Where to find information on historic forest coverage

I'm trying to write a game set in the middle ages in the British Iles. One thing that I want to get right in this game is forest coverage, and I've had some difficulty finding relevant data. Recent maps show very little forest, whereas ancient maps suggest that the entire region was mostly forest. So I don't know the right level of deforestation for the time period. I was able to find some information suggesting Scotland had very few forests at this time, but no information on most of England.

For my game, I want to model timber trade, and to provide a visually diverse terrain map, so getting right which regions are producers is important.

I figure the may be some modders or history buffs that frequent this forum that might have an idea of where to get this information.

I don't know where you'd find decent maps, but the Forestry Commission has a timeline here: I suggest that you could find a list of Royal Forests and simply expand their modern sizes by the relevant amount. Roughly speaking the dates they give are as follows:

550: 25%-30% forest cover
1066: 15% forest cover (slightly more in Scotland)
1300: 4-5% forest cover
1457: English Parliament pass a law encouraging planting
1503: Scottish Parliament declare the woods of Scotland 'utterly destroyed'
1815: Lowest level of forest cover ever
1900: 5% forest cover (up from 1815)
1947: 6% forest cover
2016: 13% forest cover

In other words, starting from a modern map, if the game starts in 550, you want to roughly double the size of forests; if in 1066, hold it roughly where it is, and if in 1300 you want to roughly reduce it to a third.

Thanks Flying Pig, that sound like a good idea, particularly focusing on Royal Forests.