جستجوی مقالات مرتبط با کلیدواژه « تاج پوشش گیاهی » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

The history of flood spreading in the lands adjacent the rivers and flood irrigation reaches several thousand years. There are evidences of the use of floods to increase plant production in different parts of Iran, including the cities of Qazvin, Baluchistan, Khorasan, Fars, Isfahan and Khuzestan. Surveys conducted in 20 arid and semi-arid regions of the country indicate that in most regions, production indices and the percentage of plant canopy cover have increased significantly in the field of flood spreading compared to the control. The purpose of this research is to investigate the effect of flood spreading on rangeland vegetation dynamics and to determine the fluctuations of plant indices corresponding to climatic indices in a 6-year period.

In order to monitoring and comparison the fluctuations of vegetation indices was selected in Aquifer Management Kowsar Station, 2 networks (representative of the flood spreading area) with the names Bisheshzard 1 and Bisheshzard 4 and adjacent to them an area of ​​5 hectares outside the networks spreading as a control. The representative of the area without flood spreading). From 2016 to 2022 for 6 years, in the second half of May every year, 10 transects with a length of 150 meters and 100 plots of one square meter were established in a systematic-randomness manner in the strips of networks and the control field. The rangeland type indice species of flood spreading Gareh Bygone Plain (GBP) of Fasa shrubs are Dendrostellera lessertii (Wikstr) Van Tiegh., Heliantemum lippii (L) Pers Astragalus ssp. with understory of annual Grasses and forbs respectively. Plant indices (species name, percentage of canopy cover, number of bases per square meter, vegetative form and species biomass) and soil surface coverage (percentage of stones and pebbles, percentage of litter and percentage of bare soil) were collected every year. Using the modified six-factor method, the rangeland condition in flood distribution networks was evaluated in wet years and in dry years. For the comparison of different rangeland treatments in the survey years, flood spreading networks and strips and control area from different statistical methods (split-split plot design in time and space in the form of complete random blocks), correlation coefficients, was used step by step regression to determine the forecasting model for the production and canopy cover of rangeland plants and for average comparisons Duncan's test at the 5% level.

The results of the analysis of variance showed that the amount of plant indices evaluated between the survey years, between the networks and between the flood spreading strips had a significant difference at the level of 1% with the control. The percentage of plant canopy cover during the survey period from 8.69% in 2021 to 55.51% in 2020 and the production rate from 175.32 kg per hectare in 2021 to 813.55 kg per hectare in the year 2020 was variable. Using the adjusted 6-factor method, the rangeland condition in the networks with flood spreading in wet years was evaluated as good and in dry years as fair, while in the control area (without flood spreading) in wet years, It was assessed as poor to fair and in dry years, very poor to non-suitable for grazing. Based on the results of the correlation analysis, a positive and significant correlation was obtained between the canopy cover and plants rangeland biomass at the level of 1% (R²=0.86). The step by step regression results also showed that in the plant production prediction model, the independent variables (climate indicators) are the annual rainfall (R²=0.34) the average minimum temperature (r=0.26), the amount of rainfall in The growing season of plants (R²=0.15), the average annual temperature (R²=0.11) and their sum (R²=0.86) and in the prediction model, of plant canopy cover percentage, the independent variable of rainfall in the growing season of plants (R²=0.87) had the main and decisive contribution in estimating the value of the dependent variable.

Conclusion and Recommendations:

In general, it can be concluded that the percentage of plant canopy cover of Bishehzard network 1 in wet years (water years 2015-2016, 2016-2017, 2018-2019 and 2020-2021) compared to Bishehzard network 4 and control. It is statistically significant and in dry years (water years 2017-2018 and 2021-2022) these percentages are higher in control compared to two networks of Bishehzard 1 and 4. In general, there is a correlation between the production of plants with a canopy cover (R²=0.86), with the amount of annual rainfall (R²=0.92), with the amount of rainfall during floods (R²=0.84), with the number of floods (R²=0.96) =), with the duration of floods (R²=0.96), with the autumn and winter rainfall (R²=0.94) and with the rainfall in the plant growth Period (R²=0.93) positive and significant correlation at the level of 1% was obtained. In general, the changes in the amount of the plant canopy cover index are in harmony with the changes in the amount of annual rainfall, the number of rainy months, its distribution, and the number and volume of effective floods in the growing season of plants. Based on the statistics from 2016 to 2022, the 6-year average dry matter production in control is 252.25 and in Bishehzard 1 and 4 it is estimated to be 528.31 and 362.17 kg per hectare, respectively. The production of flood spreading networks is about 1.43 to 2 times that of control. From 2015 to 2022, there was a significant difference in plant production index fluctuations in Bishehzard 1 and 4 networks compared to the control. In general, considering that water is one of the main factors limiting the growth and development of plants in arid and semi-arid regions, the use of flood spreading as a simple, low-cost and nature-compatible method to improve quantitative growth indices rangeland plants are inevitable

This study was conducted to evaluate the capability of the DHSVM model to simulate hydrological processes in a mountainous watershed with a minimum agricultural land use. The required climatic parameters were set for the daily time step. The inverse distance method was used to interpolate the climatic variables from the stations to the network cells. Time inputs to the model were prepared for the years 2008 to 2013. The land cover map was prepared using the supervised classification method of Landsat TM data. The stream network map was generated using the DEM map in ArcGIS software. The soil texture map was prepared using field sampling and in the laboratory. Primary tests to the determine sensitivity of input parameters showed that this model is sensitive to lateral hydraulic conductivity, exponential coefficient of hydraulic conductivity, porosity, field capacity, and minimum stomatal resistance. In this study, except for the lateral hydraulic conductivity and exponential decrease coefficient, all other parameters (soil and vegetation) were determined based on previous studies and field measurements in a similar way for both categories of data.  The time series of the data were divided into three, warm- up or preparation periods (2008-2009), calibration (2009-2011) and validation (2011-2013). The model was calibrated using stream flow data from 2008 to 2010. Different efficiency criteria were calculated between simulated and observed flows. NSE value for calibrating was 0.59 and for validation was 0.606. In general, the results of this model implementation in the studied basin with the quality and quantity of input data to the model are satisfactory.

Applying appropriate sampling methods ensure the efficiency and accuracy of from inventory and monitoring results in rangelands. Vegetation type, spatial vegetation pattern and plant size affect selection of proper plot shape and size in vegetation measurements. It enhances the measurements accuracy and reduces observed variance among measured samples and save sampling time. This study aimed to determine proper plot size and shape for vegetation study in semi-steppe rangelands dominated by Bromus tomentellus- Astragalus verus in Isfahan province. Square, rectangular and circle plots with size of one and two square meters were compared in measuring vegetation cover in a dominated random vegetation pattern. A systematic random sampling method was used and variance analysis of measured attributes was conducted. According to the results, there were significant differences between various plot sizes (P< 0.01) but plot shapes didnt differ significantly. Evaluating variation coefficient of vegetation cover in plots with different size revealed that 2 m2 plot was more efficient and accurate than 1 m2 plot size. Rectangular plots in vegetation cover measurements produced data with lower coefficient of variant than other plot shapes. Overall, 2 m2 rectangular plots is suggested as an appropriate plot size and shapes in vegetation cover measurements of rangeland with similar vegetation patterns in semi-arid rangelands.

Using satellite data is considered as one of the influential tools in the field of rangeland science. In this study, satellite data were used in order to prepare the map of canopy cover percentage Mouteh wildlife refuge in Isfahan province during 1972 and 2007. Vegetation indices were produced using MSS sensors for 1972, TM for 1987, TM for 1998 and image of LISS III sensor for 2008. To make correlation between canopy cover percentage and satellite data, 290 plot data with appropriate distribution across the region were collected by stratified random sampling method. By using data and prepared vegetation indices, canopy cover percentage was estimated for previous years and corrections between field sampling and vegetation indices were estimated. With regard to data analysis, SAVI index had the highest correlation equal to 0.78 with canopy cover percentage. Therefore, using the produced model from SAVI index, the map of canopy cover percentage was produced in four classes for each year and the changes of canopy cover percentage were detected using post classification change detection method. Results showed that during 1972 to 2008 canopy cover percentage decreased in this period so that low canopy cover areas (0-10%) increased from 40162 to 95597 hectares along with a reduction of 10-20% in canopy cover percentage.

The purpose of this study was to evaluate the success rate of planting project. Also reviews combating desertification in this region by the Project. First, plant characteristics including canopy cover and vegetation density were measured by transect of 100m and plots of 225m2 (15×15), respectively. Also physical (soil texture) and chemical properties of soil samples including salinity and acidity at three depths of 0-30, 30-60 and 60-90cm (roots development zone) were measured. A region as a flood spreading area including three phases, two phases of Atriplex and one phase of Haloxylon was selected. Also, another region was considered as the control area. The results were compared by Duncan's test according to Completely Randomized Block design. The results of physical and chemical properties of the soil samples showed that the electrical conductivity and pH have decreased in the most samples. These changes were significant at the 5% level. Soil texture and sand increased but clay has decreased in the depth of 0-30cm, therefore soil structure has improved. The results of plant characteristics showed that water spreading has positive effects on establishment and natural regeneration of the planted spices (15.75 percent increase) and these changes are significant at the 5% level. Based on canopy cover and vegetation density results, there are no significant differences between Atriplex and Haloxylon; but the establishment of endemic species has been more successful in Haloxylon phase.

Our country’s rangelands are mainly located in arid and semi-arid regions. Due to the low amount of precipitation and high rate of evapotranspiration, water stress is considered as the most crucial environmental stress for vegetation in this region. This study was conducted at Khud-e-sofla rangelands for nine years (1378- 1386) to investigate the effect of precipitation fluctuation on canopy cover and production of important plant species. For this purpose, four dominant species were selected and their canopy cover and production were monitored every year in permanent and random plots, respectively. Precipitation data were collected from the nearest synoptic station. According to the data of precipitation, cumulative rain amount was calculated at various periods. The relationship between variables of plant parameters and cumulative rain amount was analyzed by step wise regression method in SPSS 13. The results showed that plant species often reacted to the precipitation fluctuations. However, various species reacted differently to the precipitation fluctuation in terms of cover and production. The total vegetation cover as well as canopy cover of Artemisia aucheri hada negative and significant correlation with winter precipitation.Whereas, precipitation of January to April and the past year precipitation exhibited a high correlation with canopy cover of Iris songarica and Stipa barbata. The forage production was also influenced by seasonal precipitation. According to the results, total yeild and the yield of Artemisia aucheri, Lactuca orientalis, Stipa barbata could be estimated by precipitation data While, estimation of forage production through the precipitation data was not enough accurate for Iris songarica.

Satellite images are currently used as a fast and low-cost tool for rangeland assessment. In this study, 10 vegetation indices from different groups were calculated using spectral bands. The correlation of these vegetation indices with canopy cover was then measured for three vegetation types in Semirom region-Isfahan. The percentage of canopy cover and other earth surface components such as litter, rock, gravel, stone and bare ground were determined using step-point method. Ten random points were selected in each vegetation type and four 150 meters transects in two perpendicular direction were established from each point, therefore 6000 points were studied per rangeland type. Ten different groups of vegetation indices including slope-based, distance-based and plant–water sensitive indices extracted from IRS-P6 satellite data (AWiFS sensor) were evaluated against total ground cover. The results indicated that vegetation indices have higher relationships within vegetation types based on their characteristics but the correlaion for each vegetation index was not consistent among different types. Considering all photosynthetic vegetation cover, the correlation between these factors and vegetation indices were much higher than degraded sites due to greater reflectance from bare soil and less photosynthetic area. In general, the results indicate that each vegetation index is appropriate for mapping a specific vegetation type and we should consider this issue in mapping and monitoring vegetation cover.

An optimal planning system for managing the range and maintaining its vegetation is highly influenced by the humidity and rainfall of the range. In this research، the reactions of the Cornulaca monocanta species to the fluctuation of precipitation were studied at Ebrahim-Abad in Mehriz – Yazd. For this purpose three dominant Species were selected and their canopy cover and production were monitored every year along permanent line transect in random plots. Precipitation data were collected from nearby stations. According to data of precipitation، amount of cumulative rain was determined at various periods. Relationships between variables of plant parameters and amount of cumulative rain analyzed by Back ward and stepwise regression method. The Results indicate that plants species are affected by precipitation fluctuation. The Total vegetation cover has negative and significant correlation with winter Precipitation as well as canopy cover of Cornolaca monocanta. Whereas Precipitation in January-April and winter exhibited a high correlation with canopy cover of Launaea acantodes and Artemisia sieberi. The forage production was also influenced by seasonal precipitation. According to this result، annual yield of dominant plant species and annuals production can be estimated by precipitation in winter and January-April period. In the final، Result of curve estimation show that yield and canopy cover response of Cornolaca monocanta are in two forms of power and linear، respectively.