Tree size frequency distributions, plant density, age and community disturbance

Karl J. Niklas*, Jeremy J. Midgley and Richard H. Rand Department of Plant Biology, Cornell University, Ithaca, NY USA Department of Botany, University of Cape Town, Cape Town, South Africa Department of Theoretical and Applied Mechanics, Cornell University, Ithaca NY, USA *Correspondence: E-mail: [email protected] Abstract We show that explicit mathematical and biological relationships exist among the scaling exponents and the allometric constants (a and b, respectively) of log–log linear treecommunity size frequency distributions, plant density NT, and minimum, maximum and average stem diameters (Dmin, Dmax, and D, respectively). As individuals grow in size and Dmax increases, NT is predicted to decrease as reflected by a decrease in the numerical value of a and an increase in the value of b. Our derivations further show that NT decreases as D increases even if Dmin or Dmax remain unchanged. Because Dmax and the age of the largest individuals in a community are correlated, albeit weakly, we argue that the interdependent relationships among the numerical values of a, b, NT, and D shed light on the extent to which communities have experienced recent global disturbance. These predicted relationships receive strong statistical support using two large datasets spanning a broad spectrum of tree-dominated communities.