Housing and Development Newsletter What began as dense forests in prehistoric times thinned out as the number of people grew and technology improved. The dependence on timber or cleared land increased, but so did the cultural awareness of trees and their value. Natural conversion into peatland also played a role in the reduction of the forests. The most pronounced decline occurred during the time of English conquest and colonization of Ireland, though Harris-Gavin points out that colonization and commercial exploitation were not the only forces behind the decline: agriculture and development, industrialization, population growth, legislation and economy all served to take down the old forests.