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The autecology of Quercus petraea Matts (Liebl.) in the north-west Iberian Peninsula was investigated by applying the methodology based on the parametric description and classification of the species habitat. For this, it was necessary to conduct a plot discriminant analysis to identify those parameters that have a greater descriptive weight, using TWINSPAN. The distribution of the species was first determined so that a minimum number of representative samples could be selected. In total, 52 plots were chosen, in each of which 41 biotope parameters were established (six physiographic, 17 climatic and 18 edaphic), along with 19 dendrometric and silvicultural parameters. The parametric characterization allowed the description of both central and marginal physiographic–climatic and edaphic habitats of the sessile oak in the study area and an assessment of the effect of environmental factors on its present silvicultural status. Principal components analysis was used to calculate the existing variability in the stands and to compare with the groups created by TWINSPAN. The results show that, within the studied area, sessile oak forests occur at altitudes of between 540 and 1400 m, a range that corresponds to a difference in mean annual temperature of more than 6°C; however, the main climatic feature that defines these forests is the abundance of precipitation, with a annual mean around 1590 mm and precipitation in the summer months higher than 300 mm. Quercus petraea is less resistant to low temperatures than the pedunculate oak (Quercus robur L.) and generally shows a longer growth period. [ABSTRACT FROM AUTHOR]