On the horizon

News from the natural world.

Planting trees is not always best

Tree plantations have often been touted as a tool for scrubbing carbon dioxide out of the atmosphere - at least for a while - to combat global warming. But a new study suggests that new tree plantations also could degrade soil and deplete groundwater, depending on their location.

Using trees as air cleaners is one approach countries can take to meet CO2 emissions targets under the 1997 Kyoto Protocol. Industrial countries party to the pact must reduce their CO2 emissions by an average of slightly more than 5 percent between 2008 and 2012. Using field measurements and modeling studies, an international research team led by Duke University biologist Robert Jackson found that replacing grassland or farmland with evergreen or eucalyptus forests in relatively dry locations can lead to both more acidic or saltier soils and dried-up stream beds. Any water vapor the trees give off would not be enough to generate rain-bearing clouds capable of offsetting lost groundwater.

But plantations could be an environmental boon to some spots, such as southwestern Australia, where removal of trees led to saltier soils, or the US farm belt, where converting some cropland to forest would reduce pollution from pesticide and fertilizer runoff. The research appears in the current issue of the journal Science.

Uranus's new rings

Astronomers received a new set of rings for Christmas.

Using the Hubble Space Telescope, a team of scientists has discovered previously undetected rings and moons orbiting Uranus. The new discoveries lie outside the planet's better-known set of rings but inside the orbits of its major moons. The observations also show that the planet's innermost moons have changed their orbits in significant ways over the past decade. When added to the 11 other rings that scientists have spotted around Uranus since 1977, the latest discoveries suggest that the planet has a very young set of rings and moons whose orbits are very unstable. Indeed, the team, led by Mark Showalter of the SETI Institute in Mountain View, Calif., calculates that the system has undergone substantial changes at least since the time of the dinosaurs and perhaps since the time of the Roman Empire.

The discoveries suggest that Uranus hosts a ring-moon system "rivaling the other known ring-moon systems in its subtlety and complexity," the team reports. The research was published recently on Science Express, an online edition of the journal Science.

Moss as a climate sensor

A common cushion moss known as Bridel may be about to shed its "common" image. Biologists are finding that the hardy species could become an effective tool to monitor climate change and other environmental shifts.

Researchers at the University of California at Santa Cruz and at Berkeley have conducted genetic studies of Bridel specimens taken from around the state and found that the Bridel population consists of two species with an overlapping geographical range. That range varies from the Mediterranean-like region of Southern California to the southern Cascade Mountains in northern California. Like their Bridel relatives found on every other continent except Antarctica, both species are extremely drought-tolerant and can survive high temperatures and high exposure to ultraviolet light. And the moss can live on the same patch of rock for decades.

The team notes that other mosses have been used as monitoring tools to track trends in heavy-metal pollution. But such mosses are unique to a specific region, such as northern Europe or the northeastern US.

With further research, Bridel could yield information on global pollution patterns. If researchers find that different species of Bridel in different parts of the world respond in the same way to changing environmental conditions, the moss becomes a useful global sensor. If the species respond differently, they might become an even richer source of information on regional changes, the team suggests. Their work appears in the current issue of the Proceedings of the National Academy of Sciences.

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