Nahid Azizi; Hamed Joneidi; Khaled Osati
Volume 26, Issue 3 , September 2019, , Pages 717-730
Abstract
This research monitored changes in canopy cover percentage of typical species during a 10-year period in the Ghosheh rangelands to find out the relationship between two important climate variables (precipitation and temperature) and canopy cover changes. Therefore, the canopy cover ...
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This research monitored changes in canopy cover percentage of typical species during a 10-year period in the Ghosheh rangelands to find out the relationship between two important climate variables (precipitation and temperature) and canopy cover changes. Therefore, the canopy cover percentages of six typical species (separately) and annual species (overall) were measured during 10 years at the end of growing season in thirty 2-m2 plots, distributed along two 250–m transect lines. The results demonstrated that the maximum canopy cover percentage for water year 2006-2007 (wet-year) and the minimum value for water year 2012-2013 (drought) were 15% and 5.5%, respectively. The canopy cover percentage modeling was performed based on linear regression method using precipitation and temperature variables. The precipitation of April explained 65% of changes in canopy cover percentage of A. sieberiat 95% confidence level (RRMSE = 0.26 & MAE=0.49). The best simple linear regression model for estimating canopy cover percentage of S. barbata and Z. eurypterum was introduced by total precipitation of March-June and precipitation of March, representing 77% (at 99% confidence level) and 67% (at 95% confidence level) of changes in canopy cover, respectively. Considering the dominant role of A. sieberi, S. barbata and Z. eurypterum in vegetation composition of study areas, it can be concluded that most changes in canopy cover of the studied rangeland are predictable by variabilityofprecipitation during growing seasons.
Somayeh seyed ali; mohammad rahimi; Jafar Dastourani; Mohammad Khosroshahi
Volume 23, Issue 3 , January 2017, , Pages 555-566
Abstract
In this study, the impact of climatological parameters and land use on water yield of the watershed was investigated. Therefore, the trend of climatological parameters (precipitation and temperature) and stream flow discharge were studied monthly, quarterly and annually at the stations located inside ...
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In this study, the impact of climatological parameters and land use on water yield of the watershed was investigated. Therefore, the trend of climatological parameters (precipitation and temperature) and stream flow discharge were studied monthly, quarterly and annually at the stations located inside and near the watershed using Mann-Kendall test. To evaluate the land use changes and its impact on run-off, the Helsel and Hirsch method was employed. In this method, the impact of precipitation (as exogenous variable) and the serial correlation of run-off data were removed, and again the trend test was implemented on the remaining logarithmic data of run-off (adjusted).In addition, the variations of snow line during the last 20 years were investigated to determine the role of climatological variation on watershed landscape.The results revealed that precipitation and mean temperature parameters over monthly, seasonal, and annual scales as well as run-off data after removing the precipitation impact and serial correlation between data had no significant trend.Therefore, it is concluded that climatological parameters and land use changes had no noticeable influence on the surface water of the watershed.Our results clearly showed that the Helsel and Hirsch method could be used in other regions since it could remove the effects of precipitation and its variation carefully.Moreover, the snow line of the study watershed showed no significant trend. According to the minimum and average snow line height, a high annual fluctuation was observed in the watershed during the study period. These factors may be the main reasons for non-significance of stream flow discharge and run-off height trends.
Esmael Aliakbarzadeh; Hasan Yeganeh; Hadi Afrah
Volume 23, Issue 3 , January 2017, , Pages 567-577
Abstract
The aim of this study was to evaluate the production characteristics and the consumption rate of dominant forage species in different phenological stages. The study was conducted in Sabalan, Ardebil Province for four years. In this study, for each species, four average individuals were selected and marked ...
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The aim of this study was to evaluate the production characteristics and the consumption rate of dominant forage species in different phenological stages. The study was conducted in Sabalan, Ardebil Province for four years. In this study, for each species, four average individuals were selected and marked inside and outside the exclosure, and the production was harvested. The total forage production and consumption was calculated using the production and density data of average individuals in the exclosure. In order to assess the effects of year and months of harvesting on the production and consumption of the study species, the data were analyzed by combined analysis of variance in a completely randomized design using SAS software. Mean comparison was performed by Duncan's test at 5% level for the effects of year, species and month on forage production and consumption. According to the results, a significant difference was found among the species in terms of production and consumption in the months of growth season and grazing period, as well as the study years. The total forage production of plants was different among the study years. The highest and lowest forage production (1971.19 and 1635.35 kg/ha) were recorded for the years 2010 and 2008, respectively. In addition, the highest and the lowest forage consumption (with 86.72 and 67.71 kg/ha had) was obtained in the years 2008 and 2009, respectively. Since the interaction effect of year and month was significant for most of the species, it can be concluded that forage production and consumption are affected by the year and its prevailing conditions.
Saeed Rashvand; Ali Ehsani; Hasan Yeganeh; Anvar Sour
Volume 21, Issue 4 , March 2015, , Pages 591-603
Abstract
Knowledge of the phenological stages of species constituting a plant community has a considerable importance in grazing management to achieve the goals of sustainable production. The study of plant phenology is critical for monitoring, management and conservation of ecosystems. In this research, ...
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Knowledge of the phenological stages of species constituting a plant community has a considerable importance in grazing management to achieve the goals of sustainable production. The study of plant phenology is critical for monitoring, management and conservation of ecosystems. In this research, the phenology of two shrub species including Artemisia aucheri and Thymus kotschyanus was investigated for four years during 2007 to 2010. For this purpose, 10 samples were selected from each species and the phenological data were recorded every 15 days and every 7 days in the vegetative and reproductive stages, respectively. Results showed that the start and end time of growth in different years in these two species differed under the influence of temperature and precipitation. The flowering stage of Thymus kotschyanus began in the first half of June, and the seeding stage started in the first half of July, continuing to the first half of August.The vegetative growth of Artemisia aucheri started from the second half of May, the flowering stage began in the late August and the seeding stage started from the last week of September, continuing for 2-3 weeks.
Fatemeh Hadian; Seyed Zeinolabedin Hoseini; Mansoureh Seyed Hoseini
Volume 21, Issue 4 , March 2015, , Pages 756-768
Abstract
Precipitation is one of the factors affecting vegetation. Nowadays, satellite images are broadly used for monitoring the effects of precipitation variations on the vegetation changes. The aim of this study was to investigate the relationship between vegetation dynamic and precipitation variations using ...
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Precipitation is one of the factors affecting vegetation. Nowadays, satellite images are broadly used for monitoring the effects of precipitation variations on the vegetation changes. The aim of this study was to investigate the relationship between vegetation dynamic and precipitation variations using NOAA AVHRR images during the period of 1982-2006. Precipitation maps were created using the inverse distance weighting interpolation (IDW) method and time intervals of precipitation data. The study area was a forestland beside Caspian Sea, four rangeland vegetation types with grasses and shrubs, farmland areas and urban areas, located in Ardabil and Guilan provinces. To monitor the relationship between the precipitation and vegetation changes, the linear regression (NDVI, Y & Rainfall, X) method was employed. Based on the results, depending on the precipitation time, plant species, and growth form, the effect of precipitation on vegetation was different so that no significant relationship was observed between vegetation and precipitation in forestlands, farmlands, and urban areas. The highest correlation coefficient between spring precipitation and vegetation was related to the rangelands. In grassland areas, the correlation coefficient was higher than that of shrublands, whereas the reaction of grasslands to precipitation in various parts was different.
Ali Ehsani; Mamak Ahmadian; Saeed Rashvand; Mohammad Ali Dehghani Tafti; Mostafa Zare
Volume 21, Issue 1 , June 2014, , Pages 13-23
Abstract
Study of the phenology of range key species is important to regulate and apply proper management for sustainable utilization of rangeland forage. In this study, the phenological stages of Artemisia aucheri were examined as a key species at three sites of different semi-steppe regions during 2007-2010. ...
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Study of the phenology of range key species is important to regulate and apply proper management for sustainable utilization of rangeland forage. In this study, the phenological stages of Artemisia aucheri were examined as a key species at three sites of different semi-steppe regions during 2007-2010. For this purpose, in each site, 10 individuals were selected and different phenological stages were recorded in 15-day and 7-day intervals for vegetative stage and reproductive stage, respectively. In addition, meteorological data including temperature and precipitation were recorded from the nearest synoptic station for each site. Results indicated that the occurrence of phenological phenomena of Artimisia aucheriwas more affected by temperature and precipitation indices of the growing season. According to the obtained results, the start and end of grazing were determined as early May to late October for Shirkooh (Yazd province), late May and early June to mid-July for Anjadan (Markazi province), and second half of May to mid September for Alamoot (Ghazvin province). Consequently, a complete understanding on the phenological stages of Ar. aucheri enables us to plan grazing management in order to determine the time of livestock entry into and exit from rangelands, optimal number of livestock for grazing and proper grazing systems.
Mostafa Jafari
Volume 21, Issue 1 , June 2014, , Pages 139-153
Abstract
Iran faced with climate and environmental changes in past years and it is projected that some climatic changes will occur in the future. Net Primary Production (NPP) is an important index to evaluate production in natural ecosystems including forest, rangeland and desert. Climate change impact will cause ...
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Iran faced with climate and environmental changes in past years and it is projected that some climatic changes will occur in the future. Net Primary Production (NPP) is an important index to evaluate production in natural ecosystems including forest, rangeland and desert. Climate change impact will cause changes in biomass production in natural ecosystems. In this research, the vulnerability of NPP in Iranian forest, rangeland and desert ecosystem has been considered. Results of this consideration presented here in six selected climatic zones in Gilan, Mazandaran, East Azerbyjan, Kermanshah, Khorasan and Systan and Baluchestan provinces. According to the result outcomes, total NPP of forest, rangeland and desert ecosystem in Gilan, East Azerbyjan, and Khorasan provinces, under temperature and precipitation changes, has been increased in the year ended 2039. While, the amount of NPP in Mazandaran, Kermanshah, and Systan and Baluchestan provinces would have been decreased. These changes in Khorasan provinces (including North, South and Razavi) will show highest increase, indicating suitable increase of precipitation and temperature in the region. Quantitative changes in NPP depend on total biomass and changes of precipitation and temperature. As an example, these changes in forest ecosystems of Gilan, and Khorasan provinces, will increase and in Mazandaran, and Kermanshah provinces, will decrease. Also, these changes in range ecosystems of East Azerbyjan, and Khorasan provinces, will increase and in Kermanshah, and Systan and Baluchestan provinces, will decrease. While, changes in desert ecosystems of Khorasan provinces mainly will increase and in Systan and Baluchestan provinces, will decrease.
Ali Mohammad Ghaeminia; Hamid reza Azimzadeh; Mohammad Hossein Mobin
Volume 18, Issue 1 , May 2011, , Pages 42-57
Abstract
Soil temperature is one of the most important and effective factors influencing the establishment of vegetation in arid regions. Soil temperature is affected by several meteorological parameters. The study of air temperature, rainfall and sunshine hours can be useful ...
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Soil temperature is one of the most important and effective factors influencing the establishment of vegetation in arid regions. Soil temperature is affected by several meteorological parameters. The study of air temperature, rainfall and sunshine hours can be useful to understand the variation of soil temperature. Soil temperature changes and rate of heat transport in soil profile are helpful for evaluating the amount of evaporation, plants water requirements, decomposition rate of materials, biological activities and the time of seed planting. The aim of this study is to evaluate the role of atmospheric factors in determination of the soil temperature. For this purpose, after collecting daily temperatures data of different soil depths (5, 10, 20, 30, 50 and 100 cm) in Yazd synoptic station for 2006, firstly, the effective meteorological parameters were analyzed and then soil temperature at this station was simulated by using sinusoidal changes pattern during the year. Finally, soil temperature variation curve at any depth was plotted and evaluated using the models obtained. Primary results showed that there was a significant relationship between precipitation, air temperature and sunshine hours. Measured and predicted values were evaluated in a coordinate system. The results showed that with increasing depth, the sinusoidal model predicted values underestimate. The results of calculating coefficients of Nash-Sutcliffe model efficiency (RNS2) showed that the estimated values by model for the different depths (5, 10, 20, 30, 50 and 100 cm), compared to the measured ones had efficiency coefficients as 0.92, 0.91, 0.93, 0.92, 0.94 and 0.96, respectively. Since (RNS2) value varies between- ∞ to 1, and when its value is equal to 1, the model has maximum efficiency, so, sinusoidal equations have good capability for predicting temperature variations in soil different depths.
Manuchehr Farajzadeh; Aman alah Fathnia; Bohlul Alijani; Parviz Zeaiean
Volume 18, Issue 1 , May 2011, , Pages 107-123
Abstract
The aim of this research was to evaluate the effect of climatic factors on vegetation in rangelands of Zagross with normalized difference vegetation index (NDVI) derived from Advanced Very High Resolution Radiometer (AVHRR) sensor, and climatic data. The study area was rangelands of Zagross with ...
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The aim of this research was to evaluate the effect of climatic factors on vegetation in rangelands of Zagross with normalized difference vegetation index (NDVI) derived from Advanced Very High Resolution Radiometer (AVHRR) sensor, and climatic data. The study area was rangelands of Zagross with 51-75, 26-50 and 10-25 density. Satellite images and climatic factors were respectively studied from January to October 2006 and from September 2005 to October 2006. Effects of seven monthly climatic variables (precipitation, temperature and relative humidity (maximum, mean and minimum) were studied on monthly NDVI. Zoning was performed by geostatistical method and Multivariate Ordinary Least Squares regression (MOLS) was applied to study the effect of climatic factors on vegetation changes. According to the Results CO-Kriging was identified as the best method for zoning, and Inverse Distance Weighting (IDW) only in mean temperature showed a better distance. Vegetation responses to precipitation of last two months, and temperature and relative humidity of last one month. Results of MOLS showed higher correlation in rangelands with a density of 51-75 %, but generally, correlation was low in rangelands with a density of 10-25 %, that can be due to the low altitude from sea level, effect of soil background and agricultural field margins. Also, low height in rangelands with a density of 10-25 % increased the temperature and transferred the start of leaf greenness to March, while in rangelands with a density of 51-75 % greenness started in May. The highest and lowest R2 values were calculated as 0.6478 for dense rangelands in May and 0.136 for low density rangelands in August.
Morteza Akbarzadeh; Taghgi Mirhaji
Volume 13, Issue 3 , February 2006, , Pages 222-235
Abstract
Study of vegetation changes of ungrazed rangelands is important. It is supposed that ungrazed areas tends toward climax and range condition to be improved. The major portion of our rangelands are laied in arid and semi-arid regions. For that precipitation is the major influential factor on vegetation ...
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Study of vegetation changes of ungrazed rangelands is important. It is supposed that ungrazed areas tends toward climax and range condition to be improved. The major portion of our rangelands are laied in arid and semi-arid regions. For that precipitation is the major influential factor on vegetation changes. In dry years as rainfall decreases, the vegetation cover are damage. This study were conducted on Rudshur rangelands for nine years (1996-2004), with the aim of rainfall variation and ungrazed condition effects on vegetation changes. Plant parameters as canopy cover, density and seedling numbers were estimated on permanent plots each year. A dry period were started in 1997 in the region and continued for five years. Results showed, in a period of nine years, total canopy cover declined 40 percent. Decline of canopy cover varied from 26 to 95 percent for different species. Only canopy cover of the Poa sinaica increased about three times, due to earliest vegetative period in growing season. Decline in canopy cover was greatest in forbs, and grasses had lower decline. Regeneration was high in the rainy years and 81 percent of total seedlings belonged to grasses especially to Stipa hohenackeriana. Density of most species decreased in the study period especially in dry years.