Investigation on variation trends of vegetation and yield in rangelands of Mazandaran province (2001-2005)

Rangeland assessment and recognizing changes in vegetation, yield and their affecting factors are of important issues for planning and optimum utilization management. Firstly in 2000, main habitats of Mazandaran province were determined and then a site was selected in each reference area for collecting statistical data. Vegetative factors (vegetation cover and yield) were measured in 10 sites along six transects of 200 meter length in sixty plots of one square meter. According to the results, maximum average percentage of vegetation cover (50.22) and maximum yield (417.87) were recorded for 2003. Minimum average percentage of vegetation cover (47.38) was obtained in 2001 and average yields of 391.46 and 391.63 were obtained in 2001 and 2002, respectively. Consequently, a relationship was found between vegetation cover percentage and yield with precipitation. Most of the sites in which average rainfall especially in late winter and spring of 2003 was more than that of the other years, higher average of canopy cover percentage and yield were recorded in the mentioned year. Also, livestock grazing management was effective on amount of yield and vegetation cover. The sites located in highlands showed a better condition due to the cool Mediterranean climate and higher precipitation and proper grazing management in rangelands. The condition of class I and class II species of these sites was better than that of downstream rangelands. In the sites located in lower regions with a cold semi-arid climate especially in sagebrush lands, range condition was lower than that of the highlands due to semi-arid climatic conditions and the use of rangeland in Spring and Autumn. Class III species were dominant in these sites. Precipitation affected all vegetative forms and for perennial grasses vegetation cover percentage and yield were affected. Since cushion plants were not considered in yield calculation, the increment of vegetation cover percentage had no effect on yield. Annual plants also affected the yield due to increased spring rainfall in some sites.