The results reflect long-term ecological impacts of land use changes, such as the conversion of forests to agricultural land, the researchers said.

"We know these soil animals are important controls on processes which cause nutrients and carbon to cycle in ecosystems, but there was little evidence that human-induced loss of these animals has effects at the level of the whole ecosystem, on services such as agricultural yield," said lead author Mark Bradford, an associate professor at Yale School of Forestry & Environmental Studies.

For their study, the researchers assembled 16 bathtub-sized replicas of a Scottish upland grassland and each of the models included the 10 most common plant species.

They introduced earthworms, slugs, and other small creatures to only some of the systems. There was no change in plant yield or the rate of carbon dioxide loss from the system during the first six months.

"But there were huge changes in the ecosystem processes once the model was continued for 500 days, including productivity of the plants," said Bradford.

Whereas grass yields were reduced, the quality of the yields was improved after removing the creatures.

"These findings emphasize how interconnected the below ground and above ground components of ecosystems are, and that different ecosystem processes respond in different ways to the management of grasslands," noted study co-author Stephen Wood from Columbia University.

"In this case, the loss of soil animal diversity eventually changed the dominant plant species in the meadow ecosystems, and then in turn the productivity of these grasslands and how they responded to agricultural management," Bradford concluded.

The study appeared in the Proceedings of the National Academy of Sciences.

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