The City Council hereby determines that the health of the elm and oak trees within the municipal limits is threatened by fatal diseases known as Dutch elm and oak wilt diseases, and other trees may be threatened by other epidemic diseases of shade trees. It further determines that the loss of elm, oak, and other trees growing upon public and private property would substantially depreciate the value of property within the city and impair the safety, food order, general welfare, and convenience of the public. It shall be the intention of the Council to control and prevent the spread of those diseases, and this section shall be enacted for that purpose.