FLUID MIGRATION IN TWO SPECIES OF BEECH (FAGUS SILVATICA AND FAGUS ORIENTALIS): A PERCOLATION MODEL ABLE TO ACCOUNT FOR MACROSCOPIC MEASUREMENTS AND ANATOMICAL OBSERVATIONS

Abstract

The aim of this study is to visualise, measure and understand the pathway of liquid and gas at both macroscopic and microscopic levels on specimens of beech ( Fagus silvatica and Fagus orientalis ). The permeability to air and to water has been measured using devices developed in our laboratory. The extension of the area coloured by dyed water is available as well. At the microscopic level, the permeability has been calculated using Poiseuille's equation from the vessel diameters determined on cross sections by image processing. Using dyed water, the proportion of active vessels is also reported at different distances from the injection surface. Our data confirm that the permeability decreases significantly when the sample distance increases. Moreover, the value extrapolated for a zero-length sample is similar to the value predicted from the vessel diameters. This observation stands for both for sapwood and heartwood, in spite of the great permeability difference noticed between these zones. At the microscopic level, the percentage of active vessels decreases with the increase of sample total length and the increase of the distance from the injection point. Several simulations performed using a bond percolation model confirmed our experimental results obtained at the macroscopic and microscopic levels Key words : Air; Beech; Length effect; Liquid; Percolation model; Permeability; anatomy.