Humans are leaving a heavy mark on Earth, but it's not just climate change. A new study shows that in addition to overfishing and other resource extraction, humans are also hogging nearly a quarter of the planet's yearly production of plant life. The findings suggest that humans are endangering Earth's biodiversity and call into question a leading strategy for slowing global warming--the use of biofuels to cut carbon dioxide emissions.
In recent years, scientists have made numerous attempts to determine how much vegetation, or "biomass," is appropriated by humans. Past estimates have varied widely, however, according to the models used and the data available to plug into them. A team led by Helmut Haberl, an ecologist at the University of Klagenfurt in Klagenfurt, Austria, has taken another crack at the question using a larger number of updated databases and taking into account the effects of land use by humans on overall plant growth. Haberl and his co-workers took the latest available statistics on agricultural production, forestry, and human-caused soil degradation, and mapped them.
The analysis showed that in 2000, humans used up to 23.8% of that year's biomass production, the team reports online this week in the Proceedings of the National Academy of Sciences. Of this total impact, the researchers found, 78% was due to agriculture and 22% to forestry, human-caused fires, and other activities. The team also found marked variations in human use of plant life around the world. Southern Asians topped the charts, appropriating about 63% of their area's vegetation, mostly due to more intense agricultural practices. North Americans used 22% and central Asians only about 12%. The authors warn that measures to increase the consumption of biofuels produced from agricultural and forestry products "need to be considered carefully," because they could double the amount of biomass used by humans and put even more pressure on other species trying to get their share of the Earth's plants.
Nathan Moore, an earth scientist at Michigan State University in East Lansing, says that the team's analysis is "sound" and its results are "quite alarming." Christopher Field, an ecologist at the Carnegie Institution in Stanford, California, agrees. The new estimate, he says, "is based on a conservative interpretation of the best available information." Field adds that "one species is appropriating about a quarter of the productive activity of all the world's lands. With millions of species sharing the leftovers, it is hard to know how many will be squeezed out of the game." Field also agrees with the Haberl team's concerns about biofuel use. "There simply isn't enough [biomass production] for us to solve the energy challenge of the 21st century with biofuels."