Where I live, N. Ca., most of the native tannins are leached out of the leaves and needles. And in the forested areas with deep top soil the tannins are captured by the organic layer, and the streams run clear. But in the serpentine and sandy soils with thin top soil strata the tannins pass through and the water in the streams of those areas run brownish. Real hard on house hold water systems too.
Of all the different woods I have had on the turning lathe, Hickory has been the worst, when it comes to tannin.
When I turn it wet, it reacts with the iron ions on the surface of the turning gouges and makes everything dark blue. The last log I converted into saladbowls, I had blue hands for about a week afterwards.