Indian Journal of Fundamental and Applied Life Sciences ISSN: 2231-6345 (Online) An Open Access, Online International Journal Available at http://www.cibtech.org/jls.htm 2014 Vol. 4 (2) April-June, pp.568-575/Amiri and Taei Research Article © Copyright 2014 | Centre for Info Bio Technology (CIBTech) 568 EFFECTS OF ZIZIPHUS SPINA TREE AS BIOTIC SHELTERBELT ON WIND SPEED FLUCTUATIONS IN AGRO ECOSYSTEMS *Iraj Amiri and Javad Taei Agricultural and Natural Resources Department, University of Jiroft, Jiroft, Kerman, Iran * Author for Correspondence ABSTRACT Windbreaks have been used for centuries to shelter crops from wind damage and to protect soils from wind erosion. This study was performed in 5 steps to evaluate the effects of biotic and abiotic windbreaks on mean horizontal flow and turbulent velocity fluctuations under field conditions. These steps included of granolometery analyzing, determination of field threshold velocity of soil erosion, estimation of acceptable wind speed, optimizing windbreak distance and wind speed recording. Two kinds of windbreaks were used in this study, include of biotic windbreak (Ziziphus spina christi) with 85% density and abiotic windbreak (Mud wall) with 100% density. Results of field experiment showed that optimized distances for abiotic and biotic windbreak are respectively observed at 7.87h and 4.5h after windbreak. Finally mud wall is applicable for high decreasing wind speed at the back of windbreak but its high wind speed fluctuation and high turbulent were limited these windbreak in agro ecosystem. Ziziphus spina christi with 85% density is applicable for medium decreasing of wind speed and creating low turbulent after windbreak. Keywords: Mud Wall, Ziziphus Spina Christi, Threshold Velocity, Windbreak, Wind INTRODUCTION Windbreaks are barriers used to reduce and redirect as wind blows against a windbreak, air pressure wind. They usually consist of trees and shrubs, but builds up on the windward side (the side towards the may also be perennial or annual crops and grasses, wind), and large quantities of air move up and over the fences, or other materials. The reduction in wind speed top or around the ends of the windbreak. Artificial porous windbreaks are now in widespread use for many purposes. Several types of porous windbreak are available (e.g., wooden-slotted snow-fence, plastic mesh and mud wall), and without exception, these are manufactured so as to give a uniform distribution of porosity with height. That a windbreak should be porous in order to prevent the creation of an intensely turbulent wake is beyond dispute. However, even a very porous windbreak, while not causing a lee-side recirculation zone, does cause increased levels of turbulence in a region of the leeward flow as a result of advection and diffusion of kinetic energy away from a region of strong shear-production just above the fence (Raine and Stevenson, 1977; Cleugh, 1998). The interaction between the windbreak and the airflow is complicated by the turbulent characteristics of the wind and by the complex behavior caused by natural obstacles. Although much effort has gone into the measurement and characterization of wind flow in the lee of wind barriers and isolated obstacles at a range of scales, relatively little attention has been given to the direct interaction of the air with the individual plants that can be characterized by a drag coefficient. Our understanding of wind interaction with three-dimensional, porous obstacles, however, such as tree windbreaks and isolated trees and shrubs, is much less complete (Heisler and DeWalle, 1988). The consequence of this lack of knowledge results in the use of surrogate data in models. For example, Raupach (1992) and Raupach et al., (1993), by necessity, use drag coefficients of solid roughness elements reported by Taylor (1988) to represent natural, porous vegetation. Furthermore, the very causes of wind-speed reduction, pressure perturbation related to width and structure, permeability and drag force, are largely unknown for three-dimensional, porous obstacles (Wang and Takle, 1996). Wind condition were measured around four different shelterbelts during an extensive measurement program carried out in jiroft (Iran) in 1997and 1998. The main purpose was to compare the shelter effect of different types of shelterbelts under the same weather conditions (Lindholm et al., 1988). Besides windbreak height and porosity, the actual form of the wind