ارزیابی اثر پخش سیلاب بر نوسان های شاخص های گیاهان مرتعی در ایستگاه آبخوانداری کوثر

Introduction and Objectives
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.
Materials and Methods
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.
Results and Discussions
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.