جستجوی مقالات مرتبط با کلیدواژه « drought » در نشریات گروه « جنگلداری »

Drought phenomenon stands as one of the most significant challenges of the contemporary era, exerting its influence on all ecosystems, including rangelands, at both global and regional scales. The heightened vulnerability of pastoralists underscores the necessity of embracing the concept of resilience. This research aims to investigate existing studies on the resilience of pastoralists under drought conditions and to propose a comprehensive model. A systematic review methodology was employed in this study. The findings of relevant domestic and international research were systematically analyzed using the seven-stage method of Sandelowski and Barroso. Based on inclusion and exclusion criteria, 30 studies were examined. The Waltz and Bausell method was employed to assess the validity of the extracted data. The reliability was also assessed through the Kappa coefficient, yielding a value of 0.87, indicating excellent agreement. The research results led to the formulation of a comprehensive model comprising seven factors: economic, social, individual, institutional, physical, educational-promotional, and ecological. Among these factors, the economic factor emerged as one of the most influential. The resultant model, identifying the factors that impact the resilience of pastoralists under drought conditions, provides the potential for enhancing crisis management, reducing vulnerability, and establishing the necessary groundwork for nationwide rangeland planning.

Drought in Zagros, which is one of the most important ecosystems in Iran, is a big challenge. Remote sensing has a unique application in diagnosis, monitoring and management of natural resources. The purpose of this study is to investigate and analyze the drought situation in the middle and southern Zagros basin based on atmospheric general circulation models and neural network in relation to remote sensing indices NDVI, VCI, TCI, VHI, DDI, EVI, NDWI and SAVI. At first the Modis satellite time series images were used in a 20-year period. First the mentioned indicators were produced from MOD021KM products of Terra sensor from 2000 to 2019. Then amount of precipitation were estimated by using of statistical-dynamic model MP5 under RCP 2.6, RCP 4.5 and RCP 8.5 scenarios and neural network and Remote sensing indicators during the period from 2020 to 2039, And then the state of droughts was investigated in 2 periods of 20 years based on the SPI method (2000-2019) and based on RCP scenarios and remote sensing methods and neural networks for the next 20 years (2021-2039). The results showed that both in the period of 2000-2019 and 2020-2039, the high areas of the studied area have and will have severe and very severe wet year. Also, the spatial analysis of droughts and remote sensing indices of the second period has depicted an irregular pattern in all indices, and only in NDVI and SAVI indices, the spatial analysis of droughts has been able to present a relatively regular pattern

The goal of this descriptive-survey study is to examine the situation and categorize the level of livelihood resilience of agroforestry system users in Paveh city in the face of drought. The statistical population of agricultural grove system stakeholders in Paveh city was 270 persons, of whom 156 were chosen using the stratified sampling method. A questionnaire created by the researcher was used to collect information. The data was coded in SPSS software and examined in four dimensions of vulnerability, learning capacity, self-organization, and diversity utilizing human, social, financial, physical, and natural capital. Finally, this community was shown to be more resilient than normal. The Kruskal-Wallis test was performed to assess the difference in average resilience among plantation grove subsystems. The results revealed that the gardener-pasture-farmer subsystem had a greater average resilience than the other two subsystems. The findings of this study may be of interest to the Agricultural Jihad Organization and the Environmental Organization in order to promote agroforestry systems and develop the components influencing resilience levels in order to support sustainability and boost livelihood resilience.

Proper management and planning to prevent the decline of groundwater levels, requires knowledge of the factors, indicators and criteria for changes in groundwater levels in areas affected by this phenomenon. Therefore, in order to be aware of the status of groundwater level fluctuations, it is necessary to conduct detailed studies in order to plan, operate and maintain water resources development plans and to predict and warn in time of drought periods. For this purpose, in the present study, the trend of groundwater changes in aquifers of Mahidasht study area in Kermanshah province in a statistical period of 35 years ending in 1396 was investigated. Then, the impact of droughts on the trend of groundwater level changes was analyzed using PDSI, GRI and SDI drought indices as well as changes in irrigated and rainfed arable lands. According to the results, the highest groundwater level is in the southeast and is about 1531m. Groundwater level changes in Mahidasht plain are generally declining and the groundwater level has dropped by 24.78m during the study period. Also, the results of low correlation between climatic and groundwater drought indices showed that the cause of water level decline in plain aquifers due to irregular impressions and management. Although Mahidasht aquifer has been selected as a case study in this article, the proposed method can be used in other areas to improve the protection and management of water resources.

This study was done to investigate the effect of slope aspect and crown dieback intensity on the nutrient status of leaves of Persian oak trees influenced by dieback and site soil in the forests of Ilam province. For this purpose, the Forest area of Melah-Siah was considered and two one-hectare areas on the northern and southern aspects with almost the same altitude levels were selected. In each selected area, 10 trees were sampled in two intensities of healthy and dieback affected. Leaf samples were collected from the four main sides of tree crown and the middle part of the crown and from their terminal branches. Furthermore, from the south side of the selected trees, soil samples were prepared from two depths. Collected samples were transferred to the laboratory for analysis of OC, N, P, K, Ca and Mg.  The results showed that the slope-aspect and crown dieback intensities have significant effects on the amount of phosphorus, calcium and magnesium in Persian oak tree leaves. So that, the amount of leaf phosphorus in the northern site was higher than the southern site. Leaf calcium and magnesium concentrations were higher in the north site than the south site and in dieback-affected trees than the healthy trees. Also, the amount of soil organic carbon was significantly affected by slope aspect. The OC content in depth of 0-20 cm, in the northern site was less than the southern site. The amount of pH, CaCO3 and soil moisture in the depth of 0-20 cm and soil moisture in the depth of 20-50 cm were also changed under the slope aspect. It was concluded that leaf nutrients had more changes than soil elements under the influence of considered factors and the amount of these changes was more attributed to the slope-aspect. The studied Persian oak trees with different crown dieback degrees had a similar situation in terms of soil macro elements, but had different conditions in terms of leaf macro elements. Considering the differences between their habitats in terms of soil moisture and pH, it can be said that the dieback severity of tree crowns is related to physiological mechanisms in trees for absorbing water and nutrients.

Recognition of the available moisture content and its changes in the habitat can be a dynamic ecological indicator. The aim of this study was evaluating the soil moisture storage volume with the distribution model of the Turc in the oak forest located in the Meleh-Siah Ilam.

The research was conducted from October 2013 to September 2015. Monthly rainfall and temperature data, monthly solar radiation, water holding capacity map and DEM of the region were used as input data.  To validate the soil moisture data from the water balance model, 33 humidity sensors 110 cm were installed in different locations of the habitat. Then, soil moisture was measured with TDR moisture meter in monthly time step. To evaluate the model, the mean absolute error (MAE) and mean error deviation (MBE) statistics were used and the results were analyzed.

The results showed that the accuracy of the model in estimating soil moisture in wet months is low and is overestimated, and Suitable in a dry month. Other results showed that in the first and second year of the study, precipitation was 680 mm and 383 mm, respectively and the share of evapotranspiration from precipitation is 56% and 77%, respectively. Also, in the study site the available water capacity of the soil is 125 mm, which the maximum in March and the downtrend continued until September and reached a minimum of zero. Other results indicate that the vegetation in the study area was drought tolerant in the first year (normal in terms of rainfall), in two months of August and September and increased in the second year (drought), in the months of July, August, September and October. The results also showed that 73% of the dried oak stands correspond to the areas that Soil moisture reached below the wilting point (15%) in September.

Therefore, reducing soil moisture in droughts has played an important role in the drying of oak bases and effect of the intensity and persistence of drought periods on the drying of oak trees needs further investigation.

One of the most important issues in the Zagros forests of Ilam is the dieback of oak trees, and the purpose of this research is to analyze the temporal-spatial analysis of the relationship between oak trees dieback and occurred droughts. In order to identify the dry areas of oak, using the method of determinationof. the training samples in geographic information system (GIS) and satellite images of modis were used. For temporal and spatial analysis of drought in Ilam province, NDVI index from MODIS satellite images in the statistical period of 2000 to 2018 was used. For  spatially analysis of relationship between oak forest dieback and droughts, Moran spatial autocorrelation model, one of the spatial pattern distribution models, was selected. Coincidentally, a 30-square-meter GPS device was used to find the coordinates of the dried droplets and the number of dried oak trees at each point, and a map of oak tree dieback distribution was prepared using GIS software. The results of combining drought zoning from NDVI index with oak dieback distribution map in two time series from 2000 to 2009 and 2010 to 2018 in the analysis of Moran index showed that oak dieback has a cluster pattern and the decline of oak trees is spreading in a mass. Also there was a significant relationship between drought trend in spatial and temporal dimensions and oak dieback in recent years in different parts of Ilam.

The Zagros Woodland is one of the main components of Zagros ecosystem that has significant role in water and soil conservation. Drought, as one of the climatic hazards, can have dramatic effects on forest cover. Therefore, detecting the spatiotemporal dynamics of the forest in response to drought is very important. The main objective of this study was to detect the spatiotemporal relationship of forest cover of Lorestan province in response to annual drought. In this regard, the Enhanced Vegetation Index (EVI) values were extracted from Landsat 5 and 8 images for the period 2017-2017. The Standardized Precipitation Index (SPI) was calculated for the mentioned period using monthly rainfall statistics of 9 synoptic stations in the region. By using spatial correlation analysis, the relationship between annual forest area and drought index was investigated and finally, sensitivity function of spatial variation of forest cover was obtained by fitting a linear model. The results of field sampling showed that EVI threshold> 0.4 can be considered as the province's forest cover threshold. Correlation analysis between forest cover and drought indicated that the 18-year time series of forest cover had a significant correalation of 0.68 with SPI (0.95 confidence level). The results of development of sensitivity function to SPI index indicated that the forest cover had significant sensitivity to drought so that for each 0.1 unit change in the SPI index the forest cover area will change as 14880 ha in the same direction.

Osage orange tree (Maclura pomifera L.) is a native of Central America and has numerous ornamental, ecological and medicinal values. In the present study, the effects of different culture media including animal manure, vermicompost and sesame residue on the growth rate and increasing tolerance of Osage orange tree under drought stress, were investigated. This experiment was conducted as a factorial experiment based on completely randomized block design, four culture media levels including (1- soil (control), 2- 70% v/v soil + 30% v/v vermicompost, 3- 70% v/v soil + 30% v/v animal manure and 4- 80% v/v soil + 20% v/v sesame residue) and three levels of drought include 1- without stress (control) (90% allowed water depletion) 2- mild stress (55% allowed water depletion) and 3- severe stress (35% allowed water depletion) with three replicates per treatments were applied on one year old seedlings in April 2017 in field of Yazd University. According to the results, drought stress significantly decreased the height, truck diameter, fresh and dry weight of leaves of seedlings and nutrient uptake, however, activity of ascorbate peroxidase increased. Application of a modified culture media under non-stress conditions significantly increased the growth characteristics and nitrogen and phosphorus uptake. Among the used culture media, animal manure and sesame residue had the highest effects on increasing plant height, fresh and dry weight of leaves and absorption of nitrogen and phosphorus. Maximum activity of ascorbate peroxidase enzyme was obtained in agronomic soil with 30% vermicompost during severe drought stress. In general, using the culture media, especially with animal manure and sesame residue, increased the resistance of this plant to drought stress and significantly increased its growth.

The aim of this study was to investigate the relationships between vegetation changes and climate variables including rainfall and drought using MODIS satellite images during the years 2000-2014 in Chaharmahal and Bakhtiari Province. In order to evaluate the impact of rainfall and drought on vegetation changes in 32 synoptic, climatology and rain gauge stations in and around the province, SPI index was calculated in short time series (3, 6, 9 months) and long time series (12, 24 months). All the time scales were leading to early June in which the maximum growth of vegetation of the province is occurred. To this end, SPI drought maps and NDVI images were prepared at different time scales by kriging method and linear regression analysis was performed to define their relationships. Comparisons of NDVI and SPI over the study period showed that the vulnerability of vegetation to drought mostly depends on the life forms and plant species. In this study, depending on the type of vegetation, different correlation coefficients were observed between vegetation and SPI indices. Among different rangeland and forest vegetation types, higher correlations were found between NDVI and SPI in rangeland vegetation types compared to the forest ones and the highest correlations belonged to the annual grass and annual forb vegetation cover. This confirms the higher impact of reducing rainfall on the decline of rangeland cover compared to the forest vegetation. Overall, the findings of this study indicate that the MODIS NDVI can be used to study SPI in the assessment and monitoring of drought effects on vegetation cover. By studying and recognition of vegetation cover and applying NDVI index to assess changes in vegetation cover, vulnerable types of vegetation to drought could be identified.

Iranian oak forms the dominant forest cover of Ilam province located in the South-Western region of Iranwhere by effect of climatic conditions changes and incidence of numerous drought, the oak wood borer in a rush manner mode and have been caused the damage to these trees.This research was carried out in order to identification of Oak wood borer, natural enemies and normal efficacy rate of oak wood borer Parasitoids during connective three years (2011-2014). With survey of desert investigations by splitting the dry and semi-dry oak woods were done and different growth phases of oak wood borer separately in two health and parasitoid groups monthly have been investigated. For investigating the adult oak wood borer and parasitoids, samples from contaminated trunks and branches to wood borer in the breeding chambers in the dimension of 10-15 m2 were kept. The result show wood borer pest spices including Cerambyx cerdo (Col., Cerambycidae(, Macrotoma scutellaris (Col., Cerambycidae(, Chalcophorella bagdadensis (Col., Buprestidae(, Agrilus hastulifer(Col., Buprestidae(,Chrysobothris parvipuncta(Col., Buprestidae(,Lampetis mimosa(Col., Buprestidae(.The fungus of Beauveria bassiana and foure species of parasitoids wasps including Trigonura ninae (Hym.: Chalcididae), Atanycolus sp. (Hym.: Braconidae) Oodera formosa(Hym.: Pteromalidae) , Pristaulacus compressus (Hym. : Aulacidae) were identificated.The efficacy of wasps in the host larva phase 2.1 percent and fungus efficacy in the larva and adult insects was 1.5 and 1.1 percent.

Manmade fires have been major threat to forest areas in the previous decades. The purpose of this study was to analyze the spatial distribution of forest fires and identify fire sensitive area in Saravan forests. According to the available data sets, fire areas with the highest frequency and areas affected were identified. GPS data were recorded for these areas and transferred to Arcview software to convert bridge became diverse. Map typing was conducted within and outside value layer, combining maps was done to indicate anticipated maps of sensitive areas, the impact of drought on fire was investigated by the PDSI index. Vegetation layer by a factor of 0.426 was the highest weight on the predicted maps of susceptible areas to fire and then were layers of the human factor, distance from roads, temperature, slope, distance from streams, rain, direction, and height of the priorities were next. According to the results obtained It was found that the most common type of fire in the study area were the low surface and limited area and the fire spread in forest litter with extreme heat and low humidity of the air in August and in natural areas because of lack of rain fall caused which the forested areas has become the center of the high risk area that any negligence could result in heavy losses. Also fire suppression in the forests of Guilan depends upon wind condition. Obtained by hierarchical analysis model for the evaluation process, fire dispersal maps were combined with the zoning map, and model validation was performed. Results obtained demonstrate good accuracy of the method (77%).

The effects of different irrigation regime on survival and growth of holm oak (Quercus ilex L.) plantationwas studied in a semi-arid Mediterranean climate condition located in Marzanabad region (Mazindaran province). This study was done as Randomized Complete Block design with three replicates and four treatments, including no-irrigation and irrigation with 10, 20 and 30 day periods during dry months in growing seasons (spring and summer). Climate data analysis showed that a severe frost and three to six dry months annually occurred in growing season during study years (2006-2010). Height growth and survival of saplings were measured every year and at the end of 5th year. Analysis of data showed that irrigation treatment with 10-day intervals with a 65% survival is preferred and differences are significant (p %1). No difference was seen among treatments from height growth point of view. In general, the most important restricting factor on holm oak establishment and growth in this area are alkaline soil and dry environment conditions.