I think the experience of Robert Burns' family in trying to eke out a subsistence living as tenant farmers in the latter half of the 18th century possibly gives an insight into the demographic shift away from agriculture at the time. Industry and the growth of cities was drawing people away from the land for the certainty of a regular wage as farming became a less attractive option. Burns himself said of his time farming at Mossgiel that for many years meat was "a stranger" on their table and with no money to spend on improving land, crop yields were extremely poor. Coupled with this is a lesser known fact - Scotland also suffered from the potato famine just the same as Ireland, and this too would have accelerated the flight from the land. Unable to pay rent, tenants would have been evicted and landowners amalgamated the small fields of the time into larger, more economically viable units. Plus they had access to the finance needed to improve and fertilise the land.
I doubt if there was any forced clearances of the kind experienced in the Highlands, more an economic migration brought on by new opportunities in the cities and in the overseas colonies.