This agricultural use began long ago as the first settlers arrived and began to plant crops and domesticate animals. The first farms were across the uplands, as most parts of the lowlands were too wooded or wet to make agriculture practical. Signs of these first farmers can be seen as the old settlements, cairns and even field boundaries that exist in the uplands.
Farming today is vastly different than is was for these early farmers. The most intensive agriculture occurs in the lowlands, where the removal of large areas of woodland has created pastures on fertile soils.
The Welsh Assembly Government regulates farming in Wales, you can find out more by visiting the Environment and countryside section of their website.