Fungi help the trees absorb nutrients and resist insects. Decayed trunks build soil or hold water like a sponge. The tall trees trap and hold moisture. Needles catch dust and dirt, thus cleansing the air. Plant photosynthesis removes carbon dioxide gas from the atmosphere.
Roots bind soil against erosion.
They also bring a better price. They have more 10 to 20 growth rings per inch compared to three to six rings in a smaller tree. But those qualities aren't so important now that timber can be treated with preservatives, Harwood said. It's the wood's clear grain that pays. An average old growth log, twice the diameter of a younger tree, is worth four times as much, he said.