Growth of Haloxylon spp. plantation, ten years after thinning, in Gonabad

Based on a general model, estimated number of population density for ten years old Haloxylon plantation in Gonabad was 150 trees per hectar; therefore, six density treatments were selected around the estimated density; two density treatments over estimated number, two under it, and existing density as the control treatment. The treatments consisted of T1=120, T2=135, T3=150, T4=165, T5=180, and the existing density (control) T6=250 trees per hectar. The treatment have been compared in a Randomized Complete Block Design, with four replications, since the spring 1996. After thinning, height (H) and crown diameter (CD) of the remained trees were measured. This measurement was repeated during the growth period in ten years. A size index (SI) model of the form H ×CD2 was founded to distinguish the best among the 6 treatments. The growth percentage of H, CD, and SI, between first and the last measurement were calculated. The analysis of variance of the growth percents showed that there is significant difference between treatments. The highest growth belonged to T1 and lowest belonged to T6 (control). This result show that optimized population density for ten years old Haloxylon stands in Gonabad is 20 (and or 10)% less than the estimated number based on the general model.