Weed communities of date-palm orchards in the Feiran Oasis (south Sinai, Egypt).
The vegetation of the date palm orchards of the Feiran Oasis (south Sinai, Egypt) was studied to describe the weed flora and relate it to some environmental variables. On the basis of 34 relevés representing different types of date-palm orchard, three main vegetation types were recognized: Zygophyllum simplex-Hordeum murinum, inhabiting the old orchards that occupy the relatively dry lowlands of the Oasis; Bidens pilosa-Conyza bonariensis in young orchards; and Polypogon monspeliensis-Malva parviflora in mature orchards. The last two vegetation types inhabited well-irrigated orchards in the uplands. The vegetation types identified are well segregated along the first principal component analysis axis which reflects soil texture, moisture and fertility gradients, occurring in the following sequence: Zygophyllum simplex-Hordeum murinum, Polypogon monspeliensis-Malva parviflora and Bidens pilosa-Conyza bonariensis. This sequence also reflects the gradient of human interference, starting with the vegetation of the less disturbed (old) and ending with the highly disturbed (new) orchards. The first vegetation type, inhabiting old date-palm orchards with a low salinity and high content of coarse fractions, is floristically more diverse. The least diversified vegetation is in young orchards with a high soil moisture and organic matter content.