Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Forest tree species diversity depends on individual variation

26.02.2010
Thinking flawed that all species react the same to the environment

It's a paradox that's puzzled scientists for a half-century.

Models clearly show that the coexistence of competing species depends on those species responding differently to the availability of resources. Then why do studies comparing competing tree species draw a blank?

Competitors like black gums and red maples have coexisted for millennia in the shaded understories of eastern U.S. forests, yet species-level data offer scant proof that they respond differently to environmental fluctuations that limit access to light, soil moisture and other essential resources.

These are the very differences required for their long-term coexistence. Are the models and theory flawed? Or is it the data?

A paper in this week's issue of the journal Science offers new insights that may resolve the puzzle.

"Species differences do exist, consistent with theory, but species-level data don't show them," says forest ecologist James Clark of Duke University, the paper's author. In order to see them, he says, you have to go to the individual level.

"Scientists working to address pressing ecological issues, such as the spread of invasive species, will benefit from this finding," says Todd Crowl, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the research.

Species-level studies--the preferred approach in nearly all past research on forest tree diversity--rely on average responses from sample populations to infer information such as average growth, reproduction and survival rates for entire species over time.

They're useful for many purposes, Clark says, but because they assess species' responses in only the handful of environmental dimensions that can be measured, they miss most of the subtle ways in which species differ.

"The environment varies in thousands of ways," he says. "Species can differ in how they respond in all these dimensions, and we can only measure a few of them."

Failure to find tradeoffs in how species respond in the few measurable dimensions, such as the ability to survive in a shaded understory versus growing fast in full sunlight, has promoted a false view, according to Clark.

"Looking at only a handful of averaged responses in a few dimensions may lead to the conclusion that all species react more or less the same," Clark says.

He analyzed more than 226,000 "tree years" of data from more than 22,000 individual trees of 33 species. The trees are in 11 forests in three regions of the U.S. Southeast, including NSF's Coweeta Long-Term Ecological Research (LTER) site.

Coweeta, in the eastern deciduous forests of the southern Appalachian Mountains, is one of 26 such NSF LTER sites.

In his study, Clark estimated annual rates of growth, fecundity and survival risk for every tree in the 11 stands from observations of tree diameter, canopy spread and height, reproductive status, survival, and seed dispersal.

He quantified variations between individuals within populations over time spans ranging from six to 18 years.

His painstaking analysis revealed none of the tradeoffs postulated for trees in species-level averages.

"Individuals are responding in many dimensions in different ways, but with more similarity to other individuals of the same species than to individuals of different species," Clark says.

That's important, he explains, "because as the individuals in a population react to the environment, the similarity they share with others of their own species tends to concentrate competitive pressure within species. The tendency to compete within species allows multiple species to share the landscape."

These findings, he notes, are consistent with the ecological theory that coexistence of competitors requires stronger competition within than between species.

The change in perspective yields new insights into a variety of pressing ecological issues.

"We've always wondered, for instance, how introduced species could invade existing communities where competition is already intense," says Clark. "The assumption was: since existing species are competing for limited resources, it must be especially difficult for invaders to come in, establish and compete successfully.

"But these results suggest that competitive exclusion doesn't work as well as we thought. Knowing that diversity is likely controlled by variations in many dimensions makes it easier to understand why invasions are so common--and suggests new ways of thinking about why they are so successful."

Cheryl Dybas | EurekAlert!
Further information:
http://www.nsf.gov

More articles from Ecology, The Environment and Conservation:

nachricht Safeguarding sustainability through forest certification mapping
27.06.2017 | International Institute for Applied Systems Analysis (IIASA)

nachricht Dune ecosystem modelling
26.06.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

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: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Predicting eruptions using satellites and math

28.06.2017 | Earth Sciences

Extremely fine measurements of motion in orbiting supermassive black holes

28.06.2017 | Physics and Astronomy

Touch Displays WAY-AX and WAY-DX by WayCon

27.06.2017 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>