Yes as t697 says, the section of track had notoriously bad adhesion not helped on the Eastbound with a rail section gap followed by a fairly steep climb up towards Autins Lane, Piccadilly line trains really struggled. Funnily enough it was usually the S stock that had issues on the Westbound, that decent coupled with damp conditions in the leaf fall season often lead to an intervention from the trains onboard computer akin to a wheel slip protection during wet weather.
Child of Middlesex, student of the City, resident of the Metropolitan
Given the age of some of the trees it probably hasn't been as barren for many decades! Hopefully the arboricultural people can find out a way of working with nature by planting a few new trees and shrubs of more appropriate character to lineside requirements.
They've been cutting trees all along the line to Rayners Lane. I think pretty well all the trees were planted by the Met in the first place - the earliest photos show the trains running through bare fields with just the odd hedge to break up the landscape. I live just north of Ruislip Manor and look out on to trees - when the house was built this was a large empty field. The railway giveth and the railway taketh away.