The tree removal is being done by Alberta Transportation in preparation to the start of construction of the West Calgary Ring Road in the spring of 2019 (per their website information)
Here is a link to Alberta Transportation’s West Calgary Ring Road website: https://www.alberta.ca/west-calgary-ring-road.aspx
A paragraph with information relating to the tree clearing can be found towards the bottom of the page along with links to maps and drawings from their public information sessions.
If you have any further questions regarding the Ring Road construction please direct them to Alberta Transportation as this is not a City of Calgary project. Contact information for the Province is shown at the bottom of the webpage.