An analytical treatment of root-to-shoot ratio and plant competition for soil nutrient and light.

By restricting biomass allocation to two compartments only-roots and leaves-we are able to treat plant resource competition analytically. We derive A*i, the optimum allocation strategy for invasion into a bare habitat, and A*f, the allocation strategy of the dominant species in an equilibrium habitat. Furthermore, we prove that in a given habitat succession proceeds from species A*i to species A*f, as long as enough intermediate species are present. Analysis of the relationship between A*i and A*f and the soil nutrient supply and disturbance rates of a habitat predicts that a dichotomy exists in succession. Low soil nutrient supply and disturbance rates favor successions from rooty to leafy species, and high soil nutrient supply and disturbance rates favor the converse. Experimental research is needed to determine whether this pattern exists in nature. Light "consumption" by plants is fundamentally different from soil nutrient consumption in our model. This difference in light and nutrient consumption makes all possible two-species equilibria unstable and leads to founder control. In our model founder control can result in arrested succession and contributes to community diversity.