The conclusion of the dam project located in Alqueva, in Southern Portugal, has
resulted in a significant increase of new irrigated areas, since 2006. This has meant that, in
recent years, there have been progressive flora changes in farming systems traditionally
implemented in the Alentejo region. The present work has analyzed the weed flora in an
early stage of these changes, and the impact of environmental factors on the distribution of
natural vegetation under Mediterranean climate conditions in the influence area of Alqueva.
In 2007, 105 floristic surveys were carried out in autumn-winter crop plots or other soil use,
and 264 species were identified. Families with higher expression were: Asteraceae, Poaceae,
and Fabaceae. Only three species have been identified in more than half of farms, Avena sterilis,
Phalaris minor and Lolium rigidum and they were part of the 15 species that revealed high and
very high infestation degrees. Soil texture and extractable phosphorus have been determined
as active ecological factors, according to the method of ecological profiles and Mutual
Information. Therefore, these factores were those with the greatest influence on the species
distribution. L. rigidum distribution showed to be associated with medium soil texture and
A. sterilis distribution also showed to be associated with medium and fine soil texture soils,
without showing ecological preference by extractable phosphorus. The distribution of P. minor
was not related to the soil texture but showed preference for soils with medium phosphorus
contentinfo:eu-repo/semantics/publishedVersio