Ecological catastrophes: threshold responses to climate, soil, and land use drivers of the Dust Bowl

Background/Question/Methods

The Dust Bowl was one of the largest ecological disasters, yet is among the least well-studied for regional-scale impacts. Much of the central grasslands region (CGR) of North America experienced a multi-year drought in the 1930s that combined with poor land management practices to result in broad-scale plant mortality, massive dust storms, and decreases in continental-scale air quality. Although regional accounts exist, most studies of impacts on vegetation and soils focus on a small area with the greatest losses (eastern Colorado, western Kansas and Oklahoma). A broad-scale synthesis throughout the CGR is needed to provide insights into the drivers of historical impacts, and the legacies of those impacts on present-day ecosystems. Our goal was to synthesize data and maps beginning in the 1930s from eight long-term research sites (LTAR, LTER) and twelve National Grasslands located throughout the CGR in order to: (1) determine the degree of historic impacts throughout the CGR, (2) identify the climatic, soil, and land use drivers of those impacts, and (3) evaluate long-term legacies on current ecosystems. 

Results/Conclusions

Our results show that impacts of the Dust Bowl on vegetation and soil occurred over nearly 1/3 of the continental US, and effects on air quality covered 2/3 of the area. All grassland types in the CGR were affected, but to varying degrees. The shortgrass steppe and southern mixedgrass prairie had the most severe impacts on plant mortality and soil erosion; these grasslands were also the most well-studied prior to and during the drought. In some areas, the transition between severely impacted and not impacted sites occurred over short distances, and the transitions were not easily explained by precipitation, drought indices, or soils. For example, sites in southeastern Nebraska with 60% of mean annual precipitation (MAP) in 1934 had severe losses while sites on similar soils located < 100 km to the east with 53% of MAP were not impacted. Simulation model analyses showed that interactions among climate, soils, and land use legacies can explain spatial variation in impacts along these transition zones. Given that extreme climatic events are expected to increase in the near future, an improved understanding of historic events is critical to predicting impacts of future catastrophes.