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.
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 have reported their findings 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.