Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Leaf fall in ancient polar forests still a mystery

03.07.2003


Explorers in the 1800s discovered through fossils that deciduous forests once covered the poles, but researchers still do not know why leaf-dropping trees were preferred over evergreens.



"The dominant idea since the 1940s was that because of the polar light regime of continuous darkness and warmth, leafless branches had an advantage over evergreen canopies in the polar forests," says Dana Royer, research associate in geosciences, Penn State.

This carbon loss hypothesis states that the amount of carbon lost when a canopy of leaves is shed annually is less than the total carbon lost by canopy respiration during the warm, dark winter months and the small amount of leaf loss in evergreens. This would give deciduous trees an advantage during long, very dark winters.


During much of the past 250 million years, the Earth’s poles were devoid of ice, and nearly 40 percent of the area was covered by forests consisting mostly of deciduous trees.

"Today, we do not have these types of forests in the polar latitudes so we have no analog," says Royer. "In most places, the trees we see at the tree line today are evergreens, not deciduous trees."

Working with Dr. David J Beerling, professor and Dr. Colin P. Osborne in the department of animal sciences, University of Sheffield, Sheffield, UK, the Penn State researcher tested trees considered living fossils to see if the carbon loss hypothesis was correct. They looked at gingko, dawn redwood and bald cypress, all deciduous trees that are considered living fossils because they have existed much as they are since there were polar forests. Also tested were two living fossil evergreens, sequoia and southern beech.

In Sheffield, the trees grew under controlled temperatures, carbon dioxide and light. The researchers monitored the amount of leaf litter and the amounts of carbon lost to respiration for both groups of trees.

The researchers report in this week’s issue of Nature that "the quantity of carbon lost annually by shedding a deciduous canopy is significantly greater than that lost by evergreen trees through winter-time respiration and leaf litter production. We therefore reject the carbon-loss hypothesis as an explanation for the deciduous nature of polar forests."

The trees studied where young, starting as year-old saplings and monitored for three years. The researchers used mathematical models to extrapolate to full grown mature forests, but found that even then, counter to expectations, the evergreens had an advantage. The modeling suggests that "the cost of producing a deciduous canopy of leaves remains more than twice that incurred by evergreen trees through canopy respiration and turnover."

The researchers looked at forests that would be at 69 degrees latitude, the mildest regime that is still polar because they initially feared the trees would not survive long periods of complete darkness. They are now looking to simulate even higher latitudes. Two carbon dioxide regimes were used, because it is generally accepted that atmospheric carbon dioxide was higher when these polar forests existed. The temperatures were kept warm, never dipping below freezing.

While the researchers found that the carbon loss hypothesis was not valid, they did not uncover the reasons why deciduous, and not evergreen trees, populated the polar forests.

"What we did find is that while everyone thought that the biggest problems would be during the polar winter -- when there is no sunlight -- there appears to be a problem with the polar summer, when there is uninterrupted sunlight," says Royer. "Both types of plants seem to undergo a drop in photosynthesis after long days of unremittant sun."

Andrea Elyse Messer | EurekAlert!
Further information:
http://www.psu.edu/

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

Touch Displays WAY-AX and WAY-DX by WayCon

27.06.2017 | Power and Electrical Engineering

Drones that drive

27.06.2017 | Information Technology

Ultra-compact phase modulators based on graphene plasmons

27.06.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>