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

Abstract

Evaluating the degree of success in the growth, effectiveness and durability or replacement of pioneer afforestation in dry areas of the world is one of the important issues of managing these forests. We evaluated the suitability of mesquite for afforesting degraded lands in the dry climate region of Einkhosh, Ilam province, Iran by studying the influence of stand density (180 and 250 trees per ha) and age (15, 27 and 34 years) on tree development, growth and biomass, and soil quality in. We measured tree characteristics (height, crown height, collar diameter and crown area) and calculated above-ground biomass. Soil quality index was determined at two depths (0–15 and 15–30 cm) based on the measured physical, chemical and biological soil properties. The results showed that stand age and density and their interaction significantly affected stem number, crown height growth and soil quality index. The average number of stems was the highest (7.8 per hectare) in the 15-year-old stand and the lowest (1.5 per hectare) 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. In contrast, average annual growth rates of 7.2 mm and 31 cm for collar diameter and height, respectively, in the 15-year-old stand. The surface soil quality index increased with the stand age and density, and it was highest (averaging 0.714) in the dense areas of the 34-year-old stand. In contrast, soil quality index at lower soil depths, decreased with increasing stand age, but it was still highest in the dense areas of the 34-year-old stand. The basal area at the stem collar showed a positive and strong correlation with total height, crown height, degree of competition and crown area. In general, high density mesquite afforestation plantings (250 trees per hectare) in this dry and desert area improved soil quality and increased vegetative and productivity characteristics of mesquite, especially as stands aged. Therefore, mesquite can be a suitable option for revitalization of sites in dry and sparsely vegetated areas.