فصلنامه تحقیقات مرتع و بیابان ایران
سال سی‌ام شماره 2 (پیاپی 91، تابستان 1402)

Due to the limitations of freshwater resources, using other sources, such as drainage and seawater, is inevitable for fodder production by halophytes. Salicornia species are the most salt-tolerant plants (Eu-halophytes) that grow directly in seawater. The plant shoots could be used with common fodder plants for livestock feeding. After oil extraction, Salicornia seeds contain 43% protein. The research objective was to select the most suitable Salicornia species in terms of yield and fodder quality in Bushehr Province.

To investigate the yield and nutritional value of Salicornia, this research was carried out on Salicornia bigelovii and four native ecotypes, including Bushehr ecotype (S. sinus persica Akhani), Central Plateau ecotype (S. persica Akhani subsp.Sersica), Urmiai, Gorgan and Markazi ecotypes at the Salinity Research Station of Bushehr Province. The area is characterized by a warm and wet climate with low annual precipitation (217 mm) and high annual average temperature (24.0 °C).A three-replicate randomized complete block design was used. The field was planted by seed sowing and irrigated with Persian Gulf water (60 dS m-1).Aerial plant samples were prepared at vegetative growth to determine the fodder nutritional value of different plant species and ecotypes. Values of aerial ash, crude protein, non-protein nitrogen content (NPN), acid detergent fiber (ADF), neutral detergent fiber (NDF), acid detergent lignin (ADL), and metabolizable energy were measured. At the end of the growing season, an area of one square meter was taken from each experimental unit to determine biomass dry weight. Data were analyzed using SAS software, and mean comparisons were performed using Duncan's test at the 5% level.

Results showed a significant difference in dry biomass between different Salicornia species and ecotypes. Bushehr, Central Plateau, Urmia, Gorgan ecotypes, and S. bigelovii dry biomass amounts were 18.29, 14.64, 4.22, 4.60, and 6.71 tons ha-1, respectively.The highest and lowest values of shoot ash were 54% and 46% of dry matter for Busher and S. bigelovii, respectively. There was no significant difference between species and ecotypes in crude aerial protein. The crude protein content of aerial varied between 6.9 in the Central Plateau and 8.6 in Bushehr ecotypes.The metabolizable energy of fodder was estimated between 5.17 and 5.74 MJ kg-1 of dry matter; the lowest and highest were attributed to the S. bigelovii and Urmia ecotypes, respectively. The highest and lowest cell wall indicators of neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) were related to the Gorgan and Bushehr ecotypes, respectively. Fodder gas production for different Salicornia species and ecotypes was significantly lower than for alfalfa during incubation. Among different species and ecotypes of Salicornia, the highest and lowest gas production rates were related to S. bigelovii and Urmia ecotypes.

To provide livestock fodder on the province's coasts, the Bushehr ecotype (Salicornia sinus persica Akhani) is generally recommended for planting due to its high yield and adaptability to the region. However, due to the relatively high ash content of the plant, only a part of the livestock feed could be provided by the plant fodder. Therefore, to properly use the plant fodder in livestock feed, it is necessary to determine the daily consumption of fodder in the ration.

Research has been done on different materials to control and reduce wind erosion. Among them, we can mention the performance of agar gum biopolymer in reducing dust production at different concentrations of 0.5, 1.0, and 1.5%. Its results showed that the addition of biopolymer improves the water-holding capacity, increases the surface and compressive strength of the soil, and decreases dust production. In another study, agar gum biopolymer significantly improved soil mechanical properties. This study investigates the effect of polymer nuclei (M19) on controlling sand dunes. This research investigates the effect of nucleos (M19) mulch on reducing wind erosion and controlling sand dunes and dust.

This research was carried out in Segazi Plain, a study and implementation priority due to its proximity to urban areas, military facilities, transportation, as well as industries and workshops located there, from the aspect of preventing wind erosion and desertification. After choosing the field, two plots of 500 square meters with the same conditions (an active hill with an area around it with natural and hand-planted vegetation) were selected. To determine the effect of soil cover, the area of each plot was determined by wooden stakes. In addition, the surrounding sand dunes were staked to measure their displacement. A pump sprayer mulched the measuring plot with nucleos (M19) mulch. Following the soil moisture changes, information including seedling survival and growth rate, soil cover's ability to control sand dune displacement, and compressive stress was examined during different months. Finally, the effectiveness of soil cover was compared with the control treatment using the T-test.

 The results of examining the changes in humidity and the effect of soil cover on it showed that the highest humidity in the area was after rain. No clear difference was observed between the drying process of the control plot and the mulched plot. It was also found that this mulch positively affects seedling growth rates. During the research period, the control sand dunes moved about 0.75 to 2.5 meters depending on the season and wind direction. In contrast, the mulched sand dunes remained stable. On the other hand, with time, the mulched field's surface became flaky, and signs of wear and tear were observed.

The first point about using this polymer as a soil cover is its two phases during transportation and storage until mulching. In such a way, the two layers can be clearly distinguished. As a result, mixing is necessary for the uniformity of the polymer during the preparation of the final emulsion. This can be considered as one of the negative characteristics of the used polymer. This mulch positively affected soil moisture changes and increased soil moisture retention. On the other hand, the comparison of the growth of the seedlings in the mulched field and control also shows its effect on the growth of the seedlings. This soil cover's only positive and critical feature is its high flexibility after mulching in such a way that it is possible to drive on it with caution. Finally, after a year, cracks were first detected in the research field. Gradually, the number and depth of cracks increased, which caused the mulched field surface to become flaky. Following this complication, instability and signs of wear and tear were observed in the mulched area. However, no movement or change in location was observed in the mulched hill. It should be noted that with time, more destruction occurs on the surface of the mulched area. Following more flaking, the mulched surface may be destroyed, and hill erosion may begin. Considering these cases, mulching in this and similar areas is not recommended.

 The germination and establishment of plants resistant to drought is one of the most important and effective aspects of rangeland improvement. Investigating changes in rangeland species' morphological and physiological characteristics under different pretreatments under laboratory, greenhouse, and field conditions is necessary. As a result, elite and promising species can be selected, and improvement efforts can be evaluated favorably.

 This study investigated the effect of different pretreatments on the germination and establishment of Sanguisorba minor and Elymus hispidus under drought stress. In this regard, the effect of priming treatments with distilled water, polyethylene glycol, potassium nitrate, and silver nanoparticles was studied to improve germination characteristics and establishment of species under agricultural capacity. The experiment was conducted as a factorial in a randomized complete block design in four replications. To conduct the research, 168 pots were used, and ten seeds were planted in each pot. The measured attributes included the percentage and velocity of seedling appearance from the soil, establishment and survival, length and weight of root and stem, vigor, proline, carotenoid, soluble sugar, total chlorophyll, catalase, and superoxide dismutase enzymes. After sampling the studied traits in the greenhouse and obtaining the results in the laboratory, variance and data analysis in SPSS software. A comparison of mean data with Duncan's multiple range tests at a 5% level for the studied traits was performed on both species.

 The results showed that drought stress significantly differs in characteristics, such as the dry weight of aerial parts or the length of plant roots. The mutual effects of priming and stress were significant on the traits of emergence from the soil, speed of emergence, establishment, survival, and dry weight of aerial parts. Still, it affected several other traits as well. The application of silver nanoparticles had positive or negative effects on seeds' vegetative characteristics, and seedlings grown from the seeds of the studied plants did not show significant changes to characteristics such as plant root length under different priming treatments at a specific moisture level. Some characteristics, including ability, had significant changes due to humidity levels varying up to 20 percent. The positive effects of polyethylene treatment and the negative effects of high nanoparticle concentration were evident. Applying polyethylene glycol and potassium nitrate in E. hispidus and polyethylene glycol and silver nanoparticles at a concentration of 30 mg/l in S. minor showed the highest positive effects on plant resistance under drought stress. Application of silver nanoparticles at concentrations of 60 and 90 mg/L showed negative effects on the vegetative and physiological characteristics of the two studied species.

 drought stress caused negative effects on the structural characteristics of the studied species, and using hydropriming treatments, potassium nitrate, polyethylene glycol, and silver nanoparticles (with a concentration of 30 mg/liter) reduced stress adverse effects. The reason for this is mainly the changes in the physiological factors, such as the amount of proline, catalase, and superoxide dismutase enzymes, and the application of various pretreatments causes positive changes in pretreatment factors and increases the species' drought resistance. The results related to the effect of different pretreatments on the germination of the mentioned species under laboratory and field conditions also confirm this issue.

Desertification is a multidimensional process initiated by the interlinking of environmental and human constructs. It is expanded by combining and synergizing natural conditions, climate change, and human pressure factors. This study aimed to combine economic, social, and managerial factors affecting desertification in the Niatac dust corridor in Sistan and using the application framework of multi-criteria decision-making models, the most important indicators of desertification Human-making is prioritized and introduced in the study area to be used in management and control of desertification and dust phenomenon in the region.

This research is survey research. At first, based on the sources and conventional models of desertification assessment, 20 appropriate indicators were selected in the form of 5 criteria using a combination of different models such as IMDPA, MICD, and MEDALUS, along with the opinions of experts and experts familiar with the region, as well as the research executive team. Data and values related to the indicators were collected through various information sources, including reports from the Statistical Center of Iran, the Ministry of Energy, the Agricultural Jihad Organization, and the General Directorate of Natural Resources of the province, as well as structured interviews in the region, and then the factors and indicators under study were ranked using TOPSIS multi-criteria decision-making method, and finally, a zoning map of the study area was prepared by each of the anthropogenic factors. And it was presented.

According to the results, policy and rules (32.5%), economics (25.1%), water, and agriculture (20.6%) had the greatest impact on desertification. The ranking of indicators showed that the Hamoon wetland rights index and Niatak River with a coefficient of 0.69, the institutional and organizational coordination index with a coefficient of 0.6743, the rural development index with a coefficient of 0.6743, the efficiency index of conservation and recovery of desert areas with a coefficient of 0.5596, poverty index and household income with a coefficient of 0.5988, grazing pressure index in rangelands with a coefficient of 0.4821 and agricultural land release index with a coefficient of 0.5596 had the greatest impact on The land was destroyed and deserted.

The results obtained in this study indicate the importance of anthropogenic factors in the desertification of Sistan. By relying on the results of this study that 62% of the land in the Niatak wind erosion corridor is subject to severe desertification, a long-term action plan implementing suitable measures for rehabilitating desert lands of the region by the custodians should be prepared. On the other hand, TOPSIS, used in this study to determine desertification intensity, is a relatively accurate method when using the appropriate indices. It also has simplicity, flexibility, and low cost. This method can help managers and planners of the desert area identify priorities affecting desertification. It can also provide appropriate programs for managing and restoring desert areas.

 The growth of the population and the increase in food needs have caused humankind to turn to manipulating nature and converting natural lands into crops, especially rainfed agriculture, to provide the food they need. For various reasons, a large part of these lands is abandoned every year, which causes many changes in the physical and chemical properties of the soil. This research aimed to compare the most important physical and chemical characteristics of soil in two land uses, including rangeland and abandoned rainfed in Kurdistan province.

 This research was carried out in Kurdistan province. For this purpose, four regions, including Kilak, Salavat Abad, Sarab Qamish, and Mamukh, were selected in Sanandaj city. In each region, two neighboring rangelands and abandoned drylands were selected. Three 100-meter transects were established in each land use by random-systematic method, and soil samples were collected from 0-30 cm depth. Depending on the conditions and area of the region, 20 composite samples were taken in Kilak, 20 Salavat Abad, 14 Sarab Qamish, and 8 Mamukh. Half of the samples were collected in rangeland, and the other half in abandoned dryland. In the laboratory, soil physical and chemical factors, including acidity, electrical conductivity, absorbable potassium, percentage of soil organic carbon, total nitrogen, available phosphorus, soil texture, and bulk density, were measured by usual laboratory methods. A factorial experiment was conducted using a completely randomized design to analyze the data. The Duncan test was used to compare the means.

 The results showed no significant difference in the percentage of clay, silt, sand, and specific mass in the comparison of rangelands in four regions, the comparison of abandoned dryland in the four regions, and the comparison of abandoned dryland in each region. The comparison of the average acidity of abandoned rangeland and dryland did not show any significant difference in any region. Electrical conductivity in Kilak, Salavat Abad, and Sarab Qamish areas was higher than in dryland. However, only in Kilak was there a statistically significant difference. The electrical conductivity of rangeland soil was 143; in abandoned wetlands, it was 109.The comparison of abandoned rangelands and drylands in terms of total nitrogen and carbon numerical values showed that rangelands were more than abandoned drylands in all areas. This meant that nitrogen was 24%, 40%, and 42.8% higher in the Kilak, Sarab Qamish, and Mamukh regions. And statistically, their difference was significant. Also, the carbon difference between the rangeland and the dryland in Mamukh was statistically significant (1.47% in the rangeland and 0.74% in the dryland). There was a significant difference in the amount of phosphorus between the rangeland, 94 mg/kg, and the abandoned dryland, with 234 mg/kg only in the Mamukh region. Only in the Sarab Qamish area was soil potassium higher than in the rangeland by 24.7% in the abandoned dryland.Comparing rangelands and abandoned drylands in terms of the numerical amount of total nitrogen and carbon, it can be concluded that in all areas, the rangeland was more than the abandoned drylands, so that nitrogen in Kilak, Sarab-Qamish and Mamukh regions was 24, 40, respectively, and 42.8% more, their difference was statistically significant and also the carbon difference in Mamukh was statistically significant (rangeland 1.47% and dryland 0.74%). There was a significant difference in phosphorus between rangeland, 94 mg/kg, and abandoned dryland, 234 mg/kg only in the Mamukh area. There was a significant increase in soil potassium in abandoned drylands by 24.7% over rangeland soil in the Sarab-Qamish region.

 This research indicates that the change of land use from rangeland to dryland and then abandonment will change the soil's physical and chemical properties. After about 40 years since the drylands were abandoned, there has been an improvement in most of the physical and chemical factors investigated in this research. In this research, 40 years have been considered. It is suggested to consider different periods in the secondary sequence in future research. This will enable us to determine more precisely when the soil can improve. Also, similar research should be done in other ecological regions with different conditions so that the effect of climatic and topographical factors can be clearly defined.

 Today, predictive models of plant species distribution play a crucial role in assessing, restoring, protecting, and developing rangeland ecosystems. It is one of the most important tools to learn about species distribution and habitat suitability. This research determined ecological factors affecting plant composition, species response to environmental factors changes, and the potential of the target species in the study area using multivariate analysis. Based on this, with a better understanding of the ecological niche of this plant, the necessary recommendations can be made for using the species in rangeland improvement programs in similar habitats.

 Vegetation sampling was done by a systematic-random method during 2016-2018.Vegetation studies were carried out, including the percentage of canopy cover of species and the density of species inside the plots. Also, the percentage of litter, bare soil, stones, and pebbles was determined in each plot. For this purpose, five transects with the same distance were used. Then, six plots (with 2 x 2 meters dimensions) were established on each with the same distance. To investigate the effect of environmental factors on the distribution of the studied species, three soil samples were taken from each plot at a depth of 0 to 30 cm, and their physical and chemical properties were measured in the laboratory. Climatic factors such as average rainfall and annual temperature were collected using data from weather stations near the study area. To investigate the relationship between effective and significant environmental variables and vegetation and to choose the appropriate linear and non-linear method, DCA was performed on the vegetation data, and the gradient length was determined. A generalized additive model predicted plant species' response to environmental changes. Canoco software version 4.5 was used to analyze the data in this section.

 The results of conventional comparative analysis showed that environmental factors such as clay percentage, geographical direction, acidity, sand, saturated moisture percentage, organic matter percentage, average annual temperature and soil lime percentage in the studied habitats, respectively 10.3, 4.4, 3.3, 3.3, 1.6, 1.4, 1.4 and 1.3 percent of the variance in plant composition, play an important role in changes in vegetation in the habitats.It showed that A.specigera species respond to the amount of phosphorus, percentage of organic matter, electrical conductivity, percentage of nitrogen, percentage of clay, percentage of organic carbon, and altitude. This is following the monotonic decrease model. The response pattern of this species to the percentage of silt, percentage of sand, average annual temperature, average annual rainfall, the direction of slope, acidity, potassium, the apparent specific gravity of soil, percentage of soil saturation and percentage of slope follows the bell model (Unimodal) and limit its growth optimum for each of these factors is 21%, 60%, 16°C, 400mm, for eastern and southern slopes, 8, 650mg/liter, 1.4g/cm3, 39% and 40-50%.

 The generalized incremental model provides valuable information to determine species' ecological needs. This information can be used in vegetation management and rangeland improvement operations in similar areas using the data from this research. Forage production is high in the studied species, suggesting its potential for increasing rangeland vegetation cover.

Social and economic studies are important in investigating rangeland destruction. Investigating the role of social and economic issues in rangeland destruction can reduce destruction in this ecosystem. For this reason, this research has been done to identify the most important socioeconomic factors affecting rangeland destruction in the Niyuk region and prioritize the mentioned criteria using an Analytical Hierarchical process to provide complete information about the causes of rangeland destruction in the region. Considering that no research has been done in this area so far, it increases the necessity of conducting the present research.

Niuk area is located in Yazd province according to country divisions. In this research, first, by studying the sources and consulting with the relevant experts, the most important socioeconomic criteria involved in the destruction of rangelands in the area were determined, and a questionnaire was designed to score and calculate the weight and priority of these criteria. Enough experts completed it. The region's socioeconomic indicators, criteria, and sub-criteria were identified using experts' opinions and research records, and a hierarchical structure was formed. The main criteria include economic and social indicators. Economic indicators are divided into three sub-criteria: livestock and animal husbandry, cutting and harvesting, and change of land use and plans.The sub-criteria considered for the standard of livestock and livestock farming includes a large number of livestock, indiscriminate grazing of rangelands, type of livestock, change of livestock farming method from traditional to industrial, non-observance of livestock entry and exit time, improper distribution of livestock in the rangelands and improper grazing system. Three main sub-criteria of population, poverty, and institutional factors were identified for social indicators. Three main criteria and 14 sub-criteria were identified for social indicators.

A paired comparison between economic and social indicators showed that economic indicators weighing 0.667 have the priority in destroying rangelands. Social indicators with a weight of 0.333 have second priority. Among the main criteria examined by economic indicators, the sub-criterion of change of use and plans with a weight of 0.683 has been allocated the most. It is below the livestock and animal husbandry standard with a 0.200 weight. It was ranked third for cut and harvest with a 0.177 weight.Among the main criteria of social indicators, the criterion of institutional factors with a weight of 0.637 is the priority, and the factors of poverty and population are in the next ranks with weights of 0.258 and 0.105. The results showed that the sub-criteria of converting rangelands into mines, building access roads to mines, and political interference in natural resources were ranked first to third with weights of 0.176, 0.083, and 0.082. The first two sub-criteria of economic indicators and the third criterion of social indicators are the destruction of rangelands in the Newek region. The sub-criteria of literacy status and age composition of the population with weights of 0.004 and 0.003 were placed in the last priority. These sub-criteria were related to social indicators.

It can be concluded that the most important factors of the region's destruction are the change of land use and conversion of rangelands to mines, construction of access roads to mines, institutional factors and interference with natural resources, and lack of integrated management of natural resources. To prevent the destruction of rangelands in the region, it is necessary to minimize the construction of any mines and communication ways related to mines, and it is suggested that considering the activity of mines, the customary rights of pastoralists should be considered and the participation of ranchers in decision-making should be expanded to maximize the possibility of the success of projects with the support of stakeholders.

 Dealing with rangeland degradation factors and rehabilitating these resources are fundamental and necessary steps toward sustainable development. So, decisions and protection programs can reduce land use change and tenure. In this regard, the present study has excavated and analyzed strategies to prevent land use change and tenure of rangelands from the perspective of experts in Gonbad Kavous city of Golestan province.

This research is a descriptive-survey type in which the statistical population consists of 45 judges, experts, and conservation guards in the city. Forty individuals were randomly selected as a sample size based on the Krejcie Morgan table. The data collection tool was a researcher-made questionnaire. Through five focus group interviews, we obtained items related to it. So that after removing the common and unrelated items, 25 items were summarized as protection solutions from the rangelands of the city. Based on that, a questionnaire was prepared and distributed. Each of the specified items was evaluated on a five-point Likert scale. The questionnaire validity was assessed using natural resources experts' opinions. The reliability was determined by calculating Cronbach's alpha coefficient, equal to 0.81. After collecting and analyzing the data, the mean and standard deviation were used to describe and prioritize the items in the SPSS25 software environment. An exploratory factor analysis technique was used to examine the internal correlation and categorize the protection strategies of land use change and rangeland tenure in the form of several strategies and to determine the amount of variance explained by each. After collecting and categorizing the data, descriptive and inferential statistics were used in the SPSS25 software environment.

 According to the results obtained from factor analysis, the values of KMO and Bartlett were respectively equal to 0.806 and 967.830, significant at 99% confidence. This indicated the appropriateness of the variables' correlation in the analysis. Based on this, five strategies were extracted that explained 71.74% of the total variance of the variables. The educational-cultural solution to preventing land use and land tenure change in the study area was ranked the highest, and the legal-control solution was ranked the lowest in importance. The results indicate that the items "culturalization and information in crime prevention" from the educational-cultural strategy, "creating job opportunities, empowerment and alternative sources of income for local communities and pastoralists" from the strategy support-service, "privatization of rangeland and handing it over to qualified pastoralists" from the management solution, "correct implementation of laws by executive organizations" from the legal-control solution and "using the potential of mobilizing local communities and their participation in rangeland conservation" from the collaborative approach, with the highest amount of factor load, had the greatest impact in different protection strategies on preventing rangeland tenure. The sample t-test results showed that the most effective strategy in preventing land use change and rangeland acquisitions was related to educational-cultural, and the least effective was related to participatory.

 According to the research results, the focus is on culture and information using advancing communication technologies and social networks, monitoring and evaluating pastoralists, and creating a control process to neutralize crime in rangelands. This is proposed as the most effective prevention strategy. Developing a two-way comprehensive program, one side of which is related to government support and services, and the other side is related to the mobilization of local communities and their participation in the activities of conservation, restoration, improvement, and fundamental exploitation of rangelands, can be another recommendation to reduce rangelands degradation.

 Although man-made biochars positively affect soil properties and plant performance, their preparation and use, especially on a large scale, are costly. On the other hand, mineral biochar can be considered an alternative method. However, there is no information about the effect of this type of biochar and its method of use on soil characteristics and plant performance.

 Effect of levels of 0 (control), 5, 12, and 25% of mineral biochar (obtained from the mine of Koohbanan city, Kerman province) in three forms of use (including mixed with surface soil, mixed with deep bottom soil, and mixed with total volume soil) on the vegetative performance of bush Fortuynia bungei, shrub Calligonum comosum and tree Ziziphus spina-christi were evaluated in a completely randomized factorial design in the nursery during four months. Cultivation operations in two stages included the germination section (without biochar) and studying the treatments' effects on the species' vegetative characteristics. The seeds were planted in pots containing 100 grams of sand. After sprouting the seedlings and their three to five leaves, one seedling was selected from each pot and transferred to larger pots containing biochar. The amount of water required was determined based on the measurement of soil field capacity. Seedling characteristics were measured at 20-day intervals for four months, and biomass production was measured at the end of the experimental period. At the end of the test period, some soil properties were examined, including organic carbon, total nitrogen, absorbable phosphorus, absorbable potassium, acidity, and electrical conductivity.

 The application of different levels and the manner of using biochar to the evaluated characteristics showed that the most noticeable effect was related to the level of biochar. In other words, although using biochar or the cultivated species resulted in varying results, the amount of biochar had the greatest effect on the evaluated characteristics. The findings showed the effect of higher levels of biochar and the mixture of biochar with the total soil volume on plant species performance (Sig.0.005). Also, the species performed differently, so C. comosum had the highest growth height (65 cm), and F. bungei had the lowest growth height (19 cm). The method of using biochar also had a significant effect on plant biomass, so the highest biomass was related to F. bungei (9.2 grams) under the influence of 25% biochar mixed with the entire soil profile. The levels of biochar or plant species alone affected soil properties. However, the combined effect of the species and the level of biochar used on soil properties was not noticeable. With the application of 25% of biochar, nitrogen (from 0.14 to 0.25%), organic matter (0.88 to 4.1%), and electrical conductivity (0.76 to 1.33 dS/m) showed the most changes (Sig.<0.001).

 By increasing biochar levels, improved soil properties and plant performance were observed. On the other hand, biochar application affects plant performance depending on species. The method of using biochar also significantly changed the performance of cultivated plants so that, considering the economic discussion of using biochar, its mixture with the entire soil profile leads to higher production than mixing biochar with surface or deep soil. However, more studies are needed regarding biochar's effect on soil properties and plant performance.

Over the past decade, the Zagros region, specifically its Zagros oak trees, has experienced significant impacts from droughts and climate change. Climate change has resulted in heightened desertification and oak forest decline. This study examines and analyzes meteorological droughts and their correlation with climate change. This is a prominent contributing factor to oak tree decline in Ilam Province. The focus is on study sites in the northern and southern Serabaleh regions, where oak decline has been observed.

For this study, comprehensive data on daily precipitation and minimum and maximum temperature were obtained from the synoptic station in Ilam, covering the period from its establishment until 2019. The Standardized Precipitation Evapotranspiration Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI) were developed to assess meteorological drought and identify wetter and drier years. The SPI measures the deviation of precipitation from the mean value and normalizes it by the standard deviation. In contrast, the SPEI considers the discrepancy between precipitation and evapotranspiration. These indices were calculated on various time scales, including 3, 6, 12-month, and annual periods, and drought status was analyzed based on their respective classifications. To examine the role of climate change and identify influential precipitation and temperature patterns in drought occurrence, a set of four precipitation indices and eight temperature indices were calculated using ClimPACT software. These indices, developed by climate change experts, capture changes in mean or extreme weather conditions. The analysis also included wind speed. The relationship between drought indices and climate change was assessed through regression analysis and the Pearson correlation coefficient. Moreover, the study employed the Mann-Kendall and Pettitt Test to identify change points or significant abrupt changes in the time series. These tests were conducted at 5% significance and 95% confidence levels.

The study findings indicate a decreasing trend in the highest consecutive 5-day rainfall since 1995. In addition, there are insignificant reductions in the annual sum of wet days and the highest rainfall events of one or two days since 1998. This decrease in rainfall has been accompanied by increased maximum air temperatures since 1998, with a significant intensification observed from 2007 to 2015. Additionally, there has been a slight increase in minimum temperatures since 2002 and a significant wind speed since 1996. These factors have contributed to increased evaporation since 1998 and the occurrence of droughts on different time scales, ranging from six and twelve months since 1998 to three months since 2003. Global warming has influenced droughts. Three-month droughts have resulted in milder six- and twelve-month droughts, but more severe three-month droughts in oak decline, primarily due to significant changes in maximum temperatures since 2007. The occurrence of these droughts has been associated with an increase in the percentage of days with temperatures above the average since 2007, leading to more severe droughts from 2007 to 2015, with the peak in 2008 coinciding with the highest level of oak decline during the study period and under the influence of climate change phenomena.

The SPEI drought index indicates a higher frequency and longer duration of droughts during the study periods, albeit with less severity than the SPI index. This suggests that the rising temperatures during cold months, in addition to dry months, have played a role in influencing the drought conditions. The results demonstrate that drought and climate change are the primary influential factors contributing to oak tree dryness in the forests of Ilam Province. Considering the decreasing precipitation trend and increasing temperature trend observed in the studied region, the occurrence of climate and environmental hazards, such as heatwaves, droughts, and floods, may further increase.