Protecting the Breadbasket with Trees: The Effect of the Great Plains Shelterbelt Project on Agricultural Production
*Names in bold indicate Presenter
To empirically estimate the effect of shelterbelts planted, it is usually problematic to draw a conclusion by simply comparing the regions with shelterbelts and those without, because trees may be planted where it is feasible or has lower opportunity cost. To tackle this endogeneity problem, I use the historical variation arising from a shelterbelt zone designated in the Great Plains Shelterbelt Project as the instrumental variable to predict the actual region where shelterbelts were planted. This zone formed a 100-mile-wide belt that stretched 1,150 miles from the Canadian border into northern Texas, and was pushed as far westward as possible considering the feasibility of climate and soil conditions. Hence, the proportion of a county included in the Belt was arguably exogenous when controlling relevant climate and soil conditions. My first-stage regression shows that counties within the 100-mile-wide Belt are nearly twice as likely to be covered by shelterbelts (or 15.3 percentage points higher in coverage) as the neighboring counties outside the Belt. The second-stage results show that a 10% increase in shelterbelt coverage in a county leads to a 9-15% increase in agricultural productivity with the effect growing over time. I find heterogeneous effects by levels of soil erosion caused by the 1930s Dust Bowl. The regions with medium level of soil erosion benefit from shelterbelts whereas low or high eroded regions do not. In addition, the increase in productivity occurs in pasture rather than cropland because livestock are not adversely affected by tree planting.