I always trim my river birches in the fall to prevent the spring "bleeding." The drip of sap from wounds really doesn't hurt birch, but can be a mess on sidewalks and on your head when you walk there! Crab and linden should be fine now - although myself, I trim "non-bleeders" in spring just before bud swell to maximize the amount of time for healing and lessen the amount of time of exposed wounds. The exception to that is red oak species, to lessen the chance of infection of SOD (sudden oak death) since infection is more likely in wet spring periods. They get trimmed in fall, as well.
hortster

Never too early.

i tend to prune when i walk by with the saw.. or it pisses me off so bad.. that i go get the saw .. timing never meant anything to me ...

now.. if i had my retirement tied up in 10,000 acres of production trees.. then i would be concerned about what might be floating in the air ...

otherwise.. just do it..

do you know how to properly prune??

ken

ps: i always worry about birch.. but it really doesnt stop me.. lol ...

I'm like Ken, I prune whenever I can get to it. If I waited for the proper time, it would never get done....or very little.
Mike

For major pruning, I'd worry more about timing (and do it similar to what Hortster said). In this case, as Ken said, just do it when the saw and pruners are handy.

ken...I often browse the tree forum just to laugh at what you write. LOL

Except Hortster, SOD doesn't occur outside of the Pacific coast and doesn't require wounds for disease development.

Thanks for you help everyone!!

salicaceae, call me paranoid if you wish, but P. ramorum has been found elsewhere via the shipment of nursery stock from CA and OR, two of the main supplying states for nurseries here. It has been found in nurseries as close as TX. You are correct that wounding isn't necessary for the spread, but fresh wounds are an additional entry point.
I am a "better safe than sorry" person, and have to think back to all the other blunders that have been started and can't be stopped - EAB, Asian long-horned beetle, gypsy moth, walnut's thousand canker disease and so on. Hate to be a pessimest, but it's just a matter of time.
hortster