Hard-hat zone

Natural History, Sept, 2004

You may never hear the sound of one hand clapping, but if you visit the western reaches of Amazonia, you will certainly hear one leaf falling.

One of the most common Amazonian trees is the stilt-rooted palm Iriartea deltoidea, whose cousins you may have seen if you've ever sunned yourself on the beaches of the Caribbean or the Indian Ocean Those majestic fronds swaying in the tropical breezes are single leaves, subject, like any other leaf, to desiccation and death. And when a twenty-foot-long, thirty pound dead leaf falls to the ground from a height of, say, ninety or a hundred feet, it not only makes quite a noise but also has a long term impact.

Halton A. Peters, an ecologist at Stanford University, and his colleagues recently deter mined that even though an I. deltoidea drops just two or three fronds a year, the fronds do so much damage that they "weed out" many of the saplings beneath the tree. The saplings that survive are, disproportionately, members of species whose root systems hold large reserves of nutrients, making them better able to compensate for aboveground breakage. Because I. deltoidea is so abundant, the ecologists note, it ends up determining the composition of much of the rainforest understory. ("Falling palm fronds structure Amazonian rainforest sapling communities," Proceedings of the Royal Society of London B (Suppl.) 271 :S367-69, August 7, 2004)