Special Rules Regarding the Westfield Parkway Trees
The Parkway (or street ) trees in Westfield are planted on L.A. County roadway land and are under the jurisdiction of the County of Los Angeles.  Pruning and/or removal without specific permission from the County subjects the property owner to a fine and/or jail time.  Additional information may be obtained from any Westfield Park Board member or from the Assistant Roadside Superintendent at the County of Los Angeles Parks and Recreation Department.
Westfield Parkway Trees
The following are reprinted sections of The Los Angeles County Municipal Code:

16.76.010 Trimming, removing or injuring trees and other plants -- Permit required.

It is unlawful for any person, firm or corporation (other than the director of parks and recreation, with regard to public grounds or public property, or the road commissioner, with regard to public highways, or persons acting under their authority) to trim, prune, cut, break, deface, destroy, burn or remove any shade or ornamental tree, hedge, plant, shrub or flower growing, or to grow upon any public highway, public ground or public property within the county of Los Angeles without the written permit of the director of parks and recreation, with regard to public grounds or public property, or the road commissioner, with regard to public highways; or to deface, bend, break or destroy, or in any manner injure or remove any frame, post, trellis or other structure used to protect or support any such tree, hedge, plant, shrub or flower; or to hitch or to tie horses or other animals thereto, or to plant or place thereon or attach thereto any sign, notice or other advertising device. (Ord. 83-0163 § 3, 1983: Ord. 4447 § 1 (part), 1945: Ord. 584 § 3, 1919.)

16.76.030 Replacement of trees required when.

No permit for the removal of any tree shall be issued under this chapter unless and until the applicant agrees to replace the tree with another tree, of a type and quality to be determined by either the director of parks and recreation or the road commissioner. This condition may be waived by either the director or the road commissioner when replacement of such tree is not desirable in the public interest. (Ord. 83-0163 § 5, 1983: Ord. 6077 § 1, 1952: Ord. 584 § 5.1, 1919.)