On any given day between November and April there's a fair chance anyone traveling through the Napa Valley will see smoke columns rising from what look to be burning piles of twigs.

So what's all the smoldering about?

Most vineyard gurus say its usually mounds of old vines that have been torn out of the ground -- casualties of either some pest, disease or just plain exhaustion after decades of fruitful grape production.

But some vineyard tenders worry that the old practice of burning vine clippings -- the twiggy remnants of spring vine pruning -- is making a comeback among smaller vineyard operations.

Sam Turner, a vineyard manager for the past 25 years, says he's noticed an increase in small fires he suspects are burning not old ripped-out vines, but the smaller much twiggier vineyard clippings. Turner said this seems to be a reversal of the greener trend toward chipping and mowing the clippings or canes back into the soil. Many growers say this practice gradually increases the nutrients and structure of the soil by adding organic matter into the ground.

"(Small fires have) gotten to become a new craze with the smaller vineyard operations," Turner said, adding that with the larger vineyard operations it makes much more sense to have mowers chop up the canes into the soil, rather than have crews haul the clippings out of the long rows and pile them.