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 Air pollution leads to cardiovascular diseases
21.08.2018 | Universitätsmedizin der Johannes Gutenberg-Universität Mainz

nachricht Waste in the water – New purification techniques for healthier aquatic ecosystems
24.07.2018 | Eberhard Karls Universität Tübingen

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: It’s All in the Mix: Jülich Researchers are Developing Fast-Charging Solid-State Batteries

There are currently great hopes for solid-state batteries. They contain no liquid parts that could leak or catch fire. For this reason, they do not require cooling and are considered to be much safer, more reliable, and longer lasting than traditional lithium-ion batteries. Jülich scientists have now introduced a new concept that allows currents up to ten times greater during charging and discharging than previously described in the literature. The improvement was achieved by a “clever” choice of materials with a focus on consistently good compatibility. All components were made from phosphate compounds, which are well matched both chemically and mechanically.

The low current is considered one of the biggest hurdles in the development of solid-state batteries. It is the reason why the batteries take a relatively long...

Im Focus: Color effects from transparent 3D-printed nanostructures

New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference

Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...

Im Focus: Unraveling the nature of 'whistlers' from space in the lab

A new study sheds light on how ultralow frequency radio waves and plasmas interact

Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...

Im Focus: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

LaserForum 2018 deals with 3D production of components

17.08.2018 | Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

 
Latest News

Air pollution leads to cardiovascular diseases

21.08.2018 | Ecology, The Environment and Conservation

Researchers target protein that protects bacteria's DNA 'recipes'

21.08.2018 | Life Sciences

A paper battery powered by bacteria

21.08.2018 | Power and Electrical Engineering

VideoLinks
Science & Research
Overview of more VideoLinks >>>