Shrub Death Effect on Competition of Grasslands Species in Golestan National Park

The biotic interactions have the strong impact on the ecosystem function. This study aims on the investigation of biotic interactions influenced by shrub death in two exposures. Therefore, 20 alive and 20 dead Onobrychis cornuta cushions were selected in each exposure and for each of the plots one plot with the same size in open space were selected (in total 160 plots) and their plant species were recorded. In order to determine the main effects, GLMM were applied and T test were used to compare mean between shrub health and exposures. Our results showed that under alive and dead shrubs, perennial herbs (2.8 and 6.35 %) and shrubs (0.6 and 3.25 %) were significantly reduced, respectively. In the southern exposure, total cover of species (17.55 and 6.85), perennial grasses (1.70, 5.98), perennial herbs (2.38, 5.28) and shrubs (1.18, 3.40) were declined under dead shrubs respectively. GLMM results showed that shrub health has the strongest effects (F=21.25; P<0.009) on RII. In the southern exposure, competition was higher under dead shrubs (-0.58) than alive shrubs (-0.14). Exposure had strongest effects on the perennial grasses (F=551.47; P<0.0001) which in both dead and alive shrubs the cover in the northern exposure is higher than southern exposure. Shrub health has highest effects on perennial herbs (F=7.22; P<0.009) and in the northern exposure shrub death (- 0.36) reduced RII significantly compare to alive shrubs (- 0.004).