And at first glance it looks a forlorn hope that anyone could understand the forest. It’s a green riot, a place of disorder and confusion, a jungle. The only possible statement seems to be that if a thing can grow, it will. But as the measurements build up, pattern begins to emerge. The number of stems we measure on each line is fairly constant. At Savegre each 50-meter run brings in about 30 plants—the range is from 25 to 37. Cacao shows a similar consistency, but the lines there have upward of 40 individuals in them. The most crowded have nearly 60. As Brad says, “It’s a busy forest.” But whereas the biggest trees at Savegre have trunks more than a meter wide, there are no such giants at Cacao. The biggest stem we encounter is less than 60 centimeters across. So the Savegre cloud forest has fewer, bigger trees, whereas the forest at Cacao has a greater number of smaller ones.

It would, of course, be rash to make any firm conclusions about the world’s forests from visiting two places in one Central American country. But while the techniques of measurement and collection have changed little in the past couple of centuries, computer power and methods of data analysis have. To do a statistical regression of 100 data points by hand, finding the equation that best describes the pattern in the data, requires a day or two of laborious calculations. A computer can do it before your finger comes off the return key. The Internet makes it much easier to find and share data from different sources. Through a combination of their own fieldwork and ferreting in the scientific literature, the Enquist lab has collected a set of gentrasos three times larger than that collected by Gentry himself. And the more measurements you collect the more strongly order emerges.

How to Build a Forest

Think about the differences between Cacao and Savegre in the population densities and sizes of trees. It’s obvious that any area will support fewer big individuals than small ones, because big plants (and animals) need more space and more resources. This scenario is played out in time as well as between different places. In a forest after a fire or in a gap created by a fallen tree, many saplings will sprout—many more, in fact, than the number of full-grown trees that previously lived on the



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