Effect of livestock grazing on the yield of gum tragacanth in Astragalus gossypinus Fischer habitats

Livestock grazing and trampling on Astragalus sp habitats can negatively affect gum production potential in these natural habitats. This study aims to evaluate the effect of livestock grazing intensity on gum tragacanth yield in Astragalus gossypinus habitats of Golpayegan, Esfahan province, central Iran. Quantity of discharged tragacanth in each individual plant and above-ground attributes including height from soil surface, canopy diameter and canopy size of corresponding plants were measured using randomized-systematic sampling procedure on all transects in three grazing intensities, i.e., low, moderate and heavy in 2014. Data were analyzed with One-way Analysis of Variance and the means with significant difference were separated with Duncan test. Tragacanth production in habitats with heavy grazing intensity was differed from that in habitats grazed moderately by animals. The quantity of tragacanth secretion in habitats of A. gossypinus with heavy grazing intensity was 54.75% lower than that in the habitats grazed moderately (P < 0.05). Tragacanth yield in heavily grazed habitats was 60.18% lower than that in the habitats with low grazing intensity (P < 0.05). However, gum production in habitats with moderate and low grazing intensities was generally similar (P > 0.05). Correlation coefficient (r) between individual plant height from the soil surface and canopy diameter with the quantity of tragacanth were 0.21 and 0.33, respectively (P < 0.05). In addition, there was a positive significant relationship between canopy size and the quantity of gum in A. gossypinus habitats (r = 0.45; P < 0.05). Livestock grazing affects gum yield in A. gossypinus through changing of above-ground attributes of individual plant particularly in heavily grazed sites.