Effects of Herbivory on Plant and Soil Characteristics; Allometric Relationships Change among Different Grazing Sites

In this study we developed and compared allometric relationships at the branch and at the whole plant levels of Artemisia sieberi in three grazing rate treatments in Miandasht Protected area, Iran. Three 100 m2 plots in nograzed, mildly-grazed and over-grazed sites were selected. In each plot four soil samples and five A. sieberi were randomly selected for laboratory analyses. For the soil samples, bulk density, soil water content, soil organic matter, pH, N and P were measured. For the plant samples, density (m-2), BD, CA and aboveground biomass were determined. Coarse and fine roots biomasses were measured in different soil depths in six soil sample columns taken per plot. Vegetation coverage was significantly lower for the overgrazed site than the two other sites but the density of A. sieberi was highest for the mildly-grazed site. Correlations among plant characteristics were significant for all three sites. All of the relationships were significant among the three sites. Coarse and fine roots biomasses were highest and lowest for the mildly- and over-grazed sites, respectively. Aboveground biomass was highest for the mildly-grazed and then for the no-grazed and over-grazed sites, respectively. Vertical distribution pattern of fine root biomass was not significantly different between the no-grazed and mildly-grazed sites (P > 0.05) but it was significantly different for the over-grazed site. This study also revealed that a light grazing in some cases may increase vegetation biomass.