- A team of more than 80 researchers collected data in 44 countries covering nearly all major forest ecosystems.
- In natural forests, they were able to show accelerating declines in productivity as the forest loses more tree species.
- Based on their calculations, the value of tree species biodiversity is $166-$490 billion.
A few years back, Jingjing Liang started to notice a pattern in his work as a forest ecologist who spends a lot of time studying the complex relationships within forests. Whether he was in the taiga of Alaska where pine-rich stands push into the Arctic Circle, amid the western hemlocks and Douglas firs that predominate in the Pacific Northwest, or in the hardwood forests that bring their autumn color to the eastern U.S. each year, his investigations revealed a consistent trend: Wooded areas with more tree species tended to be more productive – that is, more diverse systems were generating more wood.
That association has cropped up in numerous localized forestry studies for years, Liang said, but whether that tendency applied to all forest types wasn’t clear. So three years ago, he and his colleagues decided to look at the question more broadly.
“If this finding were to hold across the whole world, then it would mean a lot in terms of forestry and forest conservation,” said Liang, who works at West Virginia University.
To test their hypothesis, they reached out to ecologists studying forests all over the world and asked them to collect information about the richness of tree species in those areas and the volume of timber that they produced each year. In all, the team gathered data from sites in 44 countries containing some 30 million trees representing nearly 8,800 species covering just about every type of forest ecosystem.
They found that in natural forests across these remarkably different biomes, some in the more temperate regions with just a handful of species and others with several hundred in the tropics, the trend held. They report their findings today in the journal Science.
Not only that, but they discovered that if everything else remains the same, tree species diversity will increase forest productivity. The authors’ calculations show an “accelerating” loss of productivity as more species are removed from a particular system.
They write that a 10 percent loss of the species would lead to a 2 to 3 percent decline in productivity. Based on that, you might expect only a 20 to 30 percent productivity drop from a 99 percent loss of diversity. Instead, the authors show that in reality productivity could dip by as much as 66 percent.
“Packing stands with more species might be milking the environment of the available resources more fully than a simpler stand,” said Bill Laurance, a tropical ecologist at James Cook University in Queensland, Australia, who did not participate in the study. “More species give you a different combination and in some sense complement each other, and therefore you’re getting greater productivity overall.”
Demonstrating the existence of an important link between productivity and biodiversity confirms what many ecologists have long suspected, said Laurance, who was not involved in the research, and he lauded the study’s global reach.
“They’re saying, ‘Look, we can’t take species richness out of the equation when we’re trying to think about valuing forests,’” Laurance said. “One of the reasons why forests are valuable is the high species richness that contributes to that value.”
Liang said they decided to use annual increases in timber volume to measure productivity so the findings could have direct forestry implications.
Economic analyses of ecosystems typically include valuation of their services such as regulating the flow of water, providing habitat, and influencing the climate, but they often stop short of putting a figure to biodiversity.
“We are trying to show that biodiversity has substantial values that previously we have ignored,” Liang said.
Based on the team’s estimates, the global value of conserving biodiversity is quite substantial – somewhere between $166 billion and $490 billion per year, based on the commercial value of the timber that those forests produce. This price far exceeds what it would cost to adequately conserve all of the worlds ecosystems, according to a 2012 paper in Science.
Liang and his coauthors write in today’s paper, “The high benefit-to-cost ratio underlines the importance of conserving biodiversity for forestry and forest resource management.”
However, Liang said that the 2012 study estimate of roughly $76 billion still far exceeds what governments currently spend on conservation.
Liang and his colleagues recently took the opportunity to codify their network of more than 80 people from 19 institutions who contributed to this latest research into what they call the Global Forestry Biodiversity Initiative.
“Our next step is to [look] at the forest resources across the world and address some key questions,” Liang said, such as how forest management will shift with economic and climate change scenarios in the future and the way in which forestry decisions will impact poverty in developing countries.
Reflecting on their latest findings, Liang wondered if diversity’s impact on productivity wasn’t limited to forests.
“Maybe there is something similar going on with people,” he said. “Personally, I believe the diversity of our team is actually a key factor to relates to [our] success.”
- Liang, J. et al. (2016). Positive biodiversity-productivity relationship predominant in global forests. Science.
- McCarthy, D. P. et al. (2012). Financial Costs of Meeting Global Biodiversity Conservation Targets: Current Spending and Unmet Needs. Science.