Why Tree Shape Changes

This article attempts to formulate a model to explain why tree shape changes with respect to the latitude and soils nutrient levels. The shapes of trees found in the tropics vary greatly from the trees found in the northern latitudes. In the tropics, trees have "pizza" shaped canopies. In the northern latitudes, evergreens predominate with their cone shape. Yosef Cohen and John Pastor, the authors of the article, theorize that plant shape and the type of tree, which grows in an area, are dependant on several factors and the interaction between these factors: light intensity, canopy density, nitrogen and the rate of uptake, rate of growth, size of the plant, photosynthesis conversion efficiency, time and the slope of the canopy of the tree (848). The authors think that photosynthesis and the nitrogen content, of a tree, should be considered constraints on the plant, not a cause and effect (847).

The authors state that the problem that are addressing, in the paper, is the lack of a comprehensive theory that accounts for the apparent "correlation between canopy shape, growth habit, photosynthesis, latitude, and nutrient relationships" (848). The patterns, between the variables, appear obvious, but there does not exist a model in biogeography which can be used to test hypotheses about their relationships to each ot

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er follow up studies to their work. They explain that the problem, with experimental testing, of their model will be that it is hard to control lighting. Control of nitrogen levels can be accomplished with the use or restriction of nitrogen based fertilizer. To test the model, the experiments must be long term, since shifts, in the tree species in an area, should only be noted after trees are mature (862). The authors suggest that results of "natural" experiments should be used (862). The authors do not give any ideas about where or how such sites of "natural experiment might be found. The authors do suggest that light flux can be moderated by the use of shade clothes, but they do not attempt to give any information on how enough physical area could be covered, in shade cloth, to make a worthwhile experiment. Two areas are considered for experimentation: the tundra because it contains a small number of plants with different growth habits, and the boreal forests because whole stand manipulation might be possible using modern technology to manipulate and enrich CO2 levels (863). Getting grants large enough, and over a long term, to fund research of this type will be difficult. Photosynthesis is the use of photons, of ra
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Some common words found in the essay are:
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Approximate Word count = 1540
Approximate Pages = 6 (250 words per page)

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