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The Center for Tropical Forest Science

What the CTFS has told us about tropical ecology

by Eric Jackson

 There is a general scientific no-brainer that comes in the form of a question: What good is an experiment if it can’t be replicated? If one cares to get deeply philosophical or into complicated processes where no two phenomena are exactly the same it can be less obvious, but even in such a subtle and intricate field as the study of tropical forests, where the work is usually more observational than experimental, there is an urge to replicate.

Back in 1979 researchers with the Smithsonian Tropical Research Institute (STRI) began a long-term study of a 50-hectare forest plot on Barro Colorado Island. The papers in scientific journals arising from the study began in 1983 and the project quickly became famous in scientific circles.

How famous? So well renowned that other scientists began similar studies at other sites around the tropics, particularly in Asia and the Americas. These studies of tropical forest plots created a demand for a central database with coordinated standards, which project began as the Center for Tropical Forest Science Asia (CTFS), which later embraced the world of tropical forest research.

An overview on forest plot studies and the things that have been learned from the world of forest plot studies was the subject of STRI biologist Egbert Leigh’s May 22 lecture at the Tupper Auditorium in Ancon.

Leigh noted that by 2000 there were studies of 10 forest plots of 10 hectares or more around the world, which he considers impressive given the difficulties of this sort of research. “It’s neither cheap nor easy,” Leigh commented. So why did the tropical forest plot study catch on so quickly?

The Barro Colorado plot was largely the idea of Stephen P. Hubbell, a biologist who had previously studied a 14-hectare plot in Costa Rica. He developed a neutral theory about the distribution of tree species in tropical forests that assumed that a tree’s species is irrelevant to its chances of mortality or reproduction, and that there is no particular process that controls species diversity in a forest plot, whose selection of trees is determined by a balance of speciation and random extinction. Leigh later opined in a 2001 paper that the data for tree species distribution taken from tropical forest plots would indicate that Hubbell’s theory would at least have to be modified.

A famous argument between Hubbell and Harvard botanist Peter S. Ashton about the former’s neutral theory played itself out in a 1986 seminar and was continued in a British pub, and that led to the establishment in Malaysia’s everwet Pasoh Forest Reserve of a 50-hectare plot study with the specific aim of disproving Hubbell’s theory.

Meanwhile in India, zoological research was underway at Mudumalai, a dry forest park with a lot of elephants and other animals, and there was a perceived need to gather botanical information to better understand the animal dynamics, so there, too, a 50-hectare forest plot was marked off and studied. A 52-hectare plot study followed in the Lambir Hills National Park on the Malaysian island of Sarawak and a 50-hectare plot study was undertaken at Huai Kha Khaeng in Thailand.

Similar tropical forest plot studies began in Singapore, Sri Lanka, the Philippines, Thailand, Taiwan, Puerto Rico, the Congo, Cameroon and Ecuador.

So, with all the data collected and compiled through the CTFS, what have scientists learned?

The proof of any grand theories of forest ecology has mostly not happened, although reality has been shown to be a bit more complicated than a number of elegantly simple ideas that had been advanced. In light of all that has been discovered in the last quarter-century, Leigh branded the neutral theory as “frivolous.”

We have learned that all tropical forests are not alike. We have learned that in general, the lower the rainfall, the lower the plant diversity. We have learned that on islands there is less diversity than on continents.

But meanwhile, a lot of things unrelated to what Hubbell and Ashton were looking for at Barro Colorado and Pasoh have been discovered. The network of 50-hectare plots has resolves some scientific arguments, Leigh said.

CTFS plots, Leigh said, have stimulated other scientific work in or near them. People working in the same places on different things, he noted, tend to talk about their findings and that in turn quite frequently suggests the next set of questions that scientists should ask.

And even if Hubbell’s theory doesn’t withstand scrutiny, was all of this expensive and painstaking work worthwhile?

“Even a wrong theory gets you to collect data that are of interest to conservation biologists,” Leigh noted about the CTFS studies. “This is a value that is not to be despised.”

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