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Wednesday, April 21, 2004

Is organic the future of farming? In its pure form, maybe not. But elements of the organic philosophy are starting to be deployed in mainstream agriculture. In this web focus, Nature's reporters analyse this trend, assess the extent of organic farming worldwide, and frame the questions on which its wider adoption will depend. Contents, including interactive graphics, are free until the end of May.

Organic FAQs
In the developed world, sales of organic produce are growing rapidly. But how far can this trend extend? That depends on how strictly you define organic farming… and the answers to three other pivotal questions.
Nature 428, 796 (22 Apr 2004)

Organic world view
Where is organic produce being grown, and where is it being consumed?
Nature 428, 794 (22 Apr 2004)
The limits to tree height
1 Department of Biological Sciences and the Merriam-Powell Center for Environmental Research, Northern Arizona University, Flagstaff, Arizona 86011, USA
2 Department of Biological Sciences, Humboldt State University, Arcata, California 95521, USA
3 Natural Science Division, Pepperdine University, Malibu, California 90263-4321, USA
Correspondence and requests for materials should be addressed to G.W.K. (george.koch@nau.edu).

Trees grow tall where resources are abundant, stresses are minor, and competition for light places a premium on height growth. The height to which trees can grow and the biophysical determinants of maximum height are poorly understood. Some models predict heights of up to 120 m in the absence of mechanical damage, but there are historical accounts of taller trees. Current hypotheses of height limitation focus on increasing water transport constraints in taller trees and the resulting reductions in leaf photosynthesis. We studied redwoods (Sequoia sempervirens), including the tallest known tree on Earth (112.7 m), in wet temperate forests of northern California. Our regression analyses of height gradients in leaf functional characteristics estimate a maximum tree height of 122–130 m barring mechanical damage, similar to the tallest recorded trees of the past. As trees grow taller, increasing leaf water stress due to gravity and path length resistance may ultimately limit leaf expansion and photosynthesis for further height growth, even with ample soil moisture.

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