Vanishing Plants reduce Earth's Productivity

Vanishing Plants reduce Earth's Productivity



November 2007 
 Scientists are warning 
that vanishing species could reduce the productivity of plants on Earth 
by half. In a new analysis, the international team led by University of 
California researchers shows that humans could lose some of the most 
important benefits that plants provide. 
Plant productivity regulates the absorption of greenhouse gases like 
carbon dioxide, as well as the ability of habitats to produce oxygen, 
food, fiber, and biofuels.
  
Both the number and types of species going extinct are changing the 
"services" that ecosystems provide to humanity, the authors conclude. 
"The process by which plants grow and produce more plant biomass is one of 
the most fundamental biological processes on the planet," said Bradley 
Cardinale, lead author of the paper and assistant professor of biology at 
UC Santa Barbara.
Dr. Cardinale said experiments to date have probably underestimated the 
impact of species loss on ecosystems. 
"We found that as experiments were run longer, they detected increasingly 
strong impacts of species diversity on plant productivity," he said. 
"Unfortunately, because most experiments have only been funded to run for 
a few years at a time, they have probably underestimated the impacts of 
extinction on natural habitats." 

The article will appear this week in the online issue of the "Proceedings 
of the National Academy of Sciences." 
The study summarized the results of 44 experiments from around the world 
that simulated plant species extinction. It shows that ecosystems with 
fewer species produce up to 50 percent less plant biomass than those with 
more "natural" levels of diversity. 
"Therefore, species extinctions could compromise the benefits that nature 
provides to society," said Cardinale. In practical terms, this means that 
diverse ecosystems are likely to be better at controlling pests, breaking 
down organic matter, and absorbing carbon dioxide.
"Our analyses provide the most comprehensive evidence yet that natural 
habitats with a greater variety of plant species are more productive," 
said co-author Michel Loreau of McGill University in Montreal. 

"This occurs partly because diverse communities are more likely to contain 
highly productive species," said Loreau. 
"But even more important, our analyses show that diverse communities are 
more productive because plants are complementary in how they use 
biological resources. In other words, different plant species play unique 
roles in the environment." 
Co-author Andy Hector, an assistant professor at the University of Zurich, 
said plant communities operate like a soccer team. 
"Teams are composed of both star players and supporting players," said 
Hector. "You probably can't win many games if you lose your top striker 
because she or he is the most productive player and can dominate a game. 
But strikers cannot win games by themselves. They need great passes from 
supporting players and solid goal-tending if the team is going to be 
successful as a whole." 
The authors say plant communities are also composed of both stars and 
supporting players. 
Until recently, scientists knew much about the causes of global species 
extinction, but very little about the ecological consequences. This 
statistical analysis shows that species extinction generally causes 
ecosystems to become less productive, and less efficient at capturing 
biological resources. 
The authors call species extinction "one of the most pronounced 
environmental changes of our time," and note that many scientists now 
argue that the Earth is in the midst of the sixth mass extinction in the 
history of life. 
Some estimates suggest that as much as 50 percent of all known species 
could be extinct by the end of this century. 

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