The effect of grazing management on indicators of species and functional diversity of rangeland and the relationship between them on aboveground biomass

IntroductionPreservation of ecosystem functions is dependent on biodiversity and due to the extent of diversity, the use of different indicators in assessing the diversity-function relationship of the ecosystem is essential. Pasture ecosystems are one of the largest terrestrial ecosystems, which occupy more than 40% of the land surface. Also, these ecosystems have extensive services and functions. In fact, ecosystem services have advantages for Maintaining the quality of life is obtained directly or indirectly from ecosystems, as a result of which the life of human societies is dependent on them, and for this reason, it seems very necessary to recognize, monitor, protect and restore them.MethodologyVegetation sampling was done in the peak season of plant growth in the middle of June 1400. After determining the type of vegetation in the region, the light and heavy grazing site was selected based on the accessibility and distance from sources such as Aghl, Abshakhor, road, etc. according to the region. Therefore, in each site (light and heavy reason), sampling of 5 main plots and 15 subplots was used to collect the variables to be measured, a total of 30 plots were discarded. Sampling was carried out in the form of random-systematic design. In this method, the location of the main plot (10 x 10 square meters) was randomly determined. Then, three sub-plots of one square meter were systematically placed inside it (in line with the main diameter). Finally, the data of three subplots were combined with each other and the basis of all calculations was done. This work was to eliminate the false repetition error in sampling. Within each plot, using 3 sub-plots of 1 x 1 square meters, sampling of the presence percentage of plant species, percentage of total coverage and ecosystem function was done.In this research, similar to previous researches, Rosemary's vitality was selected and measured as the function of the ecosystem. To measure the biomass of rosemary under the plot, the entire vegetation, both annual and multi-year, was cut from one centimeter of the soil surface, and after separating the pods, they were dried and then weighed. About the bush plants in the plot, the biomass was measured by determining the index (Adelaide method). That is, first, the branches of the bush plant that represent 10 to 20% of the whole plant were cut and this index was compared with the plants in each sub-plot, and based on visual comparison, the amount of daily rosin content of each plant was estimated. At the end of the day, Sampling was dried and weighed and the amount of biomass of plants in the plot was estimated.Measuring the functional characteristics of plants In order to measure functional diversity indices, in addition to species abundance data, functional characteristics of plants are also needed. In general, features that are easy to measure and have a relationship with the functioning of the ecosystem were selected and measured. In this study, based on the opinion of experts, as well as a review of available sources and similar research, 5 traits including: 1- leaf surface, 2- leaf dry matter content, 3- leaf specific area index, 4- plant height, 5- leaf dry weight, size direction Functional diversity was used. After determining the characteristics, to measure each plant functional characteristic (quantitative characteristics), usually 10-20 repetitions (samples) from 10 plant bases were selected and measured. Considering that it is not possible to select and measure the characteristics of all plants, therefore, the selection of plants was such that these plants make up 80% of the total composition of the plant community (Dactylis glomerata., Avena sativa., Salvia officinalis., Bromus tomentelus., Stachys byzantine., Thymus sp., Astragalus gossypinus., Onobrychis cornuta). Measuring species diversity and functional diversity Species diversity indices (richness, uniformity and diversity) were calculated in PAST software. In this regard, four indices of species diversity including: 1- species richness, 2- Shannon-Wiener diversity, 3- Simpson diversity and 4- species uniformity were calculated. Similar to species diversity, functional diversity has different dimensions that cannot be expressed with one index. In this regard, Wilgar (68) stated that functional diversity, like species diversity, includes elements of richness, uniformity, and divergence, considering the value of characteristics and species abundance. For this reason, by considering all aspects of functional diversity, all aspects of the relationship between biodiversity and ecosystem function can be revealed. In this research, the indicators of functional diversity used are community weighted average (CWM), functional richness index, functional evenness index, and functional divergence index. Functional richness indicates the spatial expansion of functional characteristics in the society. This index is shown as a minimum-maximum range for one feature, but for more than one feature, it is shown as a volume in the feature space, so that the number of dimensions is a function of the number of features under investigation. Functional uniformity is a measure of uniformity of the space between species in the space of features. Functional divergence is a quantity of how the values of the features are spread within the limited space of the features. The weighted average index of the community, which is calculated separately for each plant characteristic, is affected by the characteristic of the dominant species. If the function diversity index is based on several characteristics (function richness, function uniformity, function divergence), it indicates the diversity and difference in the functional characteristics of plant species. Therefore, the type of relationship (positive or negative) and the level of explanation coefficient (R2) will determine the relationship between biodiversity (plants) and ecosystem function.ConclutionThe results showed that species diversity indices (Eveness, Shannon and Simpson) had a significant and negative relationship with rosemary. Two indices of functional diversity based on one trait had a negative relationship with ecosystem function but the weighted average index of dry matter content had a positive relationship with function. The results of multiple regression also showed that the indices of species diversity and functional diversity based on one trait justify 0.43 and 0.68 of ecosystem function changes, respectively. Therefore, different aspects of biodiversity are related to ecosystem function and sustainable protection of ecosystem services and functions is of great importance. Heavy grazing also lost the link between biodiversity and ecosystem function. Therefore, reducing the intensity of grazing in rangeland ecosystems will improve biodiversity and ultimately improve ecosystem function.