干旱区生态环境知识资源中心

In order to determine the most suitable Site preparation method and select adaptable species for the purpose of afforestation under rainfed conditions, an experiment was laid out for the first time on the southern slope of the Oan-Ebn-Ali mountain in Tabriz, Iran in the spring of 1994. The site is characterized with the poor soil, prolonged dry period, hot summer, cold winter, and severe wind throughout the year, and hence, one of the problematic environments in semi-arid regions.

The experimental design was a nested split-split plot with three replications. The main plots involved five types of water catchment methods: 1) perlite + plastic sheet on the soil surface, 2) rice bran + plastic sheet on the soil surface, 3) only plastic sheet on the soil surface, 4) plastic sheet on the bottom of the pit + plastic sheet on the soil surface, 5) deep pit + plastic sheet on the soil surface. Two sub-plots consisted of trees and shrubs. Species within each sub-plot were represented as nested sub-plots (10 shrubs and 5 tree species). Four seedlings were planted in each plot.

Crescent form banquettes were prepared in the experiment to catch the runoff water. Water harvesting area for a tree species was about 15-20 m(2), and for a shrub species was around 10-12 m(2). Percent survival of the seedlings was measured from 1994 to 1996. The height was also measured in 1995, 1996, and the relative height growth was calculated using the two-year data. Only the data obtained in 1996 was used in the analysis of variance for percent survival. Analysis of variance did not indicate any significant differences between water harvesting methods during these preliminary years, in terms of percent survival and relative growth. But the differences among tree and shrub species were significant for both studied characteristics.

Among trees, Pinus nigra var. austriaca showed the highest relative height growth (79.43%). The relative growth of Pistacia atlantica and Pinus ponderosa were also appreciable (58.95% and 58.90%, respectively). There species are resistant to wide range of temperature variations, drought, and severe winds. Among the shrub species, Purshia tridentata, with relative growth of 33.92% acquired the first position. Next, Anygdalus orientalis (2), A. orientalis (1), A. communis, Prunus fasiculata, and Halozylon persicum ranged from 21.8 to 29.85% in terms of relative height growth. The percent survival for all five tree species was unexpectedly high. It was 97.55% for Pistacia atlantica 96.55% for Pinus ponderosa, 90.45% for Robinia pseudocacia, 89.4% for Juniperus chinensis, and 73.47% for Pinus nigra var. austriaca. Six shrub species acquired survival rates of above 84%. These species were: Rosa canina (99.24%), Amygdalus scoparia (98.06%, A. orientalis (2) with 93.3%, A. orientalis (1) with 92.4%, Purshia tridentata (88.30%), and Halozylon persicum (84.73%). In general, the range of variation for 11 species tout of 15 studied species) was from 73.47% to 99.24%.

This unexpected preliminary result based on three years of data regarding the problematic environment of the Oan-Ebn-Ali mountain, is very promising. It might be attributed to the choice of resistant species against unfavorable climatic and edaphic conditions, application of proper site Preparation techniques such as construction of crescent banquettes, and covering the soil surface of the pits with plastic mulch. These techniques may have played an important role in the regulation of water balance through the catchment of runoff water, prevention of weed growth, and suppression of evaporation. Although we have obtained very promising results from these preliminary years of experiment, for a general recommendation, the study should obviously be continued for several more years.