Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New analysis links tree height to climate

15.08.2014

What limits the height of trees? Is it the fraction of their photosynthetic energy they devote to productive new leaves? Or is it their ability to hoist water hundreds of feet into the air, supplying the green, solar-powered sugar factories in those leaves?

Both factors — resource allocation and hydraulic limitation — might play a role, and a scientific debate has arisen as to which factor (or what combination) actually sets maximum tree height, and how their relative importance varies in different parts of the world.

In research to be published in the journal Ecology — and currently posted online as a preprint — Thomas Givnish, a professor of botany at the University of Wisconsin-Madison, attempts to resolve this debate by studying how tree height, resource allocation and physiology vary with climate in Victoria state, located in southeastern Australia. There, Eucalyptus species exhibit almost the entire global range in height among flowering trees, from 4 feet to more than 300 feet.

"Since Galileo's time," Givnish says, "people have wondered what determines maximum tree height: 'Where are the tallest trees, and why are they so tall?' Our study talks about the kind of constraints that could limit maximum tree height, and how those constraints and maximum height vary with climate."

One of the species under study, Eucalyptus regnans — called mountain ash in Australia, but distinct from the smaller and unrelated mountain ash found in the U.S. — is the tallest flowering tree in the world. In Tasmania, an especially rainy part of southern Australia, the tallest living E. regnans is 330 feet tall. (The tallest tree in the world is a coastal redwood in northern California that soars 380 feet above the ground.)

Southern Victoria, Tasmania and northern California all share high rainfall, high humidity and low evaporation rates, underlining the importance of moisture supply to ultra-tall trees. But the new study by Givnish, Graham Farquhar of the Australian National University and others shows that rainfall alone cannot explain maximum tree height.

A second factor, evaporative demand, helps determine how far a given amount of rainfall will go toward meeting a tree's demands. Warm, dry and sunny conditions cause faster evaporation from leaves, and Givnish and his colleagues found a tight relationship between maximum tree height in old stands in Australia and the ratio of annual rainfall to evaporation. As that ratio increased, so did maximum tree height.

Other factors — like soil fertility, the frequency of wildfires and length of the growing season — also affect tree height. Tall, fast-growing trees access more sunlight and can capture more energy through photosynthesis. They are more obvious to pollinators, and have potential to outcompete other species.

"Infrastructure" — things like wood and roots that are essential to growth but do not contribute to the production of energy through photosynthesis — affect resource allocation, and can explain the importance of the ratio of moisture supply to evaporative demand.

"In moist areas, trees can allocate less to building roots," Givnish says. "Other things being equal, having lower overhead should allow them to achieve greater height.

"And plants in moist areas can achieve higher rates of photosynthesis, because they can open the stomata on their leaves that exchange gases with the atmosphere. When these trees intake more carbon dioxide, they can achieve greater height before their overhead exceeds their photosynthetic income."

The constraints on tree height imposed by resource allocation and hydraulics should both increase in drier areas. But Givnish and his team wanted to know the importance of each constraint.

The scientists examined the issue by measuring the isotopic composition of carbon in the wood along the intense rainfall gradient in their study zone. If hydraulic limitation alone were to set maximum tree height, the carbon isotope composition should not vary because all trees should grow up to the point at which hydraulics retards photosynthesis. The isotopic composition should also remain stable if resource allocation alone sets maximum height, because resource allocation does not directly affect the stomata.

But if both factors limit tree height, the heavier carbon isotopes should accumulate in moister areas where faster photosynthesis (enhanced by wide-open stomata) can balance the costs of building more wood in taller trees. Givnish, Farquhar and their colleagues found exactly that, implying that hydraulic limitation more strongly constrains maximum tree height under drier conditions, while resource allocation more strongly constrains height under moist conditions.

Most studies of tree height have focused on finding the tallest trees and explaining why they live where they do, Givnish says. "This study was the first to ask, 'How does the maximum tree height vary with the environment, and why?'"

###

CONTACT: Thomas Givnish, givnish@wisc.edu, 608-262-5718 (prefers email for first contact)

David Tenenbaum, 608-265-8549, djtenenb@wisc.edu

Thomas Givnish | Eurek Alert!

Further reports about: Australia conditions evaporation factor found photosynthesis rainfall ratio species stomata

More articles from Ecology, The Environment and Conservation:

nachricht Inbreeding not to blame for Colorado's bighorn sheep population decline
27.07.2015 | University of Colorado at Boulder

nachricht One of World’s Rarest Turtles Heading Back to the Wild
16.07.2015 | 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: Superfast fluorescence sets new speed record

Plasmonic device has speed and efficiency to serve optical computers

Researchers have developed an ultrafast light-emitting device that can flip on and off 90 billion times a second and could form the basis of optical computing.

Im Focus: Unlocking the rice immune system

Joint BioEnergy Institute study identifies bacterial protein that is key to protecting rice against bacterial blight

A bacterial signal that when recognized by rice plants enables the plants to resist a devastating blight disease has been identified by a multi-national team...

Im Focus: Smarter window materials can control light and energy

Researchers in the Cockrell School of Engineering at The University of Texas at Austin are one step closer to delivering smart windows with a new level of energy efficiency, engineering materials that allow windows to reveal light without transferring heat and, conversely, to block light while allowing heat transmission, as described in two new research papers.

By allowing indoor occupants to more precisely control the energy and sunlight passing through a window, the new materials could significantly reduce costs for...

Im Focus: Simulations lead to design of near-frictionless material

Argonne scientists used Mira to identify and improve a new mechanism for eliminating friction, which fed into the development of a hybrid material that exhibited superlubricity at the macroscale for the first time. Argonne Leadership Computing Facility (ALCF) researchers helped enable the groundbreaking simulations by overcoming a performance bottleneck that doubled the speed of the team's code.

While reviewing the simulation results of a promising new lubricant material, Argonne researcher Sanket Deshmukh stumbled upon a phenomenon that had never been...

Im Focus: NASA satellite camera provides 'EPIC' view of Earth

A NASA camera on the Deep Space Climate Observatory (DSCOVR) satellite has returned its first view of the entire sunlit side of Earth from one million miles away.

The color images of Earth from NASA's Earth Polychromatic Imaging Camera (EPIC) are generated by combining three separate images to create a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

3rd Euro Bio-inspired - International Conference and Exhibition on Bio-inspired Materials

23.07.2015 | Event News

Clash of Realities – International Conference on the Art, Technology and Theory of Digital Games

10.07.2015 | Event News

World Conference on Regenerative Medicine in Leipzig: Last chance to submit abstracts until 2 July

25.06.2015 | Event News

 
Latest News

Neural efficiency hypothesis confirmed

28.07.2015 | Life Sciences

Scientists study predator-prey behavior between sharks and turtles

28.07.2015 | Life Sciences

Tropical deforestation releases large amounts of soil carbon

28.07.2015 | Agricultural and Forestry Science

VideoLinks
B2B-VideoLinks
More VideoLinks >>>