Since the beginning of the 20th century Wales has experienced two World Wars and the collapse of the heavy and extractive industries. Since 1945 the productivity and efficiency of farming has greatly expanded although the number of farms and people working on them has decreased. The landscape has been altered by the construction of wind farms, hydroelectric schemes and the planting of conifer forests in the uplands. The countryside has also had to adapt to the pressures of recreation and tourism while towns have continued to expand, leading to threats to their historic character.