Study questions ability of trees to store more carbon as CO2 levels rise.

March 7 (UPI) — Some scientists have argued rising carbon levels will boost tree growth, and thus allow forests to store more carbon, but new research suggests the theory is flawed. Trees with insufficient nutrients won’t add biomass as CO2 levels rise, scientists say.

Many climate models use carbon storage data collected during experiments involving temperate forests, where soils are rich in nutrients.

“Estimates on carbon absorption do not account for nutrient shortages on forest productivity,” David Ellsworth, a professor at Western Sydney University’s Hawkesbury Institute for the Environment, said in a news release. “Since many of the world’s sub-tropical and tropical forested regions exist on low-nutrient soils, our results indicate that global estimates of carbon storage in forests could be too high.”

Scientists exposed large tracts of eucalyptus forest, where nutrients are scarce, to elevated CO2 levels. Plots treated with CO2 concentrations of 550 parts per million, 150 ppm more than natural levels, boasted accelerated photosynthesis rates but no new tree growth. Temperate forest plots, on the other hand, turned the excess carbon into new biomass.

“Many greenhouse crops such as tomatoes, cut flowers and cucumbers are given added CO2 to make them grow bigger, faster and yield more fruit,” said Ellsworth. “Yet out in Australia’s native forests, conditions for plants are not quite so ideal. Australia’s soils are very old and weathered by millions of years of sun and rain, meaning soils are very low in nutrients, and most of the available nutrients are tied up inside wood, leaves and roots.”

The findings — detailed in the journal Nature Climate Change — suggest many climate models are overestimating the ability of forests to store carbon as climate change accelerates.