Firefighters were called out after a neighbour spotted two youths setting fire to a conifer.
The two males, believed to be around 12 or 13-years-old, were disturbed and ran away but had already set light to a conifer that was part of a long row of the evergreen trees, on Jepson Lane, Elland.
A fire crew from Elland attended, at 8pm on Saturday, and the fire was under control in around 20 minutes.
A member of the crew told the Courier that because it was so dry about half the tree had burned away by the time they got there and, if left alone, the whole row would have gone up in a blaze.
Descriptions of the youths were given to the police who are investigating the incident.