Woodland history begins for practical purposes about 11,000 bc, when the last glaciation ended and the British Isles became suitable for tree growth. The trees which had retreated to southern latitudes during the Ice Age slowly migrated north again. The first to colonize our tundra were birch, aspen, and sallow. These were followed by pine and hazel; then alder and oak; next lime and elm; then holly, ash, beech, hornbeam, and maple. The process was rather like the making of secondary woodland now; the distances were greater but there was no farmland to stand in the way of the advance, nor at first was there an English Channel or Irish Sea. Birch, aspen, and sallow are relatively arctic trees. The later species were either trees of warmer climates (hornbeam, maple) or bad colonizers (lime). Latecoming species were slow to become abundant, for there was no vacant ground to occupy; they had to wait for existing trees to die.
Much the greater part of the land below 2000 ft. was originally covered with forest or scrub, and this woody vegetation was gradually removed by felling and clearing, mainly in the Middle Ages and the beginning of the Modern Period, to provide fuel and timber for human use, to make room for sheep and cattle grazing, and in the lowlands for agriculture. Though the lowlands and the lower slopes of the hills were once occupied by forest, the existing remains of native woodland are now very scanty.  In 1920 not much more than 5 per cent of the land area of Great Britain was woodland of any sort, and this included modern plantations. 
Of the old native, deciduous (or ' broad-leaved') forest, consisting mainly of oak, beech, birch, ash and alder, that which had not been cleared was maintained for the supply of timber, small wood, and oak bark for tanning, though the native timber supply became so scanty several centuries ago that much of the demand had to be increasingly met by importation.   Some of this originally native woodland which does remain is still in a more or less natural! condition, and woods dominated by all five of the trees mentioned are represented.   Many, though not all of these woods have been 'planted up', mostly on the sites of old felled woodland and often with the original kind of tree proper to the site, so that they have now come to assume most of the characters of natural woodland. This does not however, apply to modern conifer plantations, which introduce quite different conditions. The beech woods of the southern chalk, the oakwoods of the clays and loams of the southern and midland plains and of the northern and western valleysides, the ashwoods of the Derbyshire dales, the alderwoods of undrained marsh and fenland, the birchwoods of sandy soils and of northern hillsides, and also the few remaining native pinewoods of the Scottish Highlands, are all genuine representatives of native woodland.