Slide 14: What controls the growth rate of trees?
Charlie Shackleton's PhD consisted of measuring tree circumference growth of thousands of stems, in savannas all over South Africa, every year for six years. From this wonderful dataset, some patterns emerge: the two main controllers of tree growth in savannas are the size of the tree (its stem diameter), and how much tree-on-tree competition it experiences. The latter is indexed by the tree basal area, as a fraction of the maximum basal area given that climate. The graph here shows the performance of this model: about 64% of variance is explained.
The interesting thing about this relationship is that a population of small diameter trees is much more productive than one with large diameter trees - this is important, and will be discussed later.