Effect of slope gradient on vegetation, species composition and production of medicinal plants (Case study: Rom Rangelands, Qaen)

Extended Abstract Background and objectives:  In order to further protect rangeland ecosystems, range suitability in this regard should be investigated before the utilization of medicinal and industrial plants. Plant composition and production and slope of the slope are among the components that determine the suitability of rangeland for the use of medicinal plants. For this purpose, in four habitats of medicinal plants (Achillea santolinoides, Ziziphora tenuior, Sclerorhachis leptoclada and Hymenocrater calycinus) and three slope classes (less than 30%, 30-30% and more than 60%), Importance Value Index (IVI) and production were determined. Methodology:  First, after field survey and observing the presence of medicinal species as the dominant species in the rangelands of Room, Qaen, plant habitats were identified. In herbaceous and woody habitats, a plot size of 1 m2 and 2 m2 were used (respectively). Sampling was done randomly method. After measuring the slope on all sampling plots, the slope was statistically analyzed at three levels of less than 30%, 30 to 60% and more than 60%. During the slope gradient, the structural characteristics of vegetation including density, frequency, abundance and dominance of species were measured and based on that, Importance Value Index (IVI) was determined. In order to compare the total production of medicinal plants between different slopes, analysis of variance (ANOVA) and Duncan multiple range tests were used. Cluster analysis was also used to group the habitats based on species composition. Species abundance distribution was investigated using geometric series, broken stick, log-normal, Zipf and Mandelbrot models and the data were fitted with each of the above models. The goodness of fit of these models was measured by the Akaike information criterion (AIC). All statistical analysis was performed by R. Results:  The floristic list of the study area showed that in total, 47 plant species belonging to 15 plant families were identified, 31 herbaceous species, 8 bush species, 7 grasses and 1 shrub species were observed. Among the observed species, 66% of medicinal and industrial plants, 23% of forage plants and 11% of invasive and thorny plants, respectively. Medicinal plants mostly belong to Compositae, Apiaceae, Lamiaceae and Brassicaceae. The results showed that Ziziphora tenuior and Achillea santolinoides had the highest density and Artemisia aucheri and Sclerorhachis leptoclada had the highest density. Medicinal and industrial plants have the lowest share in the plant composition of low slopes and the highest share in habitats located on moderate and high slopes. The rank-abundance curve showed that the species abundance distribution (SAD) of the whole study area was fit by Mandelbrot model and log-normal, which indicates a stable community. The results showed that with increasing slope, the production of medicinal plants decreases. Achillea santolinoides and Ziziphora tenuior, located on slopes of less than 30%, have the highest production and relative importance, and in terms of these two factors, have the necessary competence for exploitation.  Conclusion:  Although the relative composition of medicinal plants in the region increases with increasing slope, but in terms of plant composition and production, habitats with a slope of more than 60% are not suitable for the use of medicinal plants. In general, in range suitability assessment studies, vegetation cover percentage alone is not enough, because there may be species that are pharmacologically and industrially valuable that have a low cover percentage. Although in this study, not all factors affecting rangeland suitability have been studied directly, but the important value index for rangeland suitability studied and the effect of slope on some vegetation characteristics have been investigated and the results showed that the moderate and high slope and production of medicinal plants decreased. Therefore, with increasing slope, rangeland's suitability for medicinal and industrial plants also decreases. Keywords: Plant Composition, IVI, Slope, Range Suitability, Medicinal Plants.