If you cover a pile of close packed fresh green logs completely with a tarp in a damp location, you trap the moisture and heat and create the perfect conditions for rot. I've found uncovered loose log heaps left in a clearing dry quite nicely when exposed to the sun and wind, only any ones in direct contact with the ground for a year or more show signs of spalting and decay. Ventilation and not having them too close together are important to dry them out, the wood needs to breath and be exposed to the elements to season. Big logs will need to be either split or cut into rounds. Its the same principle with planked commercial timber, its carefully stacked with spacers so that the air can get through it, under cover but ventilated so that the moisture can escape.
Suggest in future you try leaving logs loosely stacked, exposed and uncovered, off the ground on bearers and where they get a bit of air, for no more than a few months before then chopping to size and putting in in a wood store. There's that nice new book on Norwegian wood stacking in the shops in time for Christmas.
There are dormant fungus spores in all woods, waiting for a nice dead damp log. The less ventilation on the log, the happier they are.
On a positive note, sounds like you've created some great rotting deadwood heaps for bugs which should benefit the ecology.
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