جستجوی مقالات مرتبط با کلیدواژه "شاخص تنوع شانون" در نشریات گروه "آبخیزداری، بیابان، محیط زیست، مرتع"

Measuring the diversity and identifying plant vegetation traits and functional groups and classifying them, in addition to helping to accurately identify the vegetative capacity of the area, helps us to understand the vegetation response of the area to disturbances and presence. Potentially resistant species with similar or invasive traits help. The purpose of this study was to investigate and evaluate the vegetative status of the region, the trend of changes and evaluation of the second sequence of dust centers in Khuzestan after planting seedlings in different ways. Functional groups (PFTs) were used. To evaluate the changes in the vegetation of the area by field survey, 15 transects of 100 meters with distances of 50 meters were systematically randomly selected (the first transect was randomly selected and the rest with a defined distance of 50 meters). Due to the uniformity of plant species composition and the absence of environmental effects, a total of 180 fixed plots with dimensions of 1 square meter (location recording with GPS device) were installed. The results of a recent study in three areas of the dust center in the southeast of Ahvaz showed that in selected areas, various irrigation methods along with rainfall will cause significant changes in the percentage of cover (frequency) and the number of species from 2017 to 2020. Functional groups in the Tovayel region with surface irrigation (Faro) In 2020, nine groups were identified, in Bagan region with tanker irrigation and hole digging with seven excavators, and in Hanitieh region with tanker irrigation and hole digging seven functional groups. The results of T-test analysis also showed that there is a significant difference between the average of the two values of all indicators, including the diversity of Shannon and Simpson in March 2017 and March 2020 for all three regions so diversity indicators raised since number of species and cover increased.

The study of vegetation and the measurement of diversity indices are suitable tools for studying the status of forests and rangelands and evaluating them. The purpose of this study is to evaluate the trend of vegetation changes during four consecutive years and in two seasons in the Bagan region. For this purpose, 5 transects of 100 meters with distances of 50 meters in the study area were considered systematically randomly. A total of 30 plots of one fixed square meter were installed along the transects. In two growing seasons, spring and fall, from 2017 to 2020, the type and percentage of cover of native species were harvested. Dominance, uniformity and diversity of Simpson, Shannon and Hill species were measured using PAST and R software. The results of one-way analysis of variance (ANOVA) showed that there is a significant difference between the mean of dominance, Shannon and Simpson indices, percentage of cover, and the number of species in the spring of different harvest years. In fall, except for the dominance index in other indices during July 2019 compared to 2018, there was a significant difference. From the results, it can be concluded that despite the return of some annual or short-lived species such as Bienertia cycloptera Bunge and Salsola jordanicola Eig. following irrigation of cultivated seedlings and rainfall, the study area is still sensitive and fragile and needs to be managed and confined until proper rehabilitation.

Khormarud is one of the Rivers in Azadshahr County in Golestan Province, which is originates from southeast elevations and discharges to the Gorganrud River that reach to the Caspian Sea. Diatoms constitute the dominant algal flora in aquatic ecosystems. In order to identifying diatom flora of Khormarud River, specimens were collected from stony and sediment substrates during summer and autumn of 2017. In total, 60 species belong to 32 genera and 20 families were identified, from which 59 species were belonging to class Bacillariophyceae and only one species to class Coscinodiscophyceae. Nitzschia with 7 species were the most species rich genus and Navicula and Gomphonema with 5 sp. were in the next order. The most abundant taxa were Achnanthidium gracillimum, Achnanthidium nanum, Cocconeis placentula, Cymbella affinis, Encyonopsis minuta, Gomphonema olivaceum and Nitzschia inconspicua. According to the results of diversity indices, site 3 which affected by runoff from fishery activities, had lowest species diversity and high pollution level. In total epipelic samples in all sites had high diversity than epilithic samples which could explain by the fact that algae on sediments are affected weakly by water column chemistry than epilithic algae.

Salinity is one of the environmental parameters that its impact on plant species diversity requires further studies. In this research, change of plant diversity was studied along a salinity gradient that was resulted from proximity of water table to the land surface in Incheh Borun plain due to the altitudinal change in northern part of Aq-Qala city. A transect with the length of 1 km was laid out along one of the hills in the region. Sampling units (plots) with the size of 3×3 m were established at 100 meters intervals along the transect. A floristic list was compiled and plants canopy cover was estimated in each sampling unit in the direction of dominant altitudinal gradient. Shannon-Wiener and Simpson indexes were calculated by using of PAST software. β-diversity was calculated between the sampling units using the Whittaker index. The relationship of salinity changes between sampling units along the altitudinal gradient and Alfa diversity, Simpson and β-diversity was studied using the linear regression. Results showed that there are significant relationships between the altitude, soil salinity and plant diversity indices. Soil salinity increases by decrease of altitude and the biodiversity decreases by increasing of soil salinity. These changes occur due to increasing of salinity.

In the present study, the effect of soil factors on above-ground vegetation and soil seed bank diversity under grazing and exclosure conditions was studied. Soil sampling was done in winter 2010 using randomized systematic method along four transects in the grazing and exclosure areas of Vaz watershed. Along each transect, 10 plots of 1m2 were established and soil samples were collected from a depth of 0-10 cm for seed bank and physico-chemical studies. Vegetation cover was measured in each plot in late spring of 2011. Soil factors such as porosity, bulk density, relative humidity, EC, pH, nitrogen, organic matter, and stone percentage were measured. Shannon and Simpson diversity indices were calculated for above-ground cover and soil seed bank and the most important factors influencing on the diversity were specified using multiple linear regression by backward elimination method. Results showed that the porosity, bulk density and organic matter had the greatest effect on the diversity of seed bank in the exclosure area. On the other hand, EC, nitrogen, organic matter, soil bulk density and porosity were the most important factors affecting the seed bank diversity of grazing area. According to the obtained results, organic matter and nitrogen were the main factors affecting the plant species diversity in the exclosure area, while in the grazing area, physical parameters such as bulk density, porosity and stone percentage had the highest impact on species diversity.

In this study، the effects of reconstruction and conservation were investigated on plant diversity of the region of the international Carbon Sequestration Project in Hussein-Abad، South Khorasan province. In the study area، four vegetation types including Haloxylon persicum، Atriplex conescens، Haloxylon persicum + Atriplex conescens and Zygophyllum eurypterum were planted in 2004. Six years after that، the plant diversity indices of four replanted vegetation types along with control vegetation type (no replanting and conservation programs) was studied in two different dates (April and May) in 2011. For this purpose، 51 quadrates (2 × 2 m) were used in each vegetation type. Results showed that the maximum plant diversity and vegetation coverage were observed in Haloxylon persicum + Atriplex conescens (30 species and 22. 5%، respectively) vegetation types، and the minimum values of these indices were recorded in control (20 species and 5. 5%، respectively) vegetation type. The highest and the lowest values of plant density were obtained in Atriplex conescens (539،000 plant. ha-1) and control (179000 plant. ha-1) vegetation types، respectively. The Margalef’s richness index was higher in all protected vegetation types، while uniformity index and Shannon diversity index were higher in the control vegetation type. The frequency of 65% of plant species was less than 20% and about 45% of the plant species belonged to therophytes. Overall، the experimental results showed that desert ecosystems could play an important role to improve global biodiversity if proper management programs are employed.