In the present study, we test the response to soil compaction of Fraxinus angustifolia Vahl. seedlings in two soil types under greenhouse conditions. We used F. angustifolia as a model plant, as it is a woody species with a fast growth (Ant๚nez et al., 2001). We studied four categories of variables: root morphology, root anatomy, plant physiology and plant growth and architecture. The first objective of this study was to find out which of these groups of variables are affected by soil compaction and/or soil type and to what degree by each one. The second objective was to build a causal model which aims to explain how soil compaction affects root traits and how
these changes explain whole-plant level functioning.