عنوان مقاله [English]
Since the amount of species production and consumption varied at different grazing intensities, this study was conducted to determine the amount of production and consumption of Bromus tomentellus and Festuca ovina species in mountainous rangelands of Chaharbagh. Three sites with different grazing intensities (exclosure, moderate grazing and high grazing intensity) were considered and species production and consumption were measured at the end of grazing season. Five transects of 100 m were applied for each sites. Then, two random points were selected in each transect and sampling were carried out from 5 plants near these points. The growth values of plant inside the exclosure for the current year considered as the average production of the species. The difference between the mean biomass of plant inside the exclosure, and other sites, was evaluated as the amount of livestock consumption of the species. Thus, percentage of consumption (rate of utilization) of each species was obtained by dividing the amount of species usage in each site by the amount of production inside the exclosure. T-test was used to determine the differences of biomass of each site with the exclosure and also to compare the amount of species usage at different grazing intensities. Results showed that the highest density and production of B.tomentellus and F.ovina were 19000 stand per ha, 76 gr per stand and 25000 stand per ha, 50 gr per stand, respectively for exclosure site and the lowest density and production for high intensity grazing site. Most consumption rate of B.tomentellus and F.ovina species was observed in high and moderate intensity grazing sites, respectively. Due to the higher consumption of Br. tomentellus Compared to other species, conservation measures should focus more on this species.
Rangeland species have different quantitative and qualitative vegetative characteristics, different phenological stages as well as various vegetative forms. The amount of forage production in the rangeland varies at different times of the grazing season and in the same months of different years. Without knowing the production characteristics of plants and the amount of forage consumption of a rangeland during the grazing period, planning and management of rangeland is not possible. On the other hand, knowledge of forage production of rangeland species is one of the main issues in rangeland assessment studies and also in order to calculate grazing capacity in rangeland management. Low availability of palatable species compared to less palatable species leads to a decrease in their preferred value, and with increasing access to palatable forage, the amount of consumption of this type of forage also increases until it reaches a fixed threshold and then هt does not change. Therefore, for proper management, planning livestock intensity in the rangeland; knowledge and awareness of seasonal and annual changes of plant species seems necessary. Therefore, this study was conducted to investigate the changes in production and consumption of Bromus tomentellus and Festuca ovina species under different grazing intensities in Chaharbagh Golestan mountain rangelands.
This study was carried out in the mountain ranegaldns of Chaharbagh region with the geographical position of 36° 35' 44"to 36° 40' 39" north latitude and 54° 28' 39" to 54° 33' 43" east longitude in 20 km south of Gorgan and 45 km northwest Shahroud and in the altitude range of 2120 to 2320 above sea level. The climate of the region is based on the climatic classification of Emberger, the climate is cold and humid and its average annual rainfall is 325 mm, which is the highest precipitation in winter and in the form of snow. The predominant grazing livestock in the rangelands of the region is Zel sheep and a small number of Pakistani goats. For plant sampling, three rangeland sites including exclusion (control), key area (light grazing intensity) and critical area (around livestock watering point) were selected in the study area. Due to the fact that in rangeland ecosystems, the area of villages, pens and watering points are known as crisis centers and the intensity of grazing around them is high and with moving away from them, the grazing intensity decreases, so the area around the watering points was selected as an area with heavy grazing (critical area). The basis for selecting the key area (light grazing intensity) was based on the distance from the critical areas. Thus, a region was considered as a key area that has a medium distance from the critical areas of the rangeland and has moderate grazing intensity. The control site covers an area of 12 hectares, which is more than 10 years old, and the entry of livestock is prevented by net wires. The mentioned places were selected in such a way that they are similar in terms of rangelands characteristics, but the intensity of grazing and the livestock density in them are different. Then, in each of them, at the beginning of the grazing season and before the livestock entered the rangeland, five transects of 100 meters were placed in parallel and at a distance of 75 meters from each other. In each location, the production of 50 bases of each species was cut and weighed and production was calculated based on measured data. The difference between the average productions in the control, with the average of their production in other places, was evaluated as the amount of livestock consumption of that species in each of the light and heavy grazing places. Thus, the amount of consumption of each species in each grazing intensity was divided by the amount of its production in the control and the product was multiplied by 100, which indicates the percentage of exploitation of the species in different grazing intensities. The density of plants were also recorded within one square meter plots. To determine the difference in production of each different grazing intensities with biomass in the control and also to compare the amount of species consumption and their utilization in different grazing intensities, t-test was used.
The results showed; the highest density and production of Br. tomentellus and Fe. ovina respectively with 19000 (base per hectare); 76 (grams per base) and 25,000 (base per hectare); 50 (g per base) was obtained for the control site. The lowest density and production was obtained for the place with heavy grazing intensity. Also the consumption of Br. tomentellus in place with heavier grazing intensity is higher than Fe. ovina species. While the consumption of Fe. ovina species in light grazing intensity is greater than Br. Tomentellus. The exploitation coefficient of the species Br. tomentellus in medium grazing is less than in severe grazing. According to the results, the exploitation coefficient of Br. Tomentellus in light grazing intensity is equal to 2.71% and there is a significant difference at the level of 5% between heavy and light grazing intensities. Regarding the species Fe. Ovina, there is a significant difference between light and heavy grazing intensities at the level of 1%. So that the amount of exploitation coefficient in conditions with light grazing intensity equal to 37.61% and heavy grazing equal to 73.84% has been obtained.
In general, determining the production and consumption of rangeland species and understanding the diet and grazing behavior of livestock with proper grazing management, given the potential of soil and vegetation in each area can help improve the status of rangeland areas and forage crops and finally a more stable animal will be obtained. According to the results, the species Br. tomentellus is mostly used by livestock, so it is possible to diminish this palatable species from the rangeland due to high grazing pressure, so it is necessary to pay close attention to this valuable species in management plans as well as restoration and conservation projects. About the palatability of the species Fe. Ovina, it can be stated that with the maturation of the plant, the digestibility of selected forages decreases, but the ability to select animals is not affected by reduced digestibility.