The causes of drying of Haloxylon in Hussein Abad Mish-Mast, Qom, Iran

Haloxylon is a resistant tree naturally found in some desert areas of Iran, which sometimes faces dieback. This research was conducted to investigate the factors affecting the dieback of this species in Hossein Abad Mish-Mast Qom. Growth and yield traits including the density of trees, number of branches, trunk diameter and height, canopy area, tree age, trunk form, pests, and diseases were recorded in the field. Leaf samples were taken from the trees with varying drying and the amount of sodium, potassium, phosphorus, and chlorine was measured. Soil profiles were dug and soil samples were taken from areas with different drought stress of trees to measure physico-chemical characteristics of the soil at different depths. The results showed that there was a direct relationship between the density of trees and their drying. The results of soil analysis showed that soil salinity was an important factor in the establishment of trees since the density of trees decreased by increasing soil salinity. Also, low concentrations of nutrients have been found to be effective in tree growth and yield. The results of leaf analysis showed that the amount of sodium and chlorine in the leaves was very high and in the older trees the amount of these elements was higher in the leaves. The results showed that salinity was not the only cause of drying of the trees but the higher density was more important in causing this problem. Ecological problems and nutritional deficiencies associated with high density and lack of proper planting intervals were the main causes of drying of trees.