基于防护保证率的农田防护林林带间距调控

Farmland shelterbelt interval setting based on protection insurance rate

农田防护林林带间距的设置关系到防护林防护效益和农田单位经济效益的权衡。该文以新疆南疆枣树防护林为例,引用水文学中防护保证率的概念和方法,以枣树受风害危害的概率特征为基础,兼顾防护林防风生态效益和经济效益最大为目标,建模分析和野外试验相结合,研究了农田防护林林带间距调控方法。结果表明:1)运用防护保证率的方法能够实现对农田防护林防风生态效益与经济效益权衡的优化;2)枣树防护林的防护保证率在95%,林带间距为132.1 m左右时,单位经济价值达到最优,高出常规防护林间距经济产量6.2%;3)林带疏透度为0.34大于疏透度为0.49的防护效益。该研究可为农田防护林林带间距定量调控提供参考。

Setting appropriate farmland shelterbelt intervals is critical for ensuring an appropriate trade-off between shelterbelt protection benefits and unit economic benefits. If the shelterbelt interval is very large, the protection benefits will be reduced, and consequently the crops will suffer serious damage; however, if the shelterbelt interval is very small, more farmland area will be occupied, resulting in crop failure. With the development of precision and intensive agriculture, a new agricultural concept has been developed in which the ecological benefits that shelterbelts provide through the prevention of wind damage can be optimized against the economic benefits. In this study, we chose the jujube （Ziziphus jujuba） shelterbelts in southern Xinjiang, China as an example to develop a model for calculating a protection guarantee rate and farmland economic benefits, using the concept and method of the protection guarantee rate from hydrology. The protection guarantee rate was used to describe the number of wind damage incidents in this region, and the Weibull curve was used for the fitting of the number of wind damage incidents per hour in which the wind speed was greater than the threshold value during the jujube flowering phase. The results showed that the Weibull curve provided a good fitting for the number of wind damage incidents in the study area（R2=0.88）. The farmland economic benefits included the protection benefits of shelterbelts with different levels of aerodynamic porosity and their corresponding economic benefits. These protection benefits were obtained from the field experiments, using a wind speed profile meter at a height of 1.5 m in 5 representative shelterbelts in the study area, which showed that the shelterbelt protection benefits were the greatest at a porosity of 0.34. The economic benefits were calculated by considering both expenditure and income; the expenditure included the amount that was spent on managing and maintaining the shelterbelt, and on planting and maintaining the jujube, and the income included both the jujube and the lumber benefits. To ensure that the expenditure and income were comparable across different time periods, we used the same method to calculate the compound interest over several years. Furthermore, the total revenue was calculated based on the expected protection guarantee rate and the corresponding benefits. The results showed that the benefits of the jujube shelterbelt increased when the protection guarantee rate changed from 100% to 95%, reaching a maximum value at the protection guarantee rate of 95%, and then decreased when the protection guarantee rate changed from 95% to 60%. Therefore, the optimal jujube shelterbelt interval was smaller when there was a greater shelterbelt protection benefit. Therefore, when assessing the probability characteristics of jujube hazard by wind damage, both the shelterbelt protection benefits and the unit economic benefits of the farmland should be considered. The regulation and control of farmland shelterbelt intervals was investigated using a combination of modeling analysis and field tests. The results showed that： 1） the trade-off between the ecological benefits of a farmland shelterbelt as a windbreak and the economic benefits could be assessed using the protection reliability method; 2） when the protection guarantee rate of the jujube shelterbelt was set at 95%, a shelterbelt interval of 132.1 m achieved an optimal unit economic value; and 3） the shelterbelt protection benefits were better at a porosity of 0.34 than at a porosity of 0.49. This study provides a new quantitative approach for the regulation of farmland shelterbelt intervals.