What do you mean by “Old-Growth Ancient woodland”?

Woodland originating from the retreat of the glacial period 12 millennia ago is likely to be a fragment of the ancient wildwood (ie natural).  These I refer to as Old-Growth Ancient Woodland to distinguish them from the technical term ‘Ancient Woodland’ which is defined as 400 or more years old. 
* Wales is particularly well endowed with Old-Growth Ancient Woodlands that have survived on the steep sided ‘nants’ (glens) unsuited to anything other than woodland.  Their longevity, richness and diversity make them of world significance, on a par with the rainforests, old-growth coniferous, Siberian tundra, etc.  Yet in Wales their true value is unrecognised without special protection.
* Old- Growth woodland has various characteristics and is exceptionally rich and diverse- including a diversity of ferns, bryophyte, lichens, fungi (especially mycorrhizal), ancient and hollow trees, as well as trees with multiple stems from a single stump (eg lime and oak), soil (see below) and topography.  Any one is not sufficient to indicate age, but rather diversity and abundance is what makes them indicative of age.  Observations lead me to believe that the older the woodland the greater may be the diversity of species and the more interesting its geography.
* Old-growth soil is also different, for where the ground has never been cultivated, the surface layer is very thin (except a brown earth), whereas soil that has been cultivated is the depth of a plough (varying with horse or mechanical).  Ploughing damages the mycorrhizal fungi and the application of fertiliser may have killed them off completely.