جستجوی مقالات مرتبط با کلیدواژه "evenness" در نشریات گروه "اکولوژی"

Awareness of biodiversity status is one of the requirements for adopting a conservation approach in rangelands ecosystems. In this regard, the present research was conducted in order to investigate the effect of slope direction on the values of plant diversity indices in the Astraglaus shrubland of Nazluchai region in 2017. For this purpose, in total, with the use of 230 sample plots of one square meter, which were placed at a distance of five meters from each other, along 50-meter transects; the crown cover percentage of plant species were collected in each of the main directions of the range (eight northern directions, five southern directions, five eastern directions and five western directions). Then, with the PAST software, the most important and widely used indicators of species diversity (Margalef, Taxa, Menhinick and Berger-Parker as species richness indices, Dominance, evenness, Simpson and Pielo as species evenness indices, Shannon and Brillouin as heterogeneity indicators) were calculated. Finally, using the one-way analysis of variance method, statistical comparison of the averages was carried out. The results showed; A total of 41 plant species were identified in the studied areas, and Margalef, Taxa, Shannon, Brillouin and Fisher's Alpha indices had a significant difference at the five percent level in different geographical directions. So that the highest value of these indices was related to the western direction, respectively 2.55, 12.2, 2.1, 1.88 and 4.05. Simpson's, Menhenik's, Dominance, evenness, Pielo and Berger-Parker indices were also not significantly different from each other in different directions. Although the two western and southern aspects were significantly different from each other regarding most of the indicators, nevertheless, the clustering results of the plant composition of the sites classified these two domains in one cluster with high similarity rate (around 70%). This finding indicates that the diversity indices are not able to provide information about the plant composition and should pay attention to the plant composition when using these indices. Finally, it should be mentioned that although Margalef, Taxa, Shannon, Brillouin and Fisher's alpha indices were able to separate the sites, but the proposal of using these indices in the monitoring plans of rangleands with the dominance of Astragulus microcephalus species in the northwest of the country, requires another researches.

Choosing management strategies are influencing the vegetation characteristics and plant diversity in rangelands. We have studied the effects of three management treatments including overgrazing, exclusure, and exclusure with restoration operations on vegetation characteristics of plant cover, composition, and diversity in Kiasar Chardange summer rangelands. In each management treatment, three random transects with the length of 50 m were established in the pasture and in five random plots of one square meter nested in the transects, the percentage of canopy cover, the composition of three palatability classes were recorded and the indices of plant diversity, plant evenness, species richness were calculated. For comparing the effects of different treatments on vegetation characteristics and diversity indices, an analysis of variance with equal subsamples was performed. Nonmetric multidimensional scaling was used to interpret the scattered patterns of plant compositions in relation to different management treatments. The results showed that all diversity, evenness, and richness indices were significantly different in three management treatments (p<0.05) The exclusure with restoration treatment had the highest indices of Simpson diversity (0.74), Shannon-Weiner diversity (2.12), Margalov richness (1.44), Mehnick (1.04), alpha diversity (6.13), and beta diversity (20.87). In contrast, the overgrazed site had the lowest values. The Camargo (0.77) and Smith-Wilson (0.87) evenness indices had the highest values for exclusure and the lowest values for exclusure with restoration treatments. Our findings could be a road map for future planning in similar sites. For rehabilitation of rangelands and improving plant diversity, restoration treatments in exclusures are recommended.

A biodiversity investigation was carried out in the wild pistachio research forest located in southwest of Fars Province between 52˚ 30́́ to 52˚ 40́́ longitude and 29˚ to 29˚ 15́ latitude in an areaof 9374 Ha area. 72 sampling transects fifty meters long were designated using systematic-random design. In each sampling plot a list of bush, shrub, and tree species and their abundance were recorded. The area was divided into 3 slope levels (level 1: >10%., level 2:10%-30%., and level 3: <30 %), 4 aspects levels (north, east, south, and west) and 3 altitudinal levels (level 1: >1,800 m., level 2: 1,800–2,000 m., and level 3: <2,000 m. a.s.l.) using ARC GIS softwear. Data were analyzed using different indices of heterogeneity, richness and evenness by PAST software and were compared in each of the abovedivisions. Gratest heterogeneity and richness indices were observed in area with slope greater than 30%. Results show that the area with 10-30 percent slope has the highest uniformity. Also, indices of heterogeneity and richness showed that north aspect has higher value than the other directions. Evenness indices indicate that the east direction has greater uniformity. Diversity indices among altitudinal levelrevealed that diversity,eveness and richness in altitudes greater than 2000 meter above see level  is more than other altitudinal levels. The results showed that the vegetation diversity of the region are affected by the physiographical condition.

<p</pThis study was conducted to compare regeneration density and biodiversity indices in the natural and man-made gaps in the Tutaki forests of Siahkal in Gilan province. Data were collected from 60 gaps (including 30 natural and 30 man-made gaps). The results of species composition indicated that three tree species including Diospyros lotus L., Carpinus betulus L. and Alnus glutinosa L. in both gaps. In the shrub floor, for both gaps and all kinds of species, the  average number in hectares of man-made gaps (with the exception of  Ilex) was  higher than that of natural gaps. Ilex & Crataegus pentagyna indicated the significant difference at 95% level between 2 gaps. Also, the regeneration density for all species at the natural gaps was more than man-made gaps and the average number in hectares for Diospyros lotus, Alnus glutinosa and Acer sp indicated the significant difference at the 95% level between the 2 gaps. So the regeneration of Fagus orientalis Lipsky was observed only in the natural gaps. The results of biodiversity indices  also revealed that in natural gaps, the average of diversity, evenness and richness had the highest value, whereas in shrub, the average of these indices had the highest value.

Exclosure is considered as a management method to improve vegetation. This study aimed to evaluate the effects of exclosure on species diversity in Zayanderod dam station in Chadegan, Isfahan. The study area was stratified based on the various management types and slope directions, and samples were collected randomly in each layer. Four perpendicular transects, 500m in length were established along the gradients. Fifteen plots (1×1.5m) were established along each transect. The cover percentage, density and scientific name of the perennial species and the management condition were recorded in each plot. Diversity index of Simpson and Shannon, richness indices of Margalef and Menhinick, Simpson evenness indice, and Parametric methods (curve of frequency) were calculated in the two grazed and ungrazed areas. Independent t-test was used to compare the diversity indices. CCA Analysis was used to evaluate the relationships between species and management factors with the diversity indices. The results showed that although the diversity, richness and evenness indices in the exclosure area were more than the grazed area, there was no significant difference between the diversity and evenness indices in the areas. The log-normal was the significant fitted graph in the study area which represents relatively stable societies. The ordination results showed that grazing area and exclosure area are well separated from each other and confirmed the higher richness in the exclosure site.

In order to investigate the effects of range management plans on species diversity, richness and evenness in Semirum rangelands, 52 sites (28 with treated plan and 24 without treated plan) were selected. The non-parametric indices for species richness (Margalof, Menhinick, Jacknife and counting method) and species diversity (Simpson, Camargo, Smith and Wilson and modified Nee) were compared in two management plans. The mean comparisons were made by independent T Student Test and Mann-Witheny U Test, and correlation was determined between diversity indices and vegetation parameters. Based on the results there was no significant difference between the two management systems regarding environmental features, while the implementation of range management plans caused significant reduction of stocking rate. Among the studied indices, evenness of species in sites without treated plan was significantly more than the sites with treated plan. The correlation matrix showed that there was a significant positive correlation between species richness and vegetation cover, production of perennial plans, and the rangeland condition and trend, while evenness showed significant negative correlation with these indices. Generally, implementation of range management plans has considerable effect on increasing climax species, dominance of Bromus tomentellus and it causes improvement of rangeland condition and reduction of evenness. This behavior could be explained by the balance between species competition and grazing pressure. Further, succession process of the studied communities demonstrates domination of some desirable species, high production and less diversity.

This study was conducted by the aim of study the species composition and diversity in the north faced slopes of Sabalan (altitude profiles of Lahrood-Shabil) along 7 transects in three elevation classes of 1500 to 2000m, 2000 to 2500m and 2500 to 2700m in the grass-shrubland dominated habitats. Plant specimens were collected in the fieldworks, and then species were identified using the checklists and reliable literature. Overall, 64 identified species were belonged to 48 genera and 22 families. Poaceae family with 9 genera and 16 species, Fabaceae family with 4 genera and 8 species and Asteraceae family with 6 genera and 6 species are the dominant family and genera. According to the Rankaier's system hemicryptophytes with 50%, therophytes with 31%, geophytes with 16% and chamaephytes with 3% are the growing life forms at the study area. In terms of geographical distribution, 42% of the species are belong to Iran-Turonian region, 22% of those to Iran-Turonian and Euro-Siberian, 12% are cosmopolitan, 3% to Euro-Siberian and other 21% is belong to other regions. From the identified species 6 of them are in threatened status based on the International :union: for Conservation of Nature and Natural Resources (IUCN) criteria. Diversity and evenness of species were calculated using numerical indices. Results of numerical diversity indices (Simpson and Shannon-Weiner) showed significant change according to elevation. However, the evenness indices (Simpson and Smith and Wilson) show no significant change by elevation.

Soil macrofauna biodiversity has an important role in ecosystem services. In order to find how soil macrofauna biodiversity is related to trees and shrubs in riparian forest of Maroon River in Khuzestan province، soil macrofauna were collected using hand-sorting procedure from 0-10 and 10-25 cm soil depths in 50 cm × 50 cm plots، 50 meters from each other on transects 100 meters apart and perpendicular to the river. Totally، 175 sampling plots were taken. In each plot، quantitative characteristics of trees and shrubs were measured. Soil macrofauna abundance and biomass were highest at 0-10 cm soil depth. Macrofauna biodiversity had a stronger correlation with Tamarisk properties than Euphrates poplar. In contrast، macrofauna biodiversity was not different under Tamarisk and Euphrates poplar. But earthworm was higher under Euphrates poplar cover. The most important parameter of soil macrofauna biodiversity in this area was crown cover. Therefore we could state that regardless of tree species، crown cover of these forests should be conserved because it maintains soil macrofauna biodiversity.

Since the roads are considered as one of the indicators of sustainable development and much of the rural dusty roads are passed through the rangelands thus, the effect of roads has a very importance effect on rangeland ecosystems. Near-road rangelands were selected from the edge of the road until 5 meters distance and far-road rangelands were used in 5 to 20 meters from the edge of the road. For measuring canopy cover, production, density, relative importance, richness, evenness and diversity of plants used to 50 m transects and 1 m2 plots were used in each study areas. 4 transects and 40 plots randomly were put along three kilometers of road of Pishkouh Ali-Abad rangelands in the Yazd. Results showed that the road can changes the vegetation composition, production, and cover, therefore,there is reducation in production, canopy cover of near – road. The importance value of shrub species of near road has declined while the importance value of grasses has increased. Richness, evenness and diversity indices were reduced and distribution of plants, moved to the clamps. These factors indicated the site of near- road is less stable and plant community has crossed boundaries of ecological threshold. Therefore, it is suggested that making the rural dusty roads should be implemented with detailed studies and suitable reclamation may be done with paying attention to ecological condition of the study area.

This study was undertaken to investigate the role of forest management in tree diversity، regeneration and vegetation in control and managed parcels of series No. 1 of forestry plan in Khalil-Mahale، Behshahr. Thirty samples with an area of 1000 m2 were systematically and randomly taken with a 100 × 75 m grid in both parcels. In each plot، tree number and species type were recorded. In order to study the vegetation، five micro-plots (1 m2)، one in the center and four others in four main directions (half radius from the center of the plot) were taken in each plot. The type and percentage of herbaceous species were recorded in each microplot. To count the regeneration in the center of the main plot، circular sample plots with an area of 100 m2 were used. To study and compare the biodiversity in the two plots and to calculate the richness and evenness، the Simpson and Shannon-Wiener diversity indices، Margalef and Menhinic indices and the Pilo index were used، respectively، using PAST software. The results showed that the number of plant species was more in managed plots. The biodiversity of woody and herbaceous plants richness indices and regeneration of tree species were higher in managed plots. In fact، the results showed that forest management using single selection method had different effects on woody species regeneration and diversity of herbaceous and tree species.

In order to identify and determine weeds distribution in rainfed wheat fields of Kermanshah province, 58 fields in 7 counties were investgated during 2001 and 2009. After weed survey the charsterictics of weed species were evaluated. Then density, frequency, uniformity, mean density, abundance index, Shannon- Weaver diversity index and Simpson index were determined. In rainfed wheat fields of Kermakshah province 91 weed species were identified out of which 15 species belong to grass weed and 53 species belong to broadleaf weed. Poaceae, Fabaceae, Asteraceae and Rubiaceae were the most important families with, 57, 35.5, 34.6 and 18 percent of FIV, respectively. Based on the result of this study Galium tricornatum, Vicia hyrcanica, Vaccaria pyramidata and Anthemis cotula were the dominant broadleaved weeds. Avena ludoviciana, Hordeum spontaneum and Bromus tectorum were the most important grass weeds. In addition the most important troubeling preharvest weeds were Convolvulus arvensis, Carthamus oxyacanthus and Glycyrrhiza glabra in rainfed wheat fields. Shannon-Weaver diversity index showed the highest species diversity were in Kermanshah with 2.67 and the lowest species diversity in Songhor and Sarpolezohab were with 1.8 and 1.9, respectively.

Biodiversity of natural ecosystems is often studied at three levels، ecosystem، species and genetic diversity. In fact، agrobiodiversity is the outcome of species، genetic and management diversity interactions. In order to investigate the species and functional diversity and structure of weed communities in sugar beet fields of different cities in Khorassan Razavi and Khorassan Shomali، 178 farms from 12 cities were studied. Data were collected from questioners، weed population sampling and interview with farmers. The results showed that weed population in different cities composed of 56 species in 14 plant families، in which dicotyledon species were more than monocotyledons. This community، 47 species were C3 plants and others were C4 species. These 56 species also included of 36 annuals، 2 biennials and 18 prennials. Poaceae and Asteraceae families showed the most diversity amongst the monocotyledon and dicotyledon، respectively. The results also shown that Chenaran and Khauf had the most (27 species) and the least (5 species) species richness. Sorenson and Steinhaus similarity indices were showed that Chenaran and Ghouchan showed highest similarity (0. 9%) whereas، Ghouchan and Khauf showed the least similarity index (0. 2%).