Cohen, Yosef, and John Pastor. "Interactions Among Nitrogen, Carbon, Plant Shape, and Photosynthesis." The American Naturalist 147.5, May 1996: 847-865.
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 other. The authors derive a mathematical model based on measurable components which may explain the variables effects on each other and help explain why evergreens predominate in the northern latitudes.
The authors do a good job reducing the mathematics to understandable terms. They use derivative and integral equations throughout the paper. These are standard type equations which most first year calculus students should be able to follow. The explanation...