This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
Not less profound than the effect of tree-felling and cultivation upon the original forest land has been that of drainage. Apart from the conversion of the forests into corn lands by the ridge-and-furrow method which at once disturbed the plant formations native to the soil, the influence of modern drainage has been still more marked by (1) causing wet meadows to become dry, (2) causing bog and marsh plants to disappear, (3) assisting the work of tree-felling and other modern causes in making the whole country much drier as a whole.
The whole of the Fens has been converted in this way during the last two hundred years from aquatic vegetation into meadow and arable land. In other parts unreclaimed land, often swampy, boggy, or waste, more especially in lowland regions, has become ordinary pasture. Many persons living to-day can testify to this, and it is going on at the present time on a grand scale in Ireland.
So that it is only here and there, in areas largely given up to meadows to-day, that it is possible to find any traces of the original vegetation, so many different stages has it gone through owing to different causes. But there do exist what the author has called "vestiges" or "vestigial floras" that help one to understand what the virginal character of the vegetation really was. These are quite isolated and owe their isolation largely to drainage.