Exotic timber plantations found to use more than twice the water of native forests

Sep 15, 2009
This Hawaiian forest is made up mostly of native ohia trees, which grow more slowly and use up to 2.5 times less water than exotic timber plantations. Credit: Aurora Kagawa

Ecologists have discovered that timber plantations in Hawaii use more than twice the amount of water to grow as native forests use. Especially for island ecosystems, these findings suggest that land management decisions can place ecosystems - and the people who depend on them - at high risk for water shortages.

"Scientists used to think that forests in same environments use water in the same way," says Lawren Sack of The University of California at Los Angeles, who coauthored the study with graduate student Aurora Kagawa in the September issue of the ESA journal Ecological Applications. "Our work shows that this is not the case. We need to know the water budget of our landscape, from gardens to forests to parks, because water is expensive."

Although forests like these Hawaiian timber plantations can be valuable for their contributions to human society, such as fiber, fuel and , they are dominated by non-native vegetation.

Kagawa, Sack and their colleagues compared the water use of trees in native forests, composed mostly of native ohia trees, with water use in timber plantations containing exotic eucalyptus and tropical ash. The team inserted heated and unheated probes into the trees' trunks and monitored the temperature differences between the two as sap flowed past them. This technique allowed them to determine the rate of sap flow through the tree. A faster flow rate means that the tree is using more water.

"The way plants grow determines how fast they can take up water," says Sack. "Plants open their leaf pores, called stomata, to take in carbon dioxide. But when these pores are open, the plants also lose water. Like a wet towel on a clothesline, the insides of the leaf can dry pretty quickly." Since fast-growing exotic plants typically have more open leaf pores than native, slow-growing trees, Sack says, they lose more water in less time.

Exotic timber plantations, such as the one pictured, are dominated by exotic species and can use up to 2.5 times more water than native forests. Credit: Aurora Kagawa

The researchers found that individual eucalyptus and tropical ash used three and nine times more water, respectively, than individual ohia trees. Since each of these forests is dominated by these three species, the team was able to scale up their results to predict how much water a whole section of forest uses. Even when including other native plants that use water quickly, such as tree ferns, the tropical ash forests still used water at a rate of 1,800 kilograms of water per square meter per day, more than 2.5 times that of the other forests. The researchers found, however, that the non-native eucalyptus plantation used similar amounts of water as native forest. This is because water use depends on the specific tree species, stand organization and age, and location and climate, says Sack.

Hawaii's non-native tree plantations were originally intended for timber production and to conserve the islands' top soil. In the early part of the 20th century, ranches and plantations producing sugar cane and pineapple covered much of Hawaii's agricultural areas. But years of these practices led to increased soil erosion, and fast-growing non-native trees were planted to hold the soil in place and to preserve water by preventing runoff. At the time, however, the importance of biodiversity and the dangers of exotic species weren't as clear as they are today.

Especially with climate change rapidly changing many ecosystems, Sack says, it's vital that plans recognize and integrate the fact that water use by plants can affect the clean water supply.

"When making decisions to restore a native forest or preserve or establish a plantation, we need to do a more detailed valuation that includes the cost of water they're using," he says. "There are a lot of reforestation projects underway to take up carbon dioxide from the atmosphere, where people are prioritizing fast-growing trees. But we shouldn't let alien plants sweep over native forests. Our findings make a clear case that we need to know how much water landscapes are using and conserving."

Source: Ecological Society of America

Explore further: Stanford researchers rethink 'natural' habitat for wildlife

add to favorites email to friend print save as pdf

Related Stories

Faster koa tree growth without adverse ecosystem effects

Mar 27, 2008

U.S. Forest Service scientists with the Institute of Pacific Islands Forestry have completed a study on ways to make high-value koa trees grow faster, while increasing biodiversity, carbon sequestration, scenic ...

Can you rescue a rainforest? The answer may be yes

Mar 27, 2008

Half a century after most of Costa Rica's rainforests were cut down, researchers from the Boyce Thompson Institute took on a project that many thought was impossible - restoring a tropical rainforest ecosystem.

Invading trees put rainforests at risk

Mar 03, 2008

To the list of threats to tropical rainforests you can add a new one — trees. It might seem that for a rainforest the more trees the merrier, but a new study by scientists at the Carnegie Institution warns ...

Recommended for you

Plants with dormant seeds give rise to more species

5 hours ago

Seeds that sprout as soon as they're planted may be good news for a garden. But wild plants need to be more careful. In the wild, a plant whose seeds sprouted at the first warm spell or rainy day would risk disaster. More ...

Scientists tether lionfish to Cayman reefs

15 hours ago

Research done by U.S. scientists in the Cayman Islands suggests that native predators can be trained to gobble up invasive lionfish that colonize regional reefs and voraciously prey on juvenile marine creatures.

User comments : 0

More news stories

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

Plants with dormant seeds give rise to more species

Seeds that sprout as soon as they're planted may be good news for a garden. But wild plants need to be more careful. In the wild, a plant whose seeds sprouted at the first warm spell or rainy day would risk disaster. More ...

Researchers develop new model of cellular movement

(Phys.org) —Cell movement plays an important role in a host of biological functions from embryonic development to repairing wounded tissue. It also enables cancer cells to break free from their sites of ...

Male monkey filmed caring for dying mate (w/ Video)

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

Treating depression in Parkinson's patients

A group of scientists from the University of Kentucky College of Medicine and the Sanders-Brown Center on Aging has found interesting new information in a study on depression and neuropsychological function in Parkinson's ...