Periodical cicadas suffer legacy effects of century-old forest removal

Abstract

Periodical cicada (Magicicada spp.) ranges have continued to decline even as their forest habitat has rebounded from historic lows. This counterintuitive trajectory may be a consequence of Magicicadas limited dispersal capabilities combined with their requirement that individual host trees survive across decades. We studied the relationship between >150 years of landscape change and brood XIII periodical cicada activity in Johnson County, IA. We found that the presence of Magicicada breeding populations was better predicted by tree cover in 1930 than by present-day tree cover, with cicadas primarily relegated to sites that did not fall below 17.4% tree cover. While total forest has increased since 1930, this is a net increase, inclusive of considerable turnover every 17 years, and cicada ranges have declined more than they have expanded. A model based on empirical measures of forest turnover and cicada dispersal distances suggests that cicada ranges will continue to decline under nearly all conditions. A managed relocation of 20,126 adult Magicicada to a restored forest failed, reinforcing that dispersal to new sites cannot be artificially accelerated to offset declines. Preservation of forest habitat across centuries may be the only bollard standing between periodical cicadas and their extinction.