In historical ecology, particularly when dealing with forests, it is often requested to take into account all former human activities to help understand the current state of forest ecosystems. In regressive historical studies, we often find mixed together forest pasturing, pannage, types of silviculture and levels of wood harvesting, litter or other resources collection, charcoal production, pruning of trees for cattle feeding, cultivation of soils for short or long term... One of the issues of historical ecology today is to classify and, above all, to prioritize these human actions in terms of nature, intensity and above all, duration of their impacts. The absence of such a hierarchy contributes to the vagueness existing around the concepts related to ancient forests. Are they forests that have always been little or not at all managed? Or only areas that have never been deforested for agriculture, even if they have been intensely managed for wood production ... the definitions are multiple and sometimes confusing. We show here why the concept of ancient forest in the strictest sense used in the present current scientific literature, that of forests which have not been cultivated, has an important and deserved success in the plains of Western Europe, and why this acceptance seems to us one which must be preserved and promoted, because being very operational. The plains of Europe have the characteristics of having been among the most intensely cultivated areas of the globe and of having experienced an early forest transition (from deforestation to reforestation). The impact of these ancient cultivations quickly appeared to be potentially key to the understanding of the current state of biodiversity in present landscapes. Most importantly, the majority of studies published today show a strong and very long-lasting effect of previous croplands on biodiversity and soil quality in today's forests, while almost none shows such effects because of other human actions in the forest, especially those relating to the exploitation of forest resources. As a result of several studies, we have carried out on supposed cases of ancient overexploitation of forests (comparison of ancient high forest preserves with fuelwood production areas, study of woods devoted to the supply of the Lorraine salt mines, comparison between ancient coppices and ancient coppices with standards...), we show how tenuous were the after-effects of such ancient wood removal, whereas in the same regions, the cultivation had a major effect, still clearly visible in present day forests. For these reasons, the concept of ancient forest is operational for environmental managers chiefly when it takes into account the ancient cultivation of soils.