Comparison of weed flora in winter cereals in the province of Zaragoza (Spain) from 1976 and thirty years later.
In this work we compare the weed flora recorded in 1976 and in 2005-07 in winter cereal fields in the province of Zaragoza (North-East of Spain). In 2005-07 we used a very similar methodology to that used in 1976, based on surveying the fields in a zig-zag by three persons until not founding new species and assessing the abundance of species with a visual scale. It is concluded that grass species have increased, especially Lolium rigidum and Avena spp. The average number of species found in each field has decreased from 9 in 1976 to 3 in 2005-07. In 1976, 22 species were found in more than 30% of the fields studied, in 2005-07 only 4 species. Species that have declined more drastically are Daucus carota, Scandix pecten-veneris, Veronica polita, Papaver hybridum, Roemeria hybrida and Hypecoum procumbens. However, we found 23 species, which were not recorded in 1976, including: Chondrilla juncea, Phragmites australis and Cirsium sp. Some are linked to minimum tillage, others are tolerant to glyphosate pre-sowing treatments (Equisetum arvense, Malva sylvestris) and others may have advanced their emergence due to global warming.