Journal of Rangeland

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The effect of different levels of protection as a management tool on the organic carbon dynamics is important. To examine the case areas with three levels of protection, including hunting prohibited region, national park and protected areas were selected and studied. Soil samples were taken from depths of 0-10, 10-30, and 30-100 cm in a randomized-systematic method having three replications. Soil fractions were screened using meshes sized 18, 35, 60 and 270. Soils of each depth were put into 5 size fractions and their carbon were measured. The results showed that the amount of carbon in different depths of soil in the national park is the same with no significant differences. In general, the area is not used by any means and amount of the carbon for all measured soil depth, therefor, is not significantly different. For the protected areas and hunting prohibited region amount of the carbon is varied for different depths. In the protected area for the average grazing intensity, wildlife and nomadic livestock, root growth and organic matter decomposition in the lower layers are low and the highest levels of carbon only in the surface layers could be observed. In the hunting prohibited region, grazing intensity reduces the entry of plant materials and the high loss of carbon dioxide occurs, result is the low percentage of soil carbon. For all studied areas, the soil carbon content decreases when particle size is increased. The least amount of carbon therefore, is related to F1 and F2 components and the most to F4 and F5 size fractions.

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Grazing effect on vegetation cover and soil factors in natural environments is inevitable. The present study was conducted to investigate the effect of grazing on soil factors and distribution of plant species in grazed and non-grazed areas in rangelands of western parts of Hoz-e-Soltan Lake, Qom. Systematic-randomized sampling method was used alongside of 4 transects. Adjacent to the transects 10 plots of 4 square meters were put within the exclosure and its outside. In each plot, soil samples from 0-30 cm depth were taken. The list of plants and their canopy cover were determined for each study site. Also, the properties of acidity, electrical conductivity, soil texture, lime, percentage of phosphorus, sodium, potassium, calcium, Magnesium, chlorine, carbonate, bicarbonate and nitrogen were measured. Using the CANOCO software, ordination of the plant communities was drawn according to the characteristics of the soil by conventional comparative analysis (DCA, CCA). The results showed that livestock grazing have impact on the relationship between vegetation and soil in this area. As the results showed, nitrogen in addition to salinity and sodium had a significant effect on vegetation changes in the grazed area. In fact, proper grazing management increases the amount of nitrogen in the grazed area. Which could be count on as a soil improvement tool in terms of nitrogen content increase. More nitrogen in its turn increases the presence of two important species namely Suaeda aegyptiaca and Artemisia sieberi. Results suggest that as livestock grazie from the shrubs, as the dominant plants of the area, the deterioration of other plants is prevented and the quality of forage production is increased. Therefore, by managing livestock grazing in the studied area and other similar steppe regions, improvement of vegetation composition gets possible and consequently soil properties improves in the long term.

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Background: One of the important steps in assessing rangeland vegetation is determining the sample size. Adequacy of sample size and its determination is always one of the main concerns of rangeland vegetation analyzer. There are two general methods for determining the sample size in rangeland science: graphic and statistical methods. In this study, the sample size required studying the percentage of vegetation and soil in under grazing and enclosure area, in addition to the Cochran method, the analysis of power and effect size has also been used.
Methodology: This study was conducted on the habitat of Ammodendron persicum in the rangelands of Zirkouh, South Khorasan province. For sampling, initial sampling was performed with 3 transects and 30 plots of 16 m². In each plot, the percentage of vegetation was estimated; also 18 samples were taken from the soil depth of 0-30 cm. In this study, in order to perform pre-test and post-test power analysis (80% and 60%) in both groups, parametric and non-parametric statistical tests were performed. For this purpose, to compare the percentage of vegetation and sand in the two areas (under grazing and enclosure), if the data is normal, independent samples t-test and if isn't normal, Wilcoxon test were used. The normality of the data was assessed using the Shapiro-Wilk test and the homogeneity of the variances was assessed using the ratio of variance test. In this study, based on the Cochran's formula, the number of plots required for sampling was determined. To determine the sample size, and the validity of the test from the initial data, power analysis and effect size statistics were used. All statistical tests were performed by R software and psych, lsr, pwr and effectsize packages. 
Results: The results showed that, despite the absence of outliers, vegetation data did not have a normal distribution. Even after the second root conversion, the results of the Shapiro-Wilk normality test still showed that the data in this study was not normal. Therefore, in this study, non-parametric tests were used. The results showed that about 502 plots are needed to measure vegetation by the Cochran method. The Cohen effect size for the student's t test with independent samples was calculated to be about 0.23, which is a small difference between the percentages of vegetation between the two areas. The results of the present study showed that 30 pre-test samples at the levels of 0.01 and 0.05 with test power of 4.31% and 13.95%, respectively, and type II errors in the test were 95.69% and 86.05%, respectively. It indicates that the test power for this number of samples is really low. At the power level of 60% and 80%, with an "average" effect size between 46 to 73 plots for each region was calculated and the number seemed more economical. The results of the soil sampling power analysis showed that the test power was 27.21% and 52.04% at the level of 0.01 and 0.05, respectively, and type II the errors in the test were 72.79% and 47.96%, respectively.
Conclusion:  Finally, it can be said that at least 46 plots and 22 soil samples were required to study this rangeland to an acceptable level. It is suggested that if the null hypothesis is rejected, in addition to the P value, the effect size and test power be reported. According to the results of this study, in this region, the statistical test of the t-test on 30 vegetation samples had an error of about 86 to 96%. Therefore, in areas with high vegetation changes, the use of the Cochrane method and 30 plots is not recommended at all. 
 

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