Modelling below- and above-ground biomass for non-woody and woody plants

Background and Aims Intraspecific relationships between below- and above-ground biomass (M-B and M-A. respectively) have been studied extensively to evaluate environmental effect; on growth and development at the level of the individual plant. However. no current theoretical model for this relationship exists for broad interspecific trends. The aims of this paper are to provide a model and to test it: predictions using a recently assembled, large database (1406 data entries for 257 species). Methods An allometric model was derived to predict the relationship between M-B and M-A for non-woody and woody plants based on previously developed scaling relationships for leaf, stem and root standing biomass and annual growth rates. The predictions of this model were tested by comparing the numerical values of predicted scaling exponents (the slopes of log-log regression curves) with those observed for the database. Key Results and Conclusions For non-woody plants and the juveniles of woody specie;, the model predicts an isometric scaling relationship (i.e. MB proportional to MA). For woody plant;. a complex scaling function is predicted. But. for a particular set of biologically reasonable conditions, the model predicts :M-B proportional to M-A across woody plants. These predictions accord reasonably well with observed statistical trends when non-woody and woody plants are studied separately (n = 1061 and 315 data entries, respectively). Although the reliability of regression formulas to estimate M-B based on M-A measurements increased with increasing plant size, estimates of M-B can be as much as two orders of magnitude off, even when using regression formulas with r(2) much greater than 0.90 and F much greater than 53 000. (C) 2004 Annals of Botany Company.