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Assessment of the effects of shelterbelts on crop yields at the regional scale in Northeast China

Zheng, Xiao, Zhu, Jiaojun, Xing, Zefeng
Agricultural systems 2016 v.143 pp. 49-60
Landsat, afforestation, agricultural land, climatic factors, corn, fertilizers, forests, harvest index, microclimate, moderate resolution imaging spectroradiometer, planning, planting, seeds, shelterbelts, solar radiation, temperature, time series analysis, wind damage, China
The Three-North Shelter Forest Program (TNSFP), which is the largest ecological afforestation program worldwide, was launched in 1978 and will last until 2050 in the Three-North regions (accounting for 42.4% of China's territory). As a dominant component in the TNSFP, shelterbelts or windbreaks play an important role in preventing from wind damage and erosion and providing appropriate microclimate conditions for crop growth, thus improving crop yields. However, how shelterbelts influence crop yields at the regional scale has not yet been determined because there are certain difficulties in identifying the effects of shelterbelts on crop yields due to other factors such as climatic factors, crop seeds, fertilizer and management measures. In this study, a new approach is used to estimate the effects of shelterbelts on crop yields while overcoming these difficulties. The specific processes used in this study are detailed as follows. First, the climatic potential productivity, which is a combination of solar radiation, temperature and precipitation, was estimated using the multi-sensor remote data. All farmland in the region was divided into high, middle and low climatic potential productivity zones. Second, the crop (i.e., maize) yield across the Northeast China was estimated using the harvest index method and MODIS data. Third, according to the effectively protected distance, the levels of protection provided by the shelterbelts to the farmland at the regional scale were calculated by combining the stand age and the growth status of the shelterbelts using a time series of Landsat images. Finally, the levels of protection and the corresponding maize yields in pixels were extracted and averaged to identify the effects of shelterbelts on crop yields. The results of this study indicated that shelterbelts could enhance crop yields at the regional scale. The contribution rates of shelterbelts to increasing maize yields were found to be 4.68%, 4.28% and 9.45% in the high, middle and low climatic potential productivity zones, respectively. In Northeast China, the average level of protection of farmland was 18.28%, which was obviously lower than the optimal level of protection (i.e., approximately 80%); thus, many shelterbelts must be planted in the future. The findings of this study provide a sound theoretical foundation for increasing crop yields by planning shelterbelts in farmland regions similar to those in Northeast China.