hillsides, and the foot of the hills.
- Ononidetum tridentatae Br.-Bl.& O.Bolós, dense, vigorous shrub mostly found on gentle sunny hillsides, which indicates the presence of a deep layer of gypsum.
- Salsolo vermiculatae-Peganetum harmalae Br.-Bl.& O.Bolós, a community of nitrophilous species found in abandoned fields and places where organic matter accumulates (mainly as a result of the presence of sheep).
- Helianthemetum squamati Br.-Bl.& O.Bolós, a community of low, stunted shrubs and a very important lichen component which is found on very eroded hilltops.
- Suaedetum verae Br.-Bl.& O.Bolós, dense aggregations of halophilous species which occur in places that have become saline owing to poor draining.
- Roemerio violaceae-Hypecoetum penduli Br.-Bl. & O.Bolós and Carduo pycnocephali-Hordeetum leporini Br.-Bl., plant communities associated with cereal crops and waysides, respectively.