New Study Casts Doubt on Some Forest Conservation Methods

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WORLDWIDE FOREST/BIODIVERSITY CAMPAIGN NEWS

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Forest Networking a Project of Ecological Enterprises

http://forests.org/ -- Forest Conservation Archives

http://forests.org/web/ -- Discuss Forest Conservation

2/5/99

OVERVIEW & COMMENTARY by EE

A new study calls into question the widely accepted principle that

gaps in forests caused by tree falls are largely responsible for

patterns in tree diversity. Regardless of whether this finding holds

up, the point is made abundantly clear that much remains to be known

about tropical forest ecology. Developments in forest management and

biodiversity conservation are occurring at breakneck speeds with vital

consequences for human well being; and based upon a dangerously

incomplete, and perhaps wrong, knowledge base.

g.b.

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Title: Study Of Tropical Forests Overturns Important Theory In

Ecology -- Finding May Cast Doubt On Some Conservation

Methods

Source: ScienceDaily

Date: February 3, 1999

PRINCETON, N.J. -- A painstaking effort to track every square inch of

plant life in large patches of tropical forests has started to produce

significant discoveries in ecology. Princeton professor of ecology and

evolutionary biology Stephen Hubbell, a founder of the project, is

using the research to answer fundamental questions about what factors

come into play in maintaining the diversity of life on Earth.

Hubbell's latest finding, reported in the current issue of Science,

overturns one of the bedrock beliefs among ecologists about what

allows tropical forests to maintain such a dazzling variety of tree

species. The common thinking was that when a trees dies or is blown

over in a storm the resulting infusion of direct sunlight, called a

light gap, allows new species to flourish and compete to fill the open

slot in the forest. The frequency and size of light gaps was,

therefore, thought to predict type and number of species present in

the forest.

Hubbell found, however, that no such correlation exists. Using vast

amounts of data generated from the tracking project, he showed that

areas with many light gaps are no richer in species than areas with

few pockets of sunlight. The mix of species also was not notably

different. Although some species do depend on light gaps to survive,

they are such a small minority that they don't change the results.

The finding may cast doubt on one common suggestion for how to

reconcile logging and conservation efforts in tropical forests, said

John Terborgh, co-director of Duke University's Center for Tropical

Conservation. There have been many suggestions that logging could be

allowed in forests if it mimicked the natural pattern of light gaps;

the logging, then, would promote the diversity of trees rather than

harm it. That idea is based on a theory that Hubbell has now shown to

be wrong, Terborgh said.

"I think it's a very exciting paper," Terborgh said. "I think this is

doing a great service to ecology."

Hubbell's finding also may indirectly affect other conservation

efforts. One reason that the old light gap theory failed to hold up is

that the distribution of seeds in a forest is far from ideal. Light

gaps create a variation in the local growing environment, which

should, in turn, create a variation in the types of seeds that grow.

As a practical matter, however, the same old varieties tend to grow in

light gap areas because there are not enough light-loving seeds that

can take advantage of the new conditions. That lesson could have

implications for conservation efforts around the world where roads and

development isolate one section of forest from another, exacerbating

the effects of poor seed dispersal and possibly forcing the extinction

of species that would normally be good competitors.

The light gap question is just one of a series of issues being

illuminated by a research effort that Hubbell helped start nearly 20

years ago, an ambitious project to track the diversity of species in

tropical forests. The location that provided the data for his Science

paper is a 120-acre plot within a tropical forest on an island in the

Panama Canal. Starting in 1981, a team of researchers directed by

Hubbell, who was then at the Smithsonian Tropical Research Institute,

and colleague Robin Foster, a curator of the Field Museum in Chicago,

began identifying and tagging every tree and sapling that was at least

chest high and at least one centimeter in diameter. That is a far more

detailed level of sampling than had been done in any other study, most

of which looked at plants that were two or three times bigger and

sampled just a few acres. By the time the researchers finished the

study two years later, they had tagged 300,000 trees. The researchers

have gone back every few years to repeat the process. It takes a team

of 15 people nine months to comb through the plot and update the data.

From its very beginning, the project has yielded dramatic results,

said Elizabeth Losos, the director of the Center for Tropical Forest

Science, an organization within the Smithsonian that was formed to

manage the research (http://www.si.edu/organiza/centers/stri/

stri.htm). For example, the researchers discovered right away that

tropical forests are not the stable, unchanging ecosystems that they

were assumed to be. In just two years, 40 percent of all the tree

species had significantly changed with relative abundance, with some

dropping to extinction in that plot and others becoming more dominant

species.

The project's success led to a series of collaborations that

eventually resulted in the creation of 15 other 120-acre sites in 12

countries, involving scientists from three dozen institutions.

One long-term outgrowth of Hubbell's work is his discovery of what he

calls "the E=mc2 of community ecology," a theory that for the first

time links several other seemingly distinct theories about the

abundance and distribution of species. Hubbell originally published

the theory four years ago, but is now finishing a book, to be

published by Princeton University Press, that presents the idea in an

expanded form. The theory, called the unified theory of biodiversity

and biogeography, allows scientists to calculate a single number,

called the fundamental biodiversity number, that describes a whole

range of characteristics of plant and animal communities. For example,

by figuring the biodiversity number for a particular forest, a

scientist could estimate how many species the forest is likely to

contain and whether some of those species are much more dominant than

others, as well as a number of other factors.

Hubbell's work is inspired by a deeply felt concern for the planet's

future. He worries that scientific knowledge about ecological systems

and biodiversity are not keeping pace with the speed with which humans

are harming the planet. He cites a recent study that showed that

humans consume 40 percent of all the energy that goes into producing

the Earth's biomass, a number that is way out of proportion to humans'

relative abundance among species. At the same time, biologists don't

even have a rough guess for how many species the Earth holds and are

far from knowing how those species depend on and compete with each

other.

"We're still in the Middle Ages in biodiversity research," Hubbell

said. "We're still cutting bodies open to see what organs are inside."

"I've told myself, look, I need to spend the rest of my life fighting

for this," Hubbell said. "It may be a lost cause, but I at least want

to be able to say I tried."

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