It has been unusual in the American experience. However, it is no longer rare. Natural decrease is the consequence of a complex interaction between fertility, mortality and migration over a protracted period and is symptomatic of fundamental changes in the demographic structure of an area. Age structure shifts resulting from protracted, age-specific migration is the primary cause of most natural decrease. Temporal variations in fertility also contribute, but it is not usually due to below average fertility in a county.
Natural decrease is most common in rural counties remote from metropolitan centers.
Regional concentrations exist in the Great Plains, Corn Belt and East Texas, with scattered pockets in the Ozark-Ouachita Uplands, Upper Great Lakes and Florida. Natural Decrease on the Rise Natural decrease has been extremely unusual in the United States. Generally, births have exceeded deaths by a significant margin in virtually every part of the country through most of the nation's history. Aside from isolated instances when epidemics or natural disasters caused many deaths, natural decrease has been exceedingly rare. Near the end of the Great Depression, natural decrease began to occur in a few areas, but it was short-lived.