Travel Reference
In-Depth Information
come back for the next census to discover that their plot had been converted
to soybeans or condominiums.
The fi rst census, by far the most challenging, required that the 300,000
trees on the plot be located and identifi ed. An army of students had to brave
mosquitoes, chiggers, and tropical downpours for months. They also had
to survive occasional confrontations with bands of collared peccaries that
rooted and snul ed their way through the forest and threatened to attack
anyone who got in their way.
In order to keep from going crazy by trying to measure millions of tiny
threadlike saplings, Hubbell and Foster quickly decided to limit the censuses
to trees and bushes that were one centimeter or more in “diameter at breast
height.” (This imprecise and politically incorrect measure has now been
replaced by the less potentially embarrassing “diameter at 1.4 meters above
the ground”—but it is still abbreviated dbh!)
The Barro Colorado plot has now been censused six times, with a sev-
enth census scheduled for 2010. The result has been by far the most extensive
set of data on a large ecosystem anywhere on the planet. And the census has
proved to be so productive of exciting research that new censuses have been
initiated throughout the world's tropics. Most recently, plots have been set
up in the temperate zones of North America, Europe, and China. There are
now more than thirty large plots, or collections of smaller ones, throughout
the world, many of which have been censused more than once.
My own contribution to this immense project began when I returned
to the USA from Manù. In collaboration with Hubbell and his colleagues I
began to examine the forest data to see whether frequency-dependent ef ects
are actually operating, and how many of the species in the forests are af ected
by them.
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Frequency-dependent models like Janzen-Connell and N-C predict that
if trees of a given species are common in a certain part of the forest, they
should be less successful at reproducing than in other regions where they
are rare. Locally common trees should be at a disadvantage, and locally rare
ones at an advantage.
The data from the Barro Colorado Island plot are not ideal for this kind
of study, because information about the tiniest seedlings in the forests is not
