Hi Riptide. I've moved your very interesting post to the 'How do I???' section where you may get more replies.
I think the answer to your Ross vs. Mortimer question may be that it depends on the country and method of measurement. Medieval England was quite densely populated (although this fluctuated with the plague) compared to a lot of mainland Europe. I found the 7% woodland stat in 'The Time Traveller's Guide...' (a fantastic book and my main 'go to' guide when creating medieval fantasy worlds) surprising too. A little google-fu led me to this corroborating piece:
A list of percentage forest distribution in the modern world can be found here : interestingly it has England and Scotland at 17% woodland - 10% more than in Medieval times - if the figures are accurate and if we are comparing apples to apples - I suspect methods of measurement give huge differences in results.
Before consulting the archaeological research, my assumption — widely shared, I suspect — was that England was largely wooded until the arrival of the Romans. Prehistoric Britons might have made a few inroads into the densely forested valleys, but preferred the wide-open expanses of Salisbury Plain or other high, treeless places such as Dartmoor or the Berkshire Downs. The Romans cleared some lowland areas for their settlements and built connecting roads. With the arrival and gradual domination of the Anglo-Saxons during the Dark Ages, more woodland was slowly lost, and a pattern of villages emerged, ready for the Domesday Book to record after the Norman conquest.
This understanding has now been shown to be wholly inaccurate. Much of England had been cleared as early as 1000 BCE, some two millennia beforehand. The Bronze Age saw intensive farming on a scale that we are only just beginning to appreciate. As Oliver Rackham puts it in The History of the Countryside:
It can no longer be maintained, as used to be supposed even 20 years ago, that Roman Britain was a frontier province, with boundless wild woods surrounding occasional precarious clearings on the best land. On the contrary, even in supposedly backward counties such as Essex, villa abutted on villa for mile after mile, and most of the gaps were filled by small towns and the lands of British farmsteads.
Rackham describes the immense clearance undertaken during the Bronze Age, boldly claiming that ‘to convert millions of acres of wildwood into farmland was unquestionably the greatest achievement of any of our ancestors’. He reminds us how difficult it was to clear the woodland, as most British species are difficult to kill: they will not burn and they grow again after felling. Moreover, in his dry phrase, ‘a log of more than 10 inches in diameter is almost fireproof and is a most uncooperative object’. The one exception was pine, which burns well and, perhaps as a consequence, disappeared almost completely from southern Britain, the presumption being that prehistoric man could easily burn the trees where they stood: the image of pine trees burning like beacons across the countryside is a strong one. Only with the Forestry Commission in the 20th century were large numbers of conifers reintroduced.
Having said all of that, if what you are writing is fantasy then you may need the landscape to serve the story: much fantasy requires remote areas and you will often need to factor travel time into your work which means you might need to take liberties with the landscape so it fits into you pacing and plot. For example, if you were to use an accurate landscape model, then it might require a character weeks to travel on foot or horse from a densely populated area to a remote one. If that doesn't fit with your story-line, then nobody is going to pick you up for compressing your landscape somewhat and removing vast areas of suburbia or satellite villages and towns to cities.
Best of luck with your novel!