Enquist et al. 1 present data from 37 plant species showing that the use of resources by individual plants scales approximately as the 3/4 power of plant mass, as predicted previously from a model of resource use in fractal-like branching structures2. Thus, Q ∝ M3/4, where Q is the resource use, estimated as xylem transport, and M is the plant mass. In addition, their re-analysis of data from 251 populations1 showed that the ‘thinning law’ between maximum plant population density (Nmax) and plant mass also obeys 3/4-power scaling, with Nmax∝ M−3/4. From these two data sets, they inferred that population resource use per unit area is approximately independent of plant mass, with NmaxQ ∝M0, a relation termedenergy equivalence3.