Tropical forests that have been heavily logged -- cleared and replanted, cleared and replanted -- may never recover. According to a new study, published Tuesday in the journal Global Change Biology, continually logging tropical forests depletes the reserve of vital nutrients in the soil, diminishing the forest's odds of long-term recovery.

"Old-growth tropical forests that have been the same for millions of years are now changing irreversibly due to repeated logging," lead study author Tom Swinfield, a plant scientist in the University of Cambridge Conservation Research Institute, said in a news release.

When scientists surveyed the health of trees in previously logged forests on the island of Borneo, they found their leaves were thicker and featured lower concentrations of nitrogen and phosphorous.

Soil nutrients are essential to healthy vegetation. When trees die and decompose naturally, the nutrients are returned to the soil. When forests are logged, the nutrients are carried away with trees. Logging also increases soil erosion, further depleting the land of nitrogen and phosphorous.

Scientists estimated that as much as 30 percent of a forest's phosphorous is lost when it is logged.

"We see that as the logged forests start recovering, they're actually diverging from the old growth forests in terms of their leaf chemistry and possibly also species composition, as the amount of available nutrients goes down," said Swinfield. "At the moment the trees can cope, but the fact that they're changing indicates phosphorus levels in the soil are dropping. This could affect the speed at which forests recover from future disturbances."

Swinfield and his colleagues surveyed the health of new and old growth forests using a LiDAR surveys, which image the forest canopy at several different frequencies. The research team also collected and analyzed hundreds of leaf samples from individual trees.

Researchers found forests that had been logged multiple times were worse off, nutrients wise, than forests that had only been logged once.

"Phosphorus limitation is a really serious global issue: it's one of the areas where humans are using a vital resource beyond sustainable levels," said David Coomes, director of the Conservation Research Institute at the University of Cambridge.

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