JANUARY 18


Seeing the forest for its trees

THE HINDU [JAN. 18]

ONE OF the most contentious debates during the recent climate talks centered on the possible use of forests as credit towards reducing atmospheric carbon dioxide.

Although it has long been assumed that these areas will act as sinks for excess carbon, the effects of species composition on the process of carbon sequestration is still largely unknown.

A team of researchers working on eucalyptus plantations in Hawaii has discovered an important aspect of how carbon sequestration processes work in tropical tree plantations.

The researchers have published their findings in the journal Ecology, discovered that carbon sequestration was significantly boosted when the composition of tree stands included nitrogen fixing trees.

Jason Kaye and his colleagues from Colorado State University researched carbon storage on a former sugar cane farm which had been turned into a plantation for Eucalyptus trees (Eucalyptus saligna) in Hawaii.

The team discovered that the acres which were interplanted with albizia trees (Albizia falcataria) were able to sequester more carbon than areas where eucalyptus trees were planted alone. The researchers believe that this is due to the nitrogen-fixing qualities of the albizia trees. Albizias, which are sometimes also referred to as mimosa trees, are not a cash crop like eucalyptus.

Although many tree plantations employ monoculture planting schemes, planting one tree species over hundreds of acres, the atbizia trees’ effect on soil quality has prompted some farmers to test the potential benefits of interplanting the two species.

This kind of practice is increasingly common in tropical areas, where the nutrient level of soil is often limited.

Kaye and his colleagues studied carbon storage in forest stands planted 17 years ago with differing species composition. Some stands were planted as pure eucalyptus, some as pure albizia, and some with the two trees planted together.

The researchers found that in stands where the two species were interplanted, the forest contained twice as much carbon in trees as monocrop areas. In addition, areas of pure albizia sequestered about 20 percent more carbon in soil than did the pure eucalyptus stands.

The researchers suggest that nitrogen which is added to the soil by the albizias may be inhibiting the decomposition of old, sugarcane derived, soil carbon relative to eucalyptus. Many previous studies have demonstrated that nitrogen additions tend to inhibit humus decomposition in laboratory experiments.

This study, however, is the first to examine the possibility that nitrogen additions may decrease carbon turnover in the field.

The ramifications of the findings could have a large impact on the way in which the carbon sequestering potential of tropical tree plantations is measured. The global coverage of tropical tree plantations has increased dramatically in the past two decades. In 1980 it was estimated that some 21 million hectares of tropical land were being used for tree plantations globally; by 1999 estimates stood at 60 million.

In addition, nitrogen deposition has become an increasing concern worldwide, and so any information indicating that nitrogen deposition may aid in carbon sequestration may prove to be especially relevant to policymakers such as those who were in attendance at the recent Hague meetings.

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Crater linked to mass extinction of dinosaurs

THE HINDU [JAN. 18]

NEW GEOPHYSICAL clues to a cataclysmic event that may have killed off the dinosaurs has been found. The Chicxulub structure in Mexico was formed 65 million years ago when a large celestial body-a comet or an asteroid-slammed into the Yucatan Peninsula with a force that makes a nuclear blast seem like a firecracker. This is supposed to have caused the extinction of the dinosaurs according to by Gail Christeson of University of Texas at Austin’s Institute for Geophysics (UTIG). The results are to be presented at the fall meeting of the American Geophysical Union in San Francisco.

The impact produced fires, acid rain and tsunami-like destructive waves. The collision gouged a crater nearly eight miles deep and sent 12,000 cubic miles of rock, dirt and debris spinning into the earth’s atmosphere. The material blocked the sun, causing extreme changes in the Earth’s climate, which many scientists believe resulted in mass extinctions.

The collision marked the abrupt end of the Cretaceous period in geologic time and the start of the Tertiary period. And many scientists currently believe that the event wiped out 80 percent of all living species in the ocean. It also may have destroyed many terrestrial species, including the dinosaurs.

The aim of the researchers was to determine the Chicxulub crater’s actual size and to characterize its internal structure. Such details should make it easier for scientists to understand how the crash actually could have caused mass extinctions. It should also allow them to assess the present day risk posed by the thousands of comets and asteroids that cross earth’s orbit.

The team collected seismic reflection, refraction, gravity and magnetic data over the crater. This research has provided the first direct evidence of a crater with the multi-ring basin shape that is typical of the largest impact craters on the moon and Venus. The impact was so enormous it changed the shape of the earth’s crustù22 miles below the surface of the planet. The Chicxulub crater is the first location where deformation at the base of the crust has been found in a terrestrial impact crater.

The team concluded that the Chicxulub crater is about 125 miles in diameter, and that 12,000 cubic miles of debris was blasted out of the earth by the impact. The impact carved out a cavity about 7.5 miles below sea level. Mount Everest, in comparison, is 5.5 miles high. Prior to this research, the size and morphology of the Chicxulub crater had been in dispute, with estimates of its diameter ranging between 180 and 300 kilometers.

Such a large discrepancy in size translates to a factor of ten differences in the energy of the impact with quite different consequences for the Earth’s environment. The energy released by the impact that blew out the Chicxulub crater was equivalent to about 100 million megatons, many orders of magnitude greater than the nuclear explosion at Hiroshima, a 15-kiloton blast.

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