| چکیده انگلیسی مقاله |
Introduction
Rangeland provides numerous ecosystem goods and services. Most rangeland management decisions focus on forage production, and this can lead to the loss of other rangeland ecosystem services. One of those services is carbon sequestration, the removal of carbon dioxide from the Earth's atmosphere and its storage in the ground. Rangeland, which covers approximately half of terrestrial ecosystems, is one of the most important sinks for atmospheric carbon dioxide. Photosynthesis, respiration and decomposition are the main processes in the ecosystem that determine how carbon is stored in the soil. Anthropogenic activities like livestock grazing can significantly alter soil carbon storage. Unfortunately, human activities have resulted in lower soil carbon and increased global climate change. Livestock grazing is one of the most significant factors affecting the structure and functioning of ecosystems. Grazing livestock can affect the amount of carbon in the soil through reduced vegetation cover, altered species composition, soil degradation, urination and defecation. On the other hand, changes in the quantity and quality of forage production by livestock grazing have a strong effect on the welfare of the beneficiaries. Consequently, knowledge of the relationship between forage production and other ecosystem goods and services such as soil carbon is essential to the sustainability of ecosystems. It is important to study the quantity and quality changes in rangeland production in relation to different livestock grazing intensities on soil carbon. However, this information can assist range managers in providing techniques to promote soil carbon storage. The purpose of the study is 1) to determine annual forage production in rangelands at different grazing intensities, 2) to study the quality of rangeland forages produced, 3) to assess soil carbon content at different grazing intensities, and 4) to assess the relationship between rangeland production and soil carbon content at different grazing intensities.
Material and Methods
A rangeland adjacent to Khabr National Park in Kerman province was selected as the study area. The study area is shrub- dominated species Artemisia aucheri Boiss. Three sites with different grazing intensities (for example, exclosure, high grazing and moderate grazing) were sampled. At
each site, three 100m transects with 50m intervals were set up. Ten quadrats were randomly assigned to each transect. For each quadrat, the species met were recorded and their number of individuals and the amount of forage produced were measured. The annual forage production (forage quantity) was measured using the clip and weigh method. To determine forage quality, crude protein, acid detergent fibre (ADF), dry matter digestion and metabolizable energy were estimated for each species. Additionally, a soil sample was taken from each of the quadrats. The samples were air-dried and sieved with a 2 mm sieve. The organic carbon of the soil samples was determined through wet oxidation with Walkley-Black chromic acid. Then, the species importance index (IVI) was estimated using relative frequency (Fr), relative density (Dr) and relative dominance (Dor). One-way ANOVA and LSD were used to compare different grazing intensities in terms of soil carbon, annual production, crude protein, ADF and metabolizable energy. Pearson's correlation was used to examine the relationship between soil carbon and annual production with the qualitative attributes of production, ie. The primary component analysis (PCA) was used to identify the most important species in terms of production at the three sites with different grazing intensities (exclosure, high grazing and moderate grazing). Principal Component Analysis (PCA) was used to identify the most important species in terms of production at the three sites with differing grazing intensities (exclosure, high grazing and moderate grazing).
Results and Discussion
The quantity and quality of forage has been reduced in the livestock grazing sites. The study area has a long history of cattle grazing, which has significantly altered the composition of the vegetation. About 26% of the exclosure site species had been removed from the plant composition of medium pasture sites, most of which are appetizing species. Although the amount of organic carbon in the soil increased at the exclosure site, it was not significantly different from grazing sites. Therefore, despite the improvement in forage quality and quantity, soil organic carbon had shown a lower reaction to the exclosure. Due to the presence of acceptable species, there was a positive relationship between forage quantity and quality at the exclosure site. Although A. aucheri was still dominant shrub species in the site with medium grazing intensity, there was no significant relationship between forage quantity and quality due to the decrease of palatable species. With the increase in the number of non-platable species in the high grazing site, there was a significant negative relationship between forage quantity and quality. There was a positive and meaningful relationship between soil carbon and the amount and quality of forage at the exclos site. The relationship between soil carbon and forage quantity and quality was not significant on grazing sites because of a change in plant composition. In the sites under grazing, palatable forbs such as Tragopogon jesdianus Boiss. and Lathyrus annuus L. were not observed and perennial grasses were significantly reduced. It should be noted that forage production of forbs has not changed much on the site with average grazing compared to the exclosure site. Perennials, especially woody plants, were severely reduced at the site with high grazing intensity. There were no bushes observed at that location. Annual grasses had increased in the site with heavy browsing. As perennials decrease, space and resources become available for the invasion of annual plants, especially annual grasses. Therefore, Bromus tectorum L. had the highest forage production in the high grazing area. In terms of crude protein, the high grazing area had low quality forage. Since livestock grazing and subsequent changes in plant composition do not greatly impact soil carbon, livestock management can contribute to the improvement of plant composition and forage production at this site. Taking into account the impact of grassland management on other ecosystem functions, it is suggested to explore the relationship between the amount of production and other functions of quality rangeland ecosystems in order to sustainably manage rangeland ecosystems. |