Current is _generated_ in static lengths of wire. At any point the voltage exceeds the design, it arcs. Current passing through imperfect conductors are heating elements.

Both sparks from shorts and excess heating of conductors are possible ignition points.

n.b. I have not look at the paper.

Oh, so you mean it might just be power (or other metal) lines causing fires indirectly?

I'd be very surprised if anything naturally occurring in a forest would be long and/or conductive enough to be a problem even during very strong geomagnetic storms.

The paper's a bit hard to read but I don't think it suggests a mechanism, or that the correlation between CMEs and forest fires is statistically significant for that matter. If you email me (address in profile) I can send you a copy.

It does seem plausible that you could get fires as a result of electrical sparks off of long conductors (transmission and communication wires, pipelines, fences), such as with the Carrington event (https://en.wikipedia.org/wiki/Geomagnetically_induced_curren...).