Soil-borne pathogens drive tree diversity in forests, study shows

Science Daily: Why are tropical forests so biologically rich? Smithsonian researchers have new evidence that the answer to one of life's great unsolved mysteries lies underground, according to a study published in the journal, Nature.

What determines plant diversity in a forest? It's a question even Charles Darwin wanted to unravel. But most research into forest diversity demonstrates only patterns of species survival and abundance rather than the reason for them -- until now.

A team of researchers led by biologists at the University of Wisconsin-Milwaukee (UWM) has shown that soil-borne pathogens are one important mechanism that can maintain species diversity and explain patterns of tree abundance in a forest.

"We've known for a long time that tree seedlings do not grow and survive well under their mothers or other adult trees of the same species," said Scott Mangan, postdoctoral fellow at the University of Wisconsin -- Milwaukee and the Smithsonian Tropical Research Institute in Panama. "One explanation for the maintenance of the diversity of tropical trees is that adult trees harbor pests and diseases that harm seedlings of their own species more than they do seedlings of other species." The experiments show that underground organisms are key to the maintenance of species diversity and patterns of tree-species relative abundance. The detrimental effects of soil organisms from adult trees not only explain seedling growth and survival patterns, but moreover that these effects are much more severe for seedlings of rare species than for seedlings of common species….

Henri Rousseau, "Combat of a Tiger and a Buffalo," 1908-1909