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.
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.
Masoud Borhani; Hossein Arzani; Zahra Jaberolansar; Mojgan Azimi; Mahdi Farahpor
Volume 17, Issue 1 , September 2010, , Pages 1-20
Abstract
Range condition is known as an important indicator for assessment in range management. Many techniques have been exploited for determining this indicator, from which four-factor method has been used in this study. Some communities at stepic regions of Isfahan province were selected. In each selected ...
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Range condition is known as an important indicator for assessment in range management. Many techniques have been exploited for determining this indicator, from which four-factor method has been used in this study. Some communities at stepic regions of Isfahan province were selected. In each selected community, an area was chosen as key area, and a total of eight sites were selected in the key areas. Soil erosion, canopy cover, plant composition, and plant vigor were monitored for each site. The results revealed a significant difference between the sites in terms of the above mentioned parameters, as well as their rainfall (p<0.01). Moreover, there was a significant correlation between annual precipitation and range condition score. The correlation showed different patterns within years in each site, where the difference between years was significant in terms of plant vigor and canopy cover, but non-significant in terms of soil erosion and plant composition. There was also a positive correlation between the trend of individual parameters and the overall condition score. Cluster analysis grouped Aluyjeh, Northern Shahreza, and Charmshahr sites in one branch, Mooteh, Shoorabad, and Golpayegan in another, and finally Komeshcheh and Southern Shahreza in a third branch. The lowest rank for canopy cover, canopy production and soil erosion belonged to Komeshcheh and Southern Shahreza sites. Aluyjeh, Northern Shahreza, and Charmshahr sites were in better condition than the previous group, yet in poor conditions, and the rest of the sites showed the best conditions among study sites. Generally speaking, Isfahan's stepic rangelands are ranked as poor to very poor, while their condition showed a constant trend.