June 24, 2009

Researchers Study Global Patterns Of Plant Growth

A team of scientists that reviewed the size and locations of more than 7000 species of plants have determined a global pattern of plant height, BBC News reported.

They've found that tropical plants like to grow tall, while temperate zone plants are much smaller in comparison. And plant species growing at the equator are around 30 times taller on average than those at higher latitudes.

Rainfall seems to have a bigger influence on plant height than temperature or soil fertility and the researchers who conducted the analysis said finding such a clear global trend in plant height was surprising.

Angela Moles of the University of New South Wales in Sydney, Australia, who led the review, said it might seem obvious that plants are taller in the tropics since tropical rainforests are clearly taller than those in the Arctic tundra.

"However, there are plenty of tropical ecosystems that are dominated by short plants, such as savannas, and plenty of high-latitude ecosystems that are dominated by very tall plants, such as boreal forests," she said.

Interestingly, Moles noted that the tallest plants in the world do not grow in the tropics.

"The tallest plant species on earth is the coast redwood, from California, which grows over 328 feet tall and the tallest flowering plant is mountain ash, which grows in southern Australia," said Moles.

No-one had quantified the differences in plant height around the world until now, she said, noting the lack of information was "kind of surprising," given that plant height is such an important trait.

She also pointed out that the difference in the heights of plants in each ecosystem affects the variety and type of animal living there.

Therefore, Moles and an Australian and U.S. research team collated data on 7084 plant species from studies already published in databases and scientific journals. The team collated over 32,000 records of plant height around the world.

According to their results, they found that plant species at the equator are, on average, 29 times taller than those growing between a latitude of 60 degrees and 70 degrees North, and 31 times taller than those between a latitude of 45 and 60 degrees North.

The team was surprised to find that there is not a smooth decrease in plant height moving further from the tropics, but Moles said there is a zone at the edge of the tropics where plant height suddenly drops.

"This two-fold decrease in height suggests plants switch growing strategies in temperate zones. We're not sure why. But it may be to do with the deserts around this latitude," Moles said.

They also found that the best predictor of plant height was not net primary productivity"”a measure of how much plants grow in a given location, which is affected by temperature, rainfall and soil quality.

Low temperatures that can limit the growth of large trees by freezing the water inside their trunks were also determined to have lesser influence on growth than experts previously thought.

In fact, the amount of rain during the wettest month of the year was determined to be the single best predictor of plant height.

The team also noted an interesting revelation about small plants as well.

Moles said they originally thought that very cold or very dry ecosystems would lack tall plants, but there would be short plants just about everywhere.

But the team actually noted a remarkable scarcity of very short plants in very warm, wet, productive environments like rainforests.

"We hadn't predicted this, but in hindsight, it seems likely that in these highly productive ecosystems it is just so dark at ground level that there aren't many species that can actually make a living on the forest floor," she said.


On the Net: