Size and age of plants impact their productivity more than climate

"A fundamental assumption of our models for understanding how climate influences the functioning of ecosystems is that temperature and precipitation directly influence how fast plants can take up and use carbon dioxide," said Enquist, a professor in the UA's Department of Ecology and Evolutionary Biology whose research lab led the study.

"Essentially, warm and wet environments are thought to allow plant metabolism to run fast, while cold and drier environments slow down metabolism and hence lower biomass production in ecosystems," he said. "This assumption makes sense, as we know from countless experiments that temperature and water control how fast plants can grow. However, when applied to a the scale of entire ecosystems, this assumption appears to not be correct."

To test the assumption on the scale of ecosystems, the team developed a new mathematical theory that assesses the relative importance of several hypothesized drivers of net primary productivity. That theory was then evaluated using a massive new dataset assembled from more than 1,000 different forest locations across the world.

The analysis revealed a new and general mathematical relationship that governs worldwide variation in terrestrial ecosystem net primary productivity. The team found that plant size and plant age control most of the variation in plant productivity, not temperature and precipitation as traditionally thought.