Prevalence study of weeds in some economic orchards trees.

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.