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

The impact of dust storms on the Sistan and Baluchistan region is one of the most important current issues in this region. The current research is an attempt to investigate the effects of climate change on the trend of changes in dust storms in Sistan and Baluchistan province in the future perspective (until the end of 2100) compared to the base climate period (2010-2020). The study method consists of two parts, namely, analyzing the trend of dust storm events changes from the past to the present and projection the future situation. In the first step, using the multiple linear regression method, the correlation and relationship between the variable of days with dust with other climatic parameters (temperature, rainfall, relative humidity, and wind speed (during the statistical period of 2010-2020 was obtained. Then, the modeled data of the CMIP6 global model in three scenarios and 8 decades from 2020 to 2100 were used as inputs of significant regression relationships during the period 2010 to 2100 to investigate the future status of dust storms. Analysis of the results showed that, the trend of dust event change based on three scenarios of optimistic, moderate, and pessimistic in Sistan and Baluchestan provinces is increasing. As expected, the least dusty days are seen based on the optimistic scenario (SSP1-2.6). The dust trends based on the middle (SSP3-7.0) and pessimistic (SSP5-8.5) scenarios have almost the same trend and are increasing. Therefore, we can expect to have more frequent dust events in the future as climate change continues. As a result, the necessary investments for adaptation measures and mitigation against the harmful effects of dust need to be put on the agenda from now on.

To study 38 corn hybrids, an experiment based on randomized complete blocks design with three replications at the Moghan and Karj was carried out during the 2020 cropping season. The results showed that there was a significant difference between corn hybrids for grain yield, grains per ear, ear length, rows per ear, 1000-grain weight, ear diameter, and grain depth. Hybrid No. 26 (KLM81027 × K47/3) with the highest yield and ear length was identified as the best hybrid. The correlation between grain yield with grain depth and 1000-grain weight was significant. The heritability value was between 19.01% (grain yield) and 87.59% (row per ear). The regression analysis indicated that rows per ear and ear diameter had positively related to grain yield. Cluster analysis with grain yield, grains per ear, ear length, rows per ear, 1000-grain weight, ear diameter, and grain depth of 38 corn hybrids classified into four different groups, one of which has a hybrid of No. 26 (KLM81027 × K47/3), and No. 37 (TWC647) was the most desirable groups. In addition, hybrids No. 4, 9, 13, 15, 19, 20, 23, 25, 32, 37, and 38 were identified as superior and stable hybrids for cropping in warm dry climates. As a result, it seems that corn hybrids of FAO 600 can be suitable for cropping in warm dry climates, alsothe K74/2-2-1-4-1-1-1 × K3640/3 hybrid was identified as superior and stable.

The crown ratio is one of the most important attributes of trees for modeling growth and evaluating the competitive environment in forest stands. This research was carried out to determine the crown ratio for wild pistachio. Continuous transect sampling was carried out with the counting limit of 5-cm diameter at breast height. In each transect, the total height of the tree, the height of the crown, the diameter at breast height (DBH) and the elevation were measured. To study the type and severity of the relationship between elevation and DBH with crown ratio, correlation analysis was conducted. For modeling using linear regression analysis techniques, the curve estimation (including simple linear, second, third, linearized logistic, exponential, inverse and power) and nonlinear models (logistic, Richard, Weibull, and exponential) were used. The results showed that the linear model fitted to DBH data in order to predict crown ratio was statistically significant but the R-square was not noticeable (R2 = 0.33). Nonlinear models explained a maximum of 34% of variations in crown ratio with high precision. Elevation from the sea level was not a suitable predictor for the crown ratio. In this study, due to the low stand density, lack of effective competition between trees and the uniformity of the competitive environment, the crown ratio was less affected by independent variables such as DBH. Accordingly, it seems that in the low density forests of the Iran-Touranian region, the development of powerful models to predict the crown ratio will have little success.

Ordinary Kriging (OK) has been widely used for prediction and spatial distribution study of surface water quality parameters. This method uses a constant mean to capture the trend in the model. In this method, the prediction can be poor if there are strong trends. To overcome this problem, an alternative model called Blind Kriging (BK) was developed. The mean function in BK is polynomial and the unknown mean function parameters are obtained using the Bayesian variable selection technique which requires a lot of calculations. To solve these problems, in the present study, OK was modified based on BK. In the modified method, the polynomial mean function parameters were determined using linear Regression instead of Bayesian inference method. Then, the performance of OK and modified Kriging in the estimation of trophic indices and water quality parameters in Anzali Wetland was evaluated using different statistical criteria (the coefficient of determination, the root mean square error and the mean absolute error). For this purpose, the concentrations of 14 parameters in six sampling points of Anzali Wetland water were analyzed during 2018. Subsequently, the modified and Ordinary Kriging were applied to water parameters and trophic indices. The results showed that the modified Kriging had the best results. In addition, the improvement of the modified Kriging compared to OK is achieved up to 88%. The results of the present study can be useful in the planning of the future monitoring program in Anzali Wetland.

Over the past two decades, degradation damage has increased in natural ecosystems. This research focuses solely on the degradation of soil and vegetation cover in Sorkheh Eshpar National Park. For this purpose, some physical properties of the soil (specific gravity and true porosity, moisture content, a percentage of pebbles, acidity and conductivity and soil texture) were measured. Also, the diversity and density of the crop in two safe zones and other uses were calculated. Soil sampling was carried out in the form of strip transects at the beginning and the end of each joint unit and excavation of four soil profiles at a depth of 5-5 cm. The crown cover was taken with 2 × 2 squares throughout each transect and 30 plots per unit. A total of 600 plots and 480 soil profiles were taken from the study area. Shannonchr('39')s biodiversity index was selected as an output variable and soil characteristics, ecological factors, and human factors as inputs of the model. Normality of data was confirmed by Shapiro-Wilk test. SPSS software was used for soil degradation regression and vegetation cover. The combined, removable, and retrograde method was chosen with a value of = 422.0. With the MATLAB software, the artificial neural network was created with a multi-layered perceptron, with a secret layer, and 18 neurons, and a sigmoid tangent function, and a value of R = 0.5065. Considering the amount of R in the artificial neural network model, this model was selected as the optimum model for estimating and predicting soil degradation and vegetation cover in Sorkho-e Hesar National Park.

It is accepted that the global annual average temperature has been increased during recent decades. The climate of Iran is also affected by this global warming. Some studies indicated the increasing of mean annual temperature of Iran between 3.5-4.5○C by 2050. Crop phenology is directly related to temperature, so climate change could significantly change the phenology and yield of crops. Modelling phenology is a way to simulate the timing of phenological stages based on climatic factors. Amongst models, WOFOST is known as a powerful model for simulation of phenological stages and yield of wheat. In this study climate warming of Iran was evidenced. Based on this fact, trends of potential grain yield and time of flowering and maturity of wheat were studied in different climatic zones of Iran during 1992-2012. It is expected that understanding the thermal induced of phenological changes, can lead us to better field management decision making.

Weather data of 18 cities from 4 climatic zones of Iran (northern warm and humid (Zone 1), southern warm and dry (Zone 2), temperate (Zone 3) and cold and high elevation (Zone 4)) were analyzed during 1992-2012 and the long-term trends of air temperature were detected by linear regression. The crop growth simulation model WOFOST, was used to simulate the time of flowering and maturity and also the potential grain yield of winter wheat. Calibration and validation of model was conducted in 4 selected cities from each zone using statistical measures. The consequences of temperature on duration of grain filling period and also yield of wheat were determined.

Results indicated that the mean annual air temperature was significantly increased in all cities during 1992-2012. The highest increasing rate (regression line slope) belonged to Ardabil (0.159○C.y-1) and the lowest rate was observed in Pars Abad Moghan (0.06○C.y-1). Validation of WOFOST in 4 selected cities from each climatic zone, showed the perfect ability of model in simulating the flowering and maturity time of wheat. Regression analysis showed that the grain filling period was increased in accordance with temperature rise in zone 1 and 4 whereas it was shortened in zone 2 and 3. Grain yield showed the same trends predicted for grain filling period in different climates. Slop of linear regression between temperature and yield was significant except in Gorgan (Zone 1). In all cities the relation between grain filling period and yield was direct and positive.

Although temperature has increased in all climatic zones of Iran, flowering and maturity time and grain yield of wheat has showed different responses. There was a nonsignificant slope of regression line in the north humid climate, which means that the humidity of northern part of Iran (south of Caspian Sea) enhanced stability for this area. Annual mean temperature in southern warm and dry zone of Iran ranged between 24.3-27.9 ○C that could be stressful for wheat, and hence resulted in shorter grain filling period and less grain yield. It seems that in temperate zones (such as Mashhad) increasing temperature caused yield reduction due to faster GDD accumulation and lack of time to complete remobilization of photosynthetic materials. On the other hand, in cold areas increasing temperature could reduce the risk of cold stress in flowering time, resulting in longer grain filling period and higher grain yield. According to WOFOST simulation results, during 20 years study (1992-2012), mean potential yield of wheat increased 6.25 and 11.42 percent in northern warm and humid (Zone 1) and cold and high elevation (Zone 4), respectively and decreased 12.17 and 13.11 percent in southern warm and dry (Zone 2) and temperate (Zone 3), respectively. Total mean potential yield of wheat, by consideration of proportion of each zone in total wheat production of Iran, showed reduction of 1.8% and 3.28% during 1992-2001 period (10 years) and 1992-2012 period (20 years), respectively.          

In order to investigate the response of grain yield, plant height and phenological traits of maize hybrids (Zea mays L.) to planting date, a factorial experiment was carried out based on complete randomized block design with four replications during two growing seasons (2013-2014) at Moghan Research Station. Treatments consisted of two planting dates (May 1 and June 25) and five maize hybrids (namely SC704 and SC720 from a late maturing group, TWC600 and SC647 from mid maturing group and SC301 from early maturing group). The results of statistical analysis showed a significant difference between years, planting dates and hybrids. The highest grain yield and plant height were related to SC704 and SC720. The results showed that the planting date on May 1 increased plant production compared to June 25. The highest average of days to physiological maturity related to planting date was May 1. SC704 and SC301 had the highest and lowest average of days to flowering and days to pollination in two different planting dates during two growing seasons (2013-2014) in Moghan region, respectively. Multiple regression analysis by stepwise method showed that in regards to days to pollination and days to physiological maturity with grain yield of maize hybrids there was a significant positive association (P<0.01) in two different planting dates (May 1 and June 25) during two growing seasons (2013-2014) in Moghan region. In conclusion, The phenological traits with grain yield can be used to select the best maize hybrids for different planting dates.

The aim of this study was the analysis of discharge variations of two rivers i.e. Qezelozan and Shahroud, regarding the sustainable rice production in Guilan province. To achieve this purpose four trend analysis tests including Sen, Mann-Kendall, linear regression and Spearman were used. In this study, river discharge data of 49 and 37 years for respectively Qezelozan and Shahroud Rivers were used. The results of all tests in quarterly and annual periods were similar. The results of all tests showed a significant decrease in river discharge of Qezelozan and Shahroud. Furthermore, for monthly periods the Man-Kendall and the Spearman tests were used that during the periods both tests showed similar results i.e. reducing discharge during the studied periods. In both rivers, the annual river discharge was reducing by 60% from the first year to the last year of the study period. In this study, the changes in both precipitation and temperature were also investigated; the results showed a significant reduction in the amount of rainfall and a significant increase in the temperature. The results of this research could be used in predicting future drought, irrigation planning and management of integrated water resources.

To investigate the relationship between slope، aspect and elevation and quantitative characteristics of plant species، totally 125 sampling plots were selected in a block systematic design. In each sampling، plot presence، number، height، diameter at breast height (for trees) or root collar (for shrubs) and crown diameters were measured and recorded. Also، we recorded vegetation type according to the portion of species in the plot. Correlation analysis was conducted according to the scale of variables using Pierson، Spearman، Phi and Cramer and Eta coefficients. Results found that elevation is the most important factor affecting presence and density and also type in the study area. Altogether، Atlas Pistach (P. atlantica F. & M) and Wild Almond (A. scoparia Spach.) in low elevations and Maple (A. cinerascens L.)، Marsh-arrow-grass (A. lycioedes Spach.) and mountain almond (A. elaefnifolia Spach.) in higher elevations had better conditions. Slope had a negative correlation with presence of Wild Almond and Send Cherry (Ephedra spp)، and positive correlation with the presence of other species. Also، Wild Pistach trees present in southern aspects showed more basal area and volume in these aspects. Results of this research can be used in the detection of suitable points for development of plant species. Regression analysis showed that frequency of almond and Send Cherry and average height of almond and wild Pistach were predictable according to elevation and slope. Of course، coefficient of determination was low in all cases.

Effect of salinity stress on the morphological behaviors of Caucasian Hackberry (Celtis caucasica Willd) seedlings، was evaluated in a completely randomized design with 20 replicates during the summer (dry part of the growth season) in this research. The experiment was carried out in Torogh nursery، Mashad city. Without stress (tap common water in the nursery) and salt treatment (source water KavirPark-Civil of Gonabad with EC 12. 03 dS. m-1) were used every two days، each time 150 ml/day. During the summer، morphological traits including height، diameter، leaf number، leaf area and were measured at the end course of growing، fresh and dry weight of roots، stem and leaf and ratios of leaf area، specific leaf area and leaf weight were calculated. Results indicated that height growth، number of leaves، leaf area at the end of growth period and leaf area growth were significantly different at 5% level and diameter growth reduced significantly at 1% in comparison with control treatment. Results of repeated measures analysis show that in salt treatment with effect of the time in all the period of measurement terms of height and number of leaves at 5% level and diameter at 1% level are significantly different، but the number of leaves did not show significant differences. The result indicated that effect of time salinity interaction for diameter was not significant but for height at the 1% level and leaf area had significant difference at 5% level.