Spare a thought for tannins, and be surprised, like:

Tannins leached into soil can play an important role in the rate of litter decomposition, which is important to ecosystem function.

When tannin levels are high, they slow down litter decomposition. That means the leaf litter can be a food source for bugs for a long time. It also reduces soil drying and protects soil microbes.

There's much to learn about how helpful tannins can be and according to the article so much more to learn in the future.