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 International network connects experimental research in European waters
21.03.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)

nachricht World Water Day 2017: It doesn’t Always Have to Be Drinking Water – Using Wastewater as a Resource
17.03.2017 | ISOE - Institut für sozial-ökologische Forschung

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: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

When Air is in Short Supply - Shedding light on plant stress reactions when oxygen runs short

23.03.2017 | Life Sciences

Researchers use light to remotely control curvature of plastics

23.03.2017 | Power and Electrical Engineering

Sea ice extent sinks to record lows at both poles

23.03.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>