طرح ملی تحقیق در بهینه سازی انبوهی جنگلکاریهای تاغ (مرحله اول)

A general model was devoloped to explain the interrelationships between soil saturation percentage, mean annual precipitation, and population density on growth and vigority of planted Haloxylon trees. Soil saturation percent is an easy measure to determine the water (rain) availability to plants. The main recommendation of the model is thinning the stands in accordance with the above named factors. Calibrating the general model for several regions, and optimizing the stands of Haloxylon plantation are the main objective of the present project. Six thinning treatments were selcted; two densities (T1 and T2) less than estimated number based on the general model (T), and two (T4 and Ts) more than the estimated number, and existing density as the control (T6). The treatments have been compared in a Randomized Complete Block Design, with four replications, in each of the five research sites (Yazd and Kashan, since 1993, Semnan and Sabzevar, since 1994, and Gonabad, since 1995). After thinning practices, height (II) and crown diameter (CD) of the remained trees were measured. This should be repeated ends of each seasonal growth periodes in next 10 years after thinning. Because of different starting times of the regional projects, statistical analysis presented in this report is based on 10-years period measurement for yazd and Kashan, and 5-years period for three other regions. Since the CD increament between the first and last measurement was more than H increament (up to 4 times), and because of the 2 dimentions growth of CD, a size index (SI) model of the form [H x CD2] was found to distinguish the best among the 6 treatments. . The growth percentage of H, CD, and SI between the first and the last measurement were recorded. In all research sites, the growth percent of SI in thinned plots were 2 up to 50 times more than control. The analysis of variance of the SI showed that there is a significant differences between thinned plots and control in Kashan and Sabzevar, but no significat in Yazd and Gonabad. No data was reported from Semnan research site. Comparison of the factors means between thinning treatments indicated that the high growth rates belonged to 1'2, T3 and T4, all around estimated number(T3). These results indicated necesity of thinning of Haloxylon plantation in Iran for revival the vigor and increase of trees growth; it is also iridicated accuracy and correctness of the general model for identifing the optimized population density of Haloxylon plantation. Keywords: HaloxylQn, Saxaul, Thinning, Soil texture, Rainfall. . I. Research Scientist, Research Institute of Forests and Rangelands, P.O.Box: 13185-116, Tehran, Iran. [e-mail]

Keywords:

جنگل کاری , تاغ , پژمردگی , انبوهی , تنک کردن , خاک , بارندگی , یزد , کاشان , کرمان , سمنان , سبزوار , گناباد