Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Diverse tropical forests defy metabolic ecology models

25.04.2006


The complex patterns of tropical forest structure demand more complex explanations


Tropical forest tree growth, distribution and mortality may be difficult to model.



As global change accelerates, quantifying the role of forests in the carbon cycle becomes ever more urgent. Modelers seek simple predictors of forest biomass and carbon flux. Over the last decade, the theory of metabolic ecology generated testable explanations, derived from physical and biochemical principles, for a wide range of ecological patterns. However, in two Ecology Letters articles, Helene Muller-Landau and colleagues show that tree growth, mortality and abundance in fourteen tropical forests deviate substantially from metabolic ecology predictions, especially for large trees. Instead, observed variation within and among forests supports alternative models presented by the CTFS team.

Are tropical forest structure and dynamics too complex for universal explanations?


"When you walk through different tropical forests, or graph data from different forests, there are certain features that, at first glance, look similar everywhere ’" the presence of some very large trees, or the general shape of the tree size distribution curve," explains first author, Helene Muller-Landau from the University of Minnesota. "So you start to think that there might be some general explanations. But the closer you look, the more differences you find ’" differences that can’TMt be captured or even decently approximated by any single picture or formula."

Tropical forests give modelers a run for their money. Trees range from spindly understory shrubs to enormous buttress-rooted rainforest giants festooned with vines and peppered with orchids, ferns and bromeliads. Tropical trees depend on animals for pollination and seed dispersal and are constantly assaulted by insects, fungi, maelstrom and machete. Furthermore, soils, rainfall, the frequencies of hurricanes and fires, and assemblages of animals and plants in tropical forests all vary widely from one forest to another.

Prospecting in a gold mine of data

Twenty-five years ago a pair of dueling tropical forest ecologists (Robin Foster, now at the Chicago Field Museum and Steve Hubbell at the University of Georgia and the Smithsonian Tropical Research Institute, STRI) decided that the way to understanding was to measure and map every single tree in an area of lowland tropical forest on Panama’TMs Barro Colorado Island. Tree abundance, distribution, growth and mortality data from repeated five-year censuses of this site proved so useful to ecologists and foresters alike that seventeen other tropical forests around the world adopted the same methodology. Now the consortium of universities and research organizations managing forest plots in South America, Africa, India and Asia: the Center for Tropical Forest Science (CTFS), is headquartered in Panama at STRI. And the race is on to find the basic principles governing tropical forest community composition and structure based on data from three million trees.

Metabolic ecology

At a U.S. National Science Foundation supported workshop, CTFS participants examined data from across the forest plot system and discussed possible multi-site comparisons. "A couple of the key papers on metabolic ecology had just come out and were generating a lot of excitement ’" as well as considerable skepticism. And we thought, hey, we have an unprecedented opportunity to test these predictions, and to see whether these patterns are really similar across all these forests," remembers Muller-Landau. "If the proposed general rules truly applied, they would be tremendously useful - for example, they would help us predict how much above ground carbon is stored in tropical forests. There are some general similarities among sites in the tree size distributions, so it seemed plausible that there might be a general underlying explanation."

"Specifically, metabolic energy proposes a rule that total tree abundances scale as the -2 power of diameter, and we were hopeful that it would apply. But we tested that prediction on data from 14 sites around the world --over 2 million trees--and it just did not hold up anywhere," continues Muller-Landau.

The CTFS team subsequently tested other metabolic ecology-based predictions relating tree size to growth and mortality against data from 10 CTFS forests, and found that those were not supported either.

"The predictions of metabolic ecology were wrong in fundamental ways, and no one had noticed before because few datasets spanned the range from saplings to large trees. Most impressive was the consistency in the big discrepancies between observation and prediction, even in very different forests," articulates coauthor Richard Condit, STRI Staff Scientist, "For instance, diameter distribution always deviated by having far fewer large trees than the -2 slope predicts."

Shedding light on the process

The CTFS team did not stop at merely demonstrating that metabolic ecology failed to explain tropical forest structure ’" they examined what alternative models might do better. Organisms live within the limits of their environment. Maybe by modifying the metabolic ecology model to include light as a limiting resource that varies with tree size, the predictions could be improved. The necessary light data were available from only one site, and, in that case, observed growth and mortality patterns were consistent with predictions. Similarly, tree size distributions corresponded more closely to a model based on demographic equilibrium theory that incorporated differences in growth and mortality among sites.

What next?

The results of these two studies clearly demonstrate that there are both qualitative similarities and significant quantitative differences in forest structure among tropical sites. This complexity defies simple characterization ’" its explanation requires consideration of the diversity of environmental conditions and species traits in tropical forests, and complex feedbacks and interactions among species and resources. Muller-Landau and Condit are currently working on mechanistic models that attempt to better capture these complexities, and thereby attain a better understanding of what factors drive tropical forest structure and dynamics. Achieving such an understanding is particularly critical today, as tropical forests are threatened by global anthropogenic change, with still unknown implications for the integrity of their tremendous carbon stores.

Helene Muller-Landau | EurekAlert!
Further information:
http://www.umn.edu
http://www.stri.org/

More articles from Ecology, The Environment and Conservation:

nachricht Joint research project on wastewater for reuse examines pond system in Namibia
19.12.2016 | Technische Universität Darmstadt

nachricht Scientists produce a new roadmap for guiding development & conservation in the Amazon
09.12.2016 | Wildlife Conservation Society

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Water - as the underlying driver of the Earth’s carbon cycle

17.01.2017 | Earth Sciences

Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

17.01.2017 | Materials Sciences

Smart homes will “LISTEN” to your voice

17.01.2017 | Architecture and Construction

VideoLinks
B2B-VideoLinks
More VideoLinks >>>