This article doesn't actually refute the main claims: Cities (such as the one I live in) only allow "fruitless" varieties to be planted on the streets. These varieties are generally of the full male variety, and thus only produce pollen.
Yes, this isn't "sexism" and no the female trees wouldn't hoover up all of the pollen produced...but it still a problematic practice.
Tree's are made of fairly well insulated materials and contain a vast amount of chemical reactions going on, they are also elevated from the ground, so they can experience the tribolectric effect (transfer of electrons through friction), as well as ionic charge due to moving nutrients up through their cambium. It's really not hard to imagine how they could become electrically charged at their extremities.
Someone measured tree branch tip to root resistance and while I don't quite understand the poor quality chart it's in kiloohms. The tree would need to radically change some of its biology. Like no capillaries from roots to branches. I'd say no chance.
As a sci-fi author, I love thinking about this kind of "what-if biology."
I presume, if such a phenomenon was possible, that it would work the same way electric eels work: by electrochemical (dis)charge. You don't need the whole organism to be ionized relative to its medium; you just need to form an ionic gradient at the surface of the organism, by using active metabolic processes (ion pumps) to hold ions — and thus electric charge — on the "wrong" side of a membrane.
Of course, electrochemical flux is an active process that takes work; it's not something any organism can do constantly forever. I imagine a tree that (hypothetically) did this, would only do it as a periodic "tug", maybe once a minute or so — sort of like taking a breath. Its evolutionary goal behind evolving such a feature, would presumably be to just to catch enough pollen, not all of it, and even a low-duty-cycle pull would work toward that goal.
Note that the ability of a thing to create an electrical discharge, is inextricable from the ability of the same thing to induce electrostatic forces on charged particles. Electric eels move charged particles in the water as they discharge into the water. And a tree that charged itself up to act as an ionic air-purifier, would (probably lightly) "zap" anything that touched it.
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Alternately, if we let go of the constraint that this is something all trees supposedly did, and instead assumed that this was something only some specific trees did — then those trees could do it by growing some electrically-insulated — and so likely dead-matter — tissue, near each pollen receiving organ (pistil). In other words, the tree's flower petals could act like mammalian hair does: able to be charged up with static even when the animal themselves is grounded. (And then they might not even need explicit charging — just interacting with the air while being electrically insulated from the rest of the always-grounded tree around them, might be enough to leave them with a slight constant charge.)
