University of Iowa study says historic forest loss could leave periodical cicadas unable to recover

A University of Iowa study argues that historical removal of old-growth forest may leave periodical cicadas unable to recolonize restored habitat for centuries, even under favorable assumptions. That is a more accurate claim than saying the familiar 17-year cicadas are simply disappearing because of modern logging. The research addresses long-lived effects of past forest loss on insects whose survival depends on local populations persisting over many emergence cycles.

Periodical cicadas are the North American insects in the genus Magicicada that emerge every 13 or 17 years, depending on species and brood. Their synchronized appearances can be enormous and loud, but the spectacle should not be mistaken for invulnerability. The Iowa researchers say a species that relies on overwhelming numbers may be unusually fragile when suitable forest is broken into isolated pieces.

The study examines a legacy of forest removal

The research, published in Ecology as “Periodical cicadas suffer legacy effects of century-old forest removal,” focuses on the consequences of historical rather than merely current habitat change. The University of Iowa describes the finding as a warning that old-growth-forest removal can have effects long after trees return. Its model indicates that cicadas move so slowly across the landscape that recovery of a restored forest could take many centuries.

That distinction is essential. “May be doomed to extinction” is a research conclusion about risk under continuing loss and fragmentation, not a declaration that every brood has vanished. It also does not establish one simple, nationwide cause. Forest history varies across the cicadas’ range, species and broods differ, and an article should not convert a modelled scenario into a current head count for America’s periodical cicadas.

Why a 13- or 17-year life cycle changes the conservation problem

Most of a periodical cicada’s life is spent underground feeding on fluids from tree roots. Adults emerge, mate, lay eggs and die in a short period above ground; the next generation then develops below ground for another 13 or 17 years. That schedule means failures are hard to see in real time. A local population may be absent during a year when observers expect quiet, and evidence of poor recolonization can unfold across human generations.

It also means dispersal is not like the movement of a bird that can rapidly cross a changed landscape. The Iowa team used observed movement distances to model spread into restored forest. Their result was not that restoration is pointless. It was that restoration needs to reckon with the pace of the organism. Protecting remnant habitat and maintaining connections between populations may matter as much as planting trees in an isolated block.

Mass emergence is an ecological strategy, not a guarantee

When a brood emerges in great numbers, predators cannot consume every individual. That strategy, often called predator satiation, helps enough cicadas survive to reproduce. Their emergence also moves a pulse of food and nutrients through forest ecosystems. The U.S. Forest Service and National Park Service both describe these synchronized events as unusually conspicuous parts of eastern North American forest life.

But abundance during a strong emergence does not answer the study’s habitat question. A population needs appropriate forest conditions and enough nearby individuals across cycles to sustain itself. Fragmentation can make a localized loss hard to reverse even if the broader species remains common elsewhere. The practical implication is that people should be wary of judging conservation status by a single noisy spring or by the absence of a brood outside its known schedule.

Forest continuity matters over several emergence cycles

The study adds a reason to value mature forest, forest continuity and long-term habitat planning. It does not provide a shortcut for diagnosing a quiet backyard, and it does not ask the public to collect cicadas indiscriminately. For land managers, the central insight is time: a habitat decision can matter to an insect population over intervals far longer than a typical restoration grant or management cycle.

The paper says historic forest removal could leave periodical cicadas unable to recover on meaningful time scales. It is evidence about vulnerability rather than a final forecast of extinction. The conclusion is consequential because the insects’ most visible moments arrive only once or twice in a human lifetime, while the habitat changes that shape those moments can date back far longer.

The University of Iowa’s account of the research describes the “legacy effects” of forest removal. The phrase shifts attention from a single emergence to the continuity of suitable woods over centuries. A restored stand can be valuable for many species while still remaining hard for a slowly spreading cicada population to recolonize.

The peer-reviewed paper sets out the finding. Background on life cycles and ecology is available from the U.S. Forest Service, the National Park Service, and the U.S. Geological Survey.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.