Evaluation of forage production stability of a few rangeland species using univariate parametric and nonparametric methods on Gavanbane Harsin rangelands in Kermanshah province

In order to evaluate the forage production stability of rangeland species in Gavanbane Harsin, the production per hectare was estimated for eight species in a completely randomized design with five replications during four years. Combined analysis of variance for dry forage production indicated significant differences among the years and species at 0. 01 level of probability. The results of mean comparisons, at 5% level of probability, showed that maximum forage production was obtained for Bromus tomentellus, Festuca ovina and Poa bulbosa, compared to other species. The interaction effect of species×year was significant at 1% level of probability and parametric and non parametric statistics were calculated on the basis of average forage production during four years. Parametric statistics including CVi, S2di and R2i and non parametric statistic including)Si)1)Si) 2، (Si) 2، Si)3، (Si) 6، (NPi) 3 and NPi had an identical trend in introducing stable species. Based on these statistics the most forage production stability was recored for Acantholimon olivieri, Eryngium thyrsoideum and Poa bulbosa. Parametric statistics of bi، Wi2 and δi2, and non parametric statistics of NPi (1) and NPi (2) also showed similar trend in the expression of species stability and the most production stability was obtained for Astragalus flexilipes and Scariola orientalis. Our results were confirmed by group classification of species stability using cluster analysis and principle component analysis for species ranking according to the statistics of stability. In general, Bromus tomentellus and Festuca ovina had a desirable forage production while their production stability was poor. In contrast, Scariolaorientalis and Astragalus flexilipes had desirable production stability while their forage production was poor compared to other species. Acantholimon olivier, Eryngium thyrsoideumand and Poa bulbosa had relatively moderate forage production and relatively favorable production stability. The low stability of the species having favorable forage production indicated that in addition to considering the amount of production, the stability of production also should be taken into consideration as an important factor, affecting the range condition. In terms of production, production stability, and palatability class, Festuca ovina and Poa bulbosa could be introduced for range improvement programs.