WASHINGTON - Even in death, the 17-year cicadas made their mark.

Their decaying carcasses gave a super-size boost in nutrients to forest soil and stimulated seed and nitrogen production in a plant important to the forest ecosystem, researchers reported in Friday's issue of the journal Science.

Bard College professor Felicia Keesing likened it to someone pouring a pound of fertilizer per square yard over the forest floor. She co-authored an article accompanying the research paper on the impact of cicada carcasses on soil and plants.

Louie Yang, a graduate student at the University of California, Davis, conducted the studies in 2002, 2003 and 2004 in cicada-infested areas in the eastern United States.

Last summer's infestation was the largest, with 17-year cicadas known as Brood X inundating the mid-Atlantic region and filling forests from Georgia north to Pennsylvania and west through the Ohio River Valley to the Mississippi.

The beady-eyed insects spawned a public fascination - along with a multitude of cicada recipes and worries about the insects' impact on trees, plants, pets and even driving visibility.

While most worries weren't borne out, scientists have long been concerned about the impact of such outbreaks in which there is a sudden hyperabundance of organisms with potentially vast consequences for ecosystems.

In his field studies, Yang experimented with naturally occurring densities of cicada carcasses of as much as 300 bugs per square yard. For each density he measured the soil's nitrogen and bacterial and fungal growth over varying periods of time after carcasses were applied.

Soil content of a form of nitrogen used by plants was many times higher - 199 percent to 412 percent - in ground littered with cicada carcasses. Bacterial and fungal growth also increased.

Yang also measured the nitrogen content in the leaves of bellflower plants, with and without cicada carcasses applied to their soil, as well as bellflower seed production.

He found bellflowers supplemented with cicada carcasses produced seeds 9 percent larger and foliage with a nitrogen content 12 percent higher than bellflowers without cicadas.

Yang's findings that decaying cicada carcasses apparently stimulate a rush of soil nutrients might explain why other analyses have shown that tree-ring growth among oaks in areas infested with 13-year and 17-year cicadas increased for the first four years after cicada emergence, Keesing said.