Abstract
The objective of this work is to study the vegetation composition and variety of weeds in olive (Olea europaea L.) and date palm (Phoenix dactylifera L.) orchard trees in Aljouf, Saudi Arabia. The current study revealed the registration of 53 species affiliating to 51 genera in 17 families. A large number of species were registered in the family (Poaceae) that is represented by 13 species, while 11, 8 and 4 species registered in families Asteraceae, Boraginaceae and Amaranthaceae respectively. The TWINSPAN classification applied in the 40 stands resulted in 4 vegetation categories (A, B, C & D). Each vegetation category represented a group of stands. In this study, the therophytes are the most abundant life form which represented 64% of the collected species, followed by chamaephytes and hemicryptophytes are each represented by 13%, Geophytes by 8%, and phanerophytes by 2% of species. Three indicators of diversity were calculated, the species richness for vegetation group B shows a significant higher (14.04 species/stand) than the other vegetation groups, while no significant differences were interpreted by Shannon index among the different vegetation groups. On the other hand, the evenness index for vegetation group B was significantly higher than the other vegetation groups. The present study provides essential information about the ecology of weeds in olive and dates palm agroecosystem and it acts as a driving force to monitor the weedy vegetation changes in Aljouf region.