From the text: "In general, annual growth increases rapidly with size to a distinct maximum when saguaros reach a height of 2-4 m, declines steeply to a second inflection at heights between 6 and 7 m, and then decreases at a nearly constant and more gradual rate as saguaros age. The shape of the growth-height function relects stages in the phenological and morphological development of the saguaro (Steenbergh and Lowe 1983). The rapid increase in annual growth up to 2 m is a function of the increasing photosynthetic surface area and water storage capacity with increasing plant size. The decline in the mean annual growth of saguaros once they reach 2-4 m coincides with diversion of resources to flowering. [my emphasis] When plants reach ~6 m, growth rates become essentially constant with increasing plant size. This second inflection is correlated with the proliferation and growth of branches by most members of the population. Branches increase assimilation of photosynthetically active radiation (Geller and Nobel 1986). However, on Tumamoc Hill, branching does not result in an increased rate of height growth, suggesting that any increase in photosynthetic capacity with branching is largely offset by the energy cost of branch growth and reproduction."