Edited by Len Phillips

The Boost of Air Pollution and Cool Temperatures in U.S. Southeast
David Biello
Why is the southeastern U.S. getting cooler while the rest of the globe is warming? On sweltering summer days, trees and other plants emit volatile organic compounds, such as isoprene, which combine with man-made soot and other aerosols in the atmosphere to produce a cooling haze. Researchers used satellite and ground sensor data to track air pollution. Over time, the cooling induced by the atmospheric haze has outpaced the warming due to rising carbon dioxide levels in the atmosphere. Nobody realized until now that enough of these aerosols could influence cooling over an entire region. The results go a long way to explain why high temperatures in the southeastern U.S. are dipping even as global CO₂ levels rise. It isn't that there are more trees; it's that scientists now have better ways of measuring pollutants and their effect on local temperatures.

Scientific American, May 18, 2009.

Can Trees Save Us from Climate Change?
David Biello
Trees provide wood, improve health, clean up the air, and get us out of climate change. That is because carbon dioxide, the main greenhouse gas driving climate change, is plant food. The leaves of trees suck in sunlight and then chemically convert CO₂ to carbohydrates. This process called photosynthesis sustains almost all life on Earth. Just planting more trees is not the answer. Trees have a habit of dying and decomposing, which puts a lot of that CO₂ back into the atmosphere. Since our goal is to pull CO₂ from the atmosphere permanently, planting trees is not the best solution.

Humans cut down a lot of trees, making deforestation the second biggest source of the 30 billion metric tons of CO₂ put into the atmosphere yearly by people and industry. Planting trees will be a help to solve global warming, but cutting back on removing trees would be a much bigger help.

Scientific American, April 24, 2009.

Naked Trees Dominated Early Forests
By Nikhil Swami Nathan
The crown of a prehistoric tree found in a sandstone quarry in Gilboa, N.Y., has shed light on the look of the world's earliest forests believed to have thrived during the Devonian period between 360 million and 397 million years ago. The 2004 discovery of this 380-million year-old, six-foot uppermost portion of an ancient tree trunk allowed paleobotanists to create a composite picture of the entire plant when they put it together with fragments of a trunk found at the same site a year later and with tree stumps recovered more than 130 years ago in another rock quarry 10 miles away.

The stumps are part of the class Cladoxylopsida believed to be related to modern-day ferns. From the fossil reconstruction, the team of scientists determined that this tree grew about 30 feet (9 m) tall. The base would have been on the order of 30 inches (75 cm) in diameter with a large, single trunk and longitudinal ridges, probably part of the tree's vascular system, topped by a leafless crown of a material resembling fronds on ferns and palms. These fronds apparently had a structure somewhat similar to fingers protruding from the palm of a hand, with multiple branches that split into thinner branchlets. These wispy appendages would have done the work of photosynthesis for the tree and also have borne the spores with which the plant reproduced. The researchers were able to classify the tree crown into the genus Wattieza. The very small leaf like appendages have the distinctive characteristic of recurved tips, meaning they flop back toward the trunk of the tree.

By piecing together the fragments, the team was able to get an idea of what a forest ecosystem might have looked like 360 million years ago. The Wattieza trees would have been fairly closely spaced or about 3 to 15 feet (1 to 5 m) apart, and they would have dropped a lot of litter from their branches onto the forest floor. Among these trees were likely smaller plants and shrubs, and by the late Devonian period, the precursors of modern-day conifers called Archaeopteris were present. Arthropods, such as millipedes, centipedes and now-extinct spider like organisms, may have lived below these trees, which likely let more sunlight through than modern-day counterparts. This is because their branch structures did not fan out as far and were ascendant, forming a goblet-like shape.

Recent research noted that the Wattieza tree seemed to be constructed to optimize mechanical stability and reproduction. This is in contrast to modern-day trees which require more complex vascular systems to grow to larger sizes. The Wattieza tree represents an economical alternative where, beyond the necessary investment in spores to ensure reproduction, the products of photosynthesis were mainly devoted to vertical growth of the trunk. The rise of forests with trees like the Wattieza caused the removal of carbon dioxide from the air and temperatures to drop, creating climates like those experienced today. The drop in carbon dioxide levels likely led to the evolution of flat leaves on trees to attract and retain more of the gas, which plants need for photosynthesis. Additional research will focus on the internal structure of the plants to work out how they grew as well as how they functioned physiologically, particularly the relationship with atmospheric carbon dioxide.

Scientific American, April 18, 2007

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