The Performance of Ten Imported Tree and Shrub Species Grown Under the Environmental Conditions of Riyadh Region, Saudi Arabia

This study was conducted at the Nursery of General Administration of Gardens and Landscaping, Riyadh Municipality, Saudi Arabia. The study aims at evaluating the performance and growth of ten imported species of trees and shrubs under the  environmental conditions of  Riyadh region. The tree species were Acacia visco, Acacia salicina, Acacia pruinocarpa, Leucaena greggii, while the shrubs were Caesalpinia mexicana, Parkinsonia florida, Senna artemisioides  xsturtii, Senna artemisioides  xartemisioides, Senna artemisioides filifolia, and  Sophora tomentosa.  One year old seedlings of these species were planted in the field of the nursery in March 2009, and left to grow naturally. Two months later, plant growth  measurements were taken at an interval of two months for one year. The results indicated that there were differences in plant growth characteristics among the various tree and shrub species. The trees of Leucaena greggii gave the highest values of plant height (4.64m), crown height (3.31m) and crown diameter (2.6m) and had the greatest flowering rate and period. Acacia salicina reached also 4 m in height and gave the highest values of stem diameter (10.87cm) and branch number (24). Acacia pruinocarpa gave the lowest plant height (2.41m), crown height (2.27m) and branch number (17), while Acacia visco gave the lowest stem diameter (7.57cm) and crown diameter (2.03m) and had no blooming during the study period. The shrub species measurements showed that Caesalpinia mexicana gave the highest values of plant height (2.83m), crown height (2.63m) and stem diameter (9.5cm) while Sophora tomentosa gave the lowest plant height (1.07m), crown height (0.97m) and stem diameter (4.11cm). Parkinsonia florida as well as the Senna artemisioides subspecies were blooming continuously, giving mass of one yellow color for ten months, and the highest flowering rate occurred in March. These species grow in round shape and have aesthetic characteristics which allow them to be suitable for landscape uses. Although there were variations in plant growth characteristics of the studied tree and shrub species, generally they performed very well under the extreme environmental conditions of Riyadh region.