How can vegetation in between tracks affect trains

[Silent]

I just got a train from Kenton and noticed the tracks for Lioness and Bakerloo Lines have vegetation on them, in between and next to the rails, however for the WCML which runs beside the Bakerloo and Lioness Lines the tracks were clear of any vegetation. So it made me wonder.

 

[Tilting007]

On the Lioness Line the biggest risk will be fire from arcing on the conductor rails in dry spells.
Kenton notoriously floods so plenty of water to encourage growth plus no ballast renewals for a while