Predicting root architecture and the water balance in Eucalyptus stands

Background/Question/Methods

The growth of individual roots in plants is proposed to follow paths of optimal (minimal) resistance, with fractal dimensionality given by the predicted value from percolation theory, and fundamental rate described by transpiration. Further, it has been proposed that it is possible to predict watershed-scale water balance from this information using an optimization of the net primary ecosystem productivity. We have suggested that typical forest root systems that are shallow should follow a spatio-temporal scaling function based on the two-dimensional value of the optimal paths exponent. However, in species that have especially large transpiration demand, or in particularly arid climates with especially arid climates, such root systems may more likely have a three-dimensional architecture.

Results/Conclusions

Investigations of the growth rate and transpiration of Eucalypts in Victoria in Australia deliver data, with which it is possible to show that the best choice for the optimal paths fractal dimensionality in these species is the three-dimensional value. Using the associated three-dimensional value for the root mass fractal dimensionality from percolation theory then gives the upper limit of water usage in both mature forests and in recently cleared patches using published mean values of the potential evapotranspiration in these watersheds. This means that it is possible to predict the bounds on watershed run-off without recourse to adjustable parameters, as well as the actual growth rates of the trees.