Current status and conservation of the Lusitan Duriensean Orchids (Duero Basin, NE Portugal and CW Spain)

Twenty eight orchids species and subspecies are presently recognised as indigenous in the Lusitan Duriensean biogeographical sector, which covers part of the Duero Basin of Portugal and Spain. Twenty one of these (75%) are rare or very rare in this sector and under threat from different agents. This paper provides a detailed study of their distribution and estimates of the sizes of their populations. The latter were based on our own census data, collected at the sites where the species are found. All potentially reproductive individuals were counted. The causes of rarity and the factors responsible for the regression that still affects many species are analysed; main threats are destruction of woods by human activities and overgrazing. These data may be of use to the nature conservation authorities of Portugal and Spain.