Evaluation of biomass and vegetative characteristics of mesquite (Prosopis juliflora) afforestation in arid area of Iran

In this research, three afforested stands of mesquite at the ages 15, 27, and 34 years were selected in a dry climate region in Iran. In each of the stands, two density classes (180 and 250 trees per ha) were located and 4 square sample plots (40 × 40 m) were randomly selected. After measuring the tree height, crown height, collar diameter and crown area, aboveground biomass was calculated using experimental and semi-empirical allometric equations. The soil quality index was determined at two depths based on the measured physical, chemical and biological characteristics of the soil samples. The results showed that stand age, stand density and their interaction significantly affected stem number, crown height growth and soil quality index. The average number of stems was the highest in the 15-year-old stand and the lowest in the 34-year-old stand. Height, collar diameter, basal area growth, biomass, and competition between trees were significantly affected by stand age and its interaction with stand density (p < 0.01). The average annual growth of tree collar diameter and height with age was lowest (4.1 mm per year and 17.7 cm per year, respectively) in the 34-year-old stand, compared to average annual growth rates of 7.2 mm and 31 cm for collar diameter and height, respectively, in the 15-year-old stand. In general, high density mesquite afforestation plantings in this dry and desert area improves soil quality and increase vegetative and productivity characteristics of mesquite, especially as stands age.