Vegetation in an area may determine its usable water supply, ecologists find
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 carbon sequestration, 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.
Mobile ‘biochar’ machine to work the fields
An ancient technique to fertilize soil by creating charcoal from plant waste is being revived to tackle some of today’s environmental problems.
The latest company to pursue manmade charcoal, called biochar, is Biochar Systems, which has developed a biochar-making machine that can be pulled by a pickup truck. Two customers–a North Carolina farm and the U.S. Bureau of Land Management–will be begin testing the units this fall.
The unit, called the Biochar 1000, is designed to convert woody biomass, such as agricultural or forestry waste, into biochar, a black, porous, and fine-grained charcoal that can be used as a fertilizer. It uses pyrolysis–slowly burning biomass in a low-oxygen chamber–to treat 1,000 pounds of biomass per hour, yielding 250 pounds of biochar.
There still isn’t a well established market for selling biochar, but there’s growing interest among researchers in the process as a way to cut greenhouse gas concentrations. The United Nations has proposed classifying biochar as a carbon credit for sequestering carbon from the atmosphere.